Open Source Multimeter - Page 1
Forum section: electronics / general

author: House91320
author_rank: Regular Contributor
timestamp: June 30, 2011, 05:05:19 pm
content: My friends and I have been developing an open source multimeter. I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.

author: ndictu
author_rank: Regular Contributor
timestamp: June 30, 2011, 05:19:42 pm
content: Please don't be yet another one of those kickstarter projects that only have a rotating CAD model and long FAQ with answers to the most minutiae details, but no real proof-of-concept design.

author: Zero999
author_rank: Super Contributor
timestamp: June 30, 2011, 05:24:08 pm
content: It looks like a children's toy but it's only a prototype model.How much are you planning to sell it for?

author: House91320
author_rank: Regular Contributor
timestamp: June 30, 2011, 05:30:42 pm
content: Don't know yet i have to figure out the manufacturing cost.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: June 30, 2011, 05:51:49 pm
content: My first question would be WHY? The top end of the market is well served by the likes of Fluke et al. The budget end of the market is VERY price conscious and the low end is awash with One Hunglow Tat. This leaves the speciality sector, low volume and usually high accuracy. Without a very tight spec and a definite market to aim at you may find finance a rare resource.

author: Zero999
author_rank: Super Contributor
timestamp: June 30, 2011, 05:59:57 pm
content: A good open source oscilloscope would be nice.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: June 30, 2011, 06:59:28 pm
content: Quote from: Hero999 on June 30, 2011, 05:59:57 pmAgain WHY? For the same reasons above they are just not cost effective. Unless you are doing it just for chuckles it makes no sense to me , sorry.

author: Zero999
author_rank: Super Contributor
timestamp: June 30, 2011, 07:00:36 pm
content: There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 30, 2011, 07:21:04 pm
content: Quote from: FreeThinker on June 30, 2011, 06:59:28 pmA scope has MUCH more potential as an OS project as a lot of the cost on higher end commercial units is for software functionality. For the hardware cost of a Rigol you could in principle build something with the performance and features of a scope several times the price, although it would be a lot of workA DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: June 30, 2011, 07:44:35 pm
content: Quote from: mikeselectricstuff on June 30, 2011, 07:21:04 pmHmm! Good point. Do you really think that SIGNIFICANT savings could be made in the hardware (without cutting corners) to justify the effort of a home brew software firmware? I think Rigol do a pretty good job of squeezing every last cent out of there product (performance wise) and think they would be a hard act to beat. As a kickstarter project you need a significant edge, I just don't see it.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 30, 2011, 07:49:13 pm
content: Quote from: FreeThinker on June 30, 2011, 07:44:35 pmI think the key would be clever people doing smart stuff in FPGAs - The Chinese makers are not good at innovating- it;s always cheaper versions of higer-end stuff with poorly designed software. You're never going to get insane bandwidths as you're constrained by available ADCs, but I think there is plenty of scope to get things like good update rates and DPO type functionality, as well as lots of protocol analysis type functions, which are the sort of things that come as high-cost add-ons to current scopes.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: June 30, 2011, 07:49:22 pm
content: Quote from: Hero999 on June 30, 2011, 07:00:36 pmWhat? Make a crap high end scope?. Sorry I'm in a funny mood tonight!

author: FreeThinker
author_rank: Frequent Contributor
timestamp: June 30, 2011, 07:52:47 pm
content: Quote from: mikeselectricstuff on June 30, 2011, 07:49:13 pmWell that rules me out!.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: June 30, 2011, 08:06:10 pm
content: Quote from: House91320 on June 30, 2011, 05:05:19 pmWell I think that I am looking at one Gossen range switch,plus the bottom of the Fluke 28II painted red, with out the holster, and a bit more square !!Well I have a tip for you, you are in a good path, but you have to surprise us !!Yes SURPRISE US !!Its hard to happen, but if you are serious in what you do, it will not be that difficult.If you like to know what to avoid ? Look at Extech.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 30, 2011, 08:14:46 pm
content: Quote from: Hero999 on June 30, 2011, 07:00:36 pmThe nano already costs $100, and doesn't have a real scope AFE and has a pathetic sample rate, and only one channel. Put real spec hardware in there, and you are increasing the cost a lot.Quote from: FreeThinkerNo, I don't think you can make the equivalent of the 50 MHz Rigol for less than the market price, just based on parts cost alone, at least not in the volume a small open hardware project would get.The bottom end of the market is under tremendous price pressure. Manufacturers are basically selling their cheapest models near cost (at their much larger volumes) and making their profit and recovering the development costs on the premium for higher end features -- extra channels, extra bandwidth, mixed signal, and so forth all cost proportionally more than the base model.So I think the only place you could attack the scope market is to aim higher, and especially with analysis tools. If you had a few really good mixed signal designers who had been made independently wealthy and wanted to build an open hardware oscilloscope platform in their free time, you might be able to design something like a 4 channel, 200 MHz mixed signal scope where the production costs were less than a comparable commercial unit. They key then would be to be able to add in all of the bonus firmware stuff for free: the measurements, the pass/fail analysis, and the protocol decoders.If you did that right, you might end up with something that had the hardware cost and specs of the 200 MHz/4 channel Rigol, but all the unlock codes from the Agilent 3000X. Of course, you aren't going to get the obscene waveform update rate and real-time advanced triggering and protocol decoding without the agilent ASIC.There are two problems with this: it takes a really talented team a long time to design something that has the functionality of a higher end scope. You have to find those guys and convince them to work for free. Second, the scope you build is still going to end up costing considerably more than the $400 a lot of hobbyists already balk at paying. You might end up with the most powerful $1600 scope that nobody buys because the target audience can't afford it, and the people who can afford it and want the features are more interested in getting a name brand scope with support than a hackable open platform. Plus you still have to contend with the problem that the big players are sitting there with their ASICs that you can't match in terms of performance.

author: tnt
author_rank: Regular Contributor
timestamp: June 30, 2011, 08:54:06 pm
content: Personally I'm convinced that an open source scope would be a good thing.You're not going to get the low end market, I'd target something like 5000$ or so unit cost (I mean you do have to recoup the dev cost as well). But you could have in it a lot of the functionality of much higher priced scopes. Sure not every hobbyist is gonna buy it ... but I'm convinced there is enough of a market for it anyway. (I'm just a hobbyist/hacker and I have a 7500$ scope ...)If you do the design modular enough (mostly front end separate from the acq) to allow modules for scope / logic analyzer / spectrum analyzer / ...The agilent asic function could all be replaced by a good FPGA (I did and still do FPGA design for a living so I know what I'm saying). Agilent went the asic way because it's much cheaper given the volume they have and they're all about having more margin. But for a project like this, even 500$ of FPGA cost would be acceptable and for that price, you get a pretty good one that can definitely compute your 800x600 image composite of 50k wfrm/s in its internal memory.

author: ivan747
author_rank: Super Contributor
timestamp: June 30, 2011, 10:58:40 pm
content: Quote from: FreeThinker on June 30, 2011, 07:49:22 pmSo am I! I have trolled all over the forum! Sorry.

author: vtl
author_rank: Regular Contributor
timestamp: July 01, 2011, 02:21:42 am
content: Markets pretty saturated for multimeters, how about a decent LCR meter that does ESR as well? Make it cost under $100 and you got a winner, seems like you have to pay double or triple that for something worthwhile.For a hobbyist it doesn't sound great to spend that much to measure the ESR of a 10c cap of old electronics.

author: Zero999
author_rank: Super Contributor
timestamp: July 01, 2011, 03:59:06 pm
content: It would have to do RMS measurements too.

author: Afrotechmods
author_rank: Unknown
timestamp: July 01, 2011, 07:27:30 pm
content: As has been said before, I don't think you will actually be able to come up with a solution that will ever be able to compete with $40 off the shelf meters which are manufactured in quantities of 100+k.However! I would like to applaud you for what you are doing anyway, because I think the real value in this project is the educational value. If you are able to document the project and the design process thoroughly it would be a cool thing to learn from. You could make money from putting ads up on the webpage documenting the project. I am particularly interested in the process of how you will design the case and get it manufactured, as industrial design is something I never got a chance to study in school.Now to answer your questions, I think the design you've got so far looks pretty good. What does the D stand for by the way? Diode? If so, I recommend using the diode symbol instead. Also, I am used to seeing ºC instead of TMP.The bright red on black looks a bit jarring. Perhaps a slightly more subdued red would look better.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: July 01, 2011, 07:55:55 pm
content: Quote from: Afrotechmods on July 01, 2011, 07:27:30 pmAs I understand it it's a kickstarter project.. he's looking for finance.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 01, 2011, 08:40:11 pm
content: Quote from: FreeThinker on July 01, 2011, 07:55:55 pmBut the issues are the same. Would you finance a development which has that much >< of a change to become profitable?

author: FreeThinker
author_rank: Frequent Contributor
timestamp: July 01, 2011, 09:01:46 pm
content: Quote from: BoredAtWork on July 01, 2011, 08:40:11 pmExactly my point. See my first post

author: tinhead
author_rank: Super Contributor
timestamp: July 01, 2011, 10:06:25 pm
content: there is handheld open source scope "ourdso", v2 is the latest revision, Based on Cyclone EP2C8Q208, as ADC the good known AD9288 (so 2 x 100MSs).Based on NIOS , 320x240 ... far from perfect but it works already suficient. All sources available and actually can be easy modified tosupport e.g. 2 x 500MSs or even 2 x 1GSs ADC, whatever.But open source DMM ? For what reason ? Buy a 5USD single-chip DMM, few good resistors , attach cheap 8bit µC and here we go - DMM ready.

author: Zero999
author_rank: Super Contributor
timestamp: July 02, 2011, 07:58:57 am
content: Quote from: tinhead on July 01, 2011, 10:06:25 pmI don't think he's talking about building a basic meter.I often think with Fluke, you're just paying for the name most of the time. It's true that Fluke offers good safety features and excellent accuracy which is why they're popular but they don't really cost much to build. A Chinese company could probably build a meter with the same accuracy and safety features as a Fluke but it's not worth their while as the kind of people who want them would just buy a Fluke and the cheap hobbyists would just buy a cheaper Chinese meter which doesn't have them.I think an open source meter with the same accuracy and safety features of a Fluke would sell because people would be able to see the the quality of the components and would know that it's got the protection of a Fluke but at a lower price.

author: Frant
author_rank: Regular Contributor
timestamp: July 02, 2011, 11:41:12 am
content: Quote from: Hero999 on July 02, 2011, 07:58:57 amI am not sure about this because of the safety aspect. Dave's teardowns showed us that safety of a multimeter relies not only on electronic components, but also on a specific case design. It might be possible to choose an existing handheld case from a good case manufacturer if there is a product that can meet the requirements. I see no point in designing an "open source" case that can only be economically fabricated in large series. There is also a complex range switch, probably a custom LCD and a custom keyboard. There is just too many specific parts, making it pointless to be an open source project.Perhaps a modular benchtop PC-based instrument would be a better choice for an open source project. A decent metal case can be easily found, people would build their own modules for specific functions or as an upgrade, plenty of software possibilities etc. Something like a poor man's PXI or more like Agilent USB Modular Instruments, but much cheaper.

author: Polossatik
author_rank: Frequent Contributor
timestamp: July 02, 2011, 03:38:38 pm
content: Quote from: tinhead on July 01, 2011, 10:06:25 pmcan't find much about the "ourdso" not listed here:http://www.opencircuits.com/Oscilloscope#Open_Source_Oscilloscopeshttp://dangerousprototypes.com/2010/01/07/open-source-digital-sampling-oscilloscope/tried it also one timemore on topic, I do not see any real value in making an OSS handheld multimeter, there is not much functionality you can add /improve on low cost existing ones and price is also not a factor.

author: House91320
author_rank: Regular Contributor
timestamp: July 02, 2011, 09:55:36 pm
content: It is suprizing how much reaction my post has created, wasn't expecting that. Well maybe i can clear up some stuff. The meter is going to have all the functions of a normal meter, volts, amps, ect, plus an esr meter, data logging, real time graphing, tft color screen, and user customization ui. I expect the price range to be between $100 and $200.Also its going to use a rechargeable battery and is going to have USB and a corresponding software to do pc data logging and graphing.

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 01:02:39 am
content: A have to agree with the many proponents that such a project hasn't got much likelihood of being funded and/or can't compete with commercial units.It would have to offer something novel and a feature so compelling that you just have to have it.If it's just a multimeter (but open source), I wouldn't bother.Cool project as an exercise for sure, but that's all it is at present. It needs a killer feature.Dave.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 01:14:53 am
content: Quote from: EEVblog on July 03, 2011, 01:02:39 amI'll give this one the Led Zeppelin stamp too. You don't have to look much further than a Jaycar catalogue to see why.A DIY DVM kit is priced high than an equivalent fully assembled and warranted junk Chinese DVM.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 01:18:33 am
content: Quote from: House91320 on July 02, 2011, 09:55:36 pmThat sounds like a truly great price for all the features! What did you consider to arrive at these figures House91320?

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 01:43:28 am
content: Quote from: House91320 on July 02, 2011, 09:55:36 pmAny isolation with that USB?Battery life is very important in a hand held meter, beware.Dave.

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 01:51:08 am
content: Quote from: Frant on July 02, 2011, 11:41:12 amYeah, it gets messy. I'm just not sold yet on "yet another multimeter".Sure it might have a ESR meter built in, and/or maybe LCR capability, but really, there is little differentiation with commercial handhelds.It's gotta have something novel. I don't know what that is, but I'll know it if I see it!Maybe something like a Fluke 233 with just the front end module, and the display can be anything. A watch, an iPhone, PC, whatever, or it just talks to you, or, something...Like the iDVM concept that talks to your iPhone/iPad:That's at least novel (but it's specs suck arse).Stop the press!I have a concept...Might make a good blog.House91320, can I show your images in the video?Dave.

author: House91320
author_rank: Regular Contributor
timestamp: July 03, 2011, 03:29:42 am
content: Ya go ahead and use it in a video. In response to usb isolation it its going to have some opto coupling for the data lines and I am going to use a transformer and dc to ac converter for the isolation of the power.

author: MrPlacid
author_rank: Frequent Contributor
timestamp: July 03, 2011, 03:32:45 am
content: Yeah, your open source multimeter must be completed with these feature:Minimum, since these are already on the market:-LCR-Talking-Dual trigger input like function to function as mini oscilloscope.-Storage-Temp-Storage-Watt meter-luminosity-audio meter-High Voltage warningMust be added in before release:-Temperature reading without cable.-Timer, UP, Down, Clock, Alarm clock (Talking timer too)-Transmit wireless readings such as audio, video, photo, or just plain vanilla reading(You might skip the video part, and use e-ink technology for photos. Black and white photo is better than nothing.)-Emit loud sound on continuity mode for a distance.-Built in camera, photo and movie viewer (again, skip the video stuff)-Stability feature to alert if meter is accidentally knock over or moved.These are just the top of my head. But you don't want to waste time making an inferior product only to be wipe out one or two years from now.

author: MrPlacid
author_rank: Frequent Contributor
timestamp: July 03, 2011, 03:38:32 am
content: Quote from: EEVblog on July 03, 2011, 01:43:28 amI agree. Rechargeable battery is a death wish. It means that meter will never last more than 20 year max. It'll be lucky to last 5-10 years. After that time, it tells everyone how crappy the hobby multimeter is that they all die out (went extinct!)

author: House91320
author_rank: Regular Contributor
timestamp: July 03, 2011, 03:54:16 am
content: The battery is going to be user replaceable.

author: MrPlacid
author_rank: Frequent Contributor
timestamp: July 03, 2011, 04:19:51 am
content: Quote from: House91320 on July 03, 2011, 03:54:16 amIs that particular battery a standard battery that will be in production x number of years from now? Plus, the multimeter will be out of work until the replacement battery is delivered. It needs to be easy as running to any local store to pick up some fresh batteries.When you need the unit most and it's out of juice while on the field, we can't just say, "Today's work is cancel since my battery is dead. See you next week once the new battery arrived."

author: Bored@Work
author_rank: Super Contributor
timestamp: July 03, 2011, 08:14:28 am
content: Quote from: Uncle Vernon on July 03, 2011, 01:14:53 amElenco kits are such an example. They resemble fully assembled meters but the kit costs four to five times as much as the assembled junk meter. E.g. compare the Elenco M-1007K with the iconic Chinese $5 junk meter incarnations, the 830th (e.g. DT830).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 03, 2011, 10:09:25 am
content: A feature which I've not seen on any sensible-cost meter, but which would be very cheap to implement is to be able to measure simultaneous DC voltage and current, for efficiency testing voltage regulators.I say DC as it gets much tricker at AC. For DC it's just a multiplexer.PC software would allow connecting to two DMMs for direct readout of efficiency.QuoteAs regards optoisolation, you don't need a DC/DC converter as you will always have power available on the USB side. The method used my most meters today is probably the optimal one, i.e. the interface at the DMM is optical, and an external USB-optical link is used. This reduces the cost on the DMM side for people who don't want it, and avoids issues of connectors that are vulnerable to moisture and damage. Bandwidth is low so a simple LED/phototransistor provides a very low-cost solution.QuoteDon't see the point in this ( apart from the 'gadget factor') as it will kill battery life. You just don't need colour on a DMM. What you do need is good visibility from no light to sunlight and long battery lifeGetting an optimal display is a major challenge - a fully graphical display probably takes too much power, but an off-the-shelf fixed-segment one is not sufficiently flexible.The ultimate answer is a custom segmented display with small matrix areas for units and function-key labels, but this means a couple of $K for LCD tooling. Unit cost is low after that though.

author: Polossatik
author_rank: Frequent Contributor
timestamp: July 03, 2011, 10:24:40 am
content: Quote from: mikeselectricstuff on July 03, 2011, 10:09:25 am+1Colour lcd is just plain nonsense for a DMM seen you use a DMM not only on the bench but from the darkest corners up to full sunlight on a ladder .Of course you might add a pixelQ screen to it, but that would be seriously overkillI still use an old and silly (from specs perspective) vellman handheld scope for some stuff simply because it has a monochrome graphic lcd, hence you can use it in a lot of environments and actually *see* what is on the screen.I would pay a premium to have an "up to date" mobile phone (so that you can use it as 3g BT modem for example) but with a non-color LCD screen that is actually readable outside like the old nokia 6310's .well, now that's an idea

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 11:00:52 am
content: My video suggestion is rendering now as the next blog!But here is the DaveCad sketch!Dave.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 03, 2011, 11:16:18 am
content: Quote from: MrPlacid on July 03, 2011, 03:32:45 amGreat idea, I don't know how technically difficult it is to make a combined multi-meter and good LCR meter, but if possible it would be nice.QuoteDo not want. A strip-chart style display is the most "scope like" feature I need or want from a voltmeter, but I would rather have longer battery life from a non-graphic LCD. Talking is just a silly gimmick 99% of the time. Maybe it can be implemented in a useful way, but adding it as a bullet-point feature is just going to suck.QuoteIf you can add some of these features without compromising cost, battery life, usability, or form factor maybe, but I wouldn't go overboard on the kitchen sink features. Better to make a top notch meter and add features that support the basic usage. Every feature you add is another position on the range switch, or another entry in a menu, and turning your meter into a full-fledged computer will do a number on battery life. Important features for a meter are things like logging, storage, and USB/wireless links. Maybe some more flexible audible alert: rather than a talking meter, how about one where you can set a threshold voltage (or other value) and it beeps when that level is exceeded?One thing that might be nice for a rechargeable meter is one of those fancy near-field power links. I don't know how well they work or how much interference they cause, but it would solve the isolation issues, and allow you to use the meter in 'logging' mode simply by resting it in a cradle.It would be really nice if you could get a useful battery life out of 3 low-discharge AA NiMH batteries. They are cheap, replacements will be widely available for decades, last a reasonable amount of time, and can be substituted with alkaline batteries in a pinch (make sure the charging circuit doesn't try to charge alkaline batteries). Lithium ion batteries are lighter and higher capacity, but hard to find replacements for.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 03, 2011, 12:08:14 pm
content: I think you probably still want the range switch for everyday funcitons, so maybe it should have an 'other' position for fancy stuff and multi-channel functions...Diode test should go to about 5V, and it should be able to do 4-wire ohms, with ohms-to-frequency audio tone for tracing shorts.

author: firewalker
author_rank: Super Contributor
timestamp: July 03, 2011, 01:52:41 pm
content: Maybe instruments design companies that watch this forum could contribute to the cause. I believe it would be an excellent use of social networks.Alexander.

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 01:56:08 pm
content: Dave.

author: firewalker
author_rank: Super Contributor
timestamp: July 03, 2011, 01:58:25 pm
content: Just saw Dave's video. Really great IMHO. As an open source/hardware it would probably need at least couple of years to hit the market.Alexander.

author: Slobodan
author_rank: Regular Contributor
timestamp: July 03, 2011, 02:55:02 pm
content: @DaveNice video.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 03, 2011, 03:21:29 pm
content: Quote from: EEVblog on July 03, 2011, 11:00:52 amThinking about it, you don't really need 4 isolated channels - for the majority of cases you only need 2 isolated channels, each doing V & I, as it will usually be possible to arrange a common point (even if it means readings are negative) . This would save a lot of cost for not much reduction in usefulness, as you need a whole front-end and behind each isolation barrier.Also you could save more by having a 'primary' channel with all the component test stuff and a V/I channel, a secondary isolated V/I channels and isolation on the host interface.For temperature, PT100/PT1000 would be good, and no additional hardware cost.I'd prefer USB stick to SD, as all PCs have a USB interface but not all have an SD reader.However I think optoisolated serial with external USB converter gives you the most usefulness/cost ratio. Bluetooth is an option but a bit costly and power-hungry.Another benefit of a USB host port is you could plug in a USB bluetooth stick when remote use is required.

author: Frant
author_rank: Regular Contributor
timestamp: July 03, 2011, 04:21:55 pm
content: @DaveGreat video! I really admire your enthusiasm!About your suggestion to put four isolated channels... Yeah, that would be nice, but I don't really know of any isolation mechanism that could be used for this without wasting too much power for a battery powered meter. A separate ADC chip would be necessary for every channel. OK, there are low power high performance chips, such as AD779x, ADS124x or something like that, really nice. However, they would all need a dedicated isolated power supply, which is not so nice, and a separate SPI bus isolation, which is not nice at all. Analog Devices iCoupler digital isolators with integrated isolated DC/DC converters may be used for this. However, just the mentioned parts are well over $100 already...A modern reflective or "transflective" graphic LCD would not consume much power with the backlight off, probably 10 times less than the isolation of a single input channel.The range switch can be replaced with software controlled relays as in bench multimeters, but that would significantly increase the overall power consumption. A combination of opto-MOS and bistable electromagnetic relays would probably be acceptable.With all the input channels isolated and "floating", the controller side can be connected directly to a PC via the USB port. There is up to 500 mA available on a host USB port, which is more than enough for the whole thing. When using batteries, it would be essential to prevent the unused channels from drawing any supply current.

author: ivan747
author_rank: Super Contributor
timestamp: July 03, 2011, 04:37:46 pm
content: This is about Dave's multimeter:Add math features, so you can do calculations with ANYTHING, including calculations of calculations. Example:Input power = Vi*IiOutput power = Vo*IoPower loss = Input Power - Output PowerPercentage of power lost = (I can't remember and I can't figure it out on my mind without some paper and a calculator)It needs a good labeling system though.For Bluetooth / Zigbee / whatever you can use a removable module to save some money on the initial cost.

author: hans
author_rank: Super Contributor
timestamp: July 03, 2011, 04:52:12 pm
content: If you power the thing from 4x 2500mAh AA batteries, in most ideal terms you can only draw 5mA @ 6V maximum to do a simple voltage measurement. So that's 30mW. It doesn't sound like a lot to me.Of course this goes down FAST if you start to think about constant current sources, generators, quad channel, seperate temperature probes (probably requires seperate frontend), SD cards, dual screen (still draws more than a single screen!), etc.I can imagine that isolation is quite hard to achieve that way. The hardware will get quite complex as in , analog frontend, display capability, automatic ranging, calibration, measurement stability (i.e. time/temperature drift or noise).I think a quad channel accurate measurement device with all the protection circuitry is very hard to create, not even talking about batteries. Protection is a big issue because that kind of circuits use big components, which eats boardspace. Now, 4 fuses could be fitted into a device I'm sure, but you would need to have dual channel mob, power resistor and trace clearance taken into account. Powering the isolated circuit isn't an easy thing to do neither I can imagine.I think it's better to have 2 devices with 1 V/I channel (that have seperated ground terminals) than 1 device with dual V/I channel. Possibly it would be nice to have a linking cable of some sort so you could link the multimeters together to have unique capabilities (you could transfer the data between devices to log multiple channels onto an SD card, or calculate effiency from figures taken on both meters). Isolating digital communication signals (RS485/RS232) is still a whole lot easier than designing an isolated DC/DC converter + digital isolation within 1 case.Possibly , if you want a removable/external display module you could use RF to transport measurement data. This would be combined with the idea of having 2 meters linked together to do easy logging and efficiency calculations.Another advantage with 2 meters is that you got 2 battery packs, like in you don't have to power all the features of quad channel from the same AA batteries.

author: Vertigo
author_rank: Regular Contributor
timestamp: July 03, 2011, 06:28:48 pm
content: Quote from: ivan747 on July 03, 2011, 04:37:46 pmnow that sounds interesting

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 06:32:02 pm
content: Make sure this doesn't have the fate of Segway.

author: ivan747
author_rank: Super Contributor
timestamp: July 03, 2011, 07:13:10 pm
content: Quote from: Frant on July 03, 2011, 04:21:55 pm1. Maybe a variable frequency DC-DC converter could be used to reduce quiescent current.2. I would like a slider switch. It is unnecessary for most of the channels because there's only one multifunction channel and it doesn't share the thermocouple input and it is auto-ranging (at least that's what I expect). For current there must be range sliders.3. The microcontroller will take care of this. The will be lots of isolation. The opto-isolators should be off most of the time. Also please get some DC-DC converters with control inputs, not that 5 pin SOT-23 junk that doesn't even have an output disable pin nor a undervoltage protection function for the input voltage.

author: DavidJRobertson
author_rank: Regular Contributor
timestamp: July 03, 2011, 07:48:20 pm
content: Quote from: ivan747 on July 03, 2011, 04:37:46 pmI'd recommend the RFM12B by HopeRF (http://www.hoperf.com/rf_fsk/cob/RFM12B.htm). They're low cost compared to ZigBee, at £6.17 individually from Farnell (UK), are available in smaller (Yet still easy to solder by hand; XBees are pretty large), more convenient SMD modules and, if I recall correctly, they consume less power. There's quite a lot of info about this module spread around this bloghttp://jeelabs.org/(I'd recommend you take a read of this anyway, it's quite good).

author: House91320
author_rank: Regular Contributor
timestamp: July 03, 2011, 08:17:13 pm
content: Cool vid Dave do you mind if use an develop on some of your ideas. Also do you know of a good place to get cheap lcds like the one in you micro watch but bigger.

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 10:35:04 pm
content: Quote from: mikeselectricstuff on July 03, 2011, 03:21:29 pmThere are problems with such a common ground terminal, as used on the Gossen. Watch my AA battery capacity tutorial for a practical demonstration of the problem.Dave.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: July 03, 2011, 10:35:47 pm
content: Here my criticism of Dave's ideas. The few parts that are not just whining and complaining, but actual innovative ideas are bolded.QuoteSo my initial thought on Dave's idea is, four isolated channel seems a bit overkill. As Hans pointed out, what you really need most of the time is one or two V/I pairs for measuring power. And it also seems like you'd get a hard time getting the isolation done properly in that small space, even with two channels. How do you expect to power the second channel? Having a transformer for the power transfer seems like asking for interference problems, due to the AC needed to transfer the power. USB is easy in comparison since USB brings its own power. All you need is a simple USB controller and two optocouplers.QuoteWhile this might be tempting to add to the current jack, is it really a good idea? As far as I understand, it's generally a good idea to keep the current circuitry as simple as possible to minimize the risk of failure. Like, only a low resistance shunt and a fuse. Switching the shunt seems like asking for long-term reliability issues.QuoteSeems like a good idea at the surface, but does it really solve a problem? The destination is still the computer. You can do USB isolation on a whim. It also seems like the complexity of dealing with a memory card and file system would require a faster and more power-hungry microcontroller than you could get away with otherwise, unless you can live with slow transfer times. Taking the card in out of the unit is mechanically stressful to the card. Also, in terms of storage, do you really need that much space? It seems like a traditional interface (USB/IR) +something like a 1 MByte serial flash would do the job cheaper and better.The only time I could see you need that kind of logging space is if you're testing a lot of repetitive stuff, maybe on an assembly line or testing power/telephone stations in the field, or if you want to leave the thing on overnight probing something.QuoteAgain, bluetooth is a short distance protocol, and I doubt you'd get enough bang for the buck (power consumption in this case) compared to a more power-conservative wired interface. Then there's always the issue of interference. I could see the point for certain niche applications, and perhaps also for some people who want to show off, but for day-to-day work, I'm not too sure.QuoteRight on. I don't see how having three displays adds very much to the complexity compared to two, though. You'd still need to make a custom LCD panel, anyway. The number of segments should be the smallest issue. (Perhaps steal the Metrawatt layout, BTW, with one big and two small displays?)QuoteSure. However, I'm wondering ifthisis worth the complexity, unless you can fit onto the same glass as the digital display.(Novel idea, BTW: Ditch the LCD and go for an e-ink display...)QuoteSure.QuoteEww! No! It would just sound tinny and you won't be able to hear what the bloody thing is saying. And besides, by the time the meter is done reading the numbers, the values will have changed. It's simply not an efficient way of conveying information.If we're talking novel ideas, one idea could be to use a tone to indicate the displayed value. Let's say it starts at 1 kHz. If you get a load spike, the pitch of the tone will go up. It won't tell you the exact value, but it will tell you in a very direct way that something is happening, and approximately what is happening.QuoteLet me put it this way, if this was a commercial product, and this was not a feature that you wanted to use, you would complain about it. Also, putting any measuring points on the top of the device seems like a bad idea for signal integrity, since that's where you typically have all the digital stuff.QuoteI think you were the one who complained that 4xAA multimeters typically couldn't measure the forward voltage of blue/white LEDs in diode mode...

author: EEVblog
author_rank: Unknown
timestamp: July 03, 2011, 10:53:33 pm
content: Ideas like the tones etc are a given. I deliberately did not go into detail on those types of features that are nothing more than simple software additions. It's a top level idea based around a floating multi channel concept.Re. the number of common channels. As I said, go watch my AA battery capacity video where I demonstrate a real problem with the single ground System used on the Gossen Energy meter. Floating V and I inputs would fix that, or at least the jacks to allow kelvin measurement.The AA's have nothing to do with diode test voltage. Most meters have the problem, yes, but only because the designers are lazy. You simply design in an appropriate converter to fix that.The meter could be powered from a single AA and still have any test voltage you wanted.Dave.

author: House91320
author_rank: Regular Contributor
timestamp: July 03, 2011, 10:56:09 pm
content: Here is an early block diagram. also thinking of having little wireless bugs that you can measure voltage or current with an they would all transmit to the meter so you could petulantly read many different values at the same time wiresly.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: July 03, 2011, 11:23:06 pm
content: Quote from: EEVblog on July 03, 2011, 10:53:33 pmI see your point, however you don't really need true galvanic isolation in that case. You just need current measurement plus a two-terminal differential input with neither of the inputs shorted to ground. Of course that's just bickering about the exact definition of isolated more than anything else.Quote from: EEVblog on July 03, 2011, 10:53:33 pmOf course you can boost the voltage all you want, but then you need to consider things like the power consumption of the converter itself, and the noise it introduces. That's just design decisions, but I suspect that it would be easier to use a 9V battery.

author: DavidJRobertson
author_rank: Regular Contributor
timestamp: July 03, 2011, 11:27:27 pm
content: Ugh. 9V PP3 batteries are awful...

author: zunklimt
author_rank: Newbie
timestamp: July 04, 2011, 12:00:06 am
content: Hello to all !I'm happy to finally join this forum after a long time just watching all the very fine Dave's videosI love the idea of an open source multimeter !So I've made a little drawing with how I see the thinkIt's still just a first draft, there are lots of details to be adjusted/corrected but here it is by now:- ONE SINGLE BIG SCREEN (E-INK or OLED)- USB or WIFI or BLUETHOTH to configure the meter from a computer and for realtime readings on a PC- NO VOICE (numbers are universal, a voice solution would require to think about what languages to use)- USER CONFIGURABLE SCREEN DESIGN AND FUNCTIONALITIESi've included two versions of the idea: one with the connection at the bottom like standard, another with the connection over the screen to keep all the cables away when using on a flat surface (though if used vertically, the classic disposition is better)i hope you like itZundKlimt

author: EEVblog
author_rank: Unknown
timestamp: July 04, 2011, 12:07:15 am
content: Quote from: nitro2k01 on July 03, 2011, 11:23:06 pmThe converter would only switch on when required, so power consumption is not an issue.Noise, well, you design it so it doesn't interfereA 9V battery would be suicide for a meter of this complexity. Not nearly enough capacity. The AA's will struggle, power management would have to be aggressive.Dave.

author: zunklimt
author_rank: Newbie
timestamp: July 04, 2011, 01:46:09 am
content: here is a second version of my drawing, this time i separated the connections from the controls and screen into two separated type of boxesAll the necessary electronics and protection circuits are located inside the small CONNECTION BOXES which should be as flat as possible.Each connector can be freely configured as an iput or as an output and several readings can be made simultaneously at each connection.(of course, here i don't take in consideration how possible or not this would be in terms of electronic circuitry, this is just an idealized wish...INPUTS: V, mA, Watt, Capacitance, Freq, Temp, Etc...OUTPUTS; dcV+mA or WAVEFORM+FREQ+AMPLITUDE or TRIGGER or Etc...All the data is transmited via WIFI or USB between the CONNECTION BOXES and a dedicated CONTROL UNIT (including a big E-INK/OLED screen and soft buttons) or to a SMARTPHONE or to a COMPUTERseveral CONNECTION BOXES could be used with one single computer to get more channels of I/Oswith this equipment there would not be much diference between a multimeter, an osciloscope, a function generator or a power supply... this would be all in one ...well, i'll keep dreaming...

author: s_lannan
author_rank: Contributor
timestamp: July 04, 2011, 02:22:26 am
content: put a capacitor ESR meter in it...

author: Tony R
author_rank: Regular Contributor
timestamp: July 04, 2011, 02:34:19 am
content: Ok - The first couple pages of this thread makes me a little upset to see people are thinking an open source project must be cost effective. To cite the most well known and well used open source project out there, Linus Torvalds did not want to make his operating system profitable or economical, he just wanted an OS that worked the way HE wanted it to. Who says it needs to be a competitor, that's one thing I don't like about the engineering type (Which, at times, includes myself.) Linus Torvalds had no idea his OS would run on many many servers and computers, nor did he know it would be the OS of 459 of the top 500 super computers in late 2010 (which is over 90%.)My point is do not end this now, because who knows what it will become! Engineers tend to think "Is it worth doing? can I get the same thing somewhere else?" Yes, there are 1000s of different kinds of multimeter for all different markets. I can not argue with the fact that yes, it will cost more to make one then it will be to buy one. But Linus could have just got an OS and ran it instead of creating his own OS UNIX would have worked fine for him.With all that said, here is what i think the multimeter should be sure to have...*Rechargeable battery is nice*Data Logging (sd card)*A alarm - say voltage gets over or under a center value have it make a noise*Screw USB, Bluetooth would be nice, you can also avoid isolation this way.*I like the idea of having the standard thermocouple input, maybe have 2 (like dave came up with)*Of course a diode tester, one that can go beyond 3V*LSR meter*High Voltage sound, make a noise when the voltage goes above 90V (or whatever is though necessary)*I would like computer software that makes it easy to interface with MatLab*I would also like to see a DMM with no rotary switch, so if it could be all push buttons i think that would be a unique design.

author: EEVblog
author_rank: Unknown
timestamp: July 04, 2011, 03:06:12 am
content: Quote from: Tony R on July 04, 2011, 02:34:19 amLinus Torvalds never made hardware. He did not have to care about how much something cost, or how expensive or difficult it was to manufacture, or if you could get the parts etc.Cost must be considered in OSHW projects or else they the concept will fail because no one will ever build anything.The goal of OSHW projects is usually to encourage other people to build one too, and that often means custom parts like PCB's, cases etc must be made readily available. That won't happen if it's not cost effective.If your goal is to produce one unit, and not have anyone else ever build one, and just share the design info, then fine, but that's usually not the reason people do major OSHW projects like this.Dave.

author: Zad
author_rank: Super Contributor
timestamp: July 04, 2011, 03:54:15 am
content: Okay. Well, my first reaction is: Nope, not gonna happen. Seen it a thousand times before, mostly in my own notebooks. A product with lots of enthusiasm, but some huge flaws.Sanity check!Try and get a ballpark quote for the custom enclosure. Chances are that it is going to cost more than the price of the house you live in, and certainly more than the cost of the electronics. I seem to remember that tooling for the TV-B-Gone was well over $10,000, and that is a pretty simple and small case. While you are at it, try and get a quote for custom LCDs. Now realise how attractive those dot matrix greyscale trans/flective LCDs look. E-paper is currently way too hard to get hold of and has an awfully slow update rate. OLED looks sexy, but power consumption is going to be a killer in this application.So, having got the grumpy realities out of the way, what next? Well, the engineers most familiar enemy is among us: Creeping Featurage. That temptation to add more and more and more stuff, just because you can. Still, nobody is going to buy a standard A-V-O meter for $200 when they can buy one which is better for $50, so it needs extra features.Personally, I would forget about it being a hand held multimeter and go for a bench meter. Appropriate enclosures are much easier to buy (and fabricate) for bench equipment. If the problem you are dealing with is *that* difficult that it requires such a fancy meter, then you are going to be at your bench, not in the field. To get even half of the features mentioned into a hand portable case is going to be impossible, even for commercial production density.Having 4 channels alone is going to need considerable space, and to retain isolation it will need quite meaty relays for some range selection. 4 properly isolated channels with good resolution in a small space isn't easy. If you are still determined to go hand-held then consider slim high-density mobile phone batteries as an alternative to 4xAA cells. Mini-USB connection would be ideal for charging, as this would allow the use of any modern mobile phone charger. Galvanic isolation is quite easy.Why not use the standard channels in voltage configuration for temperature sensing?Using an Amps/Volts input socket for power supply / signal generation is going to run the risk of connecting it to a live mains potential (if inadvertently selected). I would feel nervous with 4 potentially mains level (or even low voltage 10A) connections physically so close to each other on a hand held device. Maybe have a secondary 2 channel V/A measurement remote headless slave unit?I would have 3 additional (or 4 if we are going for Kelvin sensing $$$) terminals for component testing, which also function as a signal generator (easy to do with a cheap DDS+buffer) and power supply. This physically separates it from the V/A, primarily for safety reasons, but it also disconnects a lot of hardware from the LCR sensing system. You want as little capacitance and inductance on the LCR measurement terminal as possible if you are going to get reasonable resolution and range. Yes, this would remove resistance sensing from the standard measurement terminals but increases precision considerably. Maybe add a separate low resolution resistance measurement? In my experience you rarely need to do precision component characterisation when you are doing mostly V/A work.SD-Card. I think having an SD card socket in the case is a BAD idea (so bad that I put it in capitals). Even when populated, that slot is going to be an entry point for dust, moisture, bits of solder, you name it. If it were a commercial design, I would make it accessible under the battery cover. As an Open Source design intended for 1-off and small runs, I would mount it on the main PCB.I don't think I would trust touch-buttons to have sufficient isolation for mains measurement. Even if the ADC modules are correctly isolated (and let us not for get this is open source, people may cut corners!) then something in my caveman survival instincts tells me not to touch even insulated metal pads. Conventional tactile pushbuttons are much more reassuring but still need ingress prevention via a shaped neoprene (or similar) button mat. A bench meter would have panel space for a rotary input device and 2 separate graphical displays.Sound generation is easy on a controller like a Cortex M3 with 512MB of onboard flash. If speech isn't used, audible cues are still very handy. With regard to remote access, I would prefer WiFi to Bluetooth / ZigBee. That way, it is possible to use your mobile phone or ipod touch etc to view web pages generated on the fly, without and application software. With an appropriate router you could (e.g.) monitor experiments at work from home, on holiday etc.So, my advice would be that if you want it all-singing all-dancing, go with a bench meter, with more room for isolated high-res low-noise ADCs in multiple channels. Power isn't a problem then, and you can use colour LCD panels. Measurement of mains level voltages and high currents can be done with remote head units.If you go with hand-held, then stick to 2 (isolated) channels with what is effectively a separate LCR meter and component analyser (2-terminal diode, 3-terminal transistor and regulator). Design an external display-less 2-channel unit for measuring 2nd and subsequent ports.One more thing. How about proper low-current measurement with a transimpedance amplifier? I think you could make a very average meter, but with zero-burden microcurrent measurement you would have a product with a distinct Unique Selling Point, which is what marketers love!

author: EEVblog
author_rank: Unknown
timestamp: July 04, 2011, 04:33:52 am
content: Quote from: Zad on July 04, 2011, 03:54:15 amI agree. Doesn't mean it's not fun to toss around ideasQuoteIIRC he paid $30K up front before the first unit rolled off the production line.And that's a project with an 8 pin PIC, a battery, one switch, and an IR LED.He went nuts though, could have done it for MUCH less than that.QuoteI agree. A bench meter with an off-the-shelf enclosure stand much better chance of success. There is a thread on that for the open hardware bench meter some time back.QuoteSimple. Then you lose the voltage channels for logging. The whole idea is being able to log voltages, currents, and temp at the same time.QuoteYes, it needs finer details sorted. There are several ways to make it work. So if you want an SD card in the meter, you can make it happen.QuoteYes, that's a given I would have thought.Dave.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 04, 2011, 06:19:09 am
content: Quote from: Tony R on July 04, 2011, 02:34:19 amYou conveniently forgot to mention that the one asking the original question mentioned this is for a kickstarter project. If you don't know kickstarter, it is a web site where people are collecting funding for their projects. This project is right from the start business, not hobby. He just chose to make the project more interesting by labeling it open source.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 04, 2011, 07:46:41 am
content: Hmm.... it just occurred to me that there is a potential issue with having the amps channel isolated from the voltage channel. It makes AC power considerably more complicated. To measure AC power you need to multiply the instantaneous voltage and current. In a non-isolated power meter you can use an analog multiplier followed by a standard sigma-delta or dual-slope ADC. The alternative is to digitize the I and V waveforms at high speed and multiply in software. This costs a bit more power both for the ADC and the CPU, but is still easy to do by using a dual-channel ADC so the I and V are automatically synchronized. The advantage of this is that you only need 2 ADCs and you can get everything in software: DC+AC volts / DC+AC amps / power / apparent power / crest factor / phase lag. With the analog multiplier, you need 3 ADCs and you don't get crest factor, phase angle, or separate DC+AC components without extra hardware.With true isolation you either need to transfer the analog signal over the isolation barrier or have a common (opto-isoated) clock and transmit the 'high bandwidth' digital signal over the link. I would probably go the first route -- the current input module would have only the range switching logic and a linear opto-coupler. The voltage measurement module would have ADCs for both channels. I would still go with the high speed digitizing approach and compute RMS and power in software because it is more flexible and powerful and you can display the waveforms if you want.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: July 04, 2011, 08:44:40 am
content: Quote from: Tony R on July 04, 2011, 02:34:19 amDidn't the OP say it was a Kickstarter project? By definition this means it MUST be cost effective, otherwise who is going to pony up for it?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 04, 2011, 10:40:26 am
content: Quote from: FreeThinker on July 04, 2011, 08:44:40 amThat assumes the project creators have a realistic idea of costs.I always wondered what happens with a kickstarter when the money raised ends up not covering costs due to unforseen issues...

author: EEVblog
author_rank: Unknown
timestamp: July 04, 2011, 11:51:49 am
content: Quote from: mikeselectricstuff on July 04, 2011, 10:40:26 amInteresting question.AFAIK, once the project reaches it's goal, the project automatically gets the money in the bank, with potentially no recourse for the donators if you don't deliver?Surely it's happened, anyone know?Dave.

author: ruku
author_rank: Contributor
timestamp: July 04, 2011, 03:21:38 pm
content: Wow, this thread has totally taken off. I had my reserves the other week when I looked at it, and thought... meh! Idealistic, not going to fly too far.While I think that the "how will people buy this" thing might be an issue, I'd TOTALLY get involved in this project, if only to learn as much as I can!Dave, I really think there'd be some merit to bringing in the forum members here to design a project together. As long as you can assign people to help moderate and finalize decisions (so we're not stuck in analysis paralysis forever), I think it'd totally be awesome to run the gamut of the engineering V and design something!

author: KuchateK
author_rank: Regular Contributor
timestamp: July 04, 2011, 06:00:44 pm
content: Someone mentioned to make it bench multimeter. I think it would be much better idea.You can use big components with loose PCB spacing and have it servicable at home. Proper input protection with nice blast shields can be made at home. You don't have to worry about AA or 9V batteries. Bench case is so big you can put there 12v ups battery and still would be portable.For the display... please don't listen to Dave (no offence)Just put the biggest mono (no color!) graphical LCD screen with backlight. Then you can display single, dual, triple, quadruple or even more channels in different layouts. You can have graphs and bargraphs. Display ton of text for help and schematics how to connect probes. This will give ton of flexibility including different fonts, symbols and anything you can imagine.Look how nice Agilent meters with OLED displays are. Or better. Check out Fluke 287 & 289!http://www.fluke.com/fluke/usen/digital-multimeters/fluke-289.htm?PID=56061&trck=289specificationsBy having dual 5 digit displays you will lock yourself to have stupid loops of "press to display channel #x". Then second display for menus... Its complicated even before it started... Lets drop that gazzilion year fixed display technology.Edit: Dave did review of Fluke:

author: ndictu
author_rank: Regular Contributor
timestamp: July 04, 2011, 06:36:16 pm
content: Quote from: KuchateK on July 04, 2011, 06:00:44 pmI agree. Once you go for bench design there is no need to conserve power so just put whatever display there you can find and then you can do all sorts of stuff with it.Also, since it's opensource it should be really easy to build at home. There can be a professional design with SMD parts and multilayer PCBs but also a bigger double-sided through hole one (since the schematic would be open I'm sure someone would redesign it). Everyone could either purchase a kit or make their own PCB, buy the parts, make changes to hardware and firmware and build their own custom version.

author: KuchateK
author_rank: Regular Contributor
timestamp: July 04, 2011, 08:45:18 pm
content: I forgot to mention. Bench instrument cases are available off the shelf, so only front/back panels must be custom.Today it may be easier to get color LCD, so we might be forced to swallow that extra power usage.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 04, 2011, 10:00:20 pm
content: Quote from: KuchateK on July 04, 2011, 08:45:18 pmMany are. But interestingly I never found a source offering my favorite bench instrument form factor, complete with a handle and rubber bumpers 254 x 104 x (303 ... 375) mm^3 stackable. Companies like Agilent use them for ages for smaller instruments. E.g.http://www.home.agilent.com/agilent/product.jspx?nid=-536902257.536881980.00If someone has a source for these specific enclosures I would be glad to hear of it.

author: Frant
author_rank: Regular Contributor
timestamp: July 04, 2011, 10:39:26 pm
content: Quote from: KuchateK on July 04, 2011, 06:00:44 pmI mentioned a bench meter, but I also said it could be a modular system. It's an open source project and people would like to make different modules to suit their needs, to add channels, to upgrade existing modules and to learn something in the process. It should be an open hardware and software platform rather than a fixed hardware design. Professional modular instrument platforms exist, and I mentioned two: PXI and Agilent USB Modular Instruments. However, this open source project should be much cheaper to build and also simple enough to be accepted by hobbyists.As for the display, it can be a part of an user interface module, so that one can choose from several options or not to have it at all. It's a bench instrument and there would probably be a PC on the same bench, with much more user interface resources.USB is a good choice because it is fast and it provides up to 500 mA for the instrument, so the mains power supply may not be needed. I'm not so enthusiastic about wireless things in situations where they are not absolutely necessary. They are inherently less reliable, they add complexity to the system and always involve batteries which must be taken care of. However, I had a surprisingly good experience with a SENA Parani-ESD200 Bluetooth-serial module, used with a Bluetooth/USB adapter connected to a PC. Once set properly, it worked flawlessly for months. It was actually used to isolate a sensitive signal acquisition system from a PC.

author: ndictu
author_rank: Regular Contributor
timestamp: July 04, 2011, 11:00:55 pm
content: Quote from: Frant on July 04, 2011, 10:39:26 pmExactly. For example, I would like to start with a simple two channel input interface, with V/ohm and current, and an USB interface with the display/data logging on the PC. Then later get some display, add some button interface and have a more stand-alone unit. Someone might want to add a big flash for data logging, someone will just leave the PC running for that. Someone wants a lot of current inputs, someone will put on 10 thermocouple inputs.Something like a modular reference design and everyone can make little changes, pick what they like, ignore the rest or add it later.

author: EEVblog
author_rank: Unknown
timestamp: July 05, 2011, 02:50:07 am
content: Quote from: ndictu on July 04, 2011, 06:36:16 pmI agree. Once you go for bench design there is no need to conserve power so just put whatever display there you can find and then you can do all sorts of stuff with it.I disagree on not conserving battery power. I'd still want a bench meter say D cell powered. (please, forget this rechargable rubbish!)With D cells you could possibly create a killer battery life logging meter, opening up new niche markets.7 segment LCD's still kill dot matrix for viewability, sorry, no contest. Having both is not such a stupid idea, and can help when you go into long term data log battery mode to conserve power yet still display status.Dave.

author: thmjpr
author_rank: Regular Contributor
timestamp: July 05, 2011, 04:03:52 am
content: Quote from: EEVblog on July 04, 2011, 11:51:49 amQuotefromhttp://en.wikipedia.org/wiki/Kickstarter

author: fchk
author_rank: Frequent Contributor
timestamp: July 05, 2011, 09:49:30 am
content: I've just seen the video and really like the idea of multiple inputs.However, I'm a very big fan of the UNIX philosophy: have small, single-purpose tools that do their things right. The video suggests some kind of feature-itis, which definitely will make the whole thing more expensive, but not neccessarily better. If I need temperatures, I'll get a thermometer. If I need to measure impedances, I take a decent RCL meter, which only does this single task, but is way superior in terms of accuracy compared to most general purpose meters. Having a single-purpose Volts-Amps-Watts-Wh meter would make the input circuits much easier and propably more precise.One or two CV/CC outputs might make sense for some tasks, but this could easily be added as an second step.For the display nothing beats VFD's in terms of readability. I really like my Agilent 34401A

author: ndictu
author_rank: Regular Contributor
timestamp: July 05, 2011, 11:55:47 am
content: Quote from: EEVblog on July 05, 2011, 02:50:07 amWell, once again, with the bench design- you have much more space, so why not. You could have one, two or three standard 7segments and one dotmatrix for menus, or extra measurements if you don't have enough 7segments.- everyone can build their own version. Someone prefers 7segments, someone wants a big dotmatrix.About the batteries, do you mean a battery powered or as a backup? Maybe while running on mains you could be using everything but when you disconnect it (or power goes out) it'll try to conserve power by switching displays off?

author: Bloch
author_rank: Unknown
timestamp: July 05, 2011, 07:27:46 pm
content: Quote from: BoredAtWork on July 04, 2011, 10:00:20 pmThat about Bopla BOTEGO240,98 mm * ( 49,96 mm, 65,20 mm, 80,44 mm) * 196,9 mm307,35 mm * ( 49,96 mm, 65,20 mm, 80,44 mm) * 196,9 mmstackable , handle as optionand a angled operating front is an optionhttp://www.bopla.de/en/product-catalog/enclosure-technology/product-category/botego-6.html

author: Bloch
author_rank: Unknown
timestamp: July 05, 2011, 07:50:02 pm
content: Quote from: EEVblog on July 05, 2011, 02:50:07 amNow that is some thing I likeI did a quick look in a catalog Varta batteriesAAA HIGH ENERGY 1,1Ah LR03 1200mAhAA HIGH ENERGY 2,6Ah LR06 2930mAhC HIGH ENERGY 7,8Ah LR14 7800mAhD HIGH ENERGY 16,5Ah LR20 16500mAhNo. Now I think about it. It is just to much power

author: Unknown
author_rank: Unknown
timestamp: July 05, 2011, 10:12:34 pm
content: Quote from: fchk on July 05, 2011, 09:49:30 am7-segment LED comes close, often superior since the digits tend to be larger. Of course they don't do text well. LCD sucks for bench use in my opinion, VFD and LED are just superior for displaying numbers if you don't care about power use. Viewing angle is important if you don't want to move equipment all the time.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 06, 2011, 12:07:03 am
content: Quote from: ronaldlijs on July 05, 2011, 10:51:07 pmForum rule No1, never say to others what to say or not.If you can not handle the conversation, ignore it.Just a friendly advice.

author: EEVblog
author_rank: Unknown
timestamp: July 06, 2011, 12:14:43 am
content: Quote from: ronaldlijs on July 05, 2011, 10:30:47 pmWow, Awesome!Dave.

author: Zad
author_rank: Super Contributor
timestamp: July 06, 2011, 01:10:52 am
content: Quote from: ronaldlijs on July 05, 2011, 10:51:07 pmRobust peer review is the basis of all sound science, but denial without explanation is simply Trolling, and is the curse of many forums around the Internet. Anyone can say "No, you are wrong", but it takes skill and intelligence to saywhy.If you care to read my post instead of jumping to conclusions, you will notice I talk about tooling (i.e. for production) not 1-off prototype enclosures. Prototypes can be milled from solid or built up using desktop prototyping methods, this is clearly not viable for production quantities.Anyway, so I don't create an entirely negative post, 256x64 monochrome OLED displays are getting quite cheap now. Crystalfontz retail them in 1000+ qty for $23:48 ($51:48 1-off). They have on-board controllers and 16 level grey-scale.http://www.crystalfontz.com/product/CFAL25664AYB1If the designer should choose to go with a bench instrument (or a big battery) Crystalfontz also do 320x240xRGB TFT with integrated controller for $18:82 in 1000+ qty. ($53.72 in 1-off) It also has a touch screen option.http://www.crystalfontz.com/product/CFAF320240F-035TThat seems phenomenally cheap for a QVGA including controller, where is the gotcha? I designed some bench test equipment about 7-8 years ago, and the display+controller came in at around £250 (100-ish qty) for a similar QVGA.

author: Tony R
author_rank: Regular Contributor
timestamp: July 06, 2011, 02:31:34 am
content: Quote from: EEVblog on July 04, 2011, 03:06:12 amVery true; however, and perhaps I should have stated it more clearly, if someone wants to make their own DMM and publish everything as to how they did it, and maybe someone else will take that design and improve upon it, why not do it? Maybe it wont be very popular, but who says it has to be?

author: Bloch
author_rank: Unknown
timestamp: July 06, 2011, 05:30:44 am
content: Display.If it is a "long time" product. I mean a product that will be interesting many years. Then I dont like LCD + oled .......I think it will be a bad choice to use a part that will not be on sale in like 3 years.But with Led´s I dont think they will go away for the next 10 years.Iphone app.This is also a bad choice.It is a "lock in" Can the app run i the old Iphone or the next one. And that about the android users ?No the only proper thing to do is a web server. As I dont thing they are going to change the internet for the next 10 years ! Not like the 6 month for phones.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: July 06, 2011, 09:02:54 am
content: Talk about hijacking a thread! The OP asked for comments on HIS kickstarter handheld meter, now we are talking (bickering?) about a non existing bench meter project! Chill out Peebs

author: joegtp
author_rank: Contributor
timestamp: July 06, 2011, 12:17:06 pm
content: This seems like a repeat of another thread a while back --https://www.eevblog.com/forum/index.php?topic=173.0Open source projects just don't start like this. It's going to take one maybe two people to be the leads and just do it. And by "do it" I mean do 90% of the initial work. You are never going to get anywhere by committee. If the decision is made to use LEDs instead of a graphical display are you still going to be motivated enough to work on the project? What about handheld vs benchtop? USB vs Wireless? Battery powered vs plugged in? There are way too many decision points and anyone of those will probably lessen your motivation to work on the project.I love the idea of having an open source electronics bench: power supply, DMM, logic analyzer, etc. But this is not how it's going to happen.

author: Zad
author_rank: Super Contributor
timestamp: July 07, 2011, 02:09:14 am
content: Yes, the larger a group gets, the less likely it is to go anywhere. Linux was 1 man (plus GNU of course) and the ARM was just 2 people with no money and no resources. Similarly, the Mars rovers team had nothing for development and a very difficult deadline to hit.The important thing is to set realistic goals and get on with it. If you get diverted with 4 isolated channels, LCR/ESR and so on, then it will never get anywhere. Publish your results when you get a good design, and then if other people want to make their own machine then that is up to them.

author: EEVblog
author_rank: Unknown
timestamp: July 07, 2011, 02:46:39 am
content: I've said it before. I'm convinced the optimum number of people to work on a project like this and make the decisions rounds down to 1, almost always.Dave.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 07, 2011, 04:24:07 am
content: well 3x, near 3K view in a week (and 7 pages) hit on "Open Source" topic! what do we have got here?

author: firewalker
author_rank: Super Contributor
timestamp: July 07, 2011, 02:13:47 pm
content: Quote from: EEVblog on July 07, 2011, 02:46:39 amAnd usually the outcome is better than a same project with many peoples taking decisions.And as we say in Hellas "When to many rosters are singing, it delays the dawn" (it really looses its value in English)."Opou laloun polloi kokoroi, argei na xhmerwsei"Alexander.

author: XynxNet
author_rank: Regular Contributor
timestamp: July 07, 2011, 03:18:48 pm
content: Some sort of a generic sensor interface would be nice.At the top of the meter you could plug in little addon sensor modules, which consists of a small mikrocontroller for callibration data and conversion tables and of course the sensor (light, sound, vibration, pressure, etc.). The meter suplies the power for the sensor module and displays and logs the sensor data.

author: ruku
author_rank: Contributor
timestamp: July 07, 2011, 07:50:44 pm
content: Quote from: EEVblog on July 07, 2011, 02:46:39 amDave, that's the way to make decisions quickly! Not necessarily the best decision, perhaps... but certainly better than design by committee. However, I still wonder if Open Source Hardware can gain a little momentum from how Open Source Software works. Perhaps once these folks get it rolling, they can bring it in for community assistance.

author: Frant
author_rank: Regular Contributor
timestamp: July 07, 2011, 08:13:07 pm
content: Quote from: XynxNet on July 07, 2011, 03:18:48 pmThe family of standards IEEE 1451.x suggests several solutions. To be more specific, 1451.1 and 1451.2, or 1451.4 could be considered, the others are too complex and don't make sense in this case. However, adding more features has to stop at some point.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 08, 2011, 02:59:41 am
content: Quote from: ruku on July 07, 2011, 07:50:44 pmduring most meeting i've attended, the more efficient way is someone (leader?) to prepare a complete program tentative for everybody to agree/discuss, rather than meet together and talk from nothing, which risk in the end of meeting you still have nothing. so, imho, in order for open source to work, someone has to prepare a working circuit/product to present and improvement or open source effort will start from there. and someone who started it has to be competent or "soundly" knowledgable so other dont have to improve trivial things/aspects.

author: EEVblog
author_rank: Unknown
timestamp: July 08, 2011, 03:18:21 am
content: Quote from: ruku on July 07, 2011, 07:50:44 pmNot if you get one really smart person who knows that they are doing.Such a person is worth a hundreds grunts working a project.QuoteLikely not, they are two different beasts.Ok, in theory it can, but in practice it never works that way.Code is just code, you don't have to worry about manufacturing, physical usability, part availability, power consumption issues etc, and everything that goes along with that. It's a whole different ball-game.For example, open source software like this BBS forum works because you can build a nice code base, and then everyone can pitch in and write plug-in modules to help expand it, building block style. The project gets bigger and better with time, but still remains the same beast underneath.You can't really do the same thing with hardware. By it's very nature, hardware lends itself more toward complete physical change with each design iteration. It's not easy to reuse and build upon existing physical blocks in the same manner.Sure you can reuse bit of schematics as building blocks, and some firmware, but that's about as far as it goes practically.Dave.

author: Harvs
author_rank: Super Contributor
timestamp: July 08, 2011, 05:04:52 am
content: Thoroughly agree with Dave's comments about open-source hardware. Lets be realistic, open hardware has been around since valves and electronic magazines, this is no new concept and it hasn't revolutionized hardware development yet. The only people who really seem to be pushing this concept are the PCB "studios" selling the boards made from other peoples designs.Maybe I'm just a cynic, however when I see phrases such as "Agile development for hardware", I tend to think they don't have a clue about how decent hardware is designed.

author: zunklimt
author_rank: Newbie
timestamp: July 08, 2011, 09:17:14 am
content: wouldn't a modular approach be best the solution?a solid base to begin with and then add new plug ins with new capacitiesif that works for audio synthesis and arduinos, it should also work for professional measurement equipment.using the smallest smd parts and good design, i'm sure it would be possible to do very small modules, maybe as small as lego pieces or with few squared centimetreseveryone could then arrange its metering system as desired: hand-held or bench, big or small, vertical or horizontal, simple or complex, wired or wireless, with as many channels as desired, with or without that or that capacity...a well thought unified system for interconnection and physical attachment between the small modules would be the key to get a solid piece of gear at the end...i know this wouldn't be the easiest to design (both ergonomically and electronically) but the result would then have the best for everyone...but then, maybe simply doing a good arduino shield with the adequate circuitry to use it as a serious multimeter would also be a way...if arduino itself is not good enough, maybe using the maple from leaflabs.com ...

author: EEVblog
author_rank: Unknown
timestamp: July 08, 2011, 09:50:12 am
content: Quote from: zunklimt on July 08, 2011, 09:17:14 amIt almost certainly won't.The design will just end up big, expensive, and clunky, and likely not satisfying anyone requirement.It been tried before many times over the decades, and it just never ends up working, there are just too many design intricacies involved with most projects.You could possibly have some module thing with a multimeter like this, in fact I was thinking separate modular boards for the inputs. But it's not like you can them go do the same thing with say displays etc.QuoteArduino or any system like that is not the right solution for something like this. It has to be fully custom.Dave.

author: EEVblog
author_rank: Unknown
timestamp: July 08, 2011, 10:02:16 am
content: Quote from: Harvs on July 08, 2011, 05:04:52 amYes, nothing new at all. Every magazine project ever published for the last 50+ years is open hardware, it just didn't have that name.Some projects even got "built on" by other people.My DSOA project for example, Jim Rowe at EA magazine took that design and produced the Mk2 unit. Used the same PC interface and core circuitry for software compatibility, but got a whole new PCB, new case, and new controls, turning it into a better unit (albeit, much more expensive).Ok, so doesn't that prove that open hardware works like software?Well, yeah, for that one iteration only.If you wanted to go beyond that (which I did with the Mk3), it quickly becomes clear you have to scrap that design entirely and start again from stratch. There is only so far you can build upon a hardware project before it become non-optimal and a better new approach is required. That usually means an almost complete re-design.Dave.

author: jahonen
author_rank: Super Contributor
timestamp: July 08, 2011, 12:56:32 pm
content: Btw, in case nobody remembers, we seem to had this kind of discussion in the past, seeCommunity Bench Meter. It didn't seem to lead to anything, as nobody did not really want to spend some time on it. Fancy things are usually 99% hard boring work, 1% of the fun stuff.Regards,Janne

author: Chasm
author_rank: Regular Contributor
timestamp: July 08, 2011, 04:43:21 pm
content: 99% of the fun stuff is usually doing the design, once you move beyond it the work starts and the fun is over. That the the moment where most remember that they don't need the device anyway and that "Because I can!" alone is not sufficient motivation.

author: Unknown
author_rank: Unknown
timestamp: July 09, 2011, 01:46:10 am
content: I'm just a little curious on peoples perceptions of open source an on the comparisons between OSH and OSS.Open source doesn't dictate design by committee it's more about freedom and transferal of effort and expertise an alternative to "get what your given" and "don't reverse engineer or we'll sue" corporate models.The comparisons between a proposed multimeter project and open source Linux don't make a lot of sense. If you think for a section about what a Linux distribution is, you can see it is a collection of tools. And just like our multimeter should be, many of those software tools are solo or small team efforts.To build the ultimate multimeter is like trying to build the best car or the ideal home, there is no such thing and there never will be. You can only achieve your ultimate, a committee driven thing will always be a collection of compromises. Look at the software comparison the Linux world is full of many similar tools with differing feature sets, open source gives the freedom to select your own best fit collection of tools.If we were to achieve the hardware equivalent of Linux, we'd be bringing together lots of different open source hardware items and sharing the knowledge. Cant find a power supply that perfectly fits your needs? Then borrow the best bits of existing designs and build your own and share the knowledge you gain along the way. Same for meters or any other piece of equipment.Open source has found favour from those who felt penned in by commercial offerings. Microsoft anyone? The need exists for any operating system that doesn't demand it's users to the company line. I'm not so sure the same need exist with a multimeter, Fluke aren't trying to tell me how to do my work, Microsoft is, and that's why I utilise Microsoft alternatives wherever I can.Where open source hardware would really thrive is in areas like domotics, where anyone could select the collection of products and designs that suits their particular want, need and cave size to achieve their unique personal build.I'm enthusiastic about open source and see it as a worthwhile pursuit, and while I see this open source meter as a bit like pushing string uphill, I'd still love to be proven wrong. Seeing what doesn't work and understanding why can still be some of the most useful engineering there is.Feel free to discuss, dismiss, agree or deride to your heart's desire.

author: Zero999
author_rank: Super Contributor
timestamp: July 09, 2011, 09:41:52 am
content: I agree with Dave that you can't compare open source software with hardware.One fundamental difference is with hardware, there's the physical cost of components and manufacture which doesn't exist with software. A software producer doesn't have to worry about cost per unit whether their open source or not. All a commercial software developer needs to do is ensure the revenue they make from sales covers the cost of development, plus a bit of profit.The physical cost of a single unit of an additional software licence is always near zero. A hardware developer needs to get their product made and sold. The physical cost per unit will always be the price of the components, plus manufacturing and shipping. This is why software piracy is not really stealing. A software vendor doesn't directly loose the value of 1000 licences because someone uploads their software to a file sharing site. A hardware developer would loose the value of 1000 DVMs if someone hijacked a lorry carrying their meters.A software developer is always foolish, if they're unwilling to negotiate on price. An extreme is example: Altium would be better off selling me a copy of their latest design package for £100 than me either not buying it or pirating it. If they don't sell the software to me the get nothing, if they do sell it to me for £100, they get £100 and their only cost is shipping a DVD to me, £10 at the most in administrative costs,, shipping etc.In my opinion, the best open source project would be something like an oscilloscope developed by a commercial seller who made the source code for all of the firmware public and encouraged people to improve it, fix bugs and write translations.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 09, 2011, 10:19:40 am
content: Quote from: Hero999 on July 09, 2011, 09:41:52 amBullshit. You are just doing the usual word games. Word games software thief do to cover up that what they do is wrong. It doesn't matter how you call it, and how many arguments you pull out of thin air. It is wrong.QuoteOh, you mean the Wittig/Wellec oscilloscope? Three years or so of community "enhancements" of the software and still doesn't beat a cheaper Hantek or Owon.

author: Zero999
author_rank: Super Contributor
timestamp: July 09, 2011, 11:32:03 am
content: Quote from: BoredAtWork on July 09, 2011, 10:19:40 amWow, what an informative post!Thanks for wiring a detailed and well reasoned argument as to why it is stealing.QuoteI didn't say that software piracy is not wrong. I just said it isn't stealing. You can't call it stealing because the unit value of a piece of software is effectively zero. Copyright infringement, voiding of a contract yes but physically stealing isn't the right word for it.Of course if everyone pirated software no one would make any money from it but they do and software companies have actually encouraged piracy in the past and still do today, especially in emerging markets to increase the user base.Anyway, I'll stop now. I don't want to turn this thread into flame war on piracy. I just wanted to point out it isn't as simple as many say.QuoteI admit I have no experiences of such oscilloscopes so can't comment. Have you?

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 09, 2011, 03:48:08 pm
content: why dont we just limit the OSH definition to schematic level, not up to pcb/product manufacturing. with only schematics to improve, we can later make our own way on how to manufacture it. and with OSH, you should not expect profit as much as the CSH (closed source) can. something like 50% will buy, 50% will diy or pirate, the figure could be wrong, i just want to demo the idea.

author: joegtp
author_rank: Contributor
timestamp: July 09, 2011, 04:44:49 pm
content: I still don't think group OSH will work. Simple scenario, I'm a project creator/lead and I want to build a single channel, no graphic LCD, really precise, handheld DMM. If you don't share that same exact goal, hardware design fall apart. If you as a contributor, add channels it will increase not only your cost but mine. If you add a graphics LCD again it would completely change the design possibly requiring a new uC more PCB space, etc.. You get the idea.In OSS if you add a wizbang GUI it doesn't really effect me. As the project leader the cost and change to what I use and want it for does not change. Although sometimes it does and that's why you see 20 flavors of linux distros.Software, at least good software, is very modular and parts can be swapped in and out without a whole lot of problem. That's why I think Arduino is so popular, shields can be added and removed, IO pins are exposed to be expanded upon. Which for a hobby, just playing around scenarios, that works great. But once you try and build a product or do something fancy it starts to fall apart.Look at Arducopter (http://code.google.com/p/arducopter/),They started off using a standard arduino mega board but the requirements required a custom board which is where they are today. I also believe it started as one guy designing the whole hardware. But now that the hardware is mature all sorts of people are contributingsoftware. Sure the board is OSH but in the end one guy design and built it to the point that it fully worked before others started stepping in.

author: Zero999
author_rank: Super Contributor
timestamp: July 09, 2011, 06:07:28 pm
content: Quote from: Mechatrommer on July 09, 2011, 03:48:08 pmSchematics aren't very helpful for modern oscilloscopes, at least half of the design is in the firmware.QuoteWhat do you mean? Being open source means you give permission to redistribute so piracy would mean someone violating the GPL such as making modifications and selling the design without releasing the source code.If you're talking about piracy of proprietary software it probably varies widely. Software with a larger user-base will obviously be pirated more and more expensive software is probably likely to have a higher piracy vs legitimate user ratio. Other factors such as the type of demographic of the user-base and DRM also make a difference. The answer is no one really knows.

author: Unknown
author_rank: Unknown
timestamp: July 10, 2011, 07:03:39 pm
content: Hello there, first post on the forum...I've been pondering with the idea of data acquisition for over a year. You know, cobbling together some sensors, do the signal munching and data crunching and pass the data to a PC to be displayed and recorded.So I was thinking whether or not it would be a good idea if I brought the subject to Dave, whom I don't know except watching his videos on YouTube. Since I don't know how to design electronics it occurred to me that it may not be such a good idea to push half baked ideas to people I don't know in order to get them to design it for me.Anyway PXI was mentioned in the thread and since I was drooling over it for long time I decided to go ahead and draw things as I imagined them. So I put together most of the ideas I liked from the forum to see what it would look like.Design criteria as follows:- Should use PXI form factor.I really like PXI. It has everything necessary for measurement and control work. Basically it is a PCI bus with a few additions like precision timing, star triggering etc.The physical layer of PXI is taken from IEEE 1101.10 which is the standard dealing with Eurocard physical dimensions which are ment to go in 19" racks. Since this is worldwide standard finding cases and hardware should be easy and cheap.http://ph-dep-ese.web.cern.ch/ph-dep-ese/crates/standards/1101_1.pdfThe backplane of PXI is largely based (but not exactly the same) on CompactPCI which is also industry standart.Other than that everything revelant is published onhttp://www.pxisa.org/Specifications.htmlAll in all a community designed multimeter has best chances of survival if it is based largely on industry standard hardware. Thus it can live inside many standard cases side by side with commercial stuff and other community gadgets like LCR's, Load cell amplifiers, Thermocouple modules, Frequency generatos, counters, relay boards, SDR's etc. etc.- Standart Commercially available caseAs I said, I am all for PXI and if this multimeter is ever developed I'd stick it in a 3U Rack with all the other community developed things to go with it. However the conversation is about a hand held device so i drew it as such. My point is that you can have both PXI and "Hand Held" at the same time. This case can house two PXI units. If it ever becomes available, users can switch one of the channels for a LCR for example.The box on the pictures is BOPLA Aluplan 51020 it measures 245mm Lenght x 143mm Width x 52mm Height. It is made from aluminium extursions. Top and bottom covers are 3mm thick everything else is thicker. Corner pieces are zinc castings. I don't know how much it costs but sure beats 30.000$ tooling cost for custom case.http://www.bopla.de/en/product-catalog/enclosure-technology/product-category/aluplan-13/product-detail/ap-51020-2.htmlIt is ment to be held sideways so that when sitting inclined on a bench the probe cables are sticking out from the right side - away from where your hands would be when pushing the buttons.- Enough space for batteriesCurrently it has 4 AA cells inside. Maybe it can accomodate 4 D cells if very slightly bigger box was chosen. I think a power input should be made available as well. So that the gadget can work for months measuring away some mundane thing an give alarm and start logging data only if some alarm condition is met.Something like "Give alarm and log data as long as Channel #1 voltage is below 6.25V AND Channel #3 Temp is above 99 Degrees Celsius" Which would mean that your chemical reaction is underway even when you are not applying power. Which may as well mean that you hit the Jackpot and you are going to be rich.- Good User InterfaceDave said he likes 7 segment dispalys but 4 dispalys with 5 digits each? I'd prefer a good ole monochrome LCD please. The one on the picture is 100mm x 70 mm (say 4 by 3 inches). Button arrangement is inspired from aircraft interfaces with a screen and soft buttons around it. A slight twist is the two row buttons on the right side which may be used to alter preferences without entering menus.Front ViewSide ViewSide View - Connection JacksCross Section - To show what goes whereThe small PCB behind the batteries is the "PXI Back-plane" of course it is not standard.it connects only 3 modules (the main board with the display is also a module)This is standard Eurocard size 3U. PXI, CompactPCI, IEEE 1101.10 and probably many others all use this form factor. Sockets at the back side change from standard to standard.Well, I'd like to hear what you thinkEdit: Dave mentioned these sketches on The Amp Hour.Starts around 0:20:05

author: Frant
author_rank: Regular Contributor
timestamp: July 10, 2011, 08:24:49 pm
content: Quote from: HLA-27b on July 10, 2011, 07:03:39 pmImpressive work!

author: Joshua
author_rank: Regular Contributor
timestamp: July 11, 2011, 01:19:36 am
content: Awesome Job! What CAD software is that?

author: Unknown
author_rank: Unknown
timestamp: July 11, 2011, 01:33:10 am
content: Quote from: Joshua on July 11, 2011, 01:19:36 amGoogle SketchUpit is free and by far the easiest one to use.http://sketchup.google.com/Edit: I attach the 3D files used to make the stuff above.Please note that the non free version of SketcUp was used to create them.

author: EEVblog
author_rank: Unknown
timestamp: July 11, 2011, 12:29:49 pm
content: Quote from: HLA-27b on July 10, 2011, 07:03:39 pmYou win the first post of the year award!Awesome.Would it fit 2 x D cells?That would still kill the capacity of 4 x AA'sDave.

author: Unknown
author_rank: Unknown
timestamp: July 11, 2011, 01:40:22 pm
content: It could fit 4 D cells if the case was some 10 - 15mm longer. So definitely possible with another case. In fact i pick this one a bit arbitrarily - it was the first one that could take 2 PXI boards so I used it straight away.I probably should post the 3D files so everybody can have a go at it.(Done look above)On the other hand I would appreciate if you Dave (and all of you guys of couse) can elaborate on some questions I have in mind.How much stuff could fit on 100mm x 160mm Eurocard?2 separate channels with amps and everything or maybe just one volts channel and one amps channel?What do you think of the PXI thing?Do you think that once a community designed multimeter and a backplane is made available to the amateurs it would spur development of many other devices to go with it? LCR's Freq Generators etc?Would you buy one if it was sold as a kit of pieces ?For example a kit of1 - PXI multimeter board (assembled and tested)1 - Main board with processing LCD screen and buttons (assembled and tested)1 - 1 backplane (to be assembled by the buyer)1 - Box to be drilled and assembled by the buyer (takes two pxi units)Any prognosis on the prices?

author: ejeffrey
author_rank: Super Contributor
timestamp: July 11, 2011, 02:48:11 pm
content: Quote from: HLA-27b on July 11, 2011, 01:40:22 pmI am not sure. On the one hand, PXI is indeed really nice, and could be useful for more advanced test gear. However, it isn't exactly very hacker friendly. Even many advanced hobbyists are not likely to have the equipment to develop and test PCI devices. It also seems like a low speed device like a DMM doesn't gain a lot here. I would prefer a low speed serial bus (SPI or CAN) for communication between the modules, and then USB and ethernet on the controller /display module for interface to the outside world. You loose the ability to directly plug into a PXI chassis and integrate with other PXI test gear, but that stuff is usually pretty expensive and out of reach of most hobbyists.

author: Unknown
author_rank: Unknown
timestamp: July 11, 2011, 04:17:16 pm
content: Quote from: ejeffrey on July 11, 2011, 02:48:11 pmOn the contrary, PXI lets you leave out features that you don't use. As a bare minimum you have to implement J1 socket.J1 is for power, 33MHz clock and 32 bit data, 10MHz precision clock and triggering.You can omit any of these unless you need 'em.If you don't need precision clock and triggering you simply don't connect to the pins.Likewise if you don't need 32 bit data you can limit yourself to 8,16,24 bits.Other boards connected to the same back-plane are not affected.(you probably knew all these but I didn't until yesterday)This only leaves out the backplane, which happens to be passive,and the processing board which I imagine as something akin to Beagle boardSo while not exactly piece of cake it is not hacker unfriendly either.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 11, 2011, 06:24:33 pm
content: that thing looks like oscilloscope.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 11, 2011, 06:40:50 pm
content: Quote from: HLA-27b on July 11, 2011, 04:17:16 pmInteresting. I haven't looked much at PXI from the hardware side, and it has been a few years since I had to deal with PCI. The precision timebase and trigger bus aren't what worry me, it is the PCI. I am under the impression that you still have to implement a complete PCI interface -- arbitration, enumeration, and so forth. That means an FPGA, a dedicated bridge chip, or a processor with PCI built in. None of those is out of the realm of a hobbyist to implement, but it can be tricky to debug without a logic analyzer.

author: Bloch
author_rank: Unknown
timestamp: July 11, 2011, 06:51:29 pm
content: Quote from: EEVblog on July 11, 2011, 12:29:49 pmSo true.But the PIX thing is not for me. I think there are a lot of work in that. But if I can buy one finished then no problem.And it seems for me to be an "old" standard. Data in parallel is not the "new" way to do it. Think on IDE / SATA or Parallel port / USB.At work i uses a lot of time on PLC's. And there is the "new" standard EtherCat. Buzzwords free and open / fast / True Time stamps / and just works on Ethernet.But if i get a votethen i think on a RS232/USB > KISS = keep it simple and straightforward

author: JimHorn
author_rank: Newbie
timestamp: July 13, 2011, 06:15:17 am
content: One DMM feature I've always wanted has been standard on oscilloscopes for decades: 1, 2, 5 range switching. With modern digital calibration and LSI, it should be simple to provide. And it would mean that a small increase in a measured value wouldn't suddenly cost you 90% of the instruments resolution.Yes, it means many measurements would have only even or just 0 or 5 as the last digit but the microprocessor running the show could easily show the error band or resolution if asked (another button function?). Most manuals include the instrument accuracy and resolution specs but who remembers those in use? The instrument should...

author: ejeffrey
author_rank: Super Contributor
timestamp: July 13, 2011, 07:27:34 am
content: I would always rather just have more counts. Unnecessary range switches are too annoying, and the resolution and dynamic range of the modern sigma-delta converters is such that the number of displayed counts is set by the display size and the component accuracy, not the ADC.

author: hisense999
author_rank: Contributor
timestamp: July 14, 2011, 04:06:29 am
content: Quote from: Hero999 on July 09, 2011, 09:41:52 amIt's a wrong point of view, Altium is not a fresh computer game which selling in milions of copies monthly but dedicated software - trust me even if this cost £10 ppl still will preffer to use pirate copies. Dedicated software must be expensive and base on selling it into companies, Altium don't care about you and your £100 Altium care about big companies selling them hundreds of seats Altium also don't care if you pirate it even this is good cuz then is possibility to make you stick with Altium software and one day maybe you open a company and must to buy original one, or in further work you push your boss to get Altium for PCB design.Anyway as I also selling software I know is better to sell 1000 copies than 10000 is same profit but more small amount of customers to handle.Just last time my company maked an experiment and we selling software really cheap, belive me we never make this mistake again amount of customers to handle was groving up day by day but amount of income money was a nothing compared to previous products, was more headache than profit on this. And at final you can discover you reach a peak point where sales only will go down cuz you cover with your dedicated software ~40% of possible end customers and then profit is decrasing month by month and wishes of existing customers are incrase whole team start to be tired of tips going from sales and huge amount of work needed to make first existing customers happy and then improvements to catch new customers.And remember dedicated software is not an game you cannot leave it with bugs and without updates or design a "Your Software 2" cuz dedicated group of customers have already this which make them happy and for prepare improvements and something which can be push as new product for which you can charge a new money is not only to redesign levels in game and a little improve graphics but built dozens of complicated things from beginning.P.S.Sorry for my poor englishB.R.

author: hisense999
author_rank: Contributor
timestamp: July 15, 2011, 03:53:41 pm
content: About whole project, is it not better with Open Source Multimeter to just make a real fun hack - just to take a most cheap multimeters which are flooding a market and sometimes cost 2$ and redesign HW inside (maybe even to add own MCU) giving for it super accurate results and new features... I know only 4 digits and no special connectors but if this must be a real open hardware multimeter then this must be something which other ppl are able to make in home without ordering special housing, 2pcs of LCD, custom PCB (the best soldered already cuz then for sure will match specs), so why is not better to pick up most cheap multimeters on the market and check which can be most easy to hack. I speak about perfect hack - additional small board with own MCU inside and only modify existing PCB for replace some crappy components with quaility ones adding some wires and then is a big chance for make open source multimeter for ~20USD which anyone can rebuild in home.B.R.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: July 15, 2011, 06:34:54 pm
content: Quote from: hisense999 on July 15, 2011, 03:53:41 pmProblem is that there is very little inside to hack & the build quality is crap! Non starter sorry

author: Unknown
author_rank: Unknown
timestamp: July 15, 2011, 07:10:07 pm
content: I think we should start to spec out this thing already.So here I ask the question:What should the analog section look like? What should be the specs?

author: rfdave#gmail.com
author_rank: Contributor
timestamp: July 16, 2011, 02:49:30 am
content: How about starting out with a simple USB/1 channel dmm box. Once that's done and working, it's a fairly simple module to plug into other systems.Dave

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2011, 01:35:53 pm
content: Quote from: hisense999 on July 14, 2011, 04:06:29 amYes, may be I took it to the extreme but you know what I mean.QuoteYou're certainly right there - I've said that before.QuoteInteresting, so you don't want too many customers because it increases support costs.So why not just reduce the price of the licence and charge more for support?Surely that sounds like the best business model? Sell relatively inexpensive licences to hobbyists with terms such as not for commercial use and no support and make the real money from big companies.Offering small companies special deals would also be a good idea.QuoteI don't know if I agree with that, I use AutoCAD electrical at work and it's as buggy as Windows 95 was at its initial release and crashes just as often.

author: Joshua
author_rank: Regular Contributor
timestamp: July 16, 2011, 02:08:21 pm
content: Quote from: Hero999 on July 16, 2011, 01:35:53 pmI don't know if there's anything I despise more than when a company won't answer a simple phone call question unless you pay for that support. I.e. Microsoft, apple, HP...

author: hisense999
author_rank: Contributor
timestamp: July 16, 2011, 02:47:19 pm
content: Quote from: Hero999 on July 16, 2011, 01:35:53 pmIs more easy to decrase than incrase prices especially when all is based on distributors network which bought stock already and software is not license based but fisical security dongle based, everything always have more deep story inside even when looks very simple.And with Altium and non-commercial use this is very good idea especially when this also include limitation to two layers boards then this can be perfect deal for hobbysts and good protection for Altium.B.R.P.S.About OpenSource multimeter the most important is to choose enclosure\housing also exist another OpenSource possibility - 3D project which everyone with MakerBot, RepRap or UP! 3D plastic printer can be able to print, just now many ppl have 3D printers and price of it is decrased every year, so community with 3D printers can be supplier for it

author: bobski
author_rank: Contributor
timestamp: July 16, 2011, 08:47:50 pm
content: Here's my own take on the subject. Feel free to pick it to pieces.As this thread demonstrates, everybody's going to have their own requirements for an ideal multimeter. As such, the thing should be made modular so the end user can swap out parts to fit their needs, rather than trying to create aone size fits allmeter as everybody and their brother has done.In that case, the base meter would be a rack-like case with some basic infrastructure that all designs would need: Physical structure for the meter, battery holder(s), a processor, slots for modules (consisting of mechanical supports and a standard set of electrical connections) and such. The modules would be in two or three from factors. A small, simple input module that could handle basic functions like voltage, current, resistance, etc. These modules would ideally interlock horizontally so 3 or 4 of them could be lined up rack style (no dead space between modules) at the bottom of the meter, resulting in the multi-input design dave is after. Measurement circuitry requiring more space could be built in double or triple-wide modules.Display modules would cover the full width of the meter and as I said above and possibly be designed around a bus so they could be stacked as necessary.Controls could be integrated into these display modules, exist as a dedicated display module, or perhaps a third control panel type module is in order.Point being, people can easily assemble a meter to meet their own needs and leave out the extra stuff.This would turn the open-meter into a set of standards… The mechanical specs of the modules, communications between each module and the processor, current demands and such. Once you've got that, anyone can create their own modules to expand the meter's abilities. To facilitate that, blank modules (just the plastic housing and maybe standard connectors) could be sold, as well as populated V/I/R/C, LCD and control modules.Since the modules and services would be standardized, alternative form factors for the meter "rack" could be created as well. Rather than the standard meter housing with lots of module slots, a compact probe-style meter could be made with one or two input slots and a display slot. In that case, the input could be either banana jacks, a point probe with common jack, or tweezers like those obnoxiously expensive LCR meters. A bench-top model would also be perfectly reasonable… Power supply module maybe? That would allow disposable batteries, rechargeable or plug-in sources.Quote from: MrPlacid on July 03, 2011, 04:19:51 amUse something that is ubiquitous like the 18650 Li-ion cells. They're cylindrical, have AA-like proportions (though with larger dimensions) and typically provide around 2300 mAh @ 3.6V. In that case, AA-style battery holder designs (snap in, cradle with cover, caped tube, whatever) would be easy to adapt and would eliminate the need for device-specific battery packs. While they don't quite make the run-out-to-a-drugstore cut, they're used as the base cell in a lot of consumer devices. My older Acer netbook uses them. Judging from the shape, dimensions and specs of the battery pack, my dust buster uses them, and my cordless drill probably does as well. Point being that even if they become hard to find new, it should still be fairly easy to scrounge them out of old battery packs. Using individual removable cells means one can carry around a few extra if spending a lot of time in the field.

author: rfdave#gmail.com
author_rank: Contributor
timestamp: July 16, 2011, 10:15:20 pm
content: A proposed Starting specusb interfacepowered from USB4 1/2 digit resolutionvolts/amps/ohms scalesautoscalingno buttons/controls on case, just banana plugs as input3 plugs-Common, Volts and AmpsContinuity test, fast response timebench focused, so input voltage levels limited to 50vThis could serve as a module in some of the fancier setups, but without this basic functionality, you've got nothing.

author: Unknown
author_rank: Unknown
timestamp: July 16, 2011, 11:41:36 pm
content: Quote from: bobski on July 16, 2011, 08:47:50 pmI agree and I don't agree. Racks are my preferred form factor as well. I wrote about PXI previously and maybe it can be made open source. Not the PXI itsel of course but a board designed to PXI may as well be open source.What I don't agree is that maybe we are trying to tie this thing to a particular shape too early. It is not that voltmeters need racks (but racks need voltmeters...and other things).Quote from: bobski on July 16, 2011, 08:47:50 pmIEEE - 1101.1 is one standard you would like to stick to. It governs the mechanical aspects of rack equipment. On the other hand what governs backplanes is not standards but industry specifications like PCI PCIe CompactPCI PXI etc. PXI is not a standard yet. At the moment it is a specification maintained by a consortium of companies. It may become standard in the future. Standards and specifications are quite an entangled mess. Maybe we should keep them beside the point for the time being. For all I know The Open Source Multimeter consists of a few guys trying to decide what ADC to use.

author: Unknown
author_rank: Unknown
timestamp: July 17, 2011, 12:38:42 am
content: Quote from: rfdave#gmail.com on July 16, 2011, 10:15:20 pm

author: bobski
author_rank: Contributor
timestamp: July 17, 2011, 01:47:30 am
content: Quote from: HLA-27b on July 16, 2011, 11:41:36 pmI see your confusion. I'm saying the meter would be like a rack in the sense that a rack provides multiple slots that can be occupied by a variety of equipment. I suppose what I'm thinking of has more in common with PLCs. For those not familiar with them, PLCs are computers used for industrial automation. The hardware consists of a rack with built in power supply and a series of slots for cards. The slots are all interconnected by a backplane board. The first card is a CPU card with processor, memory and basic run/stop controls. The remaining slots can be used for whatever is needed - input cards (analog or digital), output cards (relay-based digital, or analog), or hybrids of the two. If an assembly line gets re-tooled and different I/O connections are needed, you pop out one card, plug something else in it's place, update the software to reflect the change and away you go.The form factor I'm thinking of is handheld multimeter-sized, though there's no reason you couldn't make a bigger or smaller "rack" that makes use of the same plug-in modules.

author: Unknown
author_rank: Unknown
timestamp: July 17, 2011, 02:03:11 am
content: USB power would require at least one isolated DC-DC converter, more if you want multiple channels. Probably not worth the complexity IMO.

author: Zero999
author_rank: Super Contributor
timestamp: July 17, 2011, 07:28:40 pm
content: Quote from: alm on July 17, 2011, 02:03:11 amGood point.If you design the power supply it would need UL approval and buying one with a with a high enough isolation voltage for mains won't be cheap.I was going to suggest the one in RS linked below but it's only rated for 3kV which won't be good enough for mains, although it'll be fine for SELV i.e. automotive or telecoms use.http://uk.rs-online.com/web/p/dc-dc-converters/4943838/http://docs-europe.electrocomponents.com/webdocs/0518/0900766b80518157.pdf

author: Unknown
author_rank: Unknown
timestamp: July 18, 2011, 02:15:50 am
content: Quote from: alm on July 17, 2011, 02:03:11 amHere is some reading material about isolation and why it is required.http://zone.ni.com/devzone/cda/tut/p/id/3410For people like me who didn't know.

author: Fox
author_rank: Regular Contributor
timestamp: July 18, 2011, 10:33:48 pm
content: Quote from: HLA-27b on July 17, 2011, 12:38:42 amGoing from 4 1/2 Digits to 5 or even 6 Digits will increase the complexity dramatic.The ADC alone won't guarantee the 6Digit resolution, one will need a very good analog signal conditioning circurtry.e.g the Agilent U1242 has an 24bit ADC (ADS1242) like the LTC2415 but gives one "only" 10000 counts with its relatively "simple" input section, but the Fluke 28II with an 20Bit ADC (LTC2435) gives one 20000 counts with a better input section.So keeping 4 1/2Digits resolution would increase the possibility of success of an open source Multimeter

author: Unknown
author_rank: Unknown
timestamp: July 18, 2011, 10:59:47 pm
content: Quote from: Fox on July 18, 2011, 10:33:48 pmI agree. Trying to increase resolution places high demands on every aspect of the design. Voltage reference, clock jitter, PSRR, Analog noise etc etc...However I think we have some advantages here compared to the commercial guys. Open Source multimeter will likely be an evolutionary project. There will be many iterations and refinements. By and by it will get better. Another advantage that we have is that we don't have to worry about profit margins and product placement. Therefore we can use (hopefully justified) pricier components.What worries me is that no designs popped out yet. It is like all of the more experienced guys prefer to just watch and keep quiet. As if they are afraid of criticism or something.

author: Fox
author_rank: Regular Contributor
timestamp: July 18, 2011, 11:16:22 pm
content: Oh i have a design for my own 5.5Digit Meter project almost finished (about 70% i guess, most of the digital stuff has to be done),but i am not sure if meets the 5.5Digits resolution criteria and its still a bit in the flow, so i won't share it just yet.

author: Unknown
author_rank: Unknown
timestamp: July 18, 2011, 11:41:08 pm
content: I didn't mean to offend you or somethingHope it turns out good.

author: Fox
author_rank: Regular Contributor
timestamp: July 19, 2011, 12:05:43 am
content: No offense taken

author: Zad
author_rank: Super Contributor
timestamp: July 19, 2011, 12:56:13 am
content: It is one thing to draw what you want, but another thing entirely for it to be physically possible. For example, consider how much volume a typical meter uses for voltage and current switching, including the precision film resistor packs and 10A current shunts. Add to that a data isolation and PSU, conditioning and ADC. Now consider that on the drawing shown so far, they have to fit in <10 cu. cm.With ADCs you can always integrate readings and filter digitally, allowing the user the opportunity to offset speed for precision. If a user is looking for spikes, then they are highly unlikely to be interested in ultimate precision.Here is a graph of some investigations I made into the performance of some fast 24-bit TI ADCs. Noise free 20 bits (6 digits) at 100SPS is perfectly achievable, but note that this is purely the performance of the ADC, without any conditioning, protection etc.

author: Unknown
author_rank: Unknown
timestamp: July 19, 2011, 01:54:47 am
content: Quote from: Zad on July 19, 2011, 12:56:13 amMan if it takes space it takes space. Make it 300 cm3 and worry about miniaturizing it later.Quote from: Zad on July 19, 2011, 12:56:13 amIf we can get 20 bit resolution out of a 24 bit ADC, does that mean that we have an error budget of 4 bits? Or maybe it is not that straightforward. I need to figure out how to stack up these errors...

author: bobski
author_rank: Contributor
timestamp: July 19, 2011, 02:37:01 am
content: Quote from: HLA-27b on July 18, 2011, 10:59:47 pmAnother excellent reason for a modular design. Whether it's a eurocard form factor or something new, a modular design will allow for cheaper upgrades and modifications.I gave SketchUp a try. It may actually be one of the easiest to use 3D apps I've ever encountered. Yeah, it feels tedious and clunky at times, but much less so than other software. Sorry... No buttons, LCDs or connectors yet.That's an 18650 cell by the way.

author: Unknown
author_rank: Unknown
timestamp: July 19, 2011, 02:58:15 am
content: Glad to see SketchUp catching onWhat is the orange box made of, plastic or aluminium?

author: bobski
author_rank: Contributor
timestamp: July 19, 2011, 03:13:22 am
content: Plastic would be much lighter and provide better impact protection, so I guess I'll go with that. Some metal hardware is probably in order though... Those dovetail rails for the modules could be a weak point if they're just plastic.

author: Unknown
author_rank: Unknown
timestamp: July 19, 2011, 03:48:07 am
content: There are a few things to bear in mind when designing for plastics. If you want to get more serious about this better read about "designing plastic parts" on google.What remained in my memory from my design class is- Uniform sections - Basically you want all your walls the same thickness, otherwise they warp when they cool.- Mold draft - You need some angle of slope so that your part can come out of the mold.- Parting line - Basically you pick two opposite sides of a part. All surfaces of that part must be clearly visible from one of these surfaces. You will need to change the orientation of your battery compartment. Otherwise the manufacturers will hate you (and bill you accordingly).- Minimum part count - molds are obscenely expensive. No less than 10000$ a pop.These things will improve your designs a lot.

author: bobski
author_rank: Contributor
timestamp: July 19, 2011, 08:44:08 pm
content: Okay, I'll stop now. ^_^

author: Unknown
author_rank: Unknown
timestamp: July 19, 2011, 09:15:35 pm
content: Good job. It looks a lot better.

author: Zad
author_rank: Super Contributor
timestamp: July 19, 2011, 10:48:37 pm
content: Quote from: HLA-27b on July 19, 2011, 02:58:15 amWould you touch the case of a aluminium housed multimeter when it was measuring mains voltage?

author: Unknown
author_rank: Unknown
timestamp: July 19, 2011, 11:00:11 pm
content: Quote from: Zad on July 19, 2011, 10:48:37 pmPXI stuff has metal panels and sits in a metal case. Apparently it is safe.Amateur stuff? Not sure, it depends.

author: Unknown
author_rank: Unknown
timestamp: July 20, 2011, 08:24:50 pm
content: Most commercial bench meters have a metal case. No safety issue as long as the case has a solid ground connection, and of course the front-end is fully floating and well isolated. I wouldn't use metal for a meter that can run on batteries, however, since you can't guarantee a ground connection (like those bench scopes with battery option that some people use without the mandatory ground connection for anything but SELV). Most commercial bench meters with battery option also used a plastic case I think. It is possible to make double isolated equipment with metal cases, plenty of consumer gear is. But you would need double the clearance and creapage distances as appropriate for the voltage rating.

author: gregariz
author_rank: Frequent Contributor
timestamp: July 20, 2011, 08:27:36 pm
content: Quote from: alm on July 20, 2011, 08:24:50 pmIf your clumbsy like me you'll often be dropping your meter in the wrong place. Plastic is good when that place has some voltage.

author: Zero999
author_rank: Super Contributor
timestamp: July 21, 2011, 05:39:37 pm
content: I don't see why there's lots of contaversy over a hand-held meter with a metal case. It's perfectly safe, as long as there's sufficient insulation between the live parts and case and it's mechanically robust enough to withstand being thrown around and stamped on. A good metal case should be stronger and safer than any plastic cause.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 21, 2011, 06:20:08 pm
content: Quote from: Hero999 on July 21, 2011, 05:39:37 pmAnd is a risk on a workbench or near / inside a dangerous machine, where the case could cause a short circuit. And if you hold that instrument the moment you cause the short circuit with the case, your body could become a significant part of the circuit.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2011, 06:25:07 pm
content: Quote from: gregariz on July 20, 2011, 08:27:36 pmI see your point. metal case is not good for hand held equipment.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 22, 2011, 05:49:59 pm
content: My POV may not be anybody elses, but here it is anyway-This is 2011. We have capabilities they didn't have back in the '60s. We might want to think not in terms of traditional dedicated test equipment like DVMs, that have been around forever, but something much more flexible. I collect used test equipment and even with all the stuff I've got, I can't make the measurements I (or my customers) need at a price I can afford. The world is awash in DVMs and even the junk ones are surprisingly good. 6 1/2 digit meters with HPIB are no problem, new or used. Ditto frequency counters. What I'd really like is a black box having a synthesizer chip (Analog devices has some great ones), several DVM type measurement channels (at least 2), a phase detector in hardware, some internal impedance standards and a USB interface. Maybe a counter, but not sure.Why?Because all that stuff can be configured not only as a DVM, but as a VAW meter, an LCR meter, a network analyzer, an audio analyzer, a signal generator and perform pretty much any bench test or component test you might want. Under PC control (IMO it has to have open software) I could configure it for whatever needed to be done, like swept measurements. I have no interest in a display, other than the PC, but a lot of interest in data-logging. Note that almost all design work in the commercial world requires data-logging.Before you get the idea that this is a huge or complicated effort, look at the high level parts you can get today. The synthesizer chip solves that problem. There are phase detector solutions. Instantaneous voltage and current measurements give you the VAW meter function. It's a big design, but not nearly as difficult as it would have been a decade ago.Take a look at the $16,000 Agilent E4980ALCR meter. Once you lose the display there's no reason that can't be done for a hobbyist price. With the right software you have a network analyzer (I've done this). Now look at something like the watt meters and stuff fromClarke-Hess.That functionallity shouldn't be tough to include.I realize I've gone completely OT here, but IMO pursuing another DVM, regardless of features, will never give ROI commercially, and I can't imagine any DIY builder bothering with it. OTOH, I've been wrong before- just ask my wife!Best,Conrad

author: Unknown
author_rank: Unknown
timestamp: July 22, 2011, 06:20:28 pm
content: Welcome aboard Mr. Hoffman,I am so happy to see you here. Your ideas are most most definitely welcome.In fact it never dawned on me that this thing may include a synthesizer.PS: I received your mail. But since you are here how would you feel about posting your magazine articles (or links thereof) under your own name?

author: bobski
author_rank: Contributor
timestamp: July 22, 2011, 06:34:15 pm
content: From what I've read so far, the circuits for measuring inductance and capacitance values are both based on applying a sine or other fluctuating signal to the component and measuring its reaction. Making that signal source more dynamic and available for other functions makes perfect sense to me.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 22, 2011, 06:42:38 pm
content: Hi,Sure, these are ancient but everyone is certainly welcome to read myMini-Metrology Lab articles here.That's how things were done in the good old days. Feel free to wander the rest of the site- should be something there for just about anybody.On the multi-function meter gadget, I don't know why nobody has done this before. All the hardware is practical, but the big players keep making their very expensive traditional instruments. Heck, the most desirable low frequency network analyzer is about $40k. Put the right package together and you might have a very desirable moderate volume product.BTW, the key to LCR is the phase detector. Phase is your loss, and converts to esr, dissipation factor or however else you want to express it.Best,Conrad

author: nullsmack
author_rank: Newbie
timestamp: July 22, 2011, 08:08:45 pm
content: Have you guys ever seen this:http://mondo-technology.com/super.html?It squeezes quite a bit of functionality into something handheld size.

author: bobski
author_rank: Contributor
timestamp: July 23, 2011, 04:40:06 am
content: Quote from: nullsmack on July 22, 2011, 08:08:45 pmNow you've got me thinking about gutting my Mastech pen multimeter again.

author: KuchateK
author_rank: Regular Contributor
timestamp: July 23, 2011, 06:11:41 am
content: Ideas presented by Mr. Hoffman are great.I'm looking around for something above multimeter capabilities and much smaller and cheaper than existing alternatives for labs/professionals. Generator, LCR, capabilities that super probe has. Small, flexible multichannel replacement for three multimeters that are sometimes required and with logging capability that would allow automatic testing or graphing what is really happening over time. Such programmable device with open firmware would be great and I think there is huge market for that. Consider cost of two/three good multimeters with PC connection.Hobbyist working on project can't really justify spending thousands of dollars on lab equipment and professionals would love lab on the go.I was recently looking for LCR meter with ESR and this is just amazing how expensive they are. I can get Rigol scope for that price. It was much cheaper to replace all caps in the device than to hunt broken ones.Bobski's modular project looks great, but that amount of plastic would require significant tooling cost and is not really hobby friendly. I can't imagine someone making modules for this design at home.From hacking/modding point of view I would more likely see something that HAL-42b presented. Big PCBs for all sorts of crazy modules, big components, flexible backplane, generic off the shelf enclosures. I don't like sticking to industry standard though. Pursuing compatibility that fraction of users would utilize is huge waste of time and resources. This device should have as big microcontroller as possible with as many possible connections on the backplane as possible. Look at arduino. Minimal design compared to some alternatives. KISS rule really showed. Make it flexible and easy to duplicate.Something to extend idea presented by HAL-42b to make it easier to get and duplicate...I recommend Mike's videos. He is showing some nice stuff and ideas and has very little views.Start designing circuits guys. The rest will come later. Remember! First generation doesn't have to be perfect.

author: Unknown
author_rank: Unknown
timestamp: July 23, 2011, 01:22:02 pm
content: Well the standards are more political than technical for me. Sticking to standards makes it a lot easier for institutions to contribute. Imagine if we could develop a backplane akin to PXI which is open source (I know it is not literally a standard)- it would be immediate hit with all universities and research institutions. This would encourage them to develop more hardware for it, again open source, and to the benefit of us all. Btw. PXI is not a standard yet mainly because it is not fully open.It isn't only us amateurs that need this stuff. universities and research institutions need it too. And I am not talking multimeters here. CERN just recently announced their own open source license. There are already several projects under that license, including a very nice clock signal distribution switch. They sure have one hell of a budget, couldn't they just buy all this stuff? They could but that would have meant firing research staff, and it is not the gear that makes the science, it is the staff. The university I graduated from spent 2M$ in test and measurement equipment while I was studying there. Imagine if that could have been halved? They would have hired twice as much research staff.What I am saying is that standards are already out there. If we don't stick to them we have to develop our own, which is arguably impossible because we are talking hardware, not software. They make it easier to contribute to an open source project. They are already well documented - bad documentation is the plague of open source.

author: bobski
author_rank: Contributor
timestamp: July 23, 2011, 03:58:11 pm
content: Quote from: KuchateK on July 23, 2011, 06:11:41 amI totally agree on the financial considerations. The project would need support from a better funded, or at least better equipped, entity. I don't envision the plastic parts being molded by home inventors. Rather, get the project producer to mold the parts and make them available as blank housings on the cheap. To further the project and get a ROI, the producer could go ahead and populate the main housing to spec and sell them along with their own module designs. That would make a standard level of functionality available for purchase with a minimum of fuss, while providing the framework for private inventor types to develop their own designs and further the project as a whole by sharing with the community.Quote from: HAL-42b on July 23, 2011, 01:22:02 pmSticking to standards (at least at key points in the design) makes it easier for everyone to contribute. Standards are needed if you're going to use a modular, isolated approach. Even if your end design is a physically monolithic device, keeping the circuitry compartmentalized reduces the likelihood of one functional section unintentionally influencing another. A standard set of connections at the borders of that modular isolation make it easier for people (individuals or institutions) to construct their own functional modules and cleanly append them to the core functionality of the meter. The trick is making that set of connections flexible and powerful design-wise, yet inexpensive and easy to work with.Quote from: HAL-42b on July 23, 2011, 01:22:02 pmYes, this is what I would like to see happen. A large institution take up the cause and deal with the aspects of the design that are impractical for the independent developer to manage.Quote from: HAL-42b on July 23, 2011, 01:22:02 pmImpossible? I suppose if you want to develop a standard from the electrical and timing parameters up, that's a pretty daunting and expensive task. I don't see why that would be necessary here. There's plenty of existing hardware standards that can be pulled into the project design quickly and easily to create a project-specific standard.For instance, the input modules on my design. One would obviously need power and ground connections, preferably isolated since we're doing measurements. An analog return line or two might be good... They could be multiplexed with the lines from other modules and fed to a central high quality ADC if the designer doesn't include one in the module itself. Since noise would be a problem on those analog lines, a shielded (coax?) connector of some sort is probably in order. Digital control and data lines of some sort are probably a good idea. SPI and/or I2C maybe?Throw in some module dimensions and standard connector locations and you have a hardware standard.

author: KuchateK
author_rank: Regular Contributor
timestamp: July 25, 2011, 04:49:15 am
content: Even fancy multimeters are not using anything more than MSP430. This is processing power for SPI, I2C, RS232/485 level.The standard for such multimeter should describe boards with specific size and connector on the edge that has I2C, SPI, RS232/RS485 (and some other) interfaces and a as much as possible control digital/analog pins. Something that requires more power than some cheap 8-32 bit MCU can handle will scare people off any involvement and development.To be popular it has to be cheap. When it is popular then it is much easier to create high speed/fancy variations. I'll go back to Arduino as example. It became popular, because initial investment was ATmega8 with crystal and rs232 to a PC. Right now you can also get Arduino running ARM chip and it still works.We should hit and aim at hobby/student/small business market. Guys with Arduinos that want to measure ESR/power or inductance without spending hundreds of dollars on few multimeters. It should be small modular and customizable (!) companion for cheapest Rigol scope and nothing beyond that.Even if the tool won't satisfy CERN, it may be great for thousands of students. CERN? They have staff and money to do whatever they want (sometimes) beyond our imagination. We should leave them alone. We should focus on the other end of the market. Beginers trying to learn. When students will start to use something, then institutions will be forced to use it. They have tight budgets and they would love to have cheap open source educational tools.In my opinion it would be easier to start small and get support from agile companies such as Sparkfun than big slow moving institutions with grants that are nicely distributed between big market players.

author: Unknown
author_rank: Unknown
timestamp: July 25, 2011, 08:47:47 am
content: KuchateKI follow what you say and I agree with most of the points you make. In that light, there are some concerns that arise. Supposing that we develop an arduino shield voltmeter, I am certain that any kid picking up this voltmeter will stick it into the mains first thing out of the box. We rally can't sell this thing without at least CAT II safety. Therefore we will have to provide it in a box. Who is going to pay for certification? What will happen if somebody really gets hurt? In the country I live in, if you screw up, that's your own damn problem. If you stick an arduino shield into the mains that just means you're being stupid, you've got nobody to blame. But that's my country and that's the way I like it. Europe and US are not like that so we have to figure out how to sell this thing without causing mortal danger and legal issues to ourselves. This is the state of mind I'm in right now.OTOH developing an arduino shield voltmeter is a quick and dirty way of getting into it, so maybe exactly the reason why we should do it. There are posts on this thread that discuss the theories of measurement in depth and breadth yet no schematics came forward. Maybe it is time to leave the scalpel and get the ax.

author: KuchateK
author_rank: Regular Contributor
timestamp: July 25, 2011, 03:18:00 pm
content: Americans have this stupid idea that if something happens you can blame everyone except idiot who got hurt and his parents that they did not teach him list of "don't do this". Should we care? Hell no!What can we do to prevent accidents?If we won't write some warnings then we are to blame (a little). But every mains voltage kit I did had nice paragraph about safety and that is enough for normal people around the world. We are not going forcing anyone to use it.I think it should be a kit, not a complete product. Then you don't have to bother about some safety issues and certifications. We should not even bother providing enclosures or parts. There are many sources for that. PCBs distributed by some people would be sufficient in my opinion. Good documentation/tutorials plus code is still time consuming. Someone can create kits and distribute them later...Should we create Arduino shields? NEVER! This form factor begs to be unsafe when it comes to any higher voltages. And I don't really think useful multimeter can be made on (even big) shield.But... We should use Arduino as a base. As a coding platform and interface to real world it is great. Why? Because you can jump to C or assembly when you need to in any section of your code. Changing default MCU configuration and taking full advantage of its capabilities is easy. If controller would take Arduino code, then we have customization and easy development covered. Arduino would be great connector between some first boards and computer during initial design. We can later jump to ARM or something more powerful, and because they ported Arduino libraries, code can be reused.There is one more question that needs to be answered. Should we create mains voltage multimeter? Why not make first versions going up to 50V like an oscilloscope? Want to measure something higher? You know what to doI wrote about analog pins on the board connector, but after some consideration, I think that boards should be as independent as possible with something smart built in. Some digital interfaces only providing ready to read data. Without many connections you can then shield them and isolate cheaply.For example RS485. You have ability to connect multiple boards and external devices (programmable power supply for example). It is popular industry standard and it is quite fast on short distances and can work kilometer away. Microcontrollers are cheap and every board could have some bits without sacrificing cost that much. A chain would connect to a controller that would only handle data display/logging and user interface to modules after querying them what they are. PC would do the same even through terminal. It should be also easy to provide wireless modules for boards.Seems that there would be need for some clocking signal from controller to each board so they can be synchronized. My knowledge is rather limited and someone having more experience with more complicated measurement gear should write about how they usually work.

author: KuchateK
author_rank: Regular Contributor
timestamp: July 25, 2011, 03:56:08 pm
content: Quote from: HAL-42b on July 25, 2011, 08:47:47 amUnfortunately I cant contribute more than talking right now. For me analog circuits are mostly spaghettiDon't be shy people. Show us something.

author: Extech
author_rank: Contributor
timestamp: July 25, 2011, 05:01:50 pm
content: Quote from: Kiriakos-GR on June 30, 2011, 08:06:10 pmNice!

author: bobski
author_rank: Contributor
timestamp: July 25, 2011, 05:20:44 pm
content: Quote from: ARebelo-Extech on July 25, 2011, 05:01:50 pmHaha... Meter snobs? ^_^I have an Extech as my primary meter. I wish it had a bar graph, but otherwise it seems to be a perfectly good instrument. Fluke and Agilent meters look nice, but as an EE student (when I bought it) I couldn't justify the price: 2-3x that of the Extech for the same feature set.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 25, 2011, 06:31:29 pm
content: Here's an example of how a clever start up could take the big companies to the cleaners-http://cp.literature.agilent.com/litweb/pdf/5990-7778EN.pdfIMO, they totally blew it with the limited frequencies. With a synthesizer and good interface it would be a killer product, but they probably thought if they did that it would compete with their expensive stuff.

author: bobski
author_rank: Contributor
timestamp: July 25, 2011, 09:32:02 pm
content: Quote from: bobski on July 19, 2011, 08:44:08 pmI lied.

author: bobski
author_rank: Contributor
timestamp: July 29, 2011, 07:50:53 pm
content: In case anyone wants to fool with it themselves:http://dl.dropbox.com/u/9882625/openMeter%20Sketch%20V2.0.skp

author: Unknown
author_rank: Unknown
timestamp: July 30, 2011, 09:14:58 am
content: Mr. HoffmanWhat is involved in putting a synthesizer on board? Can you point to example chips/schematics? Also what new capabilities will that add?I think this is a new idea to most of us so you may need to bring us up to speed.Cheers

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 30, 2011, 08:54:16 pm
content: Hi,What you're looking for are Analog Devices DDS (direct digital synthesis) chips. It used to be simple, but now they have a huge family of them. I'd start by looking at AD9838, which is a simple waveform generator with an I2C interface. They even have the AD5933, which is a complete waveform generator and ADC designed for impedance measurements. Unfortunately it's aimed at higher frequencies and they say it only goes down to 100 Hz.This pagewould be a good place to start looking at all that's available. BTW, some of them don't even cost that much.IMO, once you include a signal source in your device, all sorts of possibilities open up because you can then characterize both active and passive stuff (filters, amplifiers, caps, inductors and resonant circuits). You can also use it as a stand-alone signal generator and meter (because of course you'll build in a decent 5+ digit meter and true rms circuit).People have gone in this direction before to some degree. Look up the Keithley Source-Meters. Too specialized and too expensive for most. The Agilent LCR meters I mentioned earlier IMO could have been much more, but they probably didn't want to drain sales of their more expensive products. The closest thing is a good PC sound card with a program like Visual Analyser, but the signal output from sound cards is less wonderful than they'd have you believe.Best,Conrad (my dad is Mr. Hoffman!)

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 31, 2011, 05:16:51 pm
content: Just to babble a bit, I've no idea how to package this thing- other people here are way better at that. Standards are nice, but can make the physical hardware costs very high. I remember Eurocards, with high pin count on the connectors, but also high backplane costs. There are "NIM bins", Nuclear Instrument Modules, but I don't remember much about that format, only that it was reasonably narrow. No doubt there are many other modular standards. Or, you can put everything in a single box. With a single PCB and all connectors on that single PCB, costs would probably be lowest.I imagine the basic functions to be 3 major user blocks. First you have a DVM module. Next you have another DVM module that can also be set up to measure current. Third, you have a source (synthesizer signal generator) module. So maybe the box has 3 sets of leads- bananas, BNCs or whatever. So far, pretty simple and just an enhanced DVM.The key is that the input modules are all fast ADC, feeding a "brain" (either internal CPU or external PC) instantaneous data. Now, with voltage and current, you easily get DC power- that's a no brainer. But it doesn't work for AC. However, if you do instantaneous voltage and current, that does work for AC. So now you have a proper (and high $$ value to the customer) VAW (volt-amp-watt) meter.Add the signal source, plus the ability to measure instantaneous voltage and current, and you complete the picture, being able to excite the DUT (device under test) and measure its transfer function and impedance at any frequency. IMO, the instrument should work from DC to about 1MHz to be useful.Hopefully that defines/explains things a bit better.

author: Zad
author_rank: Super Contributor
timestamp: August 01, 2011, 10:17:11 pm
content: I'm slowly developing an LCR meter using the AD5933 (see my blog) and it is a pretty good chip in general, but It does need driving from a divider (or another DDS) if you want to lower the minimum frequency, and you need to buffer the drive signal (preferably with variable gain and offset) if you want to measure below 200 ohms or so.

author: AndyM
author_rank: Newbie
timestamp: August 23, 2011, 10:15:52 pm
content: I've been reading this thread whilst on my holiday (bored without my bench and soldering iron!!).Whilst an attempt to adhere to standards is understandable I have to say that the simplest construction would be preferable.As for the front and back panels, I have used FrontPanel Express for many of my projects and I find them to be reasonable (especially for one off panels) and they give a very professional finish. They even have a range of enclosures that I have also used.A bench meter with additional functionality as detailed by Conrad gets my vote with a single main PCB and separate pcb's for mounting the external connectors or perhaps wiring the connectors from the front panel down to the PCB. I don't want it too big (perhaps something similar in size to the HP3478 would be good). I'd like it to be portable but not permanently so (how about some rechargeable AA's internally and a power brick when used on the bench).The potential is vast. It would be great to be able to replace a transistor tester, LED tester, DVM, SigGen etc., etc. with a single instrument.Love Dave's idea about the thermal probes as I built alot of vacuum tube stuff and often look at the temperature of transformers, chokes and valves.The synthesis core might also allow characteristics to be plotted when testing semiconductors.Have I gone too far??Andy

author: House91320
author_rank: Regular Contributor
timestamp: September 13, 2011, 01:26:44 am
content: Just some updates on whats happening with the meter (yes the project didn't just die out). i am currently working on the rev1 of the pcb. As it stands now its going to have a mono glcd, fram or eeprom (the code and board will allow you to chose), usb slave and host (the reason for the host is to be able to plug a usb flash drive in, should mention host and slave are iso to 5kv), and its a it can display and log 2, v channels and 2, A channel + a lcr channel. Any thing more you would like to know just shoot me a question.

author: silversteam314
author_rank: Newbie
timestamp: January 07, 2012, 05:09:05 pm
content: I just read a blog post about this somewhere and came to check what has happened since Dave talked about this on the vlog.Is there any progress, or is this project now at a standstill?

author: Bored@Work
author_rank: Super Contributor
timestamp: January 07, 2012, 06:03:56 pm
content: Quote from: silversteam314 on January 07, 2012, 05:09:05 pmIt was never a project. Dave was very clear about it that he was only doing the sketch for fun. And as you can see from the discussion here, it degraded to what always happened with such ideas. Lots of people coming up with their wishes in the hope that they find someone to do the actual work. Those doing some work quickly find out that it is really hard work and that there is little reward doing this.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2012, 08:44:19 pm
content: Actually this thread inspired me to do something entirely different but still along the lines of open source hardware.I am hoping to spill my meager beans soon.

author: Unknown
author_rank: Unknown
timestamp: April 22, 2012, 09:29:29 pm
content: Hi, this is the sort of thing i'd go for, it's called the Multimogger (Multimeter / Logger); I actually missed out the function generator out, so you have to imagine that's in there too. These could available in different widths allowing for more (expensive) or less (cheaper) features.The case is simple no-frills, no display either, all that is done in software on the smart device. One thing I thought might be nice was triggers, so i included two outputs, these would be dependent on specific user defined parameters or events. For example when temperature / voltage or current etc on channel X reaches / falls etc Y then trigger output 1 or 2. You could set it up in the UI like a typical logic analyzer trigger steps, did i tell you it had a I2C bus viewer in there too? (maybe phase 2 ;-)The UI software logic would handle most of the clever display and control stuff allowing for a minimal hardware specification for each channel plugin (shield?)All communication is done via bluetooth with the idea it works in conjunction with a smart device or a laptop.Also it's got to be really nice and heavy, filled with lots of batteries, I don't want something to slide across the bench every time I hook things up to it.It's the swiss army knife of multimeters!! and it's putting the MULTI back into multimeter! ;-)Kind RegardsJules

author: Unknown
author_rank: Unknown
timestamp: April 22, 2012, 11:13:23 pm
content: You mean something like this?I've been working on mechanical aspects it for a while. It is a very useful concept except all the difficulties in making it actually work.

author: EEVblog
author_rank: Unknown
timestamp: April 23, 2012, 02:25:23 am
content: Quote from: HAL-42b on April 22, 2012, 11:13:23 pmThose pesky minor details!Dave.

author: Unknown
author_rank: Unknown
timestamp: April 23, 2012, 09:16:39 am
content: Quote from: HAL-42b on April 22, 2012, 11:13:23 pmhehe. Now that's just weird! did you sneak into my room while I was asleep claiming to be Darth Vader from the Planet Vulcan and download my thoughts with an 80's Walkman to the sound of Eddie Van Halen?There seems to be lots of ideas and drive to build such a device, does anyone know of any websites that allow people to contribute to hardware projects in the same way as Sourceforge does for opensource software? if not would sourceforge be a place to start?

author: Unknown
author_rank: Unknown
timestamp: April 23, 2012, 11:29:53 am
content: Quote from: jucole on April 23, 2012, 09:16:39 amNo such place yet afaik. Actually I'm not sure I've seen a strong collaboration on any OSHW project yet, let alone the need to lower the participation threshold.The community does not know yet how to handle collaboration when the item in question is an actual physical object to be sold for profit. There is no unit of measurement for contribution.

author: slateraptor
author_rank: Frequent Contributor
timestamp: April 23, 2012, 03:29:59 pm
content: Quote from: HAL-42b on April 22, 2012, 11:13:23 pmLMFAO!!

author: Unknown
author_rank: Unknown
timestamp: April 24, 2012, 04:11:29 pm
content: Quote from: HAL-42b on April 23, 2012, 11:29:53 amI stumbled on a Kickstarter project which are developing a sourceforge site for openhardware, which can be found herehttp://www.kickstarter.com/projects/373493158/open-hardware-needs-a-sourceforge-of-its-ownThey actually got their funding too, and this is the site they are buildinghttps://opendesignengine.net/- looks a little like a dog's dinner, but it might be promising. They are sponsored by a Mac30http://mach30.org/Mac30 are looking into opensource space flight!! So. you never know in a few years time you might well be traveling out on a flight on your holiday, and hear "Good afternoon, welcome aboard the Airbus openhardware beta release flight ...." ;-)

author: danielpublic
author_rank: Newbie
timestamp: May 04, 2012, 05:59:13 am
content: First post, so Hi there!Woke up about three hours ago with an idea (who knows when that one comes around the bend again..) and spent time doodling inFreeCAD(its FLOSS with a great community & rapid dev.) till an half hour ago I saw dealextreme shipped my multimeter.Whereupon I thought: "Oh, hey... wonder if there is an opensource multimeter out there?"Then I slapped my forehead mosquito-hard... well I should of thought of that maybe before I ordered it, especially as I have a lifelong crush on the (free) open source realm.I'll read the thread in a bit and look for some general pcb etc dimensional measurements. Cool to just fiddle with it in the mentioned CAD application and then print it with my RepRap.Anyhow, what I'd use it for other than the usual:Would be really cool if I could learn about electronics, breadboard tuts. so forth.Would be very Nice to etch a pcb then supply a list measure between x+y and then chirp happily at me and err but most of all simple trouble shooting and generate a LOG that I could share with the wise folk. ('HI GUISE')I mean... image a easily diy home etched reprap pcb, soldered, powered and tested with one device. Now that would deserve the seal of approval. err... of course maybe not soldered with the multimeter that... could one probably develop a halfassed thrown together from a fdm-hotend if needed.

author: Unknown
author_rank: Unknown
timestamp: August 09, 2012, 05:59:17 pm
content: Quote from: House91320 on June 30, 2011, 05:05:19 pmHi, just wondering if you've managed to make any progress on your project?regards

author: poorchava
author_rank: Super Contributor
timestamp: August 10, 2012, 09:38:16 am
content: I think that cost is one of the less important issues. Since this is open hardware, you can expect people to want to build it on their own. For example they can buy bare PCB and then assemble those. If for example they don't want/need/can't afford LCR measurement (eg. because of expensive IC used in it) they simply don't assemble this module. Simple as that.Another approach is to offer a 'motherboard' assembled (containing MCU, power management, display control, comm interfaces) with some 'standarized' pinout connectors. Connectors would need to carry isolated power supply, comm bus (RS485?+some paralell). Then every individual module would be an add on with obvious possibility of building your own module even on breadboard.I think that this is an approach that would allow to sell kits to biggest group of people, because everyone could find an affordable configuration and possibly upgrade later. That way people from poorer countries (like myself) could easily contribute to the project while you would still be able to sell fully assembled and full-featured version to people who can afford those.The opnly problem is that it would take significant amount of system and software engineering to make whole system configurable and scalable, but it's definitely doable.As for the enclosure, for sure custom shapes are a dead end. Tooling for industrial methods of production (like injection molding) is extremly expensive and in most cases a minor mistake in design means that you need to pay this tooling fee once again. I like the idea of extrusion-based enclosure designed for Eurocard size pcb. 100x160 is actually a plenty of space to implement stuff (I'm generally a type of pervert who like to cram as much stuff on smallest area of pcb possible - i just feel that abusing pcb space is an unnecessary waste)

author: crispus
author_rank: Regular Contributor
timestamp: September 18, 2012, 02:55:54 pm
content: Hi guys,In these 15 pages there a lot of things that should contain a DMM. I think for sure that analog front-end is one of common subsytems.My analog knowledge is limited. Does anybody volunteers to design analog front-end?Has anybody some good readings about designing analog front-end? What are the pitfalls? What should contain? What shouldn't?Thanks.

author: Stoney
author_rank: Contributor
timestamp: March 05, 2013, 08:50:02 pm
content: Hi Folks,first post on this forum, so: Hi allSad to see that this nice idea has not been updated in quiet some time. I'd really like to contribute to a open dvm project...so why don't we get started on this oneHow about getting some basic high-level requirements done and fixed to reanimate this topic? Here are my recommendations:1. Modular Design: AFEs with a central medium micro, let's say a STM32F4 (done some nice stuff with this one; plenty of computing power, nice peripherals, etc. )2. For most of the proposed functions, we need to accurately measure VDC (Ohm, Amps, VDC, VAC, not so sure about the LC-Stuff). I think it may be possible to achieve 6 x/x digits (somewhere around 2999999 counts, around 22 noise-free bits).2.1 Guess it would be a good idea to go with a custom integrating adc. I'd suggest a multi-slope design (first up multi-slope rundown, not sure if we need continuous runup). This would give us decent speed with a nice accuracy. After all, an integrating adc isn't that hard to do...2.2 The controller and auto-ranging would be implemented in an FPGA (Xess offers some cheap Spartan-6 LX25 modules), presumeably at a speed >50Mhz for the integrator time base.2.3 Add decent protection circuits on the input, to comply with some CAT rating2.4 Decade (bought) resistor network for 5 switchable ranges: 200mV, 2V, 20V, 200V, 2000V2.5 Make sure that the buffer in front of the ADC is reasonably high quality (noise isn't that much of a problem for an integrating adc, if it's designed properly)3. With the DVM capability, we could then build additional building blocks for current measurement, resistance (with precision current source), etc.4. Figure out how to do VACrms. If the adc is fast enough - do it in software. Otherwise, use a COTS component (sorry, aerospace term here) or build the circuit (nope, don't want to do that)5. Of course bench-type one. No handheld.I'll go ahead and do a sys-architecture drawing the next days for the VDC front-end with the basic modules.So long,Stoney

author: crispus
author_rank: Regular Contributor
timestamp: March 06, 2013, 02:43:05 pm
content: Hi Stoney. Welcome.I'm interested, but I lack in analog.I think that a modular approach is the best because it gives anyone the freedom of choice.Analog front-end is the common part of any multimeter. Can you do it?

author: Stoney
author_rank: Contributor
timestamp: March 07, 2013, 12:58:15 am
content: I'm also not quite THE expert yet...I'm more into embedded computing for airborne use, but I've done some fairly complex PCBs (6 layer+, BGAs, High Speed, etc.) with no more than 2 revisions, so I guess I'm not that stupid after all...my hope is to get a guru to have a look at the schematics once they're done to give some negative feedbackBased on the requirements, I'm going to: First up, high-level block diagram and split the work. Second, do modular building blocks people can work on "independently" and put their unique knowledge into...to make it better than I ever could...There are some crucial building blocks, but with todays parts, its getting easier every day to do precision stuff. But, as I said, we have to get the requirements right and establish a baseline to work on. With the modular design in mind, I would add another requirement:6. The mesurements are streamed to a PC for display purposes, and mode selection is done there. Just to keep the interface out of the equation for the initial phase. Once the AFE is done and working, we can attach what ever interface people want to the modular µC-Board.Glad to see someone is still interested

author: crispus
author_rank: Regular Contributor
timestamp: March 07, 2013, 09:02:00 am
content: Here is a nice diagram for bench multimeter:http://www.ti.com/solution/digital_multimeter_bench_system

author: Unknown
author_rank: Unknown
timestamp: March 07, 2013, 09:56:15 am
content: I'm working on a DMM with some interesting features; I'm using some DMM chipsets; once i have a proof of concept and if it's worthy of a show'n'tell I'll post it here.

author: crispus
author_rank: Regular Contributor
timestamp: March 07, 2013, 11:57:36 am
content: Using DMM chipsets is not somehow limiting?I mean, if you need only basic/supported functions it's OK, but if you want to do something customized, it that possible?I think I would like more a discrete ADC.

author: Unknown
author_rank: Unknown
timestamp: March 07, 2013, 12:40:25 pm
content: Quote from: crispus on March 07, 2013, 11:57:36 amA while back I was messing with my cheaper DMM; I pulled up the chipset datasheet and had a look though; what I realised was in the datasheet they give the basic circuit for each aspect of the DMM; which made it even more achievable for a beginner like me, I was quite excited. But after I made up a pcb in my head all I had was just another DMM clone using the same chipset as the rest. I did a bit more reading and after looking through some more the latest chipsets I found something I thought was really interesting; and that is some of the new ones offer 2 wire I2c. Which means it can be controlled directly through software! so to me that opens up massive possibilities; for example the UI need not be rotary switching and buttons; it could be touchscreen; you could calibrate it in software using offsets. But what if you did use a screen, rotary and buttons etc in a board shape that exactly fitted the shell of any existing DMM; "pimp-my-meter" ? ;-)Edit: the other idea I had was to only use 2 input jacks and use software switching; and the other really crazy ideas; you'll have to wait and see ;-)

author: crispus
author_rank: Regular Contributor
timestamp: March 07, 2013, 01:02:22 pm
content: What chipset do you use? Are they available on European market?I tried to find some time ago, and I saw only Cyrustek chips. But those aren't available on tme or farnell...

author: Unknown
author_rank: Unknown
timestamp: March 07, 2013, 02:12:29 pm
content: I have some Cyrustek ES51990.http://www.cyrustek.com.tw/spec/ES51990F.pdfThe problem is I don't really do electronics, so I could do with some help if anyone is interested - I make no promises about completing this though, it's just a proof-of concept. The specs for the DMM would be basically as the datasheet; It would need a uC with quite a bit of program space as most of the interesting features will be done in the code - which is where I can help; the only requirement is that all work is opensource and uses opensource tools to create it.

author: kripton2035
author_rank: Super Contributor
timestamp: March 07, 2013, 03:10:10 pm
content: Quote from: jucole on March 07, 2013, 02:12:29 pmhow did you get these chips ? I asked cyrustek some time ago for samples and they told me this chip is only for lcr manufacturersthey didnt gave me any more information than the ridiculous facts in the datasheet ...if you dont have anything more than this datasheet we cannot do any chip interfacesorry I read the datasheet it is far more complete than the one we had some times agosomething can be done, but if the chip is unavailable to hobbysts this will not be very usefull ...

author: Stoney
author_rank: Contributor
timestamp: March 07, 2013, 03:17:38 pm
content: Here's a DVM the guys at the TU Berlin built in one of their lab courses. 5 1/2 digits and reasonably precise, even tough they use a simple approach.http://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/Schaltplan_DVM.pdf.

author: kripton2035
author_rank: Super Contributor
timestamp: March 07, 2013, 03:31:50 pm
content: another sorry from me. you talk about the ES51990I was refering to the ES51919/ES51920 which datasheet is very poor.

author: Unknown
author_rank: Unknown
timestamp: March 07, 2013, 04:18:41 pm
content: Quote from: kripton2035 on March 07, 2013, 03:10:10 pmEvery wannabe EE has his sources but If I told you my source; it would no longer be my source! ;-)Quote from: kripton2035 on March 07, 2013, 03:10:10 pmYeah, very true. (wack!! goes the last nail into my open DMM idea coffin, lol! );

author: Stoney
author_rank: Contributor
timestamp: March 08, 2013, 08:34:15 pm
content: I just finished the block diagram....In term of Collaboration on this Project, what would you choose? I like to start the project on thehttp://www.ohwr.org/(CERN) with the CERN OHL version 1.1. The page is on chilli-project, which will give us a nice and handy issue tracking system and the possibility to include VC-repositorys, a wiki, etc., etc.EDIT: Or should we just go with github?

author: mrflibble
author_rank: Super Contributor
timestamp: March 08, 2013, 10:10:10 pm
content: I'd say github. But basically just pick whatever works for you best. You're doing the work, so you get to pick what's easiest for you.Also, thanks for your sensible contributions to this loooong thread.So far everything you posted looks actually practical, so I am looking forward to seeing what you come up with!

author: Stoney
author_rank: Contributor
timestamp: March 09, 2013, 02:51:52 am
content: The github repo is online at:https://github.com/Stoney49th/OSHW-MultimeterFeel free to stop byI welcome everybody to join and spread the word...hope to get some feedback (issues work great) from u guysMaybe we can actually build this thing and make another really great piece of open source hardwareI wont be able to do it all by myself...so help is always welcome and appreciated!See you on github

author: mrflibble
author_rank: Super Contributor
timestamp: March 09, 2013, 03:28:41 pm
content: Couple of quick random thoughts while going over the documents:ADS1258EVM is a nice ~ EUR 50 board that can get you up and running quickly with some decent resolution measurements. It's no integrating multi-slope adc because it's a delta-sigma adc.But it is affordable and reasonably easy to integrate so you have an easy starting point.Yay! You picked spartan-6. All for it, and I might be able to contribute a bit there. The multi-slope adc + fpga combo has my interest for an entirely different non multi-meter project. Just make sure you're using (system) verilog and everything is dandy from my rather egotistically motivated standpoint.stm32f407 as mcu ... again all for it.Use that quite a bit now for current projects.regarding block diagram and ETH PHY on the right side of galvanic isolation ... ethernet has the added bonus of isolation, which IMO why it's a nice and easy interface for DIY measurement gear where 1) you want some safety and 2) don't want to have thinktoohard. I'd say aim for 100 MBit. For control alone you can probably suffice with 10 Mbit, so if the ONLY goal is commands over ethernet just do 10 mbit. But 100 MBit is easy enough with the stm32, and it gives you a nice bit of bandwidth to pump samples over to the PC in exchange for not too much effort. And yeah yeah, you can do gbit, but then you want to connect the gbit PHY to the spartan-6. Anyways, 100 mbit with a decent tcp stack on the stm32 will get you nice capabilities.Integrated PSU ... if the amperage allows, try to make it a seperate daughter PCB that you can plonk on the main PCB. That way you can reuse it in other designs, and design improvements go both ways. I see this being done in both the DIY and the industrial sphere. In fact, I am just starting to do this myself. Design a couple of PSU blocks once, and then you can use it in different designs without reinventing the wheel. Plus it makes prototyping a lot faster if you can just grab a ready to connect PSU block and plonk it on the pcb/breadboard/deadbug.Voltage ref ... try and make use of the fact that quite a few hobbyists would like an affordable lab standard. If you can define it such that the voltage ref is both usable in your design and as a standalone reference it would help the design effort. But at the same time, if this feature adds too much work for you ... skip it! Don't fall for the trap of wanting to do everything at once. It's a bit of a trade off. If making it a seperate module is hardly any effort, I'd say do it. If it is a significant effort ... screw those guys (and this guy) and their need for a lab standard. Keep it simple. Now that I think about it ... screw those guys by definition. Keep it simple. First revision should be made with as major goal Just Get Something That Works. So keep in the back of your mind you may want to seperate the reference as a module, but that's about it.And luckily your focus is a bench DMM, and not one of those Rule The World (and thereby defeat the Chinese) handheld opensauce multimeters that frollic in the pasture side by side with pixies and unicorns. A DIY bench DMM makes sense in 2013. A handheld does not IMO. Anyways, don't care for a "handheld makes no DIY sense" vs "bench is the way" discussion/flamewar. I am just glad you chose benchtop. Otherwise I would not even expend keystrokes/braincycles over it.One more random remark that is low prio, but more as a placeholder: for commands, use SCPI. there's been some discussion in another thread about it, and IMO scpi is a reasonable choice for DIY hardware like this. At this stage I would not spend too much time on it. The main reason I mention it now is so you don't go and spend time & effort on some new way to send commands to your DMM. Just write down "[ x ] Send command & receive data from instrument. Use SCPI." somewhere on your project list.No need to spend more time on that right now. The analog is where the challenge is.As for digits, I'd say aim for 5 1/2 digits for iteration #1 with an eye on 6 1/2 digits for future iterations. If you can make everything in the 6+ digit area the first go then go for it! If not, keep things simple, compromise a little and settle for a bit less accuracy. The ONLY reason I say this is to stay away from the trap of trying to be overly perfectionistic. Just get something that operates reasonably well first. After that you do incremental improvements.Plus, I think that 5.5 digits is possible by just plonking in the previously mentioned ADS1258EVM without too much thought.Anyways, enough semi-random remarks for now.

author: branadic
author_rank: Super Contributor
timestamp: March 10, 2013, 12:22:48 pm
content: There're a few other potentially delta-sigma ADCs for such a project:Texas Instruments: ADS1256, ADS1672Analog Devices: AD7190, AD7764Linear Technology: LTC2400, LTC2440The choice for the right voltage references is also not as easy as it seems to:Maxim Integrated: MAX6126, MAX6325/MAX6341/MAX6350Analog Devices: ADR44x, AD584/AD586/AD588Linear Technology: LTC6655, LM399AHTexas Instruments: LM399AHAt the beginning reduce the goal to somewhat around 5digits to reduce the frustration.There is a reason why LM399AH (maybe it's more of a LM199AH) is used in 6.5digit DMMs. But it's not only the tempco of voltage reference itself but the sum of all tempcos in front of the ADC.Always bear in mind that 6.5digits means something like 21 noise-free bits and 5.5digit still 18bits. Refer to figure 1 in AN82 for that.A few ideas could be selected from the datasheets of HP 34401.

author: crispus
author_rank: Regular Contributor
timestamp: March 11, 2013, 10:56:07 am
content: Quote from: mrflibble on March 09, 2013, 03:28:41 pmWhy do you need a FPGA?

author: mrflibble
author_rank: Super Contributor
timestamp: March 11, 2013, 11:55:29 am
content: Quote from: crispus on March 11, 2013, 10:56:07 amBecause it's cool?And more seriously ... It's Stoney's design, and I was remarking on the choice of fpga in there. He wants to use the fpga to process the comparator output of the dual slope ADC as per the block diagram. All I'm saying is that I'm glad he uses spartan-6, because I am familiar with that and those are affordable in single units and you can get them in hobby friendly packages.And as for branadic's ADC list, yeah those are some nice ones. In fact, the ADS1256 is a better choice for this sort of thing than my suggestion of ADS1258. Whatever ADC you might want to use ... just use one that for which an affordable (~ $50) dev board exists. That lowers the bar for people to join in.

author: crispus
author_rank: Regular Contributor
timestamp: March 11, 2013, 12:21:57 pm
content: Quote from: mrflibble on March 11, 2013, 11:55:29 amI quoted you because only you used the word 'FPGA' in topicFor me, it seems to be too complicated, at least for a hobby project. I will follow this, and maybe I'll took only the blocks I'm interested in.I'm a software guy. If is anything I can help, I'll be glad to.

author: mrflibble
author_rank: Super Contributor
timestamp: March 11, 2013, 03:03:40 pm
content: Quote from: crispus on March 11, 2013, 12:21:57 pmWell, for the chosen architecture I can see why Stoney put the fpga in there. It's a cost effective way to get good timing resolution for your dual-slope adc. With as added bonus that when the hard work is done, and you decide you want more channels, that is reasonably straight forward.That said, personally when I would do this I think I would go for using a ready made 24-bit ADC dev board and integrate that into the design for iteration numero uno. That get's you going faster. But, it's not my design, it's Stoney's design. And use of dual slope adc is perfectly reasonable, so if that has his interest (and as such will get built) then I'm all for it.QuoteWell, a good working (stm32f4) port of an scpi parser would be damn handy IMO. Both for this project and for the other OSHW thread going on. It's not as sexy as a pretty gui, but pretty gui's are a dime a dozen. A good scpi parser running on mcu is something that can really make the difference in usability IMO. As in, being able to script your measurements is damn handy!I love being able to set up my scope over gpib, and would love to setup a DIY bench DMM with a few commands and then receive measurement results. To me for a DMM that is worth a lot more than some gui with pretty pixels.

author: Stoney
author_rank: Contributor
timestamp: March 11, 2013, 09:30:03 pm
content: @flibble: Nice, I've never looked at verilog...but maybe it's time to learn something newIt would be nice if we could fit the design in an LX9, so we don't need that nasty BGA-Chip on the board... For the PSU: Jap, I intended to make it external...it just doesn't make sense to put it directly onto the AFE if the design should be modular. Also, it would increase the PCB size significantly, so it's kind of a no-brainer. I already have some nice and tiny switching psu building blocks in altium from my previous designs, but I'll use linear regulators for the AFE (with beefy filtering) of course! In terms of Software & Ethernet: 100MBit is the way to go here, so we get decent speed....I'm not sure if we should use 1588 here, but it would make the thing more compatible to LXI, if someone is willing to implement such a large interface (I'm not).@Delta-Sigma ADC:Puhh, long story short: I won't use one.After couple of hours diggin through lots and lots of datasheets from linear and analog, i found the resolution is just not enough. Most of them offer only 21.5 to 22 noise free bits in its best configuration. In addition, running on 7-15SPS is a bit low... To really achieve the full resolution of those devices, one needs a ultra low noise buffer in front of it, with variable gain (x10 for the smallest range). Designing a x10 buffer amp with noise <50nV over a decent temp-range with low drift is a very difficult task, if not impossible in some regards (its really always a trade off, one design is a bit noisier, but with better tempco, etc. etc. ). With an integrating ADC, noise isn't that much of a problem (well, of course you want to minimize it, but it's not that critical for 6 1/2, for 7-8 digits it certainly becomes deadly) if it is properly designed. We'll see how it turns out.I haven't had much time this weekend, but I'll try and start with the detailed blocks for each module the next days. After some thoughts, the biggest problem right now for me is the range switching and the input switch in front of the integrator (for the multi-slope thing). It has to be really fast (the faster, the better...less error when the Vmes is switched out and the +-Vref is switched in) and it must not inject too much charge into the integrator. As far as range-switching is concerned, I would like to use JFETs. But this would certainly require a part with a very low leakage current (very very low). Any Ideas on this one??? One other problem is the "master switching" just after the decade resistance. If one would apply 1kV and the device is in it's lowest range, the relay has to switch the full Voltage....in other words,it has to withstand the full voltage after it has been switched of (>=1kV in this case). So a JFET is not working here. Most designs use 2-3 quality relais for the inital switch and later on route the signal with JFETs.@FPGA: The only way to get >50Mhz counter+switchting speed for the ADC is an FPGA. I can't think of another solution, and a LX9 TQFP-1000 only costs you ~$30-$40 (28€ for me). If we're able to fit the design into 9k macrocells, it's not that expensive after all, and allows for a great deal of flexibility

author: mrflibble
author_rank: Super Contributor
timestamp: March 11, 2013, 10:40:48 pm
content: Quote from: Stoney on March 11, 2013, 09:30:03 pmWell, if all you need is say 10 ns time resolution at a relatively low repetition count then you can probably get away without an fpga. That said, you can get pretty damn good time resolution (way better than the 10 ns example) with the fpga. And as you said, you do get a lot of flexibility. As in: I can think of something that will get you 10 ns with less expensive parts, but it's not going to do much more than counting. Plus it won't get you to say 1 ns or below that.Anyways, what kind of timing resolution + repetion count do you need for your dual slope adc?

author: branadic
author_rank: Super Contributor
timestamp: March 12, 2013, 08:09:54 am
content: QuoteYou wanted to realize a DMM not a scope, right? And you have an idea about what "only 21.5 to 22 noise free bits" means? If not you better take a look at AN82 or the accuracy translator attached. I'm not sure if you realy understood the challenge of what you are going to do.Normally those types of ADCs are ASICs and not consumer parts you can buy everywhere. Refer also to:http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snoa597a&fileType=pdf

author: Stoney
author_rank: Contributor
timestamp: March 12, 2013, 09:26:44 pm
content: Oh sorry, seems like I forgot a simple word in my previous posts...so far, I only wrote about resolution, not absolute/relative accuracy. One of the requirements is 2000000 counts (ops, think there is still an error in the req. doc) which will require at least 21 noise free bits of resolution. Given the fact that the delta-sigmas in the other post only offer one slightly above that, and, lets say, the buffer in front of it kills another bit of resolution, the integrating adc is the way to go.Yap, your right, I dont want to build a scope. But 50SPS (which might be a good point to start with) isn't 2GSPS. In order to do statistical mesurements, recording, stuff like that, it's the lowest minimum i can life with (ok, 100SPS on 2000000cnts would be nice, followed by 1kSPS for 200000cnts and 10kSPS for 20000cnts).I've built a nice CAL-System for sensors used to test the structural lifetime. These sensors are currently in use for the A400M, the A380, A320. Back then (my bachelor thesis) I used a PXI-System with a 7-1/2 digit meter which was capable of 100SPS in high-res mode together with some motion controllers, precision voltage sources and so on.... The DMM had even more SPS than the max. I wrote above in 5-1/2 digit mode. Of course, the NI gear is awesome and insanely expensive, but we really used all its capabilities, which were almost the minimum required for the task (analog position sensors, really expensive and quiet precise for their underlying principle, you need good gear for that and a nice cal lab).If you think I'm on the wrong track, show me the right oneI'm always glad to hear different opinions and other, better and easier solutions!

author: mrflibble
author_rank: Super Contributor
timestamp: March 12, 2013, 11:01:54 pm
content: Quote from: Stoney on March 12, 2013, 09:26:44 pmThat right there!For ease of discussion, assume for a moment that as you say the analog stuff in in front of the adc "kill another bit of resolution". As in there's a certain voltage noise source of whatever it is uV rms. You don't magically change the characteristics of the front end by swapping out the adc. So if that "kills 1 bit at 21-bits" voltage noise source is lets say 1 uV rms, then this very same 1 uV noise source is present even if you follow it with an awesome 32 bit adc.So if you want to go and argue "but the stuff in front kills 1 bit" , then by the exact same argument this noise will kill a whole lot more of your 32 bit adc.Anyways, if you know a good way to get those 2E6 counts at a reasonable cost go for it. But I still maintain that for a first iteration it makes a lot of sense to ease up on the requirements a bit. If only because that way THE REST of the system also can be built with components that are somewhat affordable.QuoteDepends on what the goal is. If the goal is a learning exercise that you and you alone are going to be doing the next year or so go for it! If you want something that is a bit more accessible to more people then you may want to ease up on the requirements. After all, if things are so super easy as maybe you hope they are ... then you will be done in no time. And hardly any effort "lost" since you made it modular, so you can upgrade parts of the design for your higher spec next iteration. That, and you can incorporate lessons learned from iteration #1.But as said, it's your design so have at it. I'm just giving some perspective on how I'd do it.PS: now that I mentioned it ... what is the design goal? Buildable by people of <fill in> level of skill? Build cost ..., etc... A lot of those often unwritten assumptions dictate what is reasonable and what is not...PPS: Oh yeah, you didn't answer this one from previous post: "Anyways, what kind of timing resolution + repetion count do you need for your dual slope adc?" The answer to that will determine the sense vs non-sense of using an fpga. Definitely since you say you are new to verilog (and presumably new to vhdl as well).

author: branadic
author_rank: Super Contributor
timestamp: March 14, 2013, 08:20:19 am
content: QuoteListen, it's not my goal to doubt your skills or stop you from what ever you want to develope and present in here, just go for it!As an engineer I develope for example in the field of high resolution capacitive sensors together with my colleague. We're always at the limit of available circuits measuring down to Attofarad with tendency to Zeptofarad and also in here we are confronted with the same problems that occur in voltage references such as humidity in packages and pcbs, stress, temperature dependency etc. Having all that knowledge in my mind voltage references are a new challenge to me to get them under control. And the reference for sure is one of the major devices besides adc and the other stuff. You might know that every additional bit doubles the efforts. And I'm sure that the integrated gain stages in a modern 24bit ADC are much better as you would expect. The only way to reduce noise in here is to decrease bandwidth and cool down the stuff.My suggestion is, keep the "stage win" as small as possible otherwise this project will change into some kind of pyrrhic victory.

author: Stoney
author_rank: Contributor
timestamp: March 14, 2013, 11:26:22 pm
content: No offense takenI just wanted to make some sort of statement that I'm not one of those "hey lets build a 10kSPS 8-1/2 digit meter for $10 and make it open source" type of guysWell, I don't question the work of the fabulous engineers over at linear or analog, their ADCs are pretty nice. The only thing that struck me was the sampling rate...I wanted to do some sort of software-filtering after the adc to get rid of some noise and and errors and increase the resolution by some degree. I did some calculations the other day for the input buffer....and oh boy....your "decrease the bandwidth" and "double the effort for every bit" statements holdLet's just assume for a moment, one were to consider a 24-bit ADC (linear) with a decent front end. Would it be ok, if the sample rate is "only" 7-15SPS (indeed, the bandwidth of the VDC front-end itself will be very low, otherwise its very hard to keep the noise low enough)? One could of course increase the sampling rate while lowering the resolution in "streaming mode", to offer a high sample rate, for example over the (planned) ethernet interface. In terms of the update rate of a potential display connected to the µC, I'm no longer sure if a sampling rate >10SPS is really that useful for the human eye and brain. Maybe, my requirements were/are a bit optimistic and over the top right now...and the very limited bandwidth of the input stages (to achieve a high resolution) wouldn't allow for a very high sampling rate, even if resolution is sacrificed (well, we don't want to make the damn thing too complicated and expensive, right)....The integrating adc (in the current drawing) would allow for a great deal of flexibility, in terms of sampling rate/resolution and input ranges. If we find some nice solutions, the sampling rate would also clearly be higher....but with an input stage so limited in bandwidth, this advantage isn't that relevant anymore, at least for the "streaming mode". Oversampling on the other hand could be of advantage here...P.S: Jap, the reference will definitely be one of the major contributors to the actual accuracy of the frontend. Would you like to do one, as a "stand-alone" modular type? Would be really great, because my knowledge about references is very, very limited and certainly not good enough to build one

author: mrflibble
author_rank: Super Contributor
timestamp: March 15, 2013, 06:41:10 pm
content: Quote from: Stoney on March 14, 2013, 11:26:22 pmHopefully you're one of those "hey lets build a 10 SPS 5-1/2 digit meter for $100+ and make it open source" type of guys. XDQuoteAbsolutely. If your target audience is "hobbyist that like to build some of their own test gear and are able to make reasonable tradeoffs" then I'd say a bench DMM with 5 1/2 digits that does 10 SPS would be quite nice. It would have many many uses on the bench. Sure it doesn't compete with the state of the art professional meters, but I suspect (and hope) that is not the intention.

author: free_electron
author_rank: Super Contributor
timestamp: March 15, 2013, 07:02:53 pm
content: before you start arguing about what fpga to use... : go write the code for the dual slope system.it's no much more than a few counters. you don't need a 9000 macrocell fpga. you can put it in a CPLd if you want.the key to the slope system is the integrator / comparator. you will need to pick a REALLY good opamp and comparator. and you will need ultrastable caps and resistors around it. if you want the integrator to run fast you can get away with a small cap. try to find a silver/mica C0G/NP0 type.use resistors with the lowest tempco you can find ( Caddock for example)the switching balance for the current can be done using a good analog switch like a DG444, no need to muck around with jfets.and you need an ultrastable reference.absolute accuracy is irrelevant in this system. you don't want any drift.i wrote multiple posts on the forum here how this system works and is implemented in HP34401 as well as how it is calibrated.i know people that have built a 5 1/2 digit dual slope in a 64 macrocell cpld.the number crunching is done by a cpu. yuo only need the gate array to get the runup and rundown counters since the cpu can't bitbang that fast.

author: mrflibble
author_rank: Super Contributor
timestamp: March 15, 2013, 07:37:06 pm
content: Regarding the fpga my point so far has been that you probably can get away without one. If all you need is ~ 100 MHz counting frequency there's simpler ways. CPLD could be one, but since there's already a STM32F4 on the BOM you can use that. Again, it depends on the (as of yet unspecified) required timing resolution.There, fpga relegated to being a non-issue. Onward to the analog stuff.

author: mrflibble
author_rank: Super Contributor
timestamp: March 15, 2013, 07:43:37 pm
content: Also ...Quote from: free_electron on March 15, 2013, 07:02:53 pmdo you have a link to which one you mean? Right now I'm readinghttps://www.eevblog.com/forum/reviews/hp34401-teardown/but maybe you mean another thread.edit: probablythis one. reading ...

author: Marco
author_rank: Super Contributor
timestamp: March 15, 2013, 11:30:07 pm
content: Silly question ... why can't you just use dithered oversampling with a fast ADC to get high resolution? (Potentially with sine or triangle wave dither, theoretically gets resolution far faster than white noise.)

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: March 16, 2013, 05:24:55 am
content: Quote from: mrflibble on March 15, 2013, 07:37:06 pmMay be I just don't understand but I don't think you can get 100Mhz timing resolution from STM32F4 on chip counter/timers, its more like 1 or 2 Mhz. I have been itching to find an excuse to play with those small cool-Runner PLDs. I thought of making a ballistic (bullet) chronograph but stm32 timers have enough resolution for that. Something I haven't discovered yet: what quality and stability does the dual slope clock need - Ovenised or TCO?

author: ve7xen
author_rank: Super Contributor
timestamp: March 16, 2013, 08:11:24 am
content: Quote from: chickenHeadKnob on March 16, 2013, 05:24:55 amThey may only accept a clock input at relatively low frequency (though probably at least 10s of MHz), but for an integrating DAC you need input capture mode, where the clock for the timer can be derived from the system clock, and the capture input is asynchronous. In that modes I believe the STM32F4 series can run at around 150MHz, giving you ~7ns timing resolution.Can't comment too certainly on the clock stability, but I'd guess you want it to be as good as the measurements you intend to make. For absolute accuracy and long-term stability you probably want at least a TCXO.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: March 16, 2013, 09:48:56 am
content: @Ve7xen and mrflibble :My apologiesyou appear to be correct, I seem to be conflating F4 series with some other micro's spec sheet from my faulty memory. sigh -gettin old.The advance timer at least can run at system clock rate 168Mhz. as I dimly understand it you need to drive an analog switch with hardware logic (software would be to slow) when the comparator trips, so you will still need a little off chip logic. I'll shut-up now and leave you guys to it! Still might build a basic dual slope on my own just for amusement and learn-dina'tin.

author: Stoney
author_rank: Contributor
timestamp: March 16, 2013, 04:39:12 pm
content: @chickenHead:Absolutely right. I first thought I could do the switching with the Capture/Compare peripherals (they are quite good actually) but it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks. No BGA (woohoo), and its not that expensive.As far as the CPLD is concerned: No, you really dont need 9k cells for a integrating ADCBut, I really want the unit to be expandable, so people can add other front-ends, for example for L, C, F, and other stuff. So it's just a nice and versatile solutionFor the clock, I would use a FOX +-1,5ppm inital accuracy with +-2,5ppm drift TCO. They're cheap ($3-4), SMD, small and reliable (used them on quiet a number of boards, never head problems and well within specs).The DG444 is cool, after i looked it up, i also found the ISL43681. Do you think it'll be possible to make the reference +-2,5V (with a precision divider + inverter, aka. LT1043) so we could use this one? It's much faster, with equally low leakage and charge injection but its a low voltage type (+-5VDC supply and therefore input range max.)....and I guess we'll have to switch reasonably fast to reduce the errors in the integrator.But back to the input buffer stuff:I found that the LTC6240 would be a good candidate here, because of its extremely low input bias/offset current and the even lower current noise. Because the input divider/protection devices will have a very high source impedance, the current noise (together with the high source impedance) plays a role in the noise performance. The main noise contributor is indeed the input divider and not the op-amp itself (if it has a low input referred voltage noise, of course). The LTC6240 has a great performance in terms of input current and noise but has one major disadvantage. The input offset voltage drifts around 0,6-1,0µV/°C. So one has to compensate that thing, for example by chopping, which leads to a hole other set of problems.So, I've chosen the LTC1052. Equally low current noise, but higher input bias current (30pA, times 15) but significantly lower drift, noise, and offset (drift ~10-50nV/°C). The challenge here is to balance the junctions (the datasheet is quiet nice on this one, they write a lot about it). Since we basically only need need unity gain and a gain of x10 for the lowest input range (200mV, otherwise the integration time becomes too long for small signals, in other words, the error increases), a switch will bypass the divider and I'll choose a non-inverting configuration. In the unity gain feedback path, the switch will add the needed material junction so we always stick with the same number in each configuration. It's quiet critical to keep the temperature of all parts in the buffer equal, and it would be nice if the resistor values are close to each other on all paths, so cancellation occurs for the thermal/junction noises. Later on the PCB, I'll add the possibility to solder in a air-protection cap, just to make sure that no airflow can build up thermal gradients on the resistors and introduce offset drift. By default, the switching frequency of the 1052 is 330Hz, so a first order low-pass in front of the op amp will ensure that we're not running into aliasing for low frequencies, with a ~200Hz -3db point. Afterwards, the integrator will take care of it. I'll do some drawings tomorrow for the input switch, overrange limit and the input buffer and add them to the repo ^^ (nah, these modules are so closely connected, you really can't treat them seperatly).

author: branadic
author_rank: Super Contributor
timestamp: March 16, 2013, 07:19:08 pm
content: QuoteWhy not resort to something like this, the SVR-T should be a good choice at the beginning:http://www.gellerlabs.com/Voltage%20References.htm

author: ve7xen
author_rank: Super Contributor
timestamp: March 16, 2013, 07:24:36 pm
content: Quote from: Stoney on March 16, 2013, 04:39:12 pmA $30 BOM item you don't even have a use-case for? o.O

author: mrflibble
author_rank: Super Contributor
timestamp: March 16, 2013, 08:19:26 pm
content: Quote from: ve7xen on March 16, 2013, 07:24:36 pmMaybe he just want a moderately justifiable excuse to plonk in an fpga.At least that is how I interpret the "have to learn verilog" + "lack of any hard specs regarding interval timer resolution".The only number I've seen timing wise was the "> 50 MHz counter frequency". Well, 20 ns is done easy enough with the stm32f4 as mentioned. So is 10 ns. Now with say 1 ns resolution we get into territory that it might make more sense to use an fpga. You can do all sorts of tricks to get the 1 ns with the stm32f4 again with an external prescaler yadda yadda, but in that case I think I'd choose fpga. And if you are after the 500 ps - 100 ps ballpark then suddenly fpga becomes quite effective in BOM cost + design effort, compared to other solutions I can think of.But as said, since the only mention is of "something that counts at 50 MHz"... pffffrt, STM32F4. Problem solved.Quote from: branadic on March 16, 2013, 07:19:08 pmThat's actually no bad idea at all. Sure, you might do better. But ... you might also do worse.And at least this is a design that has been out there for a while and should there be any quirks, you can be fairly sure there's some info out there. Info like that also has value ... something that the hobby posse sometimes forgets in their haste to add +1 to the Not Invented Here Syndrome Count.

author: mrflibble
author_rank: Super Contributor
timestamp: March 17, 2013, 12:19:46 am
content: Alright, in the meantime I've been reading some more of free_electron's (great) posts about the multislope stuff + the HP Journal of april 1989. Damn, that multislope approach as done by HP is quite elegant.

author: Stoney
author_rank: Contributor
timestamp: March 17, 2013, 01:46:46 pm
content: @FPGA stuff: lol guys, let's just wait until we have timing requirements from the integrator. Then we decide what we actually needVDC input buffer doc online (in 03_ folder). Its a very dirty dave cad, hope u can read my handwriting....I'll do a clean one in software once it's close to finalGimme some negative feedback

author: branadic
author_rank: Super Contributor
timestamp: March 17, 2013, 02:23:46 pm
content: QuoteI wonder why Agilent and Co still use their expensive hybrids in modern devices instead of a low cost fpga or cpld, if it was that easy to get a high precision integrating adc. There must be something overlocked, such as temperature dependent latency or similar effects that decrease the real resolution.QuoteAttached you find the specifications for a TCXO series of actcrystals. They have made me a bunch of TCXOs with customer specific frequency in another project. It's not an OCXO but very good for that price.There are some other ADCs that are interesting:CS553424-Bit A/D Converters with Ultra-Low-Noise PGIAhttp://www.cirrus.com/en/products/cs5531-32-33-34.htmlPRI5610Präzisions - 26 Bit - ADChttp://www.ohh.de/5610.htmER-ADC150programmable 24-bit integrating A/D converterER-ADC180programmable 26-bit integrating A/D converterhttp://elbertresearch.com/users/editorialdisp.php?mn=110669&fn=standardProductsParticularly the last link matches the requirements for such a project and is a "ready to use" device.

author: free_electron
author_rank: Super Contributor
timestamp: March 17, 2013, 09:49:22 pm
content: Quote from: branadic on March 17, 2013, 02:23:46 pmfluke uses cyclone fpga's. so do the tek rebranded flukes.the reason agilent uses those asics is because they have their own waferfab. they can !that asic was designed many years ago and also does other things besides the logic section of the multislope system. ( display controller , digital isolation link , memory decoder etc. )

author: Marco
author_rank: Super Contributor
timestamp: March 18, 2013, 12:01:56 am
content: I don't think it's possible to get a comparator fast enough to make a FPGA worth it ... if you want decent offset you're looking at something chopper stabilized and those aren't exactly fast.

author: mrflibble
author_rank: Super Contributor
timestamp: March 18, 2013, 12:32:16 am
content: Regarding comparators, I think Stoney currently has an LT1016 on the list. That's going by the fact that the datasheet is in the git repo.I also had a look at that one and compared it to the LT1011 (from the TU Berlin design). Personally I am not yet convinced LT1016 would be better than LT1011 in this application. It does have 1 big thing speaking for it, and that is that the propagation delay has been characterized over temperature. A nice flat 10 ns over temp for the falling output. No such spec to be found for the LT1011. On the other hand the LT1016 has a worse max offset (3.5 mV) than the LT1011 (0.5 mV), and the max offsetdriftfor the LT1016 is not even mentioned. Or at least I couldn't find it. The typical offset drift is the same (4 uV/C) for LT1011 and LT1016.And as bonus the LT1016 has a differential output, but that's more of a nice to have, not a must IMO.As for comparator speed, if I understand the dual slope/multislope thingy correctly, you don't care overly much about the speed. As long as it's fast enough. The main characteristic with this sort of low repetition rate zero crossing detector is not so much speed, as it is variations in the propagation delay. For all I care it has a whopping 100 ns prop delay, as long as it is bang on 100 ns over all conditions. It is uncertainty in prop delay that is annoying because that translates into uncertainty of amount of accumulated charge. It's a similar problem to offset voltage, just a different axis. And the slope at which the zero crossing occurs dictates which of the two is the more annoying problem.This all of course is still assuming I understand the design properly (big if XD).

author: Stoney
author_rank: Contributor
timestamp: March 18, 2013, 07:21:48 pm
content: Uhm, well, I just had a look at the datasheet and thought it might be a good point to start from, no special intentions on using THIS specific comparator....we'll see how it turns out once I can make some calculations on the delay/switching delay/speed/clock/timing of the integrator.The opamp in the integrator is also very critical...it has to be quiet fast, but low drift and low input current/offset current as well! Input "leakage" current into the opamp will introduce errors directly in the runup so should be avoided, and the slew rate comes into play when the voltages are switched for the runup/rundown phases. This is also a limiting factor for the slopes of the rundown, together with the timing resolution and the resulting under/overshoot for the steepest rundown-slope. Low drift is obvious, thou not ultimately critical, since I will null and offset compensate the integrator after each measurement or at a specific rate if the drift allows for it. But still, drift within one measurement cycle should be reasonably low. This will of course depend on the temp. rise, but with a standard, fast opamp, i think the drift is going to kill us. I remember some fast "precision" AD opamp with 50V/µs (the 8-1/2 digit wizards built their own with 100V/µs) wich might be a good candidate...Anyone had a look at my (very crappy) drawing of the input overrange / VDC buffer stuff yet? I expect plenty of stupid mistakes so please correct me!

author: mrflibble
author_rank: Super Contributor
timestamp: March 18, 2013, 08:42:52 pm
content: Quote from: Stoney on March 18, 2013, 07:21:48 pmI didn't quite follow R5, R6 (near note ). This is stil purely input signal conditioning + protection, yes?If so, why the R5/R6 combo in T912 package there? As in what's the intended function of that LTC1052. I follow things right up to the + input of the LTC1052, and then I don't quite follow your intention.Don't you just want a boring unity gain buffer amplifier at that point?Also, don't you want the "To VAC"afteryou do some buffering with said boring unity gain buffer?you range switch it, you low pass it, clamp it, and then you x1 buffer it. No x1/x10 precision resistors required so far, unless I am missing a clever trick you have up your sleeve.

author: branadic
author_rank: Super Contributor
timestamp: March 18, 2013, 08:53:33 pm
content: QuoteSeems like you haven't watched the posted link (AN-260 A 20-Bit (1 ppm) Linear Slope-Integrating A/DConverter), as this critical part was already faced there and how it has been solved (page 5-6, A2-A3):http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snoa597a&fileType=pdf

author: mrflibble
author_rank: Super Contributor
timestamp: March 19, 2013, 02:04:28 am
content: While we're at it ... possibly something like this for the comparator stage:edit:reduced size of pic...

author: Stoney
author_rank: Contributor
timestamp: March 19, 2013, 09:24:44 am
content: Hm, the x10 gain would be useful in the lowest range to keep the integration time and get the signal over the leakage introduced errors within the integrator. Otherwise, you would have to integrate ten times longer in the lowest range (200mV FS) to keep the resolution.I wanted the Vac to be protected by the same overrange protection as the Vdc, otherwise another pair of diodes, more diode leakage, more resistors, etc. I thought about the aliasing error stuff and decided to use a simple first order filter after the initial, "high frequency" filter. Maybe, a active second order one with the 1052 could be better, but since the sampling rate will be reasonably low, I don't think we run into problems here. Of course, you don't want a 200Hz -3db bandwidth for the Vac stuff, so it will have it's own buffer, presumably switchable with a small smd reed switch (the meder ones are quiet cool, low EMF, and reasonably priced (4€, don't know the dollar price)).

author: mrflibble
author_rank: Super Contributor
timestamp: March 19, 2013, 05:05:29 pm
content: Quote from: Stoney on March 19, 2013, 09:24:44 amAh okay. In which case I'll keep it simple and just use a boring unity gain stage there. Especially since for iteration 1 I can live with the longer integration time. And for iteration 2 I am secretly eyeing a multi-slope approach. And in both cases at this point it's a simple buffer without any variable gain.

author: Stoney
author_rank: Contributor
timestamp: March 20, 2013, 09:53:33 pm
content: Yep, and after I started thinking about the actual integrator configuration, I realized that one can perfectly adjust this with the "integration resistor"So no stupid switchable gain, just a simple unity gain buffer...

author: mrflibble
author_rank: Super Contributor
timestamp: March 20, 2013, 10:42:29 pm
content: Heheh, that was my reasoning as well.With the change of making it just a unity gain buffer I suddenly agree with the schematic for the most part.I'd do the RC filters a bit different, but that is a minor detail that can be worked out later. As long as we can agree on the fact that the "To ADC" has been low pass filtered, clamped and buffered.Oh yeah, and I would just kick out the auto zero switch near note . Personally I plan to do auto zeroing around the integrator. Definitely not in this input stage, unless I am missing something...

author: Stoney
author_rank: Contributor
timestamp: March 20, 2013, 11:32:19 pm
content: Hm, how would you do the filter? Maybe your solution is better(active?)The autozero should, in my opinion, include the input buffer. Maybe it's placed somewhat wrong...if I would place it just behind the diodes ( between clamps and R4), one could use a low-voltage MEDER one (much, much cheaper than those bloody expensive coto ones and equally low emf). The auto-zero in front of the buffer is certainly not equal to the "each cycle integrator zero" but can be used if requested by the user to really zero the whole unit including the (temperature drifted, its certainly useless if used 2s after power-on) input buffer. The integrator is of course part of the procedure. I'm not really sure if a real auto-zero can be achieved (or makes sense) without grounding the input buffer input...

author: mrflibble
author_rank: Super Contributor
timestamp: March 21, 2013, 12:35:09 am
content: Quote from: Stoney on March 20, 2013, 11:32:19 pmWell, I don't know about better, but it is even simpler.It's passive just like yours. Only difference is that I would only use 1 RC stage, and I would use a slightly different f-3db. Remember that the"we shall use low loooow bandwidth"was from the part of the discussion where delta-sigma ADC was also on the table.In the meantime I've read a bit more about dual-slope, and I have seen the error of my delta-sigma ways.Dual slope is damn nice in many ways. So I want to try and make a 5-1/2 digit dmm based on dual slope. Not because it makes economic sense, but as a fun learning exercise. If it was to make economic sense I'd better work a bit and buy something on ebay. Definitely more time-efficient than building one. But building one is more fun efficient!I would use a single RC filter and limit it to somewhere in the 1 kHz - 10 kHz range. And I'd do that at the point where you have your 100 kHz RC filter. And then I would leave out the 200 Hz Rc filter. Why? Well, lets not forget that our trusty integrator is an integrator. You know, one of them low pass filtery thingies.In any event, it's not really worth too much discussion. You can put them both on the PCB layout and then make it an optional component fit. You would for example keep your 100 kHz + 200 Hz arrangement, and I would do 5 kHz + passthru. And depending on results we can simply change component values a bit after the initial measurements.QuoteI'm not entirely convinced I'd want an autozero there. My focus is to keep everything boringly simple for a first go. So if it is a Nice To Have, and not a crucial bit of circuitry ... out it goes! Maybe I will see how it is an advantage when I see it in context with the rest of the circuit.

author: Stoney
author_rank: Contributor
timestamp: March 21, 2013, 10:12:23 pm
content: K, I'll leave it in there for now, with the two stages, one can basically run a number of combinations or just put a simple solder bridge in there. Same for the auto-zero, I'll leave it in there as an optionSince no other complaints came up, I would call the input conditioning done for nowexcept for:Let's talk CAT-Protection and over-voltage protection (not overrange, thats already done) to finish the voltage input sectionI'd love to have CAT-II (for measuring mains stuff), which would be rated 1kV (withstanding 6kV input impulses if I remember it correctly ^^ ). I don't have access to a 61010-1...but I could certainly use the DO-160 Class 5 as an equivalent(just kidding). Maybe someone could post a quick wrap-up what the unit needs to survive in terms of energy and pulse duration....Littlefuse offers some nice gas-discarge tubes wich might do the job, with low capacitance and certainly no other leakages during normal operation:http://www.littelfuse.com/products/gas-discharge-tubes/high-voltage-gdt/cg3.aspx.My fist try would be to put a high wattage resistor after the GDT to absorb the energy once it arcs over, together with a fuse in series with the resistor after the tube, to stop the "magic-smoke-and-fire generator" if it fails (obviously sacrificing the unit, but hey, you just managed to blow the protection). I really wouldn't like to see a PTC in a "precision" instrument (all that temperature compensation stuff, and a PTC in the input path?!). But maybe one could use one in series with the high-wattage R instead of the fuse to cool down the current in a constant overvoltage condition, which might be a better idea after all instead of the fuse. I've actually never used a GDT before...so, what do you think? Any chance this arrangement could do the trick? Do we need some additional "constant high energy overvoltage, eg. plug the damn thing in your 5kV generator" protection?So long,LukasEdit:I guess I wrote some BS up there regarding the idea for the protection....basically, It wouldn't do anything to protect the unit...I'll leave it in the thread as a bad example:D

author: branadic
author_rank: Super Contributor
timestamp: March 21, 2013, 11:04:19 pm
content: What about something like the circuit shown in AN-D16 "High Voltage Protection" by Supertex?www.supertex.com/pdf/app_notes/AN-D16.pdfBTW, updated my post concerning ADCs:https://www.eevblog.com/forum/oshw/open-source-multimeter/msg203717/#msg203717

author: mrflibble
author_rank: Super Contributor
timestamp: March 21, 2013, 11:56:24 pm
content: I don't know enough about doing a "proper" CAT-II protection, while still maintaining high precision. So if you guys come up with something reasonable I'll be happy to copy that and learn from it. XD In the absence of that my plan is to not measure mains with this thing because I don't care about measuring mains in any high precision. I have my cheapo handheld for that.

author: Stoney
author_rank: Contributor
timestamp: March 25, 2013, 08:10:38 pm
content: @banadic: Hm, interesting... thehttp://www.supertex.com/pdf/app_notes/AN-D11.pdfhas some more details on that... and btw, nice ADCsBasically a off the shelf multislope thing...might be a good fallback, but I suspect them to be insanely overpriced@flibble: I certainly don't want my unit with these nice and expensive components and a costly PCB blow up into magic smoke, just because I was too lazy or too stupid to design a proper protectionAnd hey, a protection is simply a must have...one can certainly argue about some, more or less optional, features but not about the protection...The standard fluke input protection that dave explained in one of his videos (If I remember it correctly) would be a good point to start from...some (most?) of the fluke bench meters are protected CAT I 1kV, CAT II 600V (which means a 4kV impulse protectionhttp://www.ni.com/white-paper/5019/en). And I guess they also use the R-Thermistor-MOV combination on their higher precision bench type multimeters (posted in another thread here in the forum:http://headsplosive.com/2011/11/fluke-8846a-6-5-digit-multimeter-teardown/). Any idea which type/brand they use for the PTC? The MOVs look like standard ones, with the high-wattage R in series with the PTC...Seems like they also used some R's to distribute the voltage equally between the series MOVs there...Anyone here who did a HP/Agilent/BK/NI/Keithley...etc. teardown and has some insight into their input protection?? The old HP ones seem to use the GDT/Fuse/R's combination in most models...Tektronics/Fluke 8808:http://s222.photobucket.com/user/Zadpics/media/Tektronix%20DMM4020%20Bench%20Multimeter/Fluke-Input-Protection.jpg.html?sort=4&o=5Seems like some MOVs + maybe GDTs (??)Keithley 2000:http://bardagjy.com/?p=1167Also a MOV/GDT combo with presumeably a PTC (the orange thing I guess) and a series R...

author: mrflibble
author_rank: Super Contributor
timestamp: March 27, 2013, 12:06:17 pm
content: Besides input protection, a couple of other things...- Voltage reference. I am thinking LM399 based, because 1) it is affordable and 2) it has pretty good drift figures so we can get good relative precision.- 10 Volt calibration source. The suggestion to use Geller Labs 10 Volt standard is actually a pretty good one. It is affordable, has decent performance, and allows us to consider that part of the design as "problem solved". That and it's a nice standalone module that you could use in other things as well.- zero crossing detector. See the schematic I posted some time ago. Acceptable? In any event, I think I'll make a little breadboard compatible pcb of this ZCD. That way I can easily test it's performance both for this DMM project as well as for a few other things.- integrator. That's the main (as in highest priority IMO) bit of undefined circuit on the list. I was thinking of roughly the circuit in the TU Berlin schematic. LTC1150 unity gain buffer + integrator around an LT1056 is a decent starting point. As for analog switches the ADG202 is nice. The DG444 will probably do the trick just as well and is a little cheaper.Does anyone have a favorite good quality yet affordable cap we can use for the integrator?

author: poorchava
author_rank: Super Contributor
timestamp: March 27, 2013, 01:23:09 pm
content: Panasonic ECHU series of metalized PPS film smd capacitors seems nice. They are down to 2% tolerance, have a small capacitance variation over temperature range and low leakage. Cost is rather modest.There are also Cornell Dubilier's silver mica capacitors, available with tolerances down to 1/2 pF. They are THT-only and are a lot more expensive than Panaconics (~2-5€ a piece from Farnell)

author: mrflibble
author_rank: Super Contributor
timestamp: March 27, 2013, 05:44:24 pm
content: Thanks! I did a bit more reading, and looks like metallized polypropylene film is the ticket. So for example Vishay MKP1837 or MKP1840 series.The reason for MKP being that it has pretty low dielectric absorption (0.05% typical for the two series mentioned). And that's the one you want to keep low for the dual slow (or multi-slope for that matter) integrator.So right now I've got those two MKP series on the list, cap value in the range of 0.01 uF to 1 uF, depending on choice of integration times and whatnot.Probably for the dual slope approach you need something closer to 1 uF, while for a multislope approach you can get a way with a smaller 0.01 uF cap.

author: mrflibble
author_rank: Super Contributor
timestamp: March 27, 2013, 06:07:45 pm
content: Also, a bit of Bob Pease fun on the matter:http://portal.national.com/rap/Application/0,1570,28,00.html

author: Stoney
author_rank: Contributor
timestamp: March 27, 2013, 08:39:15 pm
content: Thanks for all the input on the integrator so far...hope I can start with some detail drawings soon...I've actually started with the concept for the multi-slope, but didn't get far because of some looong days at work -.-But I managed to think about the protection stuff. I've updated the repo, so please go for it and have a look at the schematic (pretty basic) and the thoughts gone into it. After that, I think it's finally time for some integrator schematicsBtw: Couldn't get the PTC out of the signal path

author: branadic
author_rank: Super Contributor
timestamp: March 27, 2013, 11:58:18 pm
content: QuoteAs far as I now the better choice is polystyrene and even better is a teflon type capacitor. Last one is for sure expensive:http://www.soundlabsgroup.com.au/p/AU-0U68-600V-Aura-Teflon/0.68uF+600V+Aura+TeflonWhat the hell...? And if you were J.W. you wouldn't care and select from a hundred the one with the best characteristics, right? The cap itself for sure exceeds the price for a 31bit ADC ADS1281 or ADS1282, so again I wonder if the slope adc principle with all the cirtical parts is reliable enough and if it wouldn't be worth to combine something like STM32 with such a high resolution ADC?By the way, I was playing around with a TDC eval kit (time to digital converter) a few weeks ago and as long as you are able to give a start and at least on (or two) stop signal this guy is a better choice for whatever into time into digital converter because of its ps-resolution ring oscillator and this for a low cost, space saving one chip solution with the ability for temperature compensation. The maximum samplerate is somewhat like 200kHz under best conditions:http://www.acam.de/tdc-gp22/Another idea could be to use their CDC and measure the "capacitance" of a varicap in series with another low temperature drift cap. This guy is at least nothing but a TDC with some integrated switches and resistors and discharge time is measured.The varicap is pre-loaded by the input voltage I want to measure, so the discharge time is somewhat proportional to the input voltage. If the whole input is designed to measure a differential capacitance instead of a single ended (how ever this could look like e.g. a double varicap) I don't need a high stability voltage reference at all and most of common-mode effects are already compensated.Max. sample rate is 500kHz, so enough values to average and this guy was spend a DSP which means full polynomal compensation for temperature and ... and ...This are just my thoughts while brainstorming the complete problem of a high resolution DVM for a good buck. And we have learned that it is easier to make (portable) high precision time measurement (thanks to DCF77, GPSDOs or cheap second source RB-references) instead of voltage measurement "without" the reference long-term stability task. Contrary to the mentioned the slope adc still needs the high precision voltage reference.

author: mrflibble
author_rank: Super Contributor
timestamp: March 28, 2013, 04:54:29 am
content: Quote from: branadic on March 27, 2013, 11:58:18 pmWhat expensive cap? All I see is an audioph00l website with an overpriced cap. Doesn't mean that the cap we will actually use is going to be super expensive.And AFAIK for this application teflon is indeed best and most expensive. Then 2nd best is polypropylene and after that polystyrene. With those last two being not too expensive, which is why I chose from that set and not teflon. And having read that Bob Pease article I thought it might be fun to grab a bunch of different types and just measure what kind of soakage you get for various integration speeds. Buuuut, since I also know how easy it is to accumulate side-track projects I decided to write that idea down in the column of "Fun but not required" things to do. It definitely is fun, and I might just do that in the future (and use the information to improve cap choice) but not now...Quote*edit: timing related thread derail removed*At any rate, I had promised myself I wasn't going to put any more time into the timing aspect until we get some hard numbers on timing resolution requirements.So chop chop, hard numbers!QuoteYeah, and if those bleeping Chinese guys would just lower the Rb price a bit I'd have bought 2 already.And unfortunately no-one has developed an affordable virtual photon counter yet with single photon resolution, so I think we're stuck with the voltage reference a while longer.

author: mrflibble
author_rank: Super Contributor
timestamp: March 28, 2013, 05:00:46 am
content: Quote from: Stoney on March 27, 2013, 08:39:15 pmCool, I'll have a look at it. Incidentally, you've got a PM.QuoteCouldn't agree more.

author: poorchava
author_rank: Super Contributor
timestamp: March 28, 2013, 03:01:38 pm
content: Quote

author: mrflibble
author_rank: Super Contributor
timestamp: April 01, 2013, 04:54:17 pm
content: Yeah, I love stuff like that!Has me wonder though, what does that even mean? Their teflon has interesting optical properties?Besides, audiences probably believe whatever they fancy after drinking Kool-Aid laced with lsd. Regardless of cost!

author: poorchava
author_rank: Super Contributor
timestamp: April 02, 2013, 06:21:32 am
content: I know that's still off-topic, but I couldn;t hold myself back:http://www.lessloss.com/blackbody-p-200.html

author: mrflibble
author_rank: Super Contributor
timestamp: April 02, 2013, 06:54:55 am
content: LESS>LOSS to sanity.MORE<LOSS to wallet.I advocate heavy use of LSD to compensate for any "coloration of sound" by those pesky stray EM near fields. That's probably more cost effective, and better for humanity alround given the target group.Anyways, I'll try to come up with something integrator related soon-ish so we can keep things on topic.

author: branadic
author_rank: Super Contributor
timestamp: April 02, 2013, 08:11:47 pm
content: It's funny, isn't it? The link to the mentioned cap was only to show how expensive such teflon caps are and you won't find lot's of sellers for teflon caps this days, except for such audio freaks. I had expected some more professionalism in here, obviously I was wrong.

author: mrflibble
author_rank: Super Contributor
timestamp: April 02, 2013, 09:36:44 pm
content: Mmmh? As said, teflon is pretty expensive and as such lets pick the not so expensive polypropylene option.So you propose some caps, they happen to be on an audiophool website. Audiophoolery gets made fun of a little. The main point being that this particular incarnation of teflon is WAY overpriced. And teflon in general is quite expensive. And so what, teflon is not the only reasonable choice available. Polypropylene it is, problem solved, onwards to the next problem. No need to get all "I had expected some more professionalism in here, obviously I was wrong"-ey about things.No slight intended towards you. But you can't blame people for having a chuckle at transparent and resolute capacitors.

author: Stoney
author_rank: Contributor
timestamp: April 03, 2013, 08:33:01 am
content: What about NP0?

author: mrflibble
author_rank: Super Contributor
timestamp: April 03, 2013, 10:00:07 am
content: As far as I understand dual slope, NP0 is not all that great for this application.We don't care too much about the absolute cap value, and as such initial accuracy is not all that important. Even drift isn't too important. As long as the cap value is stable within an X amount of precisionfor the duration of the ADC conversion cycle (i.e short amount of time)we should be fine. The figure of merit for the integrator cap would be dielectric absorption. And as said, that's not all that great for NP0.See for example:http://portal.national.com/rap/Application/0,1570,28,00.htmlandhttp://www.analog.com/library/analogDialogue/Anniversary/21.htmlEssentially we're looking for a cap that's good for sampling & holding applications. I mention S/H because the caps we're looking for are likely to be listed under "application: S/H, ..." at the cap manufacturer.I currently have Vishay MKP1837 or MKP1840 as candidates. There are bound to be better ones, but I didn't want to spend endless hours on selecting just one component. Ithinkthose will be adequate for now. But if someone knows part numbers for affordable caps with lower dielectric absorption than those, then please do tell.Caps should be in the range of 0.01 uF to 1 uF I think. And as with all the other components, in stock with the major distribustors would be preferable ... but that almost goes without saying.

author: robrenz
author_rank: Super Contributor
timestamp: April 04, 2013, 01:52:03 pm
content: TI 24 bit delta sigmaevaluation board. I know this may not fit into the direction this thread is currently going. But these features caught my eye as usefull somehow.Easy to use online and offline WEBENCH Medical AFE Designer toolClickable block diagram in toolPre-programmed 3-lead and 5-lead ECG applicationEasy-to-use evaluation software for Microsoft™ Windows XP or Windows 7Built-in analysis tools including oscilloscope and histogram displays, estimated device and measured system performances, and beats per minute calculationReal time data streaming from the demo board to the PCAbility to export data in simple test files for post processing

author: mrflibble
author_rank: Super Contributor
timestamp: April 04, 2013, 05:34:27 pm
content: Indeed, that's quite a nifty board for a nice price. I have the ADS1258EVM which was about $50 at the time. Or was it EUR 50, I forgot.For this particular project I intend to use that board to measure the integrator residue after an integration cycle, and see if there's a benifit to be had there. But at least for me the choice of delta-sigma vs dual-slope/multi-slope has been made. I started out thinking to maybe use delta-sigma, but after more reading I jumped ship to the dual-slope camp.

author: Stoney
author_rank: Contributor
timestamp: April 14, 2013, 11:50:20 pm
content: Hey guys,just wanted to let you know that mrflibble and I are working on the project and have made some progress. But we shifted our communication mostly to email/PM because we're chatting a lot about specific questions/typologies and calculations, and email is just easier in that matter.Be sure to check out the repo from time to time and feel free to comment on any of the contents!So long,Stoney

author: branadic
author_rank: Super Contributor
timestamp: April 18, 2013, 07:21:27 pm
content: QuoteIt's not a good way to make an opinion just by the words of a single person, even if it's Bob Pease. I found this website that says, that polystyrene has smaller dissipation factor and tempco is stronger specified:http://conradhoffman.com/cap_losses.htmSo you better test both types of different manufactors (not with a single example!!!) to find the better one as they will not specify all interesting parameters in their datasheets.Best choice would be an air or vacuum cap but the needed value for the integrating cap is a bit to high. Teflon is expensive and rare this days and my link showed that it seems to be reserved to the audio freaks. You shouldn't take care of their advertising slogans, but to the electrical parameters.But if there is a possibility to get one of this teflon guys in the bay you should take that chance. You better don't put several caps in parallel as the resulting cap will have a higher leackage.Concerning soakage you can for sure use one of the shown compensation circuits, but an advantage on compensating one parameter will often have a disadvantage in another, bear that in mind.

author: mrflibble
author_rank: Super Contributor
timestamp: April 18, 2013, 07:48:41 pm
content: Quote from: branadic on April 18, 2013, 07:21:27 pmAgreed.QuoteThat's the plan. Didn't I post that earlier, or was that just in PM? In any event, it's a good suggestion and it's on the TODO list.QuoteMaybe I am blind, could you send me a link where I can find the electrical parameters for that teflon cap? Because I did try, but couldn't find it. Even with a google "site:teflonvendorforgotwhatitwas.com" I came up empty. Because I was indeed curious to know what kind of specs one buys for that large chunk of money.QuoteIndeed. The prototype won't have any such compensation scheme since we'd like to keep things medium simple.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 18, 2013, 10:33:36 pm
content: Quote from: branadic on April 18, 2013, 07:21:27 pmCan some-one tell me what is the range of values you folks are considering for an integration cap? My recollection from dave's HP3457a teardown was that HP was using 10 nano farad, or was it 10 micro?. I am thinking this might be possible to make 'home rolled' from teflon sheet and copper clad. The extra physical bulk should be manageable as it is planar and can be mounted in parallel with the main circuit board, no? Copper foil isn't particularly expensive but teflon board sold to the RF guys can be. I suspect there are cheaper (and thinner) sources of teflon film as it is used as a gasket material. Capacitors aren't really all that magic, even if some are resolute and transparent.Yes just checked Mcmaster Carr they have Ptfe film. I don't normally look there as they no longer ship to new Canadian customers but here is an example 0.002 inch thick 6 inch wide $1.55 per lineal foot. - jeeze those americans and their inches.

author: mrflibble
author_rank: Super Contributor
timestamp: April 19, 2013, 02:43:17 am
content: We're talking about something in the 220 pF - 10 nF range, depending on what speeds and slew rates and such.Heh, and you justhadto mention a DIY teflon cap. Earlier tonight I was going over several datasheets and was moderately frustrated by the lack of information for this type of app. The manufacturer is perfectly happy to tell you that it's an awesome cap and you should use it for S&H application. And it has low dielectric absorption blah blah blah. But actually giving numbers? Nooooooo, that would be too easy. Some do give info, and those typically are the ones that actually have a do-able dielectric absorption. Or rather, the DA is such that it is worth testing to see if it's a good enough cap for the application.Anyways, the so-so availability of information had me almost considering a DIY cap solution. But then I remembered that no we are not going to do that because if we want to enable other people to build this as well, then we should keep all the parts as simple and available as possible. And now you tempt me with a DIY teflon cap.So yes, it might definitely be interesting to see how such a cap would stack up against off-the-shelf parts...For ease of discussion, lets say a 1 nF cap... How much would one need and where would you easily obtain it? Preferably with non-crazy shipping cost to Europe. Or samples would be great too.Edit:And to prevent misunderstandings ... this diy teflon cap would be purely to compare it to say a polypropylene, mainly just for the fun of it. It's a hobby after all.Not as the primary candidate for this design.

author: branadic
author_rank: Super Contributor
timestamp: April 19, 2013, 06:12:05 am
content: As was aksing them for an electrical datasheet but all I received was this:QuoteSo I went on and found this page in the link posted previously:http://conradhoffman.com/cap_measurements_100606.htmlIsn't it critical to do a DIY cap by just using metal (copper) and ptfe foil and roll them togehter? You can have air between the several layers and the resulting cap is somewhat a result off paralleled air and teflon caps. I would have expected that the teflon is evaporate with the electrodes material to get best performance and this is a process one can't simulate at home. But however, give it a go and tell us about the results

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 19, 2013, 10:32:18 am
content: Quote from: mrflibble on April 19, 2013, 02:43:17 amHello MrflibbleOK it is late here and I'm a little punch drunk. Here is a first pass assessment.First to calculate size, teflon dielectric constant 2.1, polypropylene 2.3 so teflon maybe going to be 10 % bigger plate area if gap is the same. I useC = 1 x 10e-9 F desired capacitancee0 = 8.854 x 10e-12 F/m electric constanter = 2.1 permittivity relative of PTFEg = 0.001 inch or 2.54 x 10e-5 plate gap in metersA = plate area in m2to be calculatedso C = (e0 x er) x A/gor A = 0.000537825 m2or 5.37825 cm2this is do able, the first time I ran through this calc. I ended up with half a square meter for 1nF and thought that can't be right. please check as I am tired and making mistakes now.There are multiple sources for copper foil 0.001 inch thick and teflon same thickness, let me continue to search for the best. Some additional notes: teflon sheet at 0.001 inch thick is listed in various places as having dielectric strength of 500 to 2000 V per 'mil' which I think means 1 thou inch thickness. Holy shit-snacks we can tie these caps across the mains! Also it is produced by 'skiving' which I think is the process where a very big solid log of teflon is put in a lathe and a thin sheet is shaved off by a very sharp cutter. Does not seem like good way to me, but what do I knowPrices are looking reasonable, more later. These materials can be purchased by one individual in some quantity and then after cutting and subdividing with a paper cutter sent to other experimenters using ordinary envelope and mail service for economy.Suggest to me the best form factor/topology, alternating rectangular plates for a rectangular package or rolled up into a cylinder. I fear rectangular might act like a patch antenna but I know nothing!Looking at conrad hoffman's page there doesn't appear to be a great advantage to teflon over polyprop in adsorption still it is fun to experiment. I am almost 'having a volt nut' now, just don't want it to happen in my pantsgoodnight my friends, going to bed

author: branadic
author_rank: Super Contributor
timestamp: April 19, 2013, 04:21:32 pm
content: Quote from: mrflibble on April 19, 2013, 02:43:17 amThis value seems much to small to me. In this range it should be no problem to get stuff in the bay. I expected a few hundreds nF (Notice to americans: this is a SI conform unit called nano farad, somewhat in the middle of micro and pico farad) up to serveral µF.QuoteThinking of such an arrangement I would expect nearly twice the cap value:http://www.jogis-roehrenbude.de/Leserbriefe/Edelmann-Ko/Image182.jpg

author: mrflibble
author_rank: Super Contributor
timestamp: April 19, 2013, 06:24:26 pm
content: Quote from: branadic on April 19, 2013, 04:21:32 pmYou're welcome to join the club and help improve the design.If you go back in the thread you will notice that I mentioned an integrator cap in the 10 nF - 1 uF range. Those are the values I was looking at for a dual slope design. Ahem, pardon my terminology. An enhanced dual slope design (different runup/rundown resistors).Right now we are looking at a relatively simple version of multi-slope with an ADC in the mix. The ADC is mainly there to drive up the BOM cost and create controversy should anyone check out the repo.It's not as if the idea is to do clever stuff with it and have fun while building this thing or anything. And the aim is to be able to do continuous integration.For this type of multi-slope 10 nF actually is on the high side. And 220 pF is on the low side, so I would expect we end up somewhere along this range...Oh and pssst chickenHeadKnob .. *cough* factor of 2.54 *cough* That, and what branadic said.Regarding getting teflon caps on ebay, yes I did look at that. But it suffers from the same type of problem as DIY caps, namely that it doesn't help in making the design available to other people. If it's easier to obtain the required parts at a reasonable cost it's more likely someone will also try the design. So I'd rather not make the cap a hard to obtain part since it central.Additional, on the subject of affordable parts ... the ADC currently in there is anything but affordable. But it's not strictly required, just for extra bells and whistles and to test some fun things. The design will (or at least that is the plan) work just fine with just comparators after the integrator.

author: mrflibble
author_rank: Super Contributor
timestamp: April 19, 2013, 07:03:27 pm
content: Quote from: chickenHeadKnob on April 19, 2013, 10:32:18 amI must admit that it would be fun to try and make some teflon caps, and then see what the results are.But after a good nights sleep ... while it would be fun to do, there is only so much time in the day. If I look at all the other work that needs to be done, it's best not to add to it unless strictly required. Case in point, take for example the caps... I would love to just be able to read the datasheets and then go "ah okay, this and this cap will do what we need, and it will behave such and such". All you can do is give it your best and make an educated guess based on the limited info that's in the datasheets. And then make a test jig and simply measure those suckers. But if I could I would rather not do the frigging test jig and just be able to trust the information in the datasheet."Simply measure everything" I hear some potential clever person say. A sound suggestion, but you don't make a test jig for every single component you put into your designs, do you? That would be a bit too much work. Since the performance of this cap is rather central I don't see any other easy way, but I would love to just plug in a known-to-work-for-this-app capacitor.The best actually quoted in the datasheet numbers for DA have been 0.05% DA (typical). That number together with the loss tangent over frequency gives you some idea, but that's about it. And before someone says, well <fill_in_material> is better than <fill_in_other_material>, gimme a link to a datasheet that has an actual number for dielectric absorption that is better than 0.05%. And that is datasheets from the manufacturer, not measurements by a third party. Actually measurements by a 3rd party are also welcome, because for example that conradhoffman stuff also was useful. But DA numbers in a datasheet are nice. So far the most informative datasheets (for this app) have been by Vishay and WIMA.I can only wonder how many types of caps (and other parts for that matter) a DMM manufacturer has to go through before they find the right ones. Then again, they probably have a slightly bigger purchasing and R&D department.Does anyone have any references for test jig to measure DA and such? Right now I am looking at doing something likethisandthis.I tried finding more on the measurement method on conradhoffman.com but couldn't find it, but I am sortof hoping I just missed it. Anyways, information on such would be appreciated.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 21, 2013, 01:06:00 am
content: Quote from: mrflibble on April 19, 2013, 06:24:26 pmHello everybodySome suggestions in no particular order:suggestion1 - to disambiguate give the inner ADC an official designation, I would chose 'residue ADC' otherwise this nested recursive ADC situation could be somewhat confusing. It looks like the idea from that american patent set in the 1990's. I like it, don't worry about cost optimization so much early on, there is more elastic expense and controversy in the FPGA.suggestion 2 - choose the best fitting easily sourced integration cap you want, just make it through hole. Once this is documented the elve(s) atHobby Posse Capacitor Companycan fabricate a near fac simile from copper/PTFE and mail to you and stoney if you want it. I am pretty sure I can duplicate most electrical parameters but will require greater physical bulk than an off the shelf polypropylene cap. The last thing I want to do is waste your time. I think you and stoney are smart guys and have similar design taste and esthetic to myself (but me not so smart) and I very much want you to succeed.I am continuing the materials search but have to interleave it with personal time.@branadic - I looked at that diagram, and yes that is the obvious way to make a rolled up foil cap, however I see a potential improvement; instead of soldering on leads at the end of the sheets/planes wouldn't it be better to solder closer to the center? The leads would have to be offset from one another if radial leads are desired, but axial is also easy. I wanted to roughly calculate the amount of material needed so I only considered single plate area. What you said in another post about included air in the dielectric gap is entirely true and further muddies the capacitance calculation.@Mrflibble - * cough 2.54 cough * I thought I took this into account. One of the annoyances is that the natural areal unit for capacitors is m2but buying sheet goods in north america is still bound to imperial units so I am always converting back and forth.

author: branadic
author_rank: Super Contributor
timestamp: April 22, 2013, 09:17:08 pm
content: QuoteThanks, but I think you've chosen your way, the design is already fixed and there is less place for other/new ideas, that are not common. I'm not familar with FPGA and think this solution is an overkill for me. But I'll give some input from time to time.QuoteMy gut instinct tells me that the cap will have less performance compared to second-hand market teflon caps, primary concerning long-term stability characteristics as you are not able to incapsulate them well against humidity and with regards to the fact that you will use a copper foil instead of directly plating the teflon foil with the electrodes. Only a few critical points, but I'm sure interested in your test results. Just show me the opposite.

author: glatocha
author_rank: Regular Contributor
timestamp: May 05, 2013, 08:49:09 am
content: Hi,I went through almost whole topic and I can see a lot of discussion about the case and usb and screen, etc.I am mostly interested in the analog front-end.I am thinking myself of making a small Voltage and Amp meter. But let's say my budget is really tight. This will be just my project not for commercial.I am totally zero on analog circuits so this should be my learning project.Let's focus on voltage. I need the +-10V with two ranges 9.99V and 99.9 mV. ADC will be build in the uC. So I need to do the range selection, divide the voltage and add the offset to have 0-2V on the ADC input.PGA's are expensive, analog multiplexers alsoI am thinking to do the Voltage dividing on resistors and then summarizing op-amp for reference offset. Then will go to my ADC and do the selection inside uC. Do you think this is the easiest solution?P.S. I could split that to another topic, but think it shares the interested people

author: Rerouter
author_rank: Super Contributor
timestamp: May 05, 2013, 09:31:52 am
content: why not have the reference into a voltage divider, for your main range you leave your micro pin high impedance as an input, then to switch to the low range pull it down to ground by outputting low, yes there will be variations in how closely to ground a micro can pull, but that can be worked out in calibration, as one cheap and very low parts method,... you should still have clamping diodes, but you can make the range switching software based

author: glatocha
author_rank: Regular Contributor
timestamp: May 10, 2013, 01:20:38 am
content: Hi,how do you plan to make the channel separation? I am thinking about the solution to measure Voltage on two channels (with range +-10V) but the potential difference on both can be high (100V).How to deal with such problems?

author: Rerouter
author_rank: Super Contributor
timestamp: May 10, 2013, 02:11:50 am
content: isolate your adc's, using optocouplers

author: glatocha
author_rank: Regular Contributor
timestamp: May 10, 2013, 02:17:40 am
content: but the reference and power supply for the ADC will be anyway same

author: branadic
author_rank: Super Contributor
timestamp: May 13, 2013, 12:26:40 pm
content: I found that we have a PREMA 5017 at work. Pretty interesting stuff about that device and lots of pictures can be found here:http://ohh.de/5017.htmhttp://www.amplifier.cd/Test_Equipment/other/Prema-5017.htmlSeems that they use their 26bit ADC:http://ohh.de/5610.htmThey use a pll to lock their adc to mains frequency. Also interesting is, they use an LM399H (Linear Technology) for the 7.5 Digit device. Would be interesting to know what reference they use in the 4x better specified (stability) device 6048.

author: branadic
author_rank: Super Contributor
timestamp: May 20, 2013, 01:34:47 pm
content: Any news about the project?

author: Legit-Design
author_rank: Frequent Contributor
timestamp: June 07, 2013, 10:52:31 pm
content: Didn't see any mentioning about this project here:https://sites.google.com/site/theopensourcemultimeter/documentsThe Open Source Multimeter by George Randel(last updated: Sep 27, 2011)No the project is not done by me.http://www.usc.edu/CSSF/History/2012/Projects/S0913.pdfhttp://www.vcstar.com/photos/2012/apr/30/165529/Picture of Mr Randel with his oshw multimeter board.That pcb seems to be 12/21/2011 and different layout.Didn't find ANY documentation whatsoever in either of the zip files.Files are for DipTracehttp://www.diptrace.com/download.phpFreeware for nonprofit use, no registration no bullshit.Pictures below are from Mulrifinalboardsr1.zipSchematic is really messy, almost looks like it was imported from some other cad program for sharing. This guy seems to have spent alot of time with this design, too bad he hasn't shared anything else. Would have preferred to see final assembled pcb working.http://www.linear.com/product/LTC2440LTC2440 - 24-Bit High Speed Differential Delta Sigma ADC with Selectable Speed/Resolutionhttp://www.st.com/web/catalog/mmc/FM141/SC1169/SS1031/LN1565/PF189782stm103QFP 48usb isolation2 voltage channels2 current channelsLC metertrue rms conversion chipmostly linear technology partsI attempted to create a BOM with the program, but since I'm not used to using this it wouldn't let me make it properly...BOMincluded below:oshwmultimeter.pdf(same part shown multiple times as quantity of 1, I removed resistors and capacitors from bom, since it started to look even more messy)Click for full size schematichttp://speedy.sh/khnA3/oshwmultimeter-full-sch.pdf9MBFull schematicfor viewing pleasure.If anyone has any knowledge about this project please share!

author: branadic
author_rank: Super Contributor
timestamp: June 09, 2013, 06:27:21 pm
content: None of the so called "Open Hardware DMM" projects with more than 4 1/2 digits are well documented or finished. For everything up to 4 1/2 digits the Intersil parts (e.g. ICL7135) are still a good choice, everything else is overkill:http://www.kmitl.ac.th/~kswichit/DVM7135/DVM7135.htmI'm not sure if this project here will ever reach a status with a functional prototype. I fear this is due to the choosen overkill FPGA solution and some disagreements how to solve several parts.I wonder why there is no project that uses softer goals like 5 1/2 up to 6 1/2 digits, dual-/multichannel input, a seperated board for each channel with some CPLD-based multislope adc or simple 24bit sigma-delta adc, a reference board with multichannel output, a STM32 board with a 7" LCD for displaying the several channels and an isolated pc interface maybe with SD card option.A big LCD allows for multichannel displaying, this would be something novel and therefore a unique feature.There is no need for a project that can't do more than commercial DVMs/DMMs as you can get them well priced as second-hand.Personally I don't like 8-segment LED, monochrome LCD or simple dot pixel matrix displays. If you can get a 7" graphic display:http://www.ebay.de/itm/STM32F103ZET6-Development-Board-7-Touch-Panel-SSD1963-TFT-LCD-Module-/170893762278?pt=LH_DefaultDomain_0&hash=item27ca0fdee6you can also display additional information such as statistics, trend for each channel and spend some logging functionallity etc.But this is just my opinion.

author: airiclenz
author_rank: Contributor
timestamp: June 18, 2013, 08:30:13 am
content: ...a >100$ display is an overkill in my mind. There are pretty good solutions out there - smaller (up to 4") but also they stay in the range of affordability.

author: ve7xen
author_rank: Super Contributor
timestamp: June 18, 2013, 08:50:01 am
content: Those displays are available for about $30 in singles. Cheaper than the 192x64 mono OLEDs I bought a few months ago for a project...e.g.http://www.ebay.com/itm/4-3-TFT-LCD-Module-Display-Touch-Panel-Screen-PCB-Adapter-Build-in-SSD1963-/360674009570?pt=LH_DefaultDomain_0&hash=item53f9d8a1e2

author: Legit-Design
author_rank: Frequent Contributor
timestamp: June 19, 2013, 10:01:04 am
content: Lets just slap in Sharp memory lcd, so we can have an awesome batterylife.http://fi.mouser.com/ProductDetail/Sharp-Microelectronics/LS027B7DH01/?qs=%2fha2pyFaduhwKuijHwmQ%252bQF18%252b4JzroItWztWhky8OowGAyTdpoDnQ%3d%3d5pcs : 34,28 € /eachSpecificationsSize: 2.7 inch (6.86cm)Pixel format: 400 × 240Outline dimension: 62.8 × 42.82 × 1.4Active viewing area: 58.8 × 35.28Dot pitch: 0.147 × 0.147Input voltage: 5VInterface type: 3V serialReflectance: 18%Power consumption*:50?WOperating temp range: -20 to +70ºCSurface hardness: - 3H or more initialpencil hardness*with static image

author: romovs
author_rank: Contributor
timestamp: July 05, 2013, 04:18:16 pm
content: Quote from: tnt on June 30, 2011, 08:54:06 pmNo. The only possibility is to squeeze into the niche between those cheap ass pc scopes and Chinese 300$ low ends.There is no way for an average (group) of electronics enthusiast to design a marketable scope matching 5k scopes feature and price wise.As for the multimeter. Go for it! Kikstarter seems to be all about gaining experience and cash through the stupidity of others

author: Marco
author_rank: Super Contributor
timestamp: August 25, 2013, 11:56:07 am
content: Quote from: branadic on June 09, 2013, 06:27:21 pmCS5532/34 has 23 bit noise free, you could easily do 6 1/2 with that (although INL would corrupt a few LSB). Although I'd try to use the MCP3903, cheaper and a faster SPI, with oversampling and some dither you could probably beat the cirrus.QuoteI'd kinda like 8 segment LED for the readability ... but you can get a 3.2" touch screen for around 10 bucks, which makes it more attractive.All in all you could have a kit with component costs in the range of 25$, so saleable for 50.

author: greatal
author_rank: Newbie
timestamp: November 08, 2013, 05:13:01 pm
content: Hi allI am kind of new in electronics and eevblog and its hard to read all these pages but as I work in Electrical meter company I think that’s maybe a good idea to use Rogowski coil (no magnetic interference like CT current sensing or no limits like shunt solutions) to measure current while measuring voltage it is so acquire and it is not so expensive there is some single chip solution by ST(it is kind of include some complete isolation solution using ordinary Ethernet network filter) although it’s so hard to setup but its working so good the meter could use only and only to probes to measure current and voltage at same time.

author: SixD
author_rank: Contributor
timestamp: December 15, 2013, 06:21:13 pm
content: I have started to make a arduino based multimeter.

author: codeboy2k
author_rank: Super Contributor
timestamp: December 16, 2013, 07:54:30 am
content: This thread pops out of the wood work occasionally.. So I read back about 6 or 7 pages to catch up today...I'll throw my comments into the mix here...1) regarding the FPGA: I think a low cost iCE40 with 384 LUTS for < $2.00 (qty 1 from digikey) is good enough to time the discharge on the downslope, from top to zero-crossing. Also, the STM32 counters might be fast enough, but not wide enough and will overflow (do you have timings done yet? How long does a cycle last?). Each iCE40 LUT has 1 LUT, 1 FF, and carry logic, so there is enough there for a few 24 bit counters, and you might even have enough to make a voltage and current ADC if you wanted to. Also see my #6 below regarding the need for voltage and current.2) the comparator needs to have low offset, and reasonably fast propagation time. Presumably less than 1 clock cycle otherwise you are losing counts. If you are counting at 100Mhz (10ns) you need a comparator that can switch it's output in < 10ns. If it's slower, you get count errors.How fast you need to count depends on your desired resolution, the charge up/charge down times, and how many conversions per second you want to achieve.3) there is an old trick from the Keithley meters to get higher resolutions without necessarily having to go to really high-speed counters (i.e. 100Mhz) and expensive high-speed comparators and precision op-amps..What they do is, for example, count with 10Mhz, then when the zero-crossing occurs, they take that count and save it. Then they amplify the residual on the integrating capacitor x10, reset the counter, and time the discharge of that amplified amount until the zero-crossing again. When it crosses zero, they add that count (divided by 10) to the previous total, then they take the residual of that, once more, x10 again, reset the counter and discharge that to zero. This gives two more digits of precision, using a slower counter, and less precise comparators. And of course it's slower and takes more time. But maybe it's something you want to consider too, to be able to use less expensive parts and still get good precision. If you do this residual discharge with a 100Mhz clock, you might get extra digits into the 7-1/2 to 8-1/2 regions (assuming that the noise, leakage etc, is well controlled).4) regarding the input buffer: I think your first choice of LTC6240 is still the best choice. It's < $4 and the chopper stabilized LT1052 is more than $12. Unless I am mistaken, the drift is not important on the input buffer (enlighten me if I am wrong about this). I think the input buffer only has to be stable for 1 conversion cycle. However, for the reference buffer you want to use a chopper stabilized opamp like the LT1052 (maybe not that one for that purpose, just pointing out that the zero-drift is more important on the reference buffer than it is on the input buffer).5) for the display, there are plenty of 4.7" and 5" 800x400 LCD with touch displays these days. usually between $20-30. That's not too bad and makes a nice user interface possible.6) finally, I am working on an LCR meter design that uses a 24bit delta sigma ADC ( I am also using the LT6240 as input buffers on that project.. they *are* very nice). You can use the STM32F4 pwm outputs to generate the sine (100Hz, 1kHz, 10Khz, 100Khz, etc), low pass filter it and send it into the device under test. Then measure the voltage across it and current through it and do the calculations. The FPU in the STM32F4 will help here. It's really, really simple to do. I'd be happy to join up on the project and do the LCR part, but the entire AFE has to support 4 wire mode and is basically floating above ground (I measure between RED/BLACK sense leads differentially with two LTC6240s and amplify that with a 3rd difference amplifier, then send it into the ADC). Current through the DUT I measure from the black sense lead through a current sense network returning to analog ground. For a multimeter we'd need to put the voltage divider in front of that. If you want LCR capabilities, you be best to consider it up front.Sounds like an interesting project,Cheers!

author: mrflibble
author_rank: Super Contributor
timestamp: December 20, 2013, 06:24:59 am
content: Quote from: codeboy2k on December 16, 2013, 07:54:30 amThe really small ICE40's do indeed have enough logic for the required counters + control logic. Unfortunately they do not have a PLL, so if you want to use a PLL then one of the bigger models is required. In the current design we have a spartan-6 however, but that is not necessarily because of the requirements for counters + control logic. It also has to do with familiarity + a couple of handy features in spartan-6 that can be used for extra functionality.QuoteThe comparator doesn't have to be super fast, but it does make life easier. Just as important is that the propagation delay is reasonably constant over temperature etc.QuoteThat sounds interesting, how does this amplification of the residual work? Presumably not by increasing the residual charge on the capacitor, so how? Do a S&H, buffer amplify it to x10, and then store that charge on the capacitor, and then do a rundown again? Main part I don't readily see is how to amplify it x10, and then get the equivalent charge on the capacitor again so you can do a rundown again.QuoteAgreed.QuoteFunky displays is waaaay at the bottom somewhere.And I hope this 800x400 lcd display comes with a decent version of android attached to it, because I for one am not interested in reinventing the gui wheel.QuoteSounds interesting.Do you have a sample schematic of how you think the LCR part should fit into it?

author: Felicitus
author_rank: Regular Contributor
timestamp: January 06, 2014, 04:34:11 am
content: Quote from: Stoney on March 07, 2013, 03:17:38 pmI've read through the schematic above, banged my head against the wallseveral times, and even did some spice simulations, however, I still don't get how they protect the ADC (or the LTC1150 opamp U100) from input overvoltage when their range switch is on the 2V range and one would feed more than 20V (or: more than 150V, because that's what the U100 opamp can handle at maximum) into it.Is it a bad design, or have I overlooked something?

author: Dave
author_rank: Super Contributor
timestamp: January 06, 2014, 04:49:10 am
content: "Baah... Who the hell needs overload protection? You just have to be careful, that's all." Said no engineer ever.

author: sync
author_rank: Frequent Contributor
timestamp: January 06, 2014, 01:15:17 pm
content: It's a fusible op amp. On an over load condition it pops and you just insert a new one.Edit:Onhttp://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/] http://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/ they wrote that it's reproducibility and linearity is on par with a 34401A.

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 02:07:10 pm
content: Quote from: Felicitus on January 06, 2014, 04:34:11 amIt's a simple design, which as you noticed has no input protection.

author: gxti
author_rank: Frequent Contributor
timestamp: January 06, 2014, 05:58:33 pm
content: Quote from: codeboy2k on December 16, 2013, 07:54:30 amYou can extend a 16 bit counter + input capture to effectively infinite width in software without much trouble, especially if the period of the signal being captured is guaranteed to be greater than the period of the 16 bit counter. I'm currently using a STM32 at 72MHz to timestamp pulse-per-second from GPS and it's been running glitch-free for quite a while. The algorithm would need adjusting to handle the case where cycles might be shorter but definitely within the realm of feasibility. Being able to just use a microcontroller without any supplemental logic would be quite nice.Also since this thread seems to mostly be for random people to drop in and barf up some unnecessary bloatware features, allow me to indulge myself: if you're going to have an OCXO anyway, why not GPS-discipline it and have a 10MHz reference output? Haha, I'll see myself out...

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 06:51:09 pm
content: Quote from: gxti on January 06, 2014, 05:58:33 pmOr the other way around, which at least for my use makes more sense. Have an external GPSDO with distribution amp and enable the multimeter to use an external 10 MHz reference.

author: Felicitus
author_rank: Regular Contributor
timestamp: January 06, 2014, 07:36:57 pm
content: Quote from: mrflibble on January 06, 2014, 02:07:10 pmYes, but overrange "protection"? So this is clearly a really bad design.

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 08:45:34 pm
content: Quote from: Felicitus on January 06, 2014, 07:36:57 pm*shrug* I found it useful as source of some inspiration.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 06, 2014, 09:24:26 pm
content: Quote from: mrflibble on December 20, 2013, 06:24:59 amI haven't caught up on this thread in a while.. basically, the residual is there already.. it's residual. On the first rundown, when the 0-crossing comparator fires, the micro switches in some analog switches that bring a x10 between the cap and the comparator, then they continue the rundown... when it crosses once more, the micro will switch in another x10 and continue running it down to get the residual until it crosses 0 once more. There is no need to sample and hold, just cross 0 three times, with the last 2 times being amplified crossings.QuoteI was going to redraw the front end for this project but I haven't got to that yet... The schematic I do have now is for a client so I can't publish any parts of it. But I'll try to find some time to put something together soon.Quote from: gxti on January 06, 2014, 05:58:33 pmAgreed. I was probably thinking that my software would be busy enough already, but you're right, just adding bits in software is not much of an extra load, so pretty easy to do.Quote... and discipline it with frickin' lasers too

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 09:44:02 pm
content: Quote from: codeboy2k on January 06, 2014, 09:24:26 pmIn which case I suspect I already know the approach you mean (multislope). The way you described it sounded a bit ... different. But yes, multislope is indeed the way to go. The current design is a simplified version of multislope (as in multi being two), to limit the number of precision resistor ratios to something affordable.

author: Felicitus
author_rank: Regular Contributor
timestamp: January 06, 2014, 09:49:46 pm
content: Quote from: mrflibble on January 06, 2014, 08:45:34 pmThat's true. I tried to figure out how multimeters handle overvoltage/range switching on the ADC; some use zener diodes, but I'm not too confident with those. Also, the Fluke 27 schematic didn't shed any light on that either…

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 10:18:26 pm
content: Quote from: Felicitus on January 06, 2014, 09:49:46 pmThe idea is to use clamping diodes so it doesn't go waaay out of range of what the opamp can handle. Then during integration you notice the input is out of range so you switch to a higher range, or open the switch or whatever is the appropriate action. When autoranging voltage I'd say when you detect out of range, you step to highest range, and then step down again to what is appropriate.And the idea behind the above is that the clamping diodes only have to work for a limited time so you don't stress things too hard. The main drawback (AFAIK) behind those diodes is the leakage current during normal operations.

author: Marco
author_rank: Super Contributor
timestamp: January 06, 2014, 10:23:42 pm
content: Generally with a current limiting input resistor and clamping to the power rails (this can be done with diodes, but BJTs and JFETs are also often "abused" for this because they can have lower leakage, also a JFET mux does it for free).

author: sync
author_rank: Frequent Contributor
timestamp: January 06, 2014, 11:15:45 pm
content: Quote from: mrflibble on January 06, 2014, 10:18:26 pmOn good meters upranging is faster than downranging, because it can detect without a full ADC cycle. And a good meter must withstand it's rated voltage on the lowest range continuously. Autoranging can be switched off. So I see no point in stepping down from the highest range.

author: mrflibble
author_rank: Super Contributor
timestamp: January 06, 2014, 11:48:54 pm
content: Quote from: sync on January 06, 2014, 11:15:45 pmI see the point in stepping down if it's a DIY approach. I was making the statement within the DIY context, not the professional goodies context. Especially when you are not 100% sure yet about getting everything right, then stepping to highest range first and then slowly (while also not being in a hurry) step it down. Because not blowing shit up is more important to me than a few seconds of productivity gain. After you gain more confidence with your DIY solution you can always change the ranging algo, since that part of the software is not all that complicated.edit: curse you typos, cuuuurse yooouuuuu

author: sync
author_rank: Frequent Contributor
timestamp: January 07, 2014, 12:02:45 am
content: Ok, I see your point. But what is about manual ranging then? Which is the bigger problem.btw: I would limit a DIY DMM to 200-300V. No need to build a 1000V one.

author: Felicitus
author_rank: Regular Contributor
timestamp: January 07, 2014, 12:58:24 am
content: I have checked the other OSS multimeter schematic, they're using low-leakage BAS116 diodes to effectively limit the overrange to 2.7V, which is appropriate for a 2.5V ADC input. Need to do some spice simulations to see if they handle transients well.

author: sync
author_rank: Frequent Contributor
timestamp: January 07, 2014, 01:19:26 am
content: I think it's not a good idea to put the ADC directly on the input. ADCs usually want a low impedance source. And a multimeter should have a high impedance input (10Mohm or more). You need an input amplifier. Then the ADC does see the transients.

author: Felicitus
author_rank: Regular Contributor
timestamp: January 07, 2014, 01:24:25 am
content: That's correct, however, the input buffer can experience the transients as well (we call that "Impedanzwandler" in german, no idea if there's a direct translation).

author: Legit-Design
author_rank: Frequent Contributor
timestamp: January 07, 2014, 01:58:54 am
content: Quote from: Felicitus on January 07, 2014, 01:24:25 amhttp://translate.google.com/#de/en/Impedanzwandlerimpedance converter ?

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 04:51:44 pm
content: Quote from: Marco on January 06, 2014, 10:23:42 pmAnyspecificexamples of both parts and exact use of said parts to achieve this?

author: sync
author_rank: Frequent Contributor
timestamp: January 07, 2014, 05:12:16 pm
content: Quote from: mrflibble on January 07, 2014, 04:51:44 pmLook at the service manuals of older bench DMMs, e.g. HP 3456A, Fluke 8840A, Keithley 19x. I attached one example from the 3456A. Just four 27k resistors and two JFET diodes for clamping. These JFET are ultra low leakage, like 2N4117A.Edit:The relay is just for range switching.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2014, 05:14:44 pm
content: Quote from: mrflibble on January 07, 2014, 04:51:44 pmNot sure if this is what you're after but Dave did a superb video on DMM input protection.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 06:11:54 pm
content: No, that doesn't contain what I was asking about... But in the meantime I did find an answer to the question, which is to use a JFET like the 2N4117A.Bit expensive though.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 06:37:57 pm
content: Quote from: sync on January 07, 2014, 05:12:16 pmLol, why didn't I notice this before? Oh wait, you edited. Or I am just blind. No matter... I got the 2N4117A from thisTexas InstrumentsBurr-Brown appnote:http://www.ti.com/lit/an/sboa058/sboa058.pdfBut now I've got double confirmation, which is always good.At any rate, given the cost I think I will stick with the BAS116 for now and when the rest is proven use the 2N4117A in the next iteration.Edit:checked an open tab ... yup, I am blind. You already posted that 2N4117A when I replied to jucole. Need glasses.Maybe you know any good price/performance MOVs as well? Or do I first have to search for those myself, and then 10 seconds before I find them you post the very part numbers I find, 100% as per Murphy's Law or some derivative?Tradition dictates that you don't know any good price/performance MOVs so I will have to look for them myself.This would be the first project I design MOVs into, so noooo idea as of yet how to find the "good ones".

author: Marco
author_rank: Super Contributor
timestamp: January 07, 2014, 07:29:41 pm
content: Quote from: mrflibble on January 07, 2014, 06:11:54 pmI found these threads insightful :https://groups.google.com/forum/#!topic/sci.electronics.design/HNi5Bb-rRbEhttps://groups.google.com/forum/#!topic/sci.electronics.design/D53KlEoxmD8If you want to use discretes I'd use one of the low leakage Central Semiconductor diodes (Mouser has them). You won't do significantly better by abusing discrete JFETs or BJTs. As the other thread points out though, some of the integrated MOSFET opamps can do a lot better still.All that said, if you want to do auto-zero calibration then you need a mux, even if not muxes are cheaper and more compact than lots of relays ... the mux will probably have protection diodes built in.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 07:56:49 pm
content: Quote from: Marco on January 07, 2014, 07:29:41 pmThanks! Those are indeed quite informative.QuoteDo you have any specific part numbers of the ones you have in mind here, so I can stare at the datasheet?Edit:search at mouser is not very useful for this one. "Parametric Search for Surface Mount-Diode-Ultra Low Leakage" at the centralsemi website does turn up some. Maybe you mean the CMAD6001 and such?QuoteSame question really, part number to enable datasheet staring?

author: Marco
author_rank: Super Contributor
timestamp: January 07, 2014, 08:16:57 pm
content: The thread mentioned the CMPD6001S, but just look up all the central semiconductor diodes on mouser there are a couple with similar specs.As for muxes, in another thread someone mentioned the MAX4051 since Maxim gives a typical leakage current of 2 fA ... that said, Ti/On semiconductor have versions of the 4051 at a fraction of the cost with a typical 10 fA in the datasheet.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 08:32:15 pm
content: Quote from: Marco on January 07, 2014, 08:16:57 pmThanks for the confirmation. Search on centralsemi.com turns up basically CMxD6001...QuoteSo not theCD4051Bthen?

author: Marco
author_rank: Super Contributor
timestamp: January 07, 2014, 08:40:57 pm
content: Quote from: mrflibble on January 07, 2014, 08:32:15 pm10 fA typical at room temperature.

author: sync
author_rank: Frequent Contributor
timestamp: January 07, 2014, 08:46:39 pm
content: Quote from: Marco on January 07, 2014, 08:40:57 pm10pA not fA.

author: sync
author_rank: Frequent Contributor
timestamp: January 07, 2014, 08:49:41 pm
content: Quote from: mrflibble on January 07, 2014, 08:32:15 pmWhat are your requirements? Voltages, resolution, ...?A CD4051 should be fine for a 3-4 digits meter and probably a disaster for a 6.5 digits one.

author: SeanB
author_rank: Super Contributor
timestamp: January 07, 2014, 08:59:35 pm
content: 10pA more like it, but clean the package, clean the board and have soldermask and guard traces and it is likely to go a lot lower. Drop supply voltage to 15V and it will be worse, as this is likely specced at the best conditions.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 10:59:15 pm
content: Quote from: sync on January 07, 2014, 08:49:41 pmI wasn't planning on using the CD4051B. I just linked to it to check where Marco got those awesome leakage figures for a 4051 device. But anoopsieof 3 orders of magnitude would explain things.

author: mrflibble
author_rank: Super Contributor
timestamp: January 07, 2014, 11:01:59 pm
content: Quote from: SeanB on January 07, 2014, 08:59:35 pmAlso pre-assembly cleaning? Or just the whole assembled board? If pre-assembly, any handy tips? Usual procedure would be to put it in an IPA filled ziplock bag in warm water in an ultrasonic bath, but maybe there's better ways?

author: codeboy2k
author_rank: Super Contributor
timestamp: January 08, 2014, 02:19:27 am
content: A bit more to add regarding the protection diodes... The BAS116 is about $0.25, and has 5-10nA of reverse leakage current.The diode connected 2N4117A has up to 200fA leakage at Vgd around -20 to -25VDC ..depending on where your signal ranges are set, then your max signal might actually be lower than this, and the leakage could be as low as 150fA @ Vgd -10VDC . It's a great part, but the 2n4117 is extremely expensive and mostly non-stocked. I might consider a purpose made low leakage diode before I chose this part, unless I absolutely needed it's fA leakage (like in a 7.5 or 8.5 digit meter)Finally, the much cheaper jelly bean 2N3904 BJT has a typical reverse leakage of between 30-50 pA, and can go as high as a few hundred pA. These are nice because they are available as MBT3904 in a TSSOP-6 or SC70-6 package for $0.25 so you get two on the same die with similar leakage for $0.12 each.The MBT3904 is what I am using for my LCR. I also happen to have many around here so they are readily available to me. Depending on your leakage budget, you can use them as is with an expected leakage max of 200pA (if that works for you) or you can bin them and choose parts with 10-20pA, an order of magnitude smaller.I use a 1k input resistance, then the MBT3904s, then a 100 ohm, then the opamp input buffer. The 200pA max leakage across the 1K series input resistance is 200nV error max, and you can bin for less. I use a 24bit ADC with a 1.00V reference, so 1 LSB is 60nV, and this error is > 3LSB but that's ok for me, I only want 22 bits, so I can accept 4LSBs error. If it turns out that I have other error sources elsewhere that I can't control and blows my error budget, then I can bin the MBT3904s for better than 60pA leakage, or 1LSB and bring it back under control.No matter what, the cheaper 2N3904, even if you use it in a TO-92, is much better than the BAS116 diode.Cheers!

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 03:45:14 am
content: Quote from: codeboy2k on January 08, 2014, 02:19:27 amThanks, that sounds like a good candidate for the protection diodes.Stupid question though, how do you get a reasonable estimate of what to expect for leakage current (in diode connected configuration) from the datasheet?

author: SeanB
author_rank: Super Contributor
timestamp: January 08, 2014, 06:08:09 am
content: Icex is a good place to look, as it is a measure of die leakage. You might want to look at higher voltage devices as well if you are going to have a high input voltage, though they will be likely to have worse leakage but still they will be better than a regular signal diode.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 03:25:11 pm
content: Quote from: SeanB on January 08, 2014, 06:08:09 amThanks. I understand the concept of "is a measure of", but that sometimes is a bit limiting in use... 50 nA max for the 2N3904 ... you state "can go as high as a few hundred pA", so lets say 500 pA. So that's a factor of ~ 100. As a wild guess ... leakage current for the diode connected bjt is very roughly collector cut-off current divided by Hfe?Regarding the collector cut-off current, for example the 2N5962 looks good with only 2 nA max. Compared to 50 nA max for the 2N3904.

author: SeanB
author_rank: Super Contributor
timestamp: January 08, 2014, 03:33:13 pm
content: When you read the appnotes look at the footnotes, where often the measured value is limited by the test equipment in the ATE cell. You basically have to do it yourself and see the best parts to use, or just buy a lot of cheap ones and bin them in a test jig for pass/fail devices.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 03:46:24 pm
content: Good point. Don't know how feasible it is going to be to run those through a test jig. I don't mind some testing because this is a hobby thing. But there's a limit to what I am willing to have-to-bin as part of a design. And binning bjt to find the ones good enough as protection diode might be one bridge too far. Hell, just buying two 2N4117A and just be done with it is "cheaper" that way.That said, I have to make a jig anyways to check forotherleakage (integrator capacitor), so if that can be used for this as well I just might do so just for the fun of it. But barring that I am not going to go on an extensive bjt hunt, because before you know it you have a little side project.

author: Marco
author_rank: Super Contributor
timestamp: January 08, 2014, 04:11:23 pm
content: Oops yeah, dunno what I was thinking there ... still don't see the point in using BJTs or JFETs when the Central Semiconductor diodes are readily available.

author: sync
author_rank: Frequent Contributor
timestamp: January 08, 2014, 04:27:11 pm
content: Quote from: Marco on January 08, 2014, 04:11:23 pm5nA leakage is a lot. An example, on a 100kOhm protection resistor 5nA causes a voltage drop of 500uV. Not a problem for a 3 digit meter but a bad for a 5 digit one.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 04:30:19 pm
content: Quote from: Marco on January 08, 2014, 04:11:23 pmWell, one reason might be that Central Semi's marketing monkey needs to have his banana supply revoked. Write a datasheet for a diode marketed as low-leakage, and then you give max leakage only at 25 degrees C. Seriously? Because who needs to know leakage over temperature when they are lookingspecificallyfor low leakage, right? Or maybe it just sucks horribly at 40 degrees C. Not saying it's a bad part, but I am saying that whoever wrote that datasheet won't be getting any bonus bananas from me any time soon.Guess we can only reasonably assume that the reverse current willquadrupleevery 10 degrees. Oh if only the datasheet had included an Ir versus junction temp graph.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 04:34:34 pm
content: Quote from: sync on January 08, 2014, 04:27:11 pmThe central semi diode Marco refers to has 500 pA max leakage.At 25 degrees C @_@So logically 234234000 pAmax at 40 degrees.Yeah yeah, roughly double every 10 degrees.

author: Marco
author_rank: Super Contributor
timestamp: January 08, 2014, 04:42:20 pm
content: John Larkin is a pretty reputable source (moreso than datasheets)

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 04:46:13 pm
content: Quote from: Marco on January 08, 2014, 04:42:20 pmBut John Larkin isn't downloadable in pdf format from centralsemi.com for easy review.

author: Marco
author_rank: Super Contributor
timestamp: January 08, 2014, 04:50:55 pm
content: From the threads I linked earlier :Quote

author: sync
author_rank: Frequent Contributor
timestamp: January 08, 2014, 04:52:14 pm
content: Quote from: mrflibble on January 08, 2014, 04:34:34 pmOops! I mixed it up with the BAS116.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 05:19:12 pm
content: Quote from: Marco on January 08, 2014, 04:50:55 pmI read that. But hopefully you agree that there is a difference between"an individual on the internet that measured several samples"and"the manufacturer that characterized a large number from different batches". If nothing else, statistical relevance. Not only that, but care to make an estimate of the sampling bias that is encapsulated in the phrase"I got some samples of item XYZ through a local rep"? I know I don't.At any rate, rest assured that I have the CMPD6001S in the schematics now as alternative to the BAS116.

author: SeanB
author_rank: Super Contributor
timestamp: January 08, 2014, 05:37:10 pm
content: Looks like a good unit to use, and preferably at lower voltages the leakage will be a lot less. Running it at 15V should give a leakage that is close to unmeasurable with most measuring tools.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 08, 2014, 08:38:08 pm
content: I hadn't really looked around for specific low leakage diodes before, they've always been too expensive. Ok, so today I looked at the CMPD6001 datasheet. looks ok, MAX 500pA, got it... but.. where's the charts(!) in their whole 2 page datasheet???where's the gaussian distribution (histogram) of leakage vs number of units? I want to know statistically what to expect from their part. This saves me having to do binning on another part, for example, if I can predict what the failure rate might be, that rate of failure might be more cost effective than time spent binning, given the part is twice as much money as qty (2) BJTs. If I can statistically trust their part to be better than 10pA 95% of the time, for example, then it's worth it to spend the extra money for these low-leakage diodes, and rework the 5% outliers that fail.Yes, Mr. Fibble.. that data sheet is a joke.

author: mrflibble
author_rank: Super Contributor
timestamp: January 08, 2014, 09:33:55 pm
content: Quote from: codeboy2k on January 08, 2014, 08:38:08 pmYou are being generous. It's one page packaging info, 1/2 page standardand 1/2 page with some actual information.QuoteSuch information would have been nice yes. Given the anecdotal evidence of low leakage (the thread Marco linked to) and the awesomely informative one-liner spec of 500 pA max @ 25 C, the part looks interesting enough that I will try it. But the datasheet doesn't really inspire all that much confidence.QuoteHeh, no kidding. That datasheet deserves anhonorable mention here.

author: Marco
author_rank: Super Contributor
timestamp: January 09, 2014, 03:24:39 pm
content: Well if you really want a low datasheet value I don't think you're going to do better than the LM662, it's cheap too.Will just slightly obfuscate the schematic.PS. this whole discussion is putting the cart before the horse though, you'll not find many muxes or opamps without input protection ... unless you build your own MOSFET input stage or something you'll get clamping diodes as a side effect of your part selection ...

author: Felicitus
author_rank: Regular Contributor
timestamp: January 10, 2014, 09:13:20 pm
content: I'm also on my way to give this a shot. Can't promise anything though…A few considerations and ideas:- 4½ digits is what I consider the minimum and yet maximum reasonable for an open source multimeter. Everything else requires a lot more effort in the analog frontend.- System performance could be optimized with software tricks by using the internal temperature sensor (this is just an idea, I have done absolutely no research on this so far)- Use 4 full-fledged, fully configurable channels - switching between V and A could be done with bipolar relais (this is also just an idea, and no further research has gone into that)Notes on the design draft, which I have done too early due to a cold and boredom in bed:- The draft below uses components which you can buy, including the case- The case is absolutely huge with 209x98x34mm (bigger than the Metrahit 25S), and a bumper is also available- The 4mm plugs fit in the case with a headroom of ~3mm- Uses tact switches and the MEC NaviMec solution. The navigation serves dual purpose - when a menu is selected, it serves as navigation buttons. Outside of menus it selects the multimeter functions. Pressing 2 buttons activates the function in that segment (no idea how to describe that)- It's using the 2.7" Sharp Memory LCD, which is slightly too small for the case, but probably I can fit everything in the Bopla BS 703 case, which is 20mm smaller in height than the BS 803.- It's notable that the cost for buttons, display and casing is already 138.79€ including VAT at quantities of 25 copies. The price includes the switches, LCD, case and input jacks (64€ for the input switches alone). Let's be realistic about the price - even if this project works out, it won't come cheap, unless it's possible to save costs somewhere. However, I'm not intending to trade of awesomeness-factor against cheaper parts; personally, even if I didn't do the project, I would be absolutely willing to pay 300-400€ for such a meter, as it replaces up to 4 meters.That draft was put together in probably 3 hours. Things might be missing, plain wrong, not doable etc - yes, I will figure that out during the further design process.

author: mrflibble
author_rank: Super Contributor
timestamp: January 10, 2014, 09:56:47 pm
content: Quote from: Marco on January 09, 2014, 03:24:39 pmWhat discussion? You mean the side track about diodes? Not as if that was the main track as far as I'm concerned. The horse & cart were already properly located even before the random discussion. But now thanks to the semi-random diode discussion I have a few alternatives for the BAS116 that was already in place.Around the opamp that was also already in place.It's the way of threads like this. People come and go, while leaving some remarks that happen to interest them at the moment.

author: Felicitus
author_rank: Regular Contributor
timestamp: January 10, 2014, 10:00:29 pm
content: Quote from: mrflibble on January 10, 2014, 09:56:47 pmI agree. Different people have different approaches to design things, and none of those is more correct than the other.

author: Marco
author_rank: Super Contributor
timestamp: January 10, 2014, 10:36:08 pm
content: Quote from: mrflibble on January 10, 2014, 09:56:47 pmMy point was that with the LTC6240 I think you're using and a 100 kOhm input resistor you're already good to 1 kV (10 kV transient) any way without diodes.

author: mrflibble
author_rank: Super Contributor
timestamp: January 11, 2014, 03:46:13 am
content: Quote from: Marco on January 10, 2014, 10:36:08 pmSpeaking of input resistors...Insync's postabout the HP 3456A input stage you can see the 4 resistors, with 2 on each side of the relay. I get the one before + one after thing for EMF purposes. Having 2 per side is also for EMF compensation I presume?

author: codeboy2k
author_rank: Super Contributor
timestamp: January 11, 2014, 08:29:41 am
content: I would say two resistors per side (4 in total) is designed to increase the voltage standoff ability. For any high voltage transient event, each of the 27k resistors would be dropping 1/4 of the voltage, and if you make those large body resistors, then they would be able to withstand 1kV each, better than 1 resistor that has to take 4kV (which would likely flash over a small resistor).For example, 4 resistors in series would have 1kV on each resistor and would not flash over from lead to lead.

author: sync
author_rank: Frequent Contributor
timestamp: January 11, 2014, 02:07:55 pm
content: Also the resistors must dissipate about 9W for 1000V input. Spreading it over several resistors make sense.

author: mrflibble
author_rank: Super Contributor
timestamp: January 11, 2014, 04:52:55 pm
content: Doh!Extra voltage standoff and dissipation capability makes a lot more sense for those extra 2 resistors. Thanks!

author: mahjongg
author_rank: Newbie
timestamp: April 27, 2014, 09:21:04 pm
content: two comments:sorry if discussed before.first, don't make the mistake to make them yellow!https://www.sparkfun.com/news/1428second, for reasons of compatibility of adapters and such space the two 4mm banana jacks that make up a signal pair exactly 0.75 inch, (19.05mm) apart!measure any multimeter (or other meters with 4mm inputs and you will note the trend of them being 0.75 inch apart, there is a reason for that, its called a pomona adapter.

author: miguelvp
author_rank: Super Contributor
timestamp: April 27, 2014, 10:48:54 pm
content: Yellow is fine, is the "dark-colored body or face and a contrasting yellow border, frame, molding, overlay, holster or perimeter." will get you in trouble.You could do a red face yellow border and you'll be fine. (unless someone else has that trade dress)

author: mrflibble
author_rank: Super Contributor
timestamp: April 28, 2014, 06:47:03 am
content: Or the ever popular alternative: not care about any of that for a DIY project.

author: abaxas
author_rank: Regular Contributor
timestamp: May 13, 2014, 08:18:15 pm
content: Quote from: miguelvp on April 27, 2014, 10:48:54 pmHow about calling it the "fruke u".

author: branadic
author_rank: Super Contributor
timestamp: June 28, 2014, 03:52:24 pm
content: QuoteSeems like another never finished OSHW Multimeter project or are there any news about your project?

author: farsi
author_rank: Regular Contributor
timestamp: July 06, 2014, 09:30:57 am
content: On the topic of open-source oscilloscope, here is a nice a blog post:http://blog.farsinotare.com/2014/07/04/my-new-lab-with-red-pitaya/

author: ludzinc
author_rank: Unknown
timestamp: July 28, 2014, 04:35:00 am
content: While not a true multimeter, I'd always wanted to build my own volt / amp meter with programmable gain and volts / current mode switching.Without using relays!Read about it here:http://ludzinc.blogspot.com.au/2014/07/multi-channel-meter.html

author: Felicitus
author_rank: Regular Contributor
timestamp: July 28, 2014, 04:49:51 pm
content: Quote from: ludzinc on July 28, 2014, 04:35:00 amLooks neat, but do you have specs? How low can it go for current measurements?

author: ludzinc
author_rank: Unknown
timestamp: August 04, 2014, 12:09:45 pm
content: http://ludzinc.blogspot.com.au/2014/08/multi-channel-meter-part-2.htmlSpecs as requested in the link.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: August 17, 2014, 12:56:17 pm
content: Recently abandoned project of the 7 1/2 digits DVM:http://radiokot.ru/forum/viewtopic.php?f=10&t=105564

author: fcb
author_rank: Super Contributor
timestamp: August 19, 2014, 06:00:04 pm
content: Without reading all 27 pages of this thread...Has someone successfully made an OSHW (high accuracy, at least 5.5 digits) multimeter yet???

author: charlespax
author_rank: Regular Contributor
timestamp: August 26, 2014, 02:16:55 am
content: Sometimes the best way to make a complex device is to do one part very well then expand on it. What would be the minimal viable product for an open source meter? Would it be useful to make a device that measures a single thing? Maybe the best place to start is an open source voltmeter. Thoughts?

author: Bloch
author_rank: Unknown
timestamp: August 26, 2014, 04:15:12 pm
content: Yep the voltmeter is the core of any multimeter.So that is a great startQuote from: charlespax onYesterdayat 12:16:55 PM

author: Piedtyper
author_rank: Contributor
timestamp: October 05, 2014, 04:02:45 pm
content: WHEW! 27 pages…I’m new to this so please be gentle. I’m an Electronic Engineering Tech student in my second year and I’m planning on a relatively simple meter for my cap stone project.I’m almost as old and dirt and was a computer programmer/IT type for about 20 years. It’s been very enjoyable competing with the significantly younger minds! I’m confident in any of the programming needed but, of course, I’ll be challenged on the electronic design portion.I’ve tried to keep the specs simple to start with the hope I can add to them in the future. This will be completely open source and since it’s for school I’m not looking for anyone to do the work on at least the first cut.As to the future…a hand held with much the same capabilities outlined by Dave in the video would be a long term goal but based on the many comments it might not be reasonable. Time will tell.Initial specs1. High input impedance in the range of 10’s of M Ohms for voltage and low impedance … less than 10 Ohm for current.2. Auto-ranging between 200 to 0 AC/DC V and input protection for > 200 V3. Accuracy in the range of 4 ½ digits4. Two channel with fully isolated grounds5. Channel 1 measures V as stated above6. Channel 2 measures current up to 1 A with auto ranging and maximum resolution range of 0-100 mA7. Simultaneous measurement of V and I for power calculationsDesign challenges and possible solutions:1. Auto-Ranginga. Start with 0-20V AC/DC only and design for a further attenuation stage before this stage. All switching in this state would be solid state. The stage in front would probably need to be a relay of some sort (digital I’d think) and would be designed to simply knock down the input voltage to the 20V range.2. Channel Isolationa. Combination of buffers and opto-isolators for I2C communication between the micro on channel 1 and the ADC/measurement circuit on channel 2. Channel 2 will need to auto range the current up to 1 amp.3. User Interface/Outputa. VERY simple to start. Probably just an LCD displaying Voltage, Current and Power. No user input except perhaps to display or not display power if both channels are in use. It’s possible the measurements are discrete and shouldn’t be used for any power measurement.4. Input Protectiona. Probably just start with Zeners (two 100V “ish” in series) through a high value resistor to ground.5. AC Voltagea. Use a RMS-DC chip. It looks like this is possible. Just feed in the appropriate level of AC and it spits out a DC value for RMS.Questions:1. Is there any way around having two distinct power supplies (even if batteries) between these two channels? If not (and I suspect this is the case) then at least for a start would 2 AA’s per channel be appropriate as a proof of concept?2. What’s the best way to handle negative voltage? The ADC’s I’m considering have a range or 0-2.048V with an internal reference. How should I handle this? I’d much rather not have to create a negative supply.I wrestled with whether or not to start a new thread for this. If anyone figgers it would be better in another forum or thread just let me know.Thanks in advance for any input!

author: David Hess
author_rank: Super Contributor
timestamp: October 05, 2014, 05:15:13 pm
content: Quote from: Piedtyper on October 05, 2014, 04:02:45 pmThis is similar to how it is normally done but low leakage diodes are used and a high input impedance buffer will be needed.QuoteBatteries can work but normally some type of isolated power supply is used. Small high isolation inverters are common and typically quieter than switching power supplies.QuoteIf you are using isolated supplies so the inputs are galvanically isolated, then adding a negative supply is simple.Instrumentation ADCs usually have no trouble handing negative inputs but the input can always be offset by half of the ADC input range.QuoteYou should start a new discussion thread.

author: Marco
author_rank: Super Contributor
timestamp: October 05, 2014, 10:24:39 pm
content: Quote from: David Hess on October 05, 2014, 05:15:13 pmLM662 will do both those things (not from -20 to +20 V though).

author: David Hess
author_rank: Super Contributor
timestamp: October 06, 2014, 11:22:53 am
content: Quote from: Marco on October 05, 2014, 10:24:39 pmThe input buffer voltage range is usually quite small which you can see from the specifications of common voltmeters which support >1 Gohm input resistance on their low voltage ranges. For instance on an HP3478A, it is only +/- 3 volts and on a DM502, it is only +/- 2 volts. Specialized designs can extend it considerably by bootstrapping the input buffer which as a side effect also reduces the common mode error present in a non-inverting buffer. A Keithley 917 for instance has an input voltage range of +/- 200 volts while maintaining an input resistance >200 Tohms.It is generally a bad idea to rely on the input protection diodes of an operational amplifier in this sort of application. Inexpensive low leakage diodes may be made from transistor junctions or JFETs. The Keithley 917 mentioned above uses transistor base-emitter junctions for this.

author: Michael Rempel
author_rank: Contributor
timestamp: October 09, 2014, 08:03:20 pm
content: Quote from: DavidJRobertson on July 03, 2011, 07:48:20 pmThen there is the NRF24L01+ 2.4GHz Wireless Transceiver. From China to the world for a buck a piece in low quantities. You could set up a whole measurement universe with these, some cheap arduinos and a fair bit of software. Each function could be its own device if you want easily enough. You could even make different ones for different ranges and applications.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: October 09, 2014, 08:10:43 pm
content: Quote from: David Hess on October 06, 2014, 11:22:53 amKeithley 917 - what's this?

author: David Hess
author_rank: Super Contributor
timestamp: October 09, 2014, 09:13:58 pm
content: Quote from: Mickle T. on October 09, 2014, 08:10:43 pmSorry. I meant Keithley 617.

author: Marco
author_rank: Super Contributor
timestamp: October 09, 2014, 10:38:34 pm
content: Quote from: David Hess on October 06, 2014, 11:22:53 amHuh, I never really thought about what would happen to leakage if you connected the input protection diodes to the bootstrapping voltage ... I guess Keithly could get away with two 1n4148s at that point (although they didn't, they used the base emitter junctions of a IT121).

author: David Hess
author_rank: Super Contributor
timestamp: October 10, 2014, 01:25:12 am
content: Quote from: Marco on October 09, 2014, 10:38:34 pmI am a little surprised Keithley did not reverse bias the base-emitter junction diodes by at least a volt or use two base-emitter junction diodes in series for four diodes total but I assume they tried those alternatives and found the configuration shown to work the best. Considering that the input resistance is specified to be greater than 200 teraohms over a range of +/- 200 volts DC with an input bias current of less than 5 femtoamps, I am hardly in a position to second guess them. I picked the Keithley 617 as an extreme example of what can be accomplished fairly easily and because documentation is available.The leakage of a 1N4148 which is a gold doped switching diode can be high even at millivolts so there is no way to really use it in this application even with close to zero volts across it. Bob Pease mentioned this very problem on page 69 of his book Troubleshooting Analog Circuits:http://goo.gl/uVInjx

author: Marco
author_rank: Super Contributor
timestamp: October 10, 2014, 04:42:49 am
content: I wish he would comment in the text on why he used the base collector junction in the picture, the text only deals with the use of the base emitter junction.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2014, 02:58:53 am
content: Quote from: Marco on October 10, 2014, 04:42:49 amHe mentions the differences between BE and BC junctions when used in this type of application but I do not know why he used the BC junction here either. The breakdown voltage will be higher but that does not matter and it will have slower recovery which seems like it would be a disadvantage.

author: Marco
author_rank: Super Contributor
timestamp: October 15, 2014, 11:27:32 pm
content: Quote from: David Hess on October 13, 2014, 02:58:53 amI couldn't see those pages of the book ... but he does talk a bit more about it in this article EDN was nice enough to dig from their archives :http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques

author: mrflibble
author_rank: Super Contributor
timestamp: October 16, 2014, 01:28:08 pm
content: Quote from: Marco on October 15, 2014, 11:27:32 pmThanks, that indeed had interesting tidbits in it.Pity the links to the (presumably) better images are dead, the EDN inlined jpg's were not super duper. But still readable enough.

author: David Hess
author_rank: Super Contributor
timestamp: October 17, 2014, 01:58:50 am
content: Quote from: mrflibble on October 16, 2014, 01:28:08 pmThat is common with EDN and related online trade magazines. I expect it more often than not.Their comment system is even less reliable than the EEVBlog forum.

author: mrflibble
author_rank: Super Contributor
timestamp: October 17, 2014, 11:23:35 am
content: Quote from: David Hess on October 17, 2014, 01:58:50 amAnd the sad part is that the machine on which those jpg's are still exists. They just decided (or probably didn't even decide anything) to not maintain those linked images. From which you can usually extrapolate amusing characteristics about the CMS & backup solutions they use.

author: EEVblog
author_rank: Unknown
timestamp: October 17, 2014, 02:11:50 pm
content: Quote from: David Hess on October 17, 2014, 01:58:50 amThe EEVblog forum is not reliable?Haven't lost a single attachment or post since it's been running...

author: Marco
author_rank: Super Contributor
timestamp: October 17, 2014, 03:12:56 pm
content: Long term reliable, with more than a few service interruptions though

author: Bloch
author_rank: Unknown
timestamp: October 17, 2014, 07:21:23 pm
content: I think he means links to external jpg/pdf.Sometime thehttps://archive.org/web/can help getting old stuff.Quote from: EEVblog onTodayat 01:11:50 AM

author: mrflibble
author_rank: Super Contributor
timestamp: October 17, 2014, 08:13:32 pm
content: Quote from: Bloch on October 17, 2014, 07:21:23 pmAgreed. Unfortunately linked images is not the wayback machine's strongest suit. It's rather hit & miss ... mostly miss. Case in point, the hi-res images from that EDN article where not to be found that way.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: October 18, 2014, 07:45:37 am
content: The first time I glanced at that EDN article I gave up too soon. After reading mr.Flibble's recommendation I went back and downloaded and magnified. Well well worth it! But one thing disturbed me, In the section marked " So you say you need a diode" Pease writes:"For extremely low leakage .. consider using collector-base junctions. If, for instance, you need leakage lower than 100pA, then it's often much less costly to test transistors with a 98% yield to this spec ....Some low leakage transistors to consider are the 2N930, 2N3707 and 2N4250. However most other small signal transistors have an excellent yield to a leakage spec of 30 pA max at 5V, even though the spec sheet guarantees 10nA."edited for brevity and all transcription errors mine.Now if someone dropped a bag of transistors in my lap I would have no clue as to how to characterize their leakage. Do you need a pico-Ammeter? or can it be done some sneaky cheap way with a bridge and some op amps?

author: SeanB
author_rank: Super Contributor
timestamp: October 18, 2014, 07:56:08 am
content: Simple, just use your 10M input impedance DVM and put the transistor in series with the positive lead, and apply a voltage that is equal to Vceo of the transistor to the whole lot. Then simply bin according to the measured voltage, the lower the voltage the lower the leakage.

author: David Hess
author_rank: Super Contributor
timestamp: October 18, 2014, 02:59:15 pm
content: Quote from: EEVblog on October 17, 2014, 02:11:50 pmEvery couple weeks I have to erase the EEVblog cookies (there is a forum thread discussing this remedy) and I have lost posts often enough that I sometimes remember to save long ones locally before pressing post just in case. Usually Firefox allows recovery of the post text but it only takes losing it once. Preview and post occasionally return an error requiring the thread to be reloaded.Given the choice, I prefer email based forums because they are both faster and more reliable.Update: It was unable to access the forum for hours not long after I posted this. Instead I got this:Lost connection to MySQL server during queryConnection ProblemsSorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.Connection ProblemsSorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.Error establishing a database connection

author: David Hess
author_rank: Super Contributor
timestamp: October 18, 2014, 03:21:57 pm
content: Quote from: chickenHeadKnob on October 18, 2014, 07:45:37 amQuote from: SeanB on October 18, 2014, 07:56:08 amThis yields 10 microvolts per picoamp which is good enough for most applications but many transistors will have a leakage low enough to require either an electrometer or some type of charge measurement to be made with something like an integrator.You also have to be careful because higher resolution voltmeters usually lack a 10 MOhm shunt on their lower voltage ranges so the shunt has to be added externally.The integration method is preferred at the highest sensitivities because it has lower noise. It can be low enough to pick up cosmic rays if the integration capacitor has too great a volume.

author: ToddBMarshall
author_rank: Newbie
timestamp: January 04, 2015, 01:12:16 pm
content: An Open Source Multimeter would be an interesting project. But I wouldn't expect to see a rotary switch on it. Rather, I would expect it to use new techniques like CTMU (Charge Time Measurement Unit). Most measurements could be made by just connecting the device to a part or to points in a circuit. It could detect a component and report resistance, capacitance, inductance, beta, etc. If connected to an active circuit it could detect voltage, current, phase, frequency, duty cycle, etc. and report ... all without the user turning a single dial. Maybe the user would press a start button ... likely built into a probe. It could have an audio annunciator so the user wouldn't have to take his eyes off what he is doing. It could take voice commands.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 04, 2015, 05:17:16 pm
content: Todd, check this thread out. It's not a multimeter, but it has features like what you describe, but not designed for in-circuit testing.https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/Todd's post brought this thread to life again, and reading back in the thread I realized I actually have the 1983 article referenced here from EDN that some people could not find. I squirrelled it away back in 2011 when the image links still worked and I made a PDF from the images in the article.So here it is.(There was always an error when attaching files to the post today, so I put it on my dropbox)https://www.dropbox.com/s/nttegd9zwfxh5j3/1983-11-10_pease_clamping_EDN.pdfCheers!

author: mrflibble
author_rank: Super Contributor
timestamp: January 04, 2015, 05:27:02 pm
content: Quote from: codeboy2k on January 04, 2015, 05:17:16 pmNice, thanks! Definitely better than the low res images.

author: ToddBMarshall
author_rank: Newbie
timestamp: January 04, 2015, 06:29:43 pm
content: Codeboy2k:Todd, check this thread out. It's not a multimeter, but it has features like what you describe, but not designed for in-circuit testing.https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/I have one. Use it all the time. $17 kit. Amazing!http://www.amazon.com/Capacitance-Multi-meter-Capacitor-Inductance-Transistor/dp/B00OFQGZH2P.S. I'm new here. Does this forum app have a threaded message option?

author: zapta
author_rank: Super Contributor
timestamp: January 04, 2015, 10:27:04 pm
content: Quote from: ToddBMarshall on January 04, 2015, 06:29:43 pmTapatalk works we with eevblog forums.

author: MAntunes
author_rank: Regular Contributor
timestamp: January 09, 2016, 11:24:24 pm
content: Hello!I'm considering building a multimeter as my first serious project.Something simple at first, but I think it is had a good analog/digital mix. After searching a bit I didn't find many information, do you know about some classes, books, articles that could help me?Best regards!

author: MAntunes
author_rank: Regular Contributor
timestamp: January 09, 2016, 11:28:24 pm
content: Quote from: MAntunes on January 09, 2016, 11:24:24 pm

author: jaromir
author_rank: Unknown
timestamp: January 10, 2016, 02:24:21 pm
content: Oh well, 29 pages and yet not that much of finished projects.Just for lulz and for the sake of cramming a few parts to 1x1 inch PCB I created this tiny "multimeter" - it was not intended as serious test device, but it works quite acceptably.It is open sourced, released under MIT license. Sources are intended to use with XC8 or open-source SDCC compiler. There are complete details, drawings, source files and build tutorials herehttps://hackaday.io/project/7988-micro-progmeterleading to herehttps://github.com/jaromir-sukuba/micro_progmeterIf you wish, you can build your open source programmerhttps://hackaday.io/project/8559-pic16f1xxx-arduino-based-programmerto FLASH the PIC on board ;-)

author: John Heath
author_rank: Frequent Contributor
timestamp: February 21, 2016, 06:36:09 pm
content: Quote from: House91320 on June 30, 2011, 05:05:19 pm

author: SaabFAN
author_rank: Frequent Contributor
timestamp: February 22, 2016, 02:03:40 am
content: Reminds me of the TNG-Tricorder

author: EEVblog
author_rank: Unknown
timestamp: February 22, 2016, 02:36:11 am
content: Quote from: Marco on October 15, 2014, 11:27:32 pmThis is gold:

author: John Heath
author_rank: Frequent Contributor
timestamp: February 23, 2016, 02:06:45 am
content: Quote from: SaabFAN on February 22, 2016, 02:03:40 amI see the similarity. Beam me up Scotty. Did they move actual atoms to do this or just use information and atoms that are already on the Enterprise , somewhat like a 3d printer. From a philosophical point of view it makes a big difference if you are the one that is being transported.

author: miguelvp
author_rank: Super Contributor
timestamp: February 23, 2016, 02:57:25 am
content: Quote from: John Heath on February 23, 2016, 02:06:45 amOff Topic and I hope this doesn't alter the course of the thread, but they did print a TRM for the enterprise tech, maybe look it up or buy the bookhttp://www.amazon.com/Star-Trek-The-Next-Generation/dp/0671704273As I recall it was just the information, but we are talking about science fiction.

author: altaic
author_rank: Unknown
timestamp: March 02, 2016, 11:40:40 pm
content: Hi all, I wasn't sure whether or not to post this in a separate thread, but I recently was looking for some quality test and measurement connectors for my own multimeter project and came acrosshttp://www.multi-contact.com. Their catalogs contain some awesomely graphic connector porn!Interestingly, and the main reason I'm posting this here,http://www.multi-contact.com/AcroFiles/Catalogues/TM_Test&Measure-O_(en)_hi.pdfis a pretty informative review of IEC 61010 (for a novice such as myself), including protection mechanisms to satisfy the various CAT ratings. It's really nicely presented, too, if you overlook their marketing stuff. Anyway, I figured you guys might find it useful.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: March 03, 2016, 12:25:54 am
content: Very interesting. Thanks for posting.

author: charlespax
author_rank: Regular Contributor
timestamp: March 03, 2016, 10:25:00 am
content: I'm wondering what everyone thinks of the landscape layout versus a traditional portrait style hand-held meter. Personally, almost always use my DMMs when they're sitting on my bench rather than held in my hand. It can be frustrating to shuffle things around on a bench and knock over or nearly knock over a multimeter. I made my temperature data logger in a landscape format to keep it nice and stable. Pulling on a cable just drags it along a bench instead of tipping it over. I wonder how suitable this format would be for a multimeter. If you want to take a closer look at the enclosure, check out the github repohttps://github.com/PaxInstruments/t400-enclosure.Since the front is mostly screen it doesn't really fit a traditional range switch. Function selection could be done with software buttons or maybe slider switch.Would a landscape design be crazy, awesome, or something in between?I have a bunch of enclosures that aren't suitable for including in my finished products. Odd colors, sink marks, cosmetic defects, etc.. If you're interested in getting one to test out, I'd be happy to ship one to you.

author: arjuna_m
author_rank: Newbie
timestamp: May 22, 2020, 06:09:31 pm
content: Hi All,(Not entirely sure if I should put it here or on another thread)Does anyone have any recommendations for a good vertical PCB mount banana jack connector/alternative connectors for a multi meter type measurement instrument?STAUBLI 66.9032-22 is the ideal part but at 5£ a peice, willing to settle for a cheap Chinese multi-meter typebare metal tube if I can find any.Any recommendations?Thanks

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2020, 12:03:39 am
content: Old thread!Sounds like Charles's open multimeter never got off the ground.

author: charlespax
author_rank: Regular Contributor
timestamp: May 23, 2020, 01:17:36 am
content: Quote from: EEVblog on May 23, 2020, 12:03:39 amThe T400 was such fun to make! I got to learn so many things and acquire new skills. Unfortunately, once the product was complete I found myself with multiple jobs I disliked: marketing, sales, shipping, etc.. It was time to pack up and move back to America to be closer to family.I'd love to make more lab instruments, but for now I am renovating a house I bought.

author: wizard69
author_rank: Super Contributor
timestamp: May 24, 2020, 02:22:30 am
content: Quote from: charlespax on May 23, 2020, 01:17:36 amKinda sorry to hear that. Your post today is what prompted me to realizing that this project even existed. Frankly if i had the money I'd like to take a shot at the instrumentation market. I always loved the Tektronix TM 500 series approach to bench instruments and see value in a modern approach. One big positive was the amount of instrumentation you got or could place in one portable chassis. With today more modern electronics the same thing could be accomplished in a much smaller chassis and offer vastly more capability. We are talking a chassis here that resembles a smaller but modern bench top scope.Interestingly modern scope manufactures seem to be trying to incorporate many support instrument features to make scopes "all in one". However they will never be able to pack every need into one chassis. Imagine an instrument meant to be an adjunct to a modern portable/bench scope. Think field work here as well as the bench.