Community Bench Meter - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: January 25, 2010, 10:34:01 am
content: Hi all, in the EEVBLOG #56 comments I said I would start this topic so here it is.Lets design a Bench Meter, that can do what we want, completely open source firmware (for micro) software for *nix, Mac Windows, Open source schematic and PCB.Something that someone with reasonable soldering skills can build (SMD is ok but we will keep it to 0805 and larger) The PCB would probably need to be commercial as we will need PTH and Double sided.OK some specs to kick the ball off, These are open to debateBattery / Mains powered.Back light LCD Graphics5000 count (we could aim for 50000, but I do not know with a DIY project if we can get it foolproof enough for the average hobbyist to get it to work)20A DC range, uA range (maybe dave would give permission for the uCurrent to be included inside)Ohms, LOW OHMSLightning fast continuity rangeRMS ACGraphing functionData LoggingI would like a retro push button range switchWhat are your Ideas ?I will keep tabs on this topic, and I am prepared to run the hardware side, keep the master schematic and PCB uptodate, I will issue the Schematic and PCB in both PDF, ADS09, Gerber format (sorry I do not use Eagle)Ok do you want to do this ?

author: joelby
author_rank: Frequent Contributor
timestamp: January 25, 2010, 12:41:41 pm
content: Jaycar actually sell a DMM kit for $24.95. The specs are undoubtedly rubbish, but it comes in a standard-looking multimeter case!L & C meter? There are plenty of schematics floating around for making these.

author: Unknown
author_rank: Unknown
timestamp: January 25, 2010, 01:02:43 pm
content: Yeah, I have seen the Jaycar Kit, But the specifications are not shown (maybe they are that badI am thinking of a design that is more accurate, that we can design as both a learning experience and a way to get a "decent bit of kit".There are lots of projects for just about everything but a "DIY" Bench meter.I think the whole design would be fun and we can all learn things along the way (I have never done high precision ADC designs).

author: SockThief
author_rank: Contributor
timestamp: January 25, 2010, 02:52:14 pm
content: Hej!Long time reader, first time caller. Actually when I saw this post, I couldn't help buy post a response. Personally I think it's a great idea, as you surf the web, reading blogs, there is, inevitably, a comment to a post "why isn't there an OpenSource X?". And, there is no reason why there can't be! It seems Dave's popularity is growing and a legion of experts find themselves following (remember the experts arguing over the CRO probe interference?), so there is the talent out ther to achieve this.While I appreciate the Jaycar kits, etc (I remember Dick Smith Funway had a Multimeter kit somewhere in the pages of time) I do feel GeekGirl is on the money when we say we should aim our sites a little higher. A good piece of test equipment is essential, and there is no more piece of kit more fundamental than a good meter (why is it Dave reviews 'em so often, and seems to get so riled up when they aint up to spec?).As a beginner, not only out of this project will you get a good meter, but you should also, out of following the design, get an appreciation out of good design practices, electronic theory etc.As a professional, you will be able to give back to the community that we all love, and pass on that knowledge that our mentors and experieces has given us.Me, personally, have been out of the electronics game for a LONG time! Seemed there was a shortage of software guys when I needed a job... so I am longing to get back into electronics scene (which is why i hang around these dark corners of web), and am always looking for a project to help and learn from. I am open to helping design any part, though, at this stage, i will confess my ability to design acurate meaurement circuits is not the best, so I will be interested to see what others come up with.As a comunity project, my personal feeling is that we should be as modular as possible, not only will this make design easier, as each part can be designed and tested independently, but it will also allow switching of various modules. For example, not confident enough to get a 50,000 count circuit running and don't need the accuracy? No problems, drop in a lower speced module. Can't get part XYZ? Easy, design one around what you can get. etc, etc, etc. So I guess the first stage we need to be looking at is some block diagrams....Looking forward to this, should be fun!

author: Unknown
author_rank: Unknown
timestamp: January 25, 2010, 07:09:29 pm
content: German computer magazin c't did a whole series about building a modular DIY measurement and control labhttp://www.heise.de/ct/projekte/machmit/ctlab/wikiIt is (multiple) MCU controlled, with LabView integration, USB, Ethernet RS232 interface. Among the published modules are general purpose I/O modules, lab power supply modules, DDS module, audio amplifier module, electronic load and whatnot.And a voltmeter module. The voltmeter module schematics are athttp://www.heise.de/ct/projekte/machmit/ctlab/browser/Schematics/schem_DIV3.pdf(24 bit ADC of which approximately 18 to 20 bits are usable, approx 5 1/2 digits). The TrueRMS extension schematic is athttp://www.heise.de/ct/projekte/machmit/ctlab/browser/Schematics/schem_TRMSC-DIV.pdf(links don't load the PDF's directly, but point to wiki pages holding links to the PDFs)The hardware design is copyrighted by the publisher. But there shouldn't be anything wrong looking at them and getting some inspiration.BTW, ICL7xxx based DIY multimeter schematics were popular in the 80th. However the same ICs and schematics are used today in $7 rubbish 3 1/2 multimeters. So there isn't much to gain going the ICL7xxx route. You can't beat $7.Oh, and I would go for a bench-top open-source multimeter to avoid the mechanical problems of squeezing everything into a handheld case. Going with the classic bench-top meter form-factor or the 19" form-factor (like c't) gives a lot of room.

author: Valhallasmith
author_rank: Contributor
timestamp: January 25, 2010, 09:15:12 pm
content: I've been thinking about building a similar tool. Except I am aiming more at something small and fits in a round Altoids tin. First project in this line is probably going to be a 24V-~0 regulated charge pump run off a wall wart. The one after that is a multimeter/lcr with a couple DAC/DDS outputs.

author: Curtisbeef
author_rank: Contributor
timestamp: January 26, 2010, 12:47:50 am
content: I'm so happy that a little comment Inspired this threadI'm pretty Amateur but I would love to help out in anyway I can. I'm pretty familiar with LCD technology/programmingFor a project like this i think the Best thing we could use would be a KS0107/KS0108 Compatible LCD They can be found everywhere in just about every color and even in OLED and VFD, the most standard size is 128x64. And they are extremely cheap for the non-fancy color ones. Also there is code out there for driving them on just about every platform you could imagine.The prices on this site are a little high but it has the largest selection, just to get a ideahttp://tinyurl.com/yfqwg6yAlso for a bonus here is some video of a KS0108 Compatable VFDand OLEDEdit: Found a great Pic of a PLED KS0108 display

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 26, 2010, 01:43:24 pm
content: Count me in! I have some experience with very low voltage precision measuring (http://www.mastrogippo.it/eeg/) and I'm pretty good at firmware if we use PICs. But I think a ti MSP430 will fit better. Good way to learn!

author: Unknown
author_rank: Unknown
timestamp: January 26, 2010, 03:41:05 pm
content: Quote from: Mastro Gippo on January 26, 2010, 01:43:24 pmDAMN youNow I want to go and work on my ECG systemI have another project to put up on the board nowYears ago I was developing an ECG monitor (similar to a halter monitor) which you could wear and it would link back to a PC / mobile phone wirelessly that if you electrocuted your self, it would shut power off to the area and place a call to the ambulance service giving a pre recorded message (stating where you are, what has likely happened etc.)One day I may actually get it finished and on the market lol.

author: dmlandrum
author_rank: Regular Contributor
timestamp: January 26, 2010, 11:01:28 pm
content: I'm a beginner electronics designer, but Iama physics major, so I hope that counts for something. One of the classes I'm taking this semester is Physics of Electronics, focusing on instrumentation, so this might be a great thing for me to get involved in. I have some software experience, but not with embedded, but I've been wanting to get into that for some time as well.

author: xani
author_rank: Frequent Contributor
timestamp: January 27, 2010, 01:09:26 am
content: im thinking, maybe "dual display" ? Some nice LED 7-segment for "main" display and 4x20 (or graphic) LCD for other things like menus and other measures.So for example u can have Vrms on nice big LEDs + other measures like Vp-p, Min-Max, or freq on LCD. Or even dual-measure, for example I on LED and V on LCD + power and resistance calculated from it

author: Unknown
author_rank: Unknown
timestamp: January 27, 2010, 04:14:18 am
content: Quote from: xani on January 27, 2010, 01:09:26 amI am liking this idea, but I do not want to use a character LCD, I want to use a graphic LCD, with one like the one posted by Curtis, you could have both in 2 lines on the LCD

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2010, 06:14:40 am
content: Cool idea.I think it's gotta be different somehow, not just a bench multimeter.I'm not sure what or how, just offer something compelling, either in form factor and/or combination of features.Be careful not to slide down the oscilloscope functionality slippery slope...Forget mains use, any meter worth building can be battery powered.This is more of a hack idea, but what about a project to design a new engine/user interface for the Fluke 233?It's got a re-flashable micro in the head (don't know about the base), and you could probably replace the LCD with a graphic one. Not exactly low cost though.Dave.

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 27, 2010, 09:04:49 am
content: Hehe Kat, I had the same idea sometime ago, but I wasn't going to wait for the heart to stop to call for help, I was thinking about a bunch of electrodes that trigger the power shutdown when they detect a voltage difference between them, caused by an electrocution.I think we can easily make a wireless display like the one Dave reviewed, but it would be hard to design the case. The wireless interface could be used to interface to a PC too. I think we can just start to design the PCB around a cheap and widely available multimeter case, maybe from Dealextreme.As Kat says, graphic LCD/OLED is a must. A micro SD slot is tempting too.I think hacking a Fluke is a bit blaspheme, but maybe if we can find a good multimeter with a nice analog front-end to harvest for cheap, it would save a ton of time.I always wanted to build one of these:http://mondo-technology.com/super.htmlwe can get a lot inspiration from that project!

author: Unknown
author_rank: Unknown
timestamp: January 27, 2010, 09:19:59 am
content: Quote from: EEVblog on January 27, 2010, 06:14:40 amHi Dave,I definitely do not want to make this a scope lol (Rigol and others have nice cheap units)I am thinking one idea to set it apart is to make the current input separate, so we can compute PowerAlso so we can display current and voltage at the sametime, compute power factor and VA for AC, Power for DC.

author: jahonen
author_rank: Super Contributor
timestamp: January 27, 2010, 09:24:33 am
content: What I would like to see, is some modern computer interface, USB or even better for long distance logging, ethernet. Of course, the isolation/safety issues will arise then.Actually, what I like about mains powered meters is that I have never had to run around finding fresh batteries before starting measuring with themUnlike my Fluke 89IV, which seems to eat AA's like bread. That is why I like the Agilent 34401A (or any similar) so much.Regards,Janne

author: Unknown
author_rank: Unknown
timestamp: January 27, 2010, 09:29:52 am
content: Quote from: Mastro Gippo on January 27, 2010, 09:04:49 amI would just use a normal SD card, it is not that hardQuote from: Mastro Gippo on January 27, 2010, 09:04:49 amUnless we are just going to be "Hackers" I do not find much appeal in modding a meter that is so cool alreadyQuote from: Mastro Gippo on January 27, 2010, 09:04:49 amNice project, some great optionsif we used one of the newer Pics (24 Serries IIRC, I am not a Pic Chick, I am an AVR Chick, but if the community wants to design with a Pic that is fine)Their case does not have enough room

author: Unknown
author_rank: Unknown
timestamp: January 27, 2010, 09:47:52 am
content: Quote from: jahonen on January 27, 2010, 09:24:33 amTwo very good points, we could do both Ethernet and USB in the one design, just drop a WizNet Module in (I think they have USB and Ethernet in the smae footprint). I would like to slip in a small PSU, if only to charge the battery. I have built in 1.2Ah 12V gel cells in equipment (they only way a couple of hundred grams.Keep the great thoughts upI hope tonight or tomorrow (I am GMT -8) to be able to produce a block diagram (nothing to complex just get some ideas on paper

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2010, 11:14:18 am
content: Quote from: GeekGirl on January 27, 2010, 09:19:59 amYes, dual inputs would be a nice differentiator.It's got to do data logging though, and hence low frequency scope stuff, but that would be it. Dual channel data logger would be a handy tool.Idea: Would be nice if it had a serial protocol analyser of some form too.And taking that a bit further, a small and simple 8 channel logic analyser input maybe?Or maybe the two primary inputs plus a simpler 8 input channels for logging.Powering it from a single D cell would be neat.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2010, 11:23:24 am
content: Quote from: GeekGirl on January 27, 2010, 09:47:52 amNooooooooooo! If you go down the charging dark path, forever will it dominate your destiny!I think it's possible to power a multi channel meter with a small graphic display for many hundreds of hours.If it was say direct D cell powered, a target of 1000 hours of operation would give you a current budget of 18mA. Obviously more once PC connectivity kicks in.Dave.

author: xani
author_rank: Frequent Contributor
timestamp: January 27, 2010, 12:20:11 pm
content: Maybe use some small ARM instead ? More horsepower and interfaces, like for example AT91SAM7X256 , builtin Ethernet and USB, ok price and plenty of space in flash and RAM.Then we could add things like USB<=>SPI/I2C/USART debugger or serial bus monitor on LCD. Or telnet into your meter from work

author: Curtisbeef
author_rank: Contributor
timestamp: January 27, 2010, 12:50:16 pm
content: I like the MicroSD card idea. Its simple enough to put a 8GB storage card in there for many hours of data logging and they are super simple to interface with almost 0 extra parts(besides the connector). Id definitely say go with the MicroSD over the standard SD the size makes it way better and there are no downsides.USB PC Connection is a MUST.I love Dave's idea about about having a simple serial terminal. That would be a Awesome feature. If we are gonna go that route might as well add I2C and SPI Analyzers Etc...My opinion about the Ethernet is that it kinda adds a huge amount of complexity / expensive parts for a feature that I don't know how useful it would be to most people. But like was said before we could always go for a modular type of a system where that could be a addon feature or something.For Micro I would probably suggest some type of MSP430 because they are know for using like insane low amounts of power. And there are a TON of options. But if we are going for Horsepower ARM would definitely be a good option.I love the idea of making it handheldish..../portable but if you guys wanna make it a bench tool thats cool too.

author: xani
author_rank: Frequent Contributor
timestamp: January 27, 2010, 02:19:26 pm
content: SD have one advantage over MicroSD, you can use card from your old phone/camera in your meter ;]. Or just make connection on PCB to both SD and MicroSD socket, problem solved ;]About ethernet, i think that using something like "Ethernet shield" for 8 bit uC is a overkill (more expensive than main CPU) but if we use some stronger CPU we could just use one with buildin Ethernet/USB (like that AT91SAM7X256 which is about $10 here in Poland). And Power over Ethernet/USB option would be nice also, one less cable on bench ;]About power consumption, we could add option to power off some parts of meter, like USB and Ethernet when on battery power and/or downclock CPU when on battery and not doing anything computation heavy work.

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 27, 2010, 03:58:56 pm
content: Usb and ethernet cables on a multimeter are just a disaster waiting to happen. It's not a good idea to connect a multimeter to the common ground, because if you don't isolate everything you will end up shorting things to ground if you measure a signal with a floating reference. I think wireless (bluetooth, zigbee, custom 2.4ghz) is a better option.I don't see any benefit in using an ARM, I think all the tasks we need can be easily handled by an easier micro.I suggested the microSD because they're, well, micro, but a regular slot will be ok too because you can find adapters everywhere.Sorry Dave, but I think that a rechargeable battery is a must if we want an OLED diaplay, wireless, SD slot.... But I wouldn't go the SLA route, li-ion are cheap and easy to work with, SLA weigh a lot and has Peukert and is big...We should try to focus on building a meter, and keeping it simple and useful (and CHEAP!!); I understand the enthusiasm, but adding tons of features that don't belong to a meter will only be frustrating in the end imho.

author: jahonen
author_rank: Super Contributor
timestamp: January 27, 2010, 04:15:58 pm
content: Quote from: Curtisbeef on January 27, 2010, 12:50:16 pmThe advantages of ethernet over USB are:1. No need for writing device drivers at computer end. All necessary things are already in every operating system on the world. Yes, you can use those RS-232-USB converters, but they still require a driver.2. Easy galvanic isolation (in fact ethernet standard requires transformers at both ends).3. Is not operating system dependent.4. Long distances (>5m) easily achieved, communicates easily to other side of the globe if requiredThat serial terminal is also easily implemented over TCP/IP using telnet. Ethernet is replacing the venerable GPIB slowly, most modern serious measurement equipment is equipped with LXI (LAN eXtensions for Instrumentation). Some kind of compatibility with HP34401 etc command set would be also nice. So you can actually say "MEAS:VOLT:DC?" to the meter (using that telnet) and it will perform a DC voltage measurement and return the result using plain ASCII. That makes it easy to program your automated testing systemOf course, that becomes with the price tag of more complex embedded software, but 32-bit ARMs (7TDMI, Cortex-M3) etc. are very cheap nowadays. Actually so cheap that one should think very carefully before using 8-bit ones, from the price standpoint.Regards,Janne

author: jahonen
author_rank: Super Contributor
timestamp: January 27, 2010, 04:51:54 pm
content: BTW, just checked local Farnell price for STM32F103C6T6 (72 MHz ARM Cortex-M3, 32 kB flash, 10 kB RAM), 4,27€/each. Compare that to 18F-series PICs, which tend to be more expensive, although just 8 bits. I have programmed PICs using assembly, ARM7s and MSP430s with C. I think that the initial difficulty of the ARM is usually just getting things up and running (like configuring the PLL etc). After you figure that out, ARM tends to be much easier. But much of that can be avoided if you bother to spend more than 15 minutes to read the MCU user manual (and that errata Dave mentioned)I guess that one would like to use floating point arithmetic for the calibration calculations and result processing to utilize the ADC resolution optimally. 32 bit ARM is much more suitable to that task. I'm not saying at all that is not possible with 8-bits and with fixed point arithmetic.I have seen so many times at work that it is better to initially choose somewhat overkill chip to do the stuff, since price of the hardware tends to come down with the time, but the complexity of the software tends to go upCustomers not realizing that will often find themselves doing re-design in panic at the very near the deadline, when it turns out that software has grown much beyond initial expectationsRegards,Janne

author: charliex
author_rank: Frequent Contributor
timestamp: January 27, 2010, 06:06:08 pm
content: I wish ethernet was in use a lot more on a lot of equipment, its so much better. There are so many stacks and solutions available as well now.

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2010, 09:11:57 pm
content: Quote from: Mastro Gippo on January 27, 2010, 03:58:56 pmFrustrating like rechargeable batteries!You can easily have an a low power dot matrix LCD display with a nice backlight, best of both worlds. And even with the backlight on you could still shoot for 1000 hours operation off D cells.The Newhaven LCD display on my new uWatch design for example takes under 200uA, and backlight works well at under 10mA.OLED would likely not allow long term data logging with continuous display.A agree with SD over micro, much less fiddly and more readily available.No built in direct connect PC comms (Ethernet or USB), it needs to be external and isolated. So some form of clip-on box with a serial IR interface.Dave.

author: badSCR
author_rank: Contributor
timestamp: January 27, 2010, 10:55:40 pm
content: Anything hard-wire to computer scars me, about the Isolation problems $$$.*Serial IR ; slower speed, but the SD-Card could be used as a buffer.*An SD-Card or usb flash drive is a must for data logging. (for high speed data logging maybe 1~2Gb RAM)*Auto Ranging?*3~5 channel Volt meter/logic And Dual channel Amp meter.*Would like the ability for 10~20 DC amps continuous.*Ability to measure Resistance, Diodes, Inductors, and Capacitors.*maybe a Transistor tester.*micro volts/amps*maximum 600 Volts to 1Kv ?*phase angle (for three phase power) ?*able to use Fluke Clamp-on Current Probes (for three phase power) ?*low frequency Oscope ability (less then 200Khz) ?*A Wall-adapter for a PSU.*Able to use a Lithium-Ion battery pack from a cordless tool (non-charging). If your some where and the battery dies then you could use the one from a power tool.*D cells or the Big 6volt battery, both are easy to find.*In Resistance mode it could tell you the color code and if it is within tolerance.*Maybe a Composite video output.

author: badSCR
author_rank: Contributor
timestamp: January 27, 2010, 11:00:43 pm
content: Could do the Ethernet and use a Wifi Bridge to connect to a PC. And use a buffer.

author: xani
author_rank: Frequent Contributor
timestamp: January 27, 2010, 11:58:10 pm
content: well, ethernet use isolating transformer, just get a good one ;]

author: Curtisbeef
author_rank: Contributor
timestamp: January 28, 2010, 01:33:16 am
content: For the USB data logging could it just be Opto-isolated serial lines going to a USB powered and Isolated from the rest of the board FTDI Serial Chip. Is that enough?

author: charliex
author_rank: Frequent Contributor
timestamp: January 28, 2010, 01:56:26 am
content: just put RS232 out on it, after that its trivial to add on Wifi or Bluetooth.

author: EEVblog
author_rank: Unknown
timestamp: January 28, 2010, 02:25:04 am
content: Quote from: badSCR on January 27, 2010, 10:55:40 pmAdd an adjustable constant current output for testing LEDs.Dave.

author: Thermal Runaway
author_rank: Contributor
timestamp: January 28, 2010, 12:33:03 pm
content: Of the features already mentioned, I have experience with the following:LCD Interfacing via serial and parallel methods, character and graphicSD Card interfacing for data storage and retrieval (currently working on a project that uses this)Infra-Red communicationsGeneral Microcontroller firmware designGeneral electronic circuit designHowever, I am unlikely to be available to contribute to fun stuff like this until the academic year has ended (around about May/June). I'll follow this thread with interest until then, and see how it's progressing in a few months time. If there are still tasks I can help with at that time, I'll volunteer for some jobs.Brian

author: SockThief
author_rank: Contributor
timestamp: January 28, 2010, 03:01:23 pm
content: It feels a bit like a kitchen in a cooking school at the moment, with everyone throwing in their own wishes, stirring it about, its going to be interesting to see what comes out. This is the part I always like about community based open-source projects, it can be anything at all! It's like giving a list to Santa and getting it all! (and yes there are probably a few people reading this at the moment, that feel a little underwhelmed by the iPad unveiling last night. The actuality had no hope of living up to the expectactions, we have no such limitations!) But this brings to me a small idea that has been floating around for a while, I always have my iPhone with me. And currently there are iPhone bases Oscilloscopes, meters etc. But as far as I can recall (I actually haven't looked at them for a while) they use the internal H/W to perform A/D conversion etc. So there are strong limitations there.But! What if there was an external module that communicated by Wi-Fi to the iPhone (or any other smart phone or Wi-Fi equipment for that matter) but let's assume an iPhone, passed all the measurements to the iPhone, then the iPhone could postprocess the results for display, emailing, sms etc. There is no reason why a PC could not stand in for this function, or another custom build module. In any case, by using an iPhone you have- data which is as high-a-quality as possible (after all its coming from a purpose designed piece of equipment)- a display is already available- a ready made communication chanel between the data-collector and the display- a ready made data analyser- 3G on the phone allows you to phone-home data to HQ (perfect for in the field work)just another idea to throw into the pot. I guess this is something Im more than willing to look into and play around with. And can largely be done in isolation from the rest of the project, merely relying on a communications protocol.Til next time!

author: xani
author_rank: Frequent Contributor
timestamp: January 28, 2010, 09:47:43 pm
content: Well, if u have ethernet u can connect it to pretty much everything everywhereAnother idea:Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB

author: jahonen
author_rank: Super Contributor
timestamp: January 29, 2010, 10:08:32 am
content: Quote from: xani on January 28, 2010, 09:47:43 pmAgilent power supplies controllable via GPIB or Ethernet are done just this way. Probably their bench DMMs too. One should be very careful about the isolation. Handheld DMM is especially critical since it is "hand held". Bench thing is somewhat easier in that sense.Ethernet line transformers are tested 1 kV RMS isolation, but that is not enough for safety. Something like 5000 V RMS would be more appropriate there. But anyway without extensive testing, there is no way to guarantee safety (or any CAT-rating), as Mr. Maxwell tends to be more imaginative than we poor design engineersAdd capacitor ESR measurement to the functionality list. This should work downto 1 milliohm (4-wire measurement required?), since most ordinary electrolytics are rated something like 10-20 milliohms.Regards,Janne

author: Unknown
author_rank: Unknown
timestamp: January 29, 2010, 11:48:28 am
content: Quote from: jahonen on January 29, 2010, 10:08:32 amHi Janne, I would like to add ESR, should not be too hardI have isolation for my Tek TDS220, I use an isolation box I built as a project for my networks course I did back in '98. It is about 4m of optic fibre cable and TX / RX pairs, it isolates RS232 (in each direction Max232 - Tx Led - Fibre Cable - Rx photo diode - Max232. Both ends were powered by 9v batteries, an would run for about 16 hours)That could be an option for this project. I am yet to find any decent voltage rated isolation devices (ie >10Kv)

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 29, 2010, 04:53:48 pm
content: Yes, ESR and Dave's uCurrent are a must!I'm a bit scared of ARMs, that's why I was supporting PICs.. But if someone manages to get an easy bootloader working, I can try to join the fun! I've been thinking about learning ARMs for a while... Maybe we can start on the mBed platform,http://mbed.org/! All the hard part is already done.

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 29, 2010, 05:57:55 pm
content: By the way, I just got myself an iphone (yes, I know, shame on me, but i got it for just 100€ broken and I repaired it so at this price it's worth it), and I think that an OS-based user interface like SockThief said can do great things.But not everyone has an expensive iphone... well, last year I got this from dealextreme:http://www.dealextreme.com/details.dx/sku.19609it has a GREAT screen, visible outside in bright sunlight (I'm not kidding; I wrote an app for it to measure and display speed and direction to skippers for a sailing boat), and it's cheap (there are even cheaper models). The nice thing is that you can program it in c# REALLY easily, debug code line by line via USB, use wide available libraries, make graphics easily, and the interface is based on win CE so it's very flexible. I even found an I2C port inside it, by looking at the radio transmitter module datasheet, and tapped into it. The port is mapped in the OS, but I was not yet able to do anything with it yet.For 5$ more you can get bluetooth too.We can do the "detachable display" trick by having a black box that deals with all the analog stuff and communicates with the display via bluetooth.It's a hack, I know, but it's the biggest bang for the buck!

author: jahonen
author_rank: Super Contributor
timestamp: January 29, 2010, 06:14:40 pm
content: Quote from: Mastro Gippo on January 29, 2010, 04:53:48 pmMost ARMs have a bootloader built in already. For example NXP ARM7s can be programmed by just connecting RxD and TxD via voltage level shifter (e.g. MAX232) to PC (USB serial ports work just fine since all communication is RS232-friendly). ROM Bootloader is started if certain pin is pulled down when reset is released. Programming software is also free, e.g.http://www.flashmagictool.com/.Regards,Janne

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 29, 2010, 06:19:38 pm
content: Cool!! Thank you!Now I just need a project to justify spending money for a dev board - and arm ones are pretty expensive.... But I've seen some nice options from olimex.

author: EEVblog
author_rank: Unknown
timestamp: January 29, 2010, 10:23:25 pm
content: It might be worthwhile considering the LXI standard interface for LAN based instruments:http://www.lxistandard.org/Dave.

author: charliex
author_rank: Frequent Contributor
timestamp: January 30, 2010, 06:44:10 am
content: I'm happy to offer to help with the code for ARM, or most processors. I've also got developer accounts for iphone, and most other phones OS's,, embedded systems ( even the nintendo wii and ds! ) for any kind of remote stuff, we use the GBA a lot like this.http://www.mikroe.com/en/tools/have an excellent selection of dev boards.

author: Thermal Runaway
author_rank: Contributor
timestamp: January 30, 2010, 09:46:18 am
content: @charliexEvery single time my Elektor issue comes through the post, I see the adverts for those development boards and think that it'd be pretty useful to have one around - they do seem quite comprehensive. But I've never got myself one. Each time I do a new project, I build a quick and dirty breadboard based dev board to suit the specific purpose.I should get one of those though, I think.@threadI've no previous experience with ARM at all, although in fairness once you get into the realms of C... I guess changing processors is not much of a problem. I've never tried it, because PIC has always suited my particular needs.I'll watch this thread with interest. After all the ideas have been thrashed around, someone (GeekGirl) is going to have to take control of the situation and decide on a specification for the design. Then organise people to contribute to it. Without the spec or the organising, nothing will get off the ground so I think it's pretty important.Brian

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 10:35:53 am
content: Quote from: Brian Hoskins on January 30, 2010, 09:46:18 amHi all,I am watching this thread closely, I was going to do a block diagram, but I am hanging off for a little while more, as there is great discussion going onI am going to ask people to nominate areas they would like to help withIf anyone wants to make up parts of the PCB layout or Schematic, as long as they provide a PDF I can incorporate it into the "master" schematic and PCB (I use ADS09 (Altium Designer Summer 09) and I do not expect other to have this package) then I will publish these back to this thread as both native ADS09 and PdfI will hope by Monday to have a list of features that have been suggested so far in one POST so we can all follow(Sunday for me is going to be hectic lol)If the group would like I can also set up a project page on Sourceforge so we can use CVS for tracking hardware, firmware and software revisionsRegards,Kat.

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 11:04:14 am
content: Quote from: Brian Hoskins on January 30, 2010, 09:46:18 amI find them, how should I say, unbalanced. 70 or 100 buttons on a board looks great, but what on earth are they good for on a dev board? Sure, if I think hard enough I can find (artificial?) applications where I would need 70 buttons on a dev board to prototype. But if I keep it real, a prototype application needing 70 buttons warrants a separate keyboard (incl. communication protocol), and even 20 buttons on a board aren't really what one needs on a dev board.IMHO these boards are made to impress, not to deliver the most value for the developer.QuoteI want to add another aspect to the discussion, more basic and down to earth than just a feature list.Since this is going to be a bench multimeter it needs an enclosure. I assume that a custom enclosure is out of the questions, so an off-the-shelf enclosure is to be used.From my experience, when you work with an off-the-shelf enclosure it is unavoidable to settle early on in the project on a particular enclosure, because the enclosure will dictate to a certain amount how things can be build. It will to a large extend dictate the mechanical dimensions of the PCB(s), their mounting, and even partly the separation of functions into different PCBs (e.g. a separate front-panel PCB, a power-supply PCB, etc.)I actually like the classic bench-top multimeter form factor like inhttp://www.home.agilent.com/agilent/product.jspx?cc=DE&lc=ger&nid=-34037.899260&imageindex=3http://www.bkprecision.com/products/photos/large/2831D_front_lrg.jpghttp://www.fluke.co.uk/comx/show_product.aspx?pid=37725in particular when they come with the rubber protection (BTW, does someone know who invented that form factor for instruments?)These enclosures are approx. 300 mm deep (including the rubber), 260 mm wide (including the handle), 110 mm high (including the rubber).Some time ago I tried to find anaffordableoff-the-shelf enclosure of the above kind, but I wasn't very successful. Just finding something with the right dimensions was a problem (typically they had the wrong depth / width ratio), most didn't have a handle bar, or they had handle bars which were completely different compared to the ones in the examples (making stacking impossible). And I didn't find a single one with the rubber.So, if someone knows a reliable source for affordable enclosures of this kind, I'd like to know it. And I would suggest that a particular enclosure is adapted very early for the bench meter.

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 11:29:34 am
content: When it comes to the enclosure I am going to suggest that we use Farnell / Newark, this is so that we can all have everything FIT, Front Panel overlays the right size etc.I think even DigiKey maybe even mouser will have similar sizes and maybe even models.Regards,Kat.

author: EEVblog
author_rank: Unknown
timestamp: January 30, 2010, 12:20:36 pm
content: Quote from: GeekGirl on January 30, 2010, 11:29:34 amWhen doing a project like this I like to start with the form factor and user interface first and how that's all going to work, and then work backwards to the detailed schematic. Because a schematic does not a project make.http://www.hammondmfg.com/http://www.serpac.com/http://www.polycase.com/are some of my favorites.Also, I'd consider a budget too, too high a price and it's going to be a show-stopper, so cost should always be factored in.I'd probably go with PIC myself for familiarity and simplicity. 32bit ARM power is not needed for such a thing, and the development tools are harder to work with for the average punter.It's hard to beat the $40 PICkit, MPLAB, and free (limited) C compilers for the PIC combo.A lot of people say ARM and GNU C is cheap and free, but when it comes down to it the tools are not consistent, and harder for a beginner to use.But of course that may not really matter if most people just want the finished pre-programmed product.Heck, I'd even seriously consider jumping on the Arduino bandwagon here. Separating the custom front end board from the processor board entirely. Gives options and lowers the development risk. And it will excite the hacker and makers (don't underestimate that market appeal)Dave.

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 30, 2010, 12:58:41 pm
content: http://www.polycase.com/item/vm-36boot.htmlthis looks nice and cheap. I would like a handheld multimeter, not a bench one...

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 01:37:09 pm
content: Quote from: Mastro Gippo on January 30, 2010, 12:58:41 pmNope, Can not use them.... They don't come in PURPLEI think if we can make it modular then we can have a simple front end display for hand held and a fully optioned desktop model ?The prices of the hand held case is VERY GOOD, for low qty.

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 01:48:20 pm
content: Quote from: EEVblog on January 30, 2010, 12:20:36 pmI want to try and use a chip and "common" compiler, I am not a huge fan of GCC (although I use it the most) as it is not like a commercial product that you install and it just works. I know GCC is getting better, but things are not there yet.I agree we do not need an ARM processor. Just an 8 or 16bit uC with a good amount of Flash and RAM.Even though I am an Atmel Gal, I see no reason to not to consider a PIC or MSP serries, (horses for coursesI am starting to picture this project as a "modular" system, basic is display and Multimeter front end, more advanced would be to add the 4wire resistance, ESR, LCR, Logic Analyser (to give us the ability to spec # of channels (less channels = more samples/longer period)) Frequency counter, Function generator, maybe even a terminal adapter ie send and receive RS232 for exercising projects.I think that we need to cull the list and not make this project a tool for every situation.I am not sure, but I am sure that in the next few days I will make a list and description of every idea so we can work out what we REALLY want in this product.

author: armandas
author_rank: Frequent Contributor
timestamp: January 30, 2010, 01:53:26 pm
content: Quote from: GeekGirl on January 30, 2010, 01:37:09 pmI think the bench-top would be most appropriate and easy to build. But hey, it's going to be open-source, so anyone can build their own version, if they like!

author: Unknown
author_rank: Unknown
timestamp: January 30, 2010, 03:43:31 pm
content: When looking for the mentioned "original instrument enclosure" I think I went through everything mentioned here and more (Hammond, Serpac, Polycase, Bopla, Pactec, Proma (now gitec), Prio, Combiplast, Teko (brrr), ...).And because of that I am of course fully educated and informed where to getPURPLEenclosures GeekGirl so desperately needs:http://www.elpac.de/categories.php?cat=200&lang=en

author: charliex
author_rank: Frequent Contributor
timestamp: January 30, 2010, 05:17:53 pm
content: ARM GCC is a lot better now, since ARM paid for it to be fixed/upgraded since it was absymal.How about a PSOC ? While i agree you don't need much of a uC to run it as is, it'll allow more room for growth. If its C then the differences aren't as difficult to overcome.

author: Thermal Runaway
author_rank: Contributor
timestamp: January 30, 2010, 05:19:55 pm
content: Quote from: GeekGirl on January 30, 2010, 01:48:20 pmI agree. Most of the things mentioned would be really cool to have on a meter actually, but it's probably better to get a decent system working first then worry about cool extras at a later time. That's what new versions are for.Someone else mentioned handheld. I have to agree - I'd prefer a handheld project meter as well. Mainly for selfish reasons, in that I already own a really cool and accurate Agilent bench meter which in all fairness would really take some beating. I guess there are some extra features that could be added to it, but the features it *does* have are pretty much perfect.Handheld... well I have quite a nice Fluke meter but... I dunno I think it could be improved quite easily. I don't think any one manufacturer has totally nailed the handheld market yet.With regard to compilers, if it is decided that the PIC route is the way to go, then I would recommend the BOOST C compiler. It's not the *best* compiler in my opinion (that award goes to Hi-tech PICC), but it's certainly the best bang for buck. Even the professional version is well within most people's budgets. I used to use Hi-Tech but found that it was priced outside of my range for my hobbyist stuff. So I've recently moved to BoostC.Brian

author: jahonen
author_rank: Super Contributor
timestamp: January 30, 2010, 07:25:34 pm
content: BTW, This looks attractive for a DMM, a 24-bit ADC with ARM7 µC (however no personal experience on this chip):http://www.analog.com/en/analog-microcontrollers/analog-microcontrollers/aduc7060/products/product.htmlLike NXP ARM7's, this one too has an integrated boot loader, so programming can be done just with level-translated RS232, even without any software pre-programmed.Nice thing about sigma-delta ADCs is that by setting the modulator rate correctly, you can get a very good rejection of 50 and 60 Hz mains-borne noise. Good for DC- and rectified AC-like (like measuring output of that true RMS converter) measurements.I agree that feature list needs to be prioritized to "must have", "nice to have" and "not needed" features. Otherwise this will not lead to anythingFeature creep is very much poison to the product development, especially on the HW side, where a seemingly small change can cause a major re-design.Regards,Janne

author: EEVblog
author_rank: Unknown
timestamp: January 30, 2010, 09:34:48 pm
content: Quote from: Mastro Gippo on January 30, 2010, 12:58:41 pmFor a bench meter, you could do worse than this one:http://www.polycase.com/category/zn-series.htmlA stackable bench instrument case.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 30, 2010, 09:42:31 pm
content: Quote from: Brian Hoskins on January 30, 2010, 05:19:55 pmIf you went PIC then you'd need a good reason the stray from the free Microchip C compiler.Sure it's one of the most inefficient on the market, but hey, it's free (optimizations crippled only) and available to everyone.You almost certainly wouldn't need a top quality compiler for this project (with the huge Flash sizes available these days), just something that works.But everyone can fight over processors choice until the cows come home, that's why I'd be looking at Arduino actually. It's fast enough, all tools are free, and adds a more "community" feel to the project I think.But it's not the best choice if you want ultra-low optimized power consumption. But that might actually be a reasonable trade-off.Dave.

author: Ferroto
author_rank: Frequent Contributor
timestamp: January 30, 2010, 09:56:14 pm
content: heh most of these posts are well above my head.I'd recommend physically intergrading the uCurrent adapter in the project.

author: badSCR
author_rank: Contributor
timestamp: January 30, 2010, 10:23:55 pm
content: If someone does not have a PICkit to program the microcontrollers, They could just order the PIC with the code already programmed into it. I have a pickit2 so its not a problem for me."Looking for a low-cost programming solution? Let Microchip do the programming in a fast, cost-effective, secure and proven method."

author: Ferroto
author_rank: Frequent Contributor
timestamp: January 30, 2010, 10:52:24 pm
content: Quote from: badSCR on January 30, 2010, 10:23:55 pmI think digikey offers that option as well.

author: dmlandrum
author_rank: Regular Contributor
timestamp: January 31, 2010, 01:50:54 am
content: I concur with Dave on this one. Using an Arduino for this project (and for the record, I'd like a bench meter) would get the attention of Make Magazine and you'd have a large DIY contingent descend upon this place like Martin Sargent at a Megan Fox convention. That can be both a good and bad thing.Arduinos also have the advantage of being relatively cheap and fairly easy to program. A shield could be designed with the extra components needed for true RMS and so on.But I'm not the expert here, so I'll leave it to you guys.

author: EEVblog
author_rank: Unknown
timestamp: January 31, 2010, 02:45:00 am
content: My train of thought on this one...Stick with bench mounted instead of handheld, because handheld has too many variables that will muddy the requirements.So, a bench meter. Well, it's gotta be more than a bench meter of course, and with the suggestions so far it's actually becoming more of a general purpose "bench instrument/lab system".So what would the average punter want from such a system?Well, all the usual multimeter stuff and data logging that's been talked about, simple very low end oscilloscope functionality, maybe a simple logic analyser / serial protocol system, some form of simple functional generator, and a lab power supply. Bingo, you have a complete mini lab in one unit.But I wouldn't try and make it all the one unit, I'd have them as separate modules. One as the bench meter/data logger/oscilloscope, one as the bench power supply (that could also power the other modules), one as a PC/Ethernet/WiFi comms module etc.Such a system would need some thought into any required comms between systems, or they could just be made separate and stackable.I'm actually working on a very low cost bench power supply at the moment, and was actually considering those stackable bench enclosures (http://www.polycase.com/category/zn-series.html). This is a spin off my almost already developed uSupply project which is another very low cost but quite capable power supply (the uSupply has made a cameo blog appearance, but everyone almost certainly missed it)Food for thought.Dave.

author: Curtisbeef
author_rank: Contributor
timestamp: January 31, 2010, 03:32:39 am
content: I definitely agree that this should be a Bench Meter and not handheld. There are too many hurtles to overcome with the handheld system. Plus with the increased size there will be more options for expandability and also case options. I think at first we should make the internals only, and let people decide what kind of enclosure they want. Then as we get going maybe someone will find a standard case that we can all use.I think that we should try to do some type of modular design. Make a Main board with some type of a standardized connector that will carry data/power/etc to the modular boards.I'd really like to do the wireless display it could be done very simply with a nRF24L01 transceiver and would have a range of 50 foot easy indoors. I think the display should sit in a cradle or something like that on the bench meter. And we could design module for a non wireless display as well, for people who do not need that functionality.I dont know if we wanna go the Arduino route, those things are so expensive for what you get. Since we will most definitely be making PCBs for modular boards and things like that, making a Main board with a ~$5 PIC Chip seems like a better option to me then having to make the Main board and the have a 30 dollar Arduino attached to it anyway. Unless you are saying that we should just use a Arduino compatible chip on our board and use the Arduino bootloader and IDE to write our code.My Vote is for a PIC24 but that is one thing that we should definitely decide on soon. I would like to make a development Board setup for our micro controller of choice as soon as possible.

author: Unknown
author_rank: Unknown
timestamp: January 31, 2010, 10:39:48 am
content: I am repeating myself here with regards to several aspects:Quote from: EEVblog on January 31, 2010, 02:45:00 amOne of my first posting in this thread pointed to such a DIY system. You can get some inspiration by looking at the pictures inhttp://www.heise.de/ct/projekte/machmit/ctlab/wiki/LayoutSeitehttp://www.heise.de/ct/projekte/machmit/ctlab/wikihttp://www.heise.de/ct/projekte/machmit/ctlab/wiki/AlleModuleQuote from: Curtisbeef on January 31, 2010, 03:32:39 amThis usually doesn't work out. Too many parameters depend on the enclosure. In my experience, if you go with an off-the-shelf enclosure, and if you don't want to go through many design iterations, you have to take care of the enclosure early in the project, not late. Otherwise you end up with the typical DIY enclosure: A huge, half empty box, taking up much more bench space than necessary, with PCB(s) somehow mounted on glued standoffs or other makeshift mechanical support.

author: EEVblog
author_rank: Unknown
timestamp: January 31, 2010, 11:51:25 am
content: Quote from: Andrew on January 31, 2010, 10:39:48 amI agree, as I mentioned before.Get the enclosure, looks, and user interface/experience wrong and it may not matter how good your electronics is.I'd actually rank the electronics at least 3rd or 4th down the list of things to do, which is getting pretty close to the bottom end :->Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 31, 2010, 12:00:50 pm
content: Quote from: Andrew on January 31, 2010, 10:39:48 amThat looks very nice and professional, but probably mega expensive.I think cost should be a huge driver behind any such DIY project.After all, we probably aren't talking about anything blazingly new, so maybe help differentiate with bang-per-buck low cost?And also, who is the target audience?Just GeekGirl to fulfill her fantasies? (;->), professionals?, hobbyists?, education?, Hackers/Makers?etc.Sure, projects can be done "just for the heck of it", but it's nicer if you can target an intended niche.Dave.

author: Unknown
author_rank: Unknown
timestamp: January 31, 2010, 12:36:00 pm
content: Quote from: EEVblog on January 31, 2010, 12:00:50 pmLets no go thereQuote from: EEVblog on January 31, 2010, 12:00:50 pmMy original idea was to build a "Bench Meter" with good specs (higher than my Fluke 29).Now people are indicating that they would like an entire DIY lab.... I have no problem with this. I personally think that if we design an open protocol for comms, we can hang anything off itI like the cases that Dave pointed at (as long as they make a BIG one for a decent PSU (2 variable and 4 fixed outputs (ir 2x 3-30V, +/- 5 and 12V))But tomorrow I am going to try and get this idea in some shape

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: January 31, 2010, 12:41:11 pm
content: The ADUC7060 looks Great! ..if only I knew how to program ARMs...Dave, can you take some pictures of the analog frontend boards of your most expensive multimeters? Only board layout can be copyrighted, schematics can't, so if we can get a ready to go schematics we can design a slightly different board and have a product as good as the cool guys, for the price of bare components.I was curious about the implementation of the auto-range too, tonight I thought about it a lot and I had some ideas so I'd like to see if I got it rigt in my mind.I hope the end product will be so cool and modular and cost effective that the target audience will be ANYONE. I suggest a vibration function in the continuity mode, so we can really fulfill GeekGirl's fantasies!(Sorry, couldn't resist.)

author: Unknown
author_rank: Unknown
timestamp: January 31, 2010, 02:17:48 pm
content: Quote from: Mastro Gippo on January 31, 2010, 12:41:11 pmThat would explain the request for a purple case. Well, partly

author: badSCR
author_rank: Contributor
timestamp: January 31, 2010, 03:34:26 pm
content: Quote from: Curtisbeef on January 31, 2010, 03:32:39 amYap, I agree.I don't like the Arduino, BasicATOM, BasicX, BASIC Stamp... They cost to much for what you get.I like the wireless display module, idea. As an option.The "Service Manual" sometimes has the schematics. They cost less then $20, some are free.

author: Thermal Runaway
author_rank: Contributor
timestamp: January 31, 2010, 05:34:12 pm
content: Quote from: EEVblog on January 30, 2010, 09:42:31 pmI must confess I've never actually tried Microchip's own compiler. The simple reason being, they don't support (or at least they didn't) the 16F range of devices. While I was learning C, these were the devices I was playing with, so I had to find a compiler that worked with them. That's how I got on to PICC.Once you're used to a compiler, you don't really want to have to swap to a different one (at least, not just for the sake of it anyway). Hence I never got around to trying Microchip's own compiler.Brian

author: jahonen
author_rank: Super Contributor
timestamp: January 31, 2010, 06:12:30 pm
content: Quote from: Thermal Runaway on January 31, 2010, 05:34:12 pmThat is probably due to that anything less than 18F is not C-friendly, as there is no RAM or stack in the usual sense. Stack is very essential thing for a typical C compiler as the arguments for a function are usually pushed on the stack and function local variables also reside there. That makes a 16F a very hostile environment for a C-compiler. Instead there is a big bunch of registers.Regards,Janne

author: charliex
author_rank: Frequent Contributor
timestamp: January 31, 2010, 08:42:30 pm
content: depends on the compiler, typically if its a restricted space or its faster, the compiler will use register based passing (fir the first few args at least) Its something you can always work around, so long as you can store the data in read/write somewhere, if it has a global storage you can use static instead of auto.I've been looking for a project to try with the Cypress PSOC, so thats why i mentioned thathttp://www.cypress.com/?id=1353

author: xani
author_rank: Frequent Contributor
timestamp: January 31, 2010, 08:56:43 pm
content: Imo it would be best to build analog part of meter in a way that u can connect any type of CPU to it so some1 who need only basic functions can use one of those 2kB FLASH micos + 2x16 LCD, and someone else can connect it to 32 bit ARM (possibly more than one analog "card") and thru that to ethernet or graphic LCD.About Arduinio, while i think that building it like arduinio isn't optimal, if it would be "Aruduinio-compatible" (possible to program directly from arduinio software) there would be a lot of possible developers for it. And if u don't like Arduinio there is alwasy plain GCC. And if its gonna be "open source" meter let's use something that can be programmed from gcc ;]

author: EEVblog
author_rank: Unknown
timestamp: January 31, 2010, 08:59:10 pm
content: Quote from: Curtisbeef on January 31, 2010, 03:32:39 amYup, that would be the best option I think. It fulfills GeekGirl's AVR fetish, keeps the cost low, and it gives the hackers free easy to use tools, gives it the requisite "community" feel, and no programmer required, just plug into USB for programming. Internal ISP header on board for initial bootloader programming of course.I see few downsides there.Dave.

author: xani
author_rank: Frequent Contributor
timestamp: January 31, 2010, 09:47:25 pm
content: Arduinio users will be happy, other can use avr-gcc or plain assemblerJust get big chip with "room to growth" like mega32 or even mega128. Tho with mega128 proce of processor is getting close to 32 bit ARMs without some of its features (mentioned by me eariler AT91SAM7X256 with USB, Ethernet and more RAM/Flash/IO).But then amount of ppl who can program in Arduinio >> amount of ppl that can program ARMand more ppl wanting it = cheaper PCBs/kits

author: desolatordan
author_rank: Regular Contributor
timestamp: February 01, 2010, 12:29:49 am
content: Quote from: EEVblog on January 31, 2010, 08:59:10 pmI don't see the benefit of plugging in USB rather than plugging in a ISP connector for programming...?There's a lot of overhead when using Arduino language,http://hackaday.com/2010/01/06/arduino-io-speed-breakdown/. The only way around this is to bypass the Arduino abstraction, in which case you might as well not use it anyways and just use gcc compiler.

author: EEVblog
author_rank: Unknown
timestamp: February 01, 2010, 12:35:28 am
content: Quote from: desolatordan on February 01, 2010, 12:29:49 amThe benefit is that no programming hardware is required, just a USB cable. Any user is then free to upgrade their firmware without needing to buy or make an ISP programmer.QuoteI don't see speed being an issue in this app. But the benefits of using Arduino are potentially quite large.Dave.

author: Chasm
author_rank: Regular Contributor
timestamp: February 01, 2010, 03:13:35 am
content: Quote from: desolatordan on February 01, 2010, 12:29:49 amAs Dave said, you won't need an ISP Programmer.Further you can't change the fuses this way, the easiest way for beginners to shut themself out of the micro.Of course you need the usb<->serial converter (the FT232 is popular). Also you need a micro with the bootloader code programmed and the correct fuses set in the first place.QuoteEach and every abstraction layer will cost you.If I've followed the discussion correctly the idea is to make the hardware Arduino compatible.As far as i can tell that means using a run of the mill AVR design that incorporates a FT232 usb converter.After that it is possible to flash a Arduino bootloader and use the Arduino toolchain. Thus making the project interesting to a larger group.Whether there will be Arduino or "native" software is up to those writing it.Since wireless connectivity and insulation against faults has been mentioned before:Using Bluetooth has become a cheap and simple way to connect micros (via RS232 & SPP) to the outside world. There is a Arduino board with BT via the WT11 module instead of usb via FT232RL.The WT11 seems to be a bit pricey with about €30, the BTM222 for €13 is vastly popular at the moment.

author: cd
author_rank: Newbie
timestamp: February 01, 2010, 05:35:38 am
content: Hi, serial out would be nice - I'd like to build a nixie tube version and a remote wireless display A buffered output after the range select would be good too - as a ready made output for a frequency counter and/or tone ohm module.Chris.

author: xani
author_rank: Frequent Contributor
timestamp: February 01, 2010, 12:29:53 pm
content: Quote from: EEVblog on February 01, 2010, 12:35:28 amAaand You don't have to use it, you can just use plain GCC so it's best of both worlds

author: badSCR
author_rank: Contributor
timestamp: February 01, 2010, 03:14:31 pm
content: We could do something similar tohttp://www.buglabs.netQuote from: GeekGirl on January 31, 2010, 12:36:00 pmI would prefer a design that I can trust with good specs, over something that has low specs and does everything.With a modular design, we could have a "Bench Meter" with good specs (higher than my Fluke 29) or even higher.We could do a whole line of DIY equipment.

author: badSCR
author_rank: Contributor
timestamp: February 01, 2010, 07:22:56 pm
content: Quote from: Mastro Gippo on January 31, 2010, 12:41:11 pmhere are some schematics that we could get some ideas from. (That were free)http://cp.literature.agilent.com/litweb/pdf/34401-90013.pdfAgilent 34401A Multimeterhttp://cp.literature.agilent.com/litweb/pdf/34420-90010.pdfAgilent 34420A NanoVolt / Micro Ohm Meterhttp://oldradio.tesla.hu/rajzok/muszerek/fluke45.pdfFluke 45http://www.testequipmentdepot.com/fluke/pdf/77iii.pdfFluke 77 Series iii Handheld meterhttp://cp.literature.agilent.com/litweb/pdf/33120-90017.pdfAgilent 33250A 15Mhz Waveform GeneratorIf you don't mind downloading multiple files and using WinRAR then: (don't change the file names)http://www.eserviceinfo.com/downloadsm/40126/Protek_6502A.htmlProtek 6502A 20-40-60Mhz Oscopehttp://www.eserviceinfo.com/downloadsm/37608/Tektronics_465m.htmlTek_465M Oscopehttp://www.eserviceinfo.com/downloadsm/37182/Agilent_33120a.htmlAgilent 33120 Function Generatorhttp://www.eserviceinfo.com/downloadsm/37180/Agilent_E3647/48A.html60Watt Power Supplyhttp://www.eserviceinfo.com/browse.phpI just been looking for what has "schematics" in the file name.

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: February 03, 2010, 07:44:11 am
content: I guess we're all busy reading the docs posted by badSCR..

author: jklasdf
author_rank: Regular Contributor
timestamp: February 04, 2010, 06:37:03 am
content: In the interest of moving things along -- while I'm sure everyone has their own opinion on what their favorite case/microcontroller -- I think most people here would agree that it's more productive to choose *something* even if its not their first choice, rather than sitting around arguing.So I propose a vote (choose only one option):1.) PIC2.) AVR/Arduino3.) ARMFor the case, I haven't seen many objection to the case proposed by Dave,http://www.polycase.com/category/zn-series.html. I definitely think that a benchtop case is a good idea for a do-it-yourself kind of a project, even though handheld might be more convenient with a production unit.

author: Valhallasmith
author_rank: Contributor
timestamp: February 04, 2010, 07:24:49 am
content: What about ignoring processor and just making SPI or I2C modules that make up various instruments. There are various items that most instruments need and people could stitch them together whatever way they need.For example a DC volt meter would need a relatively noise free A/D. It would also need a precision reference, a switch MUX of some kind, a PGA, a voltage divider network, an analog power supply and a digital power supply. Most of these are basic items that any instrument could need.If you were making an AC volt meter you would also need a True RMS converter or precision bridge. Virtual instruments made up of these sorts of components would be an interesting way to take things. Volt meters, power meters, LCR, etc could all be built from various components. People could add various modules to their box depending on what they want to do. Not everyone needs 6.5 digits of accuracy, so they could get a cheaper A/D unit and a noisier PGA. Since everything is a virtual instrument various items can just be plugged into a switch matrix.Could be a bit large of a project though.

author: charliex
author_rank: Frequent Contributor
timestamp: February 04, 2010, 08:52:21 am
content: Most of the open source projects fail because of fragmentation , general disagreement and usually biting off more than can be chewed.Simple and modular sounds good to me. its pretty easy to revise hardware these days, costs are much lower.

author: Unknown
author_rank: Unknown
timestamp: February 04, 2010, 08:57:08 am
content: Quote from: jklasdf on February 04, 2010, 06:37:03 amThis project will never hit "production"the whole idea is it is a DIY project.I have placed a poll so we can vote on processor

author: Unknown
author_rank: Unknown
timestamp: February 04, 2010, 09:00:50 am
content: Quote from: Valhallasmith on February 04, 2010, 07:24:49 amIf we are going to use SPI / I2C etc we will need a micro in each module to do this. I think personally that it will be multiple instruments all wired up on a bus that will then eventually link back to a host PC that can do display and "data manipulation".For the case I am liking Dave's suggestion of stackable casesNeed to think of the interconnect bus.

author: Unknown
author_rank: Unknown
timestamp: February 04, 2010, 01:27:53 pm
content: I agree that it should definitely be a bench unit. The build quality of a handheld unit is much more important (it's more likely to be dropped) and harder. It would probably be hard to even match the build quality of cheap $5 multimeters, let alone a Fluke.I'd caution against trying to design a complete electronics lab at once, start with just a DMM. At least build a prototype before deciding on building a function generator/power supply/oscilloscope/etc.I don't see the advantage of modular instruments beyond stackable cases. There were some series of modular instruments in the past, eg. Tektronix TM500, 7000 series, Hameg HM8000 (this one in still sold). The motivation was usually:- Common power supply. Transformers, filter caps and heatsinks for pass transistors are large and expensive. These days, you can buy a switcher for a few dollars, although I'd probably use a linear supply for a precision bench DMM for low-noise.- Common display. A CRT is also large and expensive. A simple character LCD is fairly cheap. Graphical displays are more expensive and larger.- Internal connections between instruments. I think this is more important in automated test setups than your average DIY lab. I tend to use my instruments for all kinds of jobs, not in some sort of fixed test setup.- Expensive microprocessors. An 8-bit, 8-pin micro is about $2 (eg. ATtiny13). An 8-bit, 28-pin micro (ATmega48) is $3. I'm sure there are equivalent PIC/MSP430 devices. I don't see a reason not to put one of these in every module.I don't think a good DMM would make a good low-speed scope or logic analyzer:- A multimeter is high-precision and usually single channel- A low-speed scope (beyond basic data logger) would have to sample at least 200kS/s or so (for up to 20kHz audio range), but doesn't need much accuracy (1%, 8-bit ADC usually)- A logic analyzer needs at least 8 channels, just 1-bit, and again a fairly high sample rate, even for relatively slow signals like I2C.You'd just be designing three completely different front-ends, the only common parts would probably be case, a uC, a display and some buttons.Re Arduino, I don't think there's much point in using an off-the-shelf Arduino board, since the complexity of designing a basic Freeduino circuit into the board is trivial compared to the analog part. This is not like putting a basic relay shield on an Arduino and hooking it up to a lamp. I'd also want to isolate the front-end from the digital part, which probably wouldn't fit very well as Arduino shield (needs separate power supply).Schematics, here are some service manuals of brand-name bench DMM's (with theory of operations and schematics):HP/Agilent 3478A (5.5 digit, introduced in early eighties)HP/Agilent 34401A (6.5 digit, introduced in early nineties or so, probably more custom parts)Keithley 196 (6.5 digit, introduced in late eighties, few custom parts)Fluke 8840A (5.5 digit, introduced in early nineties)These are high-precision, low-noise and high impedance designs, which means component selection and PCB layout is probably very critical. They usually feature an input impedance of more than 10 gigaohm at the lower DC voltage ranges. A 1 year accuracy specification for a good 4.5 digit multimeter is 0.03%, for a good 5.5 digit meter 0.006%, and for a good 6.5 digit meter 0.003%. Plus you need to calibrate it to something with better specifications after you've built it. I'm not an expert in high-precision design, but it seems really hard to match this to me. I'd stick to mediocre accuracy/resolution for a bench meter (say 4.5 digits), and focus on price and features compared to commercial units (plus the fun).Someone mentioned simultaneous voltage and current measurement. Since current measurement is just voltage measurement plus a shunt, I'd make it in a full dual channel unit. The extra design effort is probably almost nothing. The extra component costs are probably also marginal, and it would be very useful (I often use multiple DMM's at the same time).Alson

author: _Sync_
author_rank: Contributor
timestamp: February 04, 2010, 07:54:57 pm
content: I agree with alm, we need a good reliable base at first. This would be a good accuracy dual-slope ADC with the needed software, if we got that running one can concentrate on the input circuit and the AC measurements.From looking at the manuals I found out, that the companies often use ASICs for special tasks like input-switching, multiplexing stuff (mostly PLCs I guess) and ADC.I think we should concentrate on the Keithley because it uses no custom part for important jobs. The software should be fairly straight forward, as the theory of operation is descrbed quite nicely.What I've noticed is, that most use theAD637 RMS-to-DCconverter. It seems to be the best thing to use in that application.For the controller part I'd say we should stick to something where a opensource or at least free toolchain is avalible, which would be the AVR.One could also use an ARM, but it seems that not that much CPU-power is needed, e.g. the Keithley uses a 68B09 and the Agilent ones use processors out of the 8051 series.If someone has a meter with a MSP430 we'd be able to glitch the firmware out of itThis thing is not going to be cheap or easy to build/calibrate if we want to keep our goals in accuracy and function.

author: badSCR
author_rank: Contributor
timestamp: February 04, 2010, 08:55:26 pm
content: PIC microchipMPLAB IDE is freeHI-TECH C compiler is free, (Pro Mode is 100% Full version for 30-days)Just putting it out there.

author: _Sync_
author_rank: Contributor
timestamp: February 04, 2010, 10:07:53 pm
content: Yep, there are some free toolchains for almost every chip!I'd personally prefer AVRs because I have experience coding for them and I like gccWe could discuss that for ages, it's the old Atmel,Microchip,Younameit discussion...

author: badSCR
author_rank: Contributor
timestamp: February 04, 2010, 10:28:36 pm
content: Quote from: _Sync_ on February 04, 2010, 10:07:53 pmlol, yep we could. So far AVR is winning in the poll for this.I feel my skills are not high enough for me to contribute much of anything.But, if the specs are good enough, the price is right, and I like the design; Then i think i will probably build one. Just now getting a lab together and looking for a job.https://www.eevblog.com/forum/index.php?topic=187.0(General Chat > Whats your Work-Bench/lab look like? Post some pictures of your Lab.)sorry, not try to hijack.

author: Unknown
author_rank: Unknown
timestamp: February 04, 2010, 10:52:00 pm
content: The main argument I see for using a 32-bit micro (ARM) is a graphical LCD (or OLED). This might be nice for large numbers (your standard character LCD is a bit small for bench DMM IMO, and 7-segment is less flexible), dual display (like theFluke 45) or graphs (both bar graph and histogram). I believe 8-bit micro's are a bit short on memory for this task (unless you go for the largest parts that costs more than a basic ARM). I don't have experience with ARM though, I've only used AVR.Apart from this, an 8-bit micro should be plenty. The fastest most commercial units can sample is 2kS/s (Agilent 34401A, Keithley 2000, the most recent modules might be faster), and this is obviously at reduced resolution. A 20MHz 8-bit micro should be able to handle this unless you do tons of floating point math. I think sampling this fast is only useful in assembly line testing anyway, where you want to test a continuous stream of products. It's nice if you have a bar graph that's reasonably fast (most Flukes do 50S/s AFAIK). We will need a fair amount of I/O's though (display, buttons, ADC, relays for things like range selection, serial/USB/ethernet out).Alson

author: _Sync_
author_rank: Contributor
timestamp: February 05, 2010, 12:17:34 am
content: As I said, I think our major concern should be designing a usable ADC!The userinterface and interfacing with other stuff is not really complicated.I don't have much time on my hands now but I will look into reverse-engineering and drawing schematics for something that is based on the Keithley 196. This should provide a good basis from which we can work on...And I agree, only fancy graphical interfaces would require a bigger ammount of computation time, but people get along with just 8-seg displays

author: xani
author_rank: Frequent Contributor
timestamp: February 05, 2010, 01:16:15 am
content: Quote from: alm on February 04, 2010, 10:52:00 pmFor me main argument in favour of ARM is not graphical LCD but fact that those micros have much more things inside, like AT91SAM7X256 with Ethernet, USB and several serial interfaces and it doesn't cost much more than similar AVR ( 10$ vs. 6$ for atmega128)But then, if u get analog frontend right, u can use pretty much any micro u want and AVG have advantage of large community behind it (thousands of ppl possibly hacking meter ;]Imo analog frontend should be something like i2c/SPI for adc + few lines for switching multiplexers etc. or some small cheap 8 bit micro as "controller"So someone who want "just meter" can get some atmega8 + 2x16 LCD, few buttons and encoder, but someone else can connect 8 analog "cards" to atmega128 hooked to LCD touchscreen to create "meter to end all meters"

author: desolatordan
author_rank: Regular Contributor
timestamp: February 05, 2010, 03:01:58 am
content: Quote from: _Sync_ on February 05, 2010, 12:17:34 amI agree, any of those microcontrollers would work fine. But because the analog front-end shouldn't be limited by the microcontroller, analog design can be developed parallel to microcontroller and user interface. I say whoever is most inclined to start programming with their favorite microcontroller be the deciding factor.Get started with:isolated external communication (ir, usb, wireless, ?)physical user interfacegraphical interface

author: Mastro Gippo
author_rank: Regular Contributor
timestamp: February 05, 2010, 07:13:43 am
content: Quote from: alm on February 04, 2010, 10:52:00 pm*aehm*..http://rossum.posterous.com/teeny-avr-media-thing-the-nanotouch-0

author: Unknown
author_rank: Unknown
timestamp: February 05, 2010, 08:22:26 am
content: If I want 32 Bit, I would go to the AVR32 line before ARM, but that is only due to the fact I have no experience with ARMalthough I am prepared to jump in an learn

author: Unknown
author_rank: Unknown
timestamp: February 05, 2010, 08:40:16 am
content: Quote from: Mastro Gippo on February 05, 2010, 07:13:43 amYeah, as long as you can avoid using a frame buffer it can work.It would be possible to use two different micro's for measurement and control. The HP 3478A does this: one micro connected to the ADC, and one to the buttons/display/GPIB. I don't think it would be a good idea to mix two different micro families here, since only people that know both would be able to hack it, but it's possible.I would isolate the signals as soon as possible, as opposed to isolating USB/RS232/Ethernet. Commercial meters are often rated for about 500V between input low and ground (and more between input high and ground). The less area you have to protect, the easier (i.e. connecting buttons to this potential would mean your buttons have to be rated for 500V). It's not practical to isolate the analog signals, so I'd put the isolation device right behind the ADC (SPI is easy to isolate, there are devices for I2C), or behind the front-end micro if we go that way. Relays are isolated, not sure what the isolation rating of small-signal relays is.The analog part is definitely the hard part, and doesn't depend on the digital part, so it seems a good idea to start there.Alson

author: xani
author_rank: Frequent Contributor
timestamp: February 05, 2010, 11:48:45 am
content: Quote from: GeekGirl on February 05, 2010, 08:22:26 amWell both are supported by GCC so probably biggest difference would be how to configure things like SPI/UART etc., probably some code can be even ported from avr ^^

author: _Sync_
author_rank: Contributor
timestamp: February 05, 2010, 02:35:46 pm
content: After reading a bit, I think that we might get around usingthischip for a start, it should provide satisfactory accuracy.I'm still reading into integrating ADCs, but it seems that getting reliable results will require quite some effort. I will start experimenting as soon as I get the FPGA project for school done...I'll keep you posted, if I get some progress!

author: Unknown
author_rank: Unknown
timestamp: February 05, 2010, 03:22:03 pm
content: Quote from: _Sync_ on February 05, 2010, 02:35:46 pmFrom a quick glance at the datasheet, this device doesn't seem much better than the ICL7106 used by all cheap multimeters, just 2000 counts (decimal).Quote from: _Sync_ on February 05, 2010, 02:35:46 pmBuilding a high-accuracy ADC is probably quite hard. If we have to use an off-the-shelf ADC, there are plenty available with a higher resolution. A quick parametric search at Digikey shows several 24-bit ADC's below $10 (eg. AD7192), although getting 24 bits of usable data out of them won't be easy either. Not sure what the important specs in this application are, it may well be that what required a custom circuit in the eighties can be easily solved with modern parts.Alson

author: _Sync_
author_rank: Contributor
timestamp: February 06, 2010, 02:33:58 am
content: Well the designs don't use regular ADCs because they are quite unstable and not very accurate in the low bit levels.Yep, the chip isn't that accurate, I just had a quick looks in a coding break earlier.I'll see what I can achieve with some crude design and then refine from there

author: Unknown
author_rank: Unknown
timestamp: March 01, 2010, 06:14:50 am
content: ...woooooooooooooooooooooooooooooooooooooooooooooooooooooow...what an awesome topic god saint...first of all i want to thank everybody for the information this topic is amazing...i hope you finish this project some how because i think that it is one of the most wonderful things i found in internet...and i want to build my own "eevblog community bench meter"good luck...

author: SockThief
author_rank: Contributor
timestamp: March 01, 2010, 03:38:37 pm
content: Hej everyone,been a bit busy lately, so ive not been here much, and so i appologise if this has already been posted, but its well worth a look anywayhttp://www.gadgetfactory.net/gf/project/butterflylogic/cheersSockThief

author: Unknown
author_rank: Unknown
timestamp: March 02, 2010, 11:12:48 am
content: Hi everyone,I have not forgotten this project, just with the first week of Uni and a few urgent repairs, I have been waylaid. On Friday I hope to be able to do up a block diagram, so that we can split up the project in to manageable chunksIf anyone has any ideas, or has started anything on this. speak up

author: free_electron
author_rank: Super Contributor
timestamp: March 12, 2010, 07:54:46 pm
content: Take a look at a 7129 for example. 4 1/2 digit dual slope converter.Other solution may be to brew your own. These things are very sensitive and difficult to maintain. one good one is an ADuC624. these have 24 bit a/d convertor and integrated cpu that is running in time step with the convertor( cpu sleeps while conversions is done).The advantage is that you can do autoscaling algorithm and relay ( range select) on the cpu. You spit out your measurement through the built in uart , go over 2 optocouplers into the backend processor ( ground referenced electronics)The backend processor handles user interface ( display / keyboard / usb interface / ethernet interface / gpib / whatever.the measurement board has its own transformer winding powering it. communication goes between the measurement block and the main electronics through optocouplers. That was you have galvanic isolation. Your measurement electronics must be floating !. Otherwise there is no point starting this development at all. you will have groundloops all over the place.if you want to learn how to make good input circuitry ( scalers / protection / current sense / true rms whatever ) go to agilents website and download the servicemanual for the 34401. they have fll schematics published. You won't be able to copy since there are a couple of asic's in it, but you can learn a lot from it.i see a lot of posts in this topic about cpu selection. that is all irrelevant. the hardest part is getting the analog done right. You need to come up with a list of requirements therevoltage range for DC and AC ( flashover protection )current range for AC and DC ( overcurrent protection. current sense resistor and gainstage ...resistance range .. ( 4 wire ? ) protection against users that want to measure the internal resistance of their wall socket while it is live ...Diode check ( use current source with voltage scaling so you can test zener diodes )continuity checkFrequency count ?capacitor / coil test ? ESr metering ?I myself don't care about being able to measure 1 kilovolt and 10 ampere. give me something that is accurate in the 0 to 5 volt range with 3 useful digits after the comma.current wise i'd like to see microamps to 1 amp range..and then there is another biiiiiiig question. How do you calibrate this thing ?The measurement logic should NOT use floating point anywhere. everything should be scaled integer math, preferrably even bcd encoded.you can solve some of the problems by selecting the correct reference for tha a/d . analog devices has the REF19x family. there are reference diodes that produce exactly 2.048 and 4.096 volt. ideal to hook up to a/d convertors since they prodice directly binary weighted scales.feed that with a stable suppy from a current source (lm319 for example. that thing has an oven on board ) and you are now very accurate. You can self calibrate the inl dnl of the on board a/d and compensate with some smart software.for current sensig you will need a kelvin contact setup with a gainstage. susumu makes great kelvin resistor in the 20 milliohm to 50 milliohm range with 0.01% accuracy. for half a dollar you have one.sense the drop over it using something like an AD8220 instrumentation amp and you can get somewhere..These are the first things to consider. the instrument stands or falls around the aquisition section. get that one right and the rest is smooth sailing.

author: dds
author_rank: Contributor
timestamp: March 22, 2010, 07:12:49 pm
content: Hi GeekGirl, there is already a block diagram at the TI site:http://focus.ti.com/graphics/blockdiagram/blockdiagram_images/6279.gif(for handheld DMM)http://focus.ti.com/docs/solution/folders/print/591.htmlhttp://focus.ti.com/docs/solution/folders/print/593.html(bench DMM)I don't know if you have already seen those docs, if yes - sorry

author: _Sync_
author_rank: Contributor
timestamp: March 31, 2010, 11:54:40 pm
content: Now that my FPGA project for school is over (well unfinished but that's another story) I am able to more on this project.From what it looks like a dual-slope ADC is the standard used in common multimeters. I can understand that, because it cancels possible errors through integration. The issue with those ADCs is that you need very good parts in order to get high resolution and accuracy.I found that todays common ADCs e.g. delta-sigma ones (e.g. LTC2410) should be able to produce a acceptable performance over a period of time.The LTC2410 in particular is a 24 bit delta-sigma ADC (with even five more bits after the LSB!) with SPI interfacing and good accuracy. Everything is contained in a SSOP-16 package, which is well, quite small but it should be possible to use.After I got my hands on this guy I'll see what I can do on the input side.TrueRMS should also be possible with the help of the AD637 that seems to be widespread in this application.AD637 DatasheetLTC2410 Datasheet

author: logictom
author_rank: Unknown
timestamp: April 13, 2010, 11:38:31 pm
content: Read this thread couple of days ago, any news on the specs being written up? Interested to see where this goes

author: gbowne1
author_rank: Contributor
timestamp: May 17, 2010, 06:31:51 am
content: I love the bench meter design, but you could optionally add a remote panel in handheld format or make the remote panel moutable.Make sure you have a good input protection as you don't want to have a bench meter explode on ya either. Dave, your video blogs on that were 'spot on'.

author: Bloch
author_rank: Unknown
timestamp: December 19, 2010, 06:03:57 am
content: Quote from: EEVblog on January 30, 2010, 12:20:36 pmI like the hammond 1455 series. But I dont think they can "stack" or have a option for a foot.So that about bopla.de the Ultramas series have a folding foot set=21899]http://www.bopla.de/index.php?id=228&L=0&tx_commerce_pi1=21899And Farnell have them.

author: Psi
author_rank: Super Contributor
timestamp: December 19, 2010, 07:34:45 am
content: Its probably been said before, but i dont have time to read 8 pages to cheakIt would be cool to have duel,tri or even quad input. Being able to plug in 2,3, or 4 sets of probes (isolated from each other) and measure multiple things at once.Not only can you then do 4 wire resistance measurement like in the recent blog but you can program the mcu to do lots of other interesting things too like...* measure volts and current and the meter displays watts, as well as all the other combinations of V= IR and P = VI* measure temperature and current and the meter displays the relationship* measure two voltages and two currents and the meter displays the input power/output power and efficiency of a power supplyetc..

author: mindspan
author_rank: Newbie
timestamp: December 20, 2010, 06:40:38 pm
content: First off, let me say I ran across this forum and site while looking to see what others were doing in the way of building a bench DMM, and I am bookmarking it as a new interesting source.I end up doing a lot of traveling for work and have been wanting to put together a combined set of test instruments in a single bench package for when I travel. One of the key pieces will be a DMM since I hate having to leave my HP 3457A behind when I travel (it has actually come with me around the world at least once). Anyway, i figured I'd share where some of my thought processes on this type of project have gone.1. Case- I agree with many on here that have discussed picking a form factor and building around it. I find this is key to not later having to try and stuff things in badly or ending up with huge cases. The simple act of defining a board or panel outline with constraints placed by the enclosure is to me very helpful. As to case manufacturers I have used most that have been listed before and I would add one more. For handhelds (although bench is definitely my preference I build a lot of hand held prototypes) I recommend Box Enclosures. My preference for them is they are one of the few that have rubber boots for most of their handhelds.2. Design style - normally I try to make things as modular as possible, especially on prototype or low volume things. I actually was just looking at a spectrum analyser design that takes this to an interesting levelhttp://www.scottyspectrumanalyzer.com/slim.htmlis a page on their modular approach; essentially small modular boards with mounting solder pads on the edges that can be tacked to a large pcb with cutouts for a grid of the smaller pieces.3. Included pieces - Personally my goals is to include a lot of different pieces of test equipment into on travel package, so not really applicable to the goals you have here, however I would suggest maybe adding one thing that for me is a big part of the design. I plan on adding a digitally controlled DC power supply since a supply is the second most used piece of test equipment on my bench after the DMM (maybe first). I was looking at doing something similar tohttp://www.tuxgraphics.org/electronics/200707/bench-power-supply-unit.shtmlbut using whatever micro I settle on for the DMM and other functions. For my work the biggest upside to this is being able to see input voltage, current, and power all at once, and I will add logging since I build a lot of wireless battery powered items and need to see average power usage logged over various power states (sleep, transmitting, etc.)4. MCU - For the DMM section I have narrowed my choices down to 3 possibilities. The first two are basic - ADUC845 or similar from analog (similar to the ADUC7060 mentioned before but 8052 based), one of the new PSoC's based on 8052 from cypress. Both of these offer precision ADC on chip with PGA's and MUX's as well as plenty of DIOs for controlling input, range and measurement type switching. The larger PSoC's also offer various filters and opamps on board, USB, and lots of flexibility for pinout and pin function (nice if you want to just break out a block of pins to cover various functions dependent on code). Partially driving these choices is that I have dev kits for both, and in the case of the aduc I have considered just integrating the dev kit board into the meter and saving a lot of design on the analog layouts. PSoC also has a new high precision analog dev kit that would make a good starting point for the meter.My third possibility is something interesting if you are looking for very high precision. TI has a 32bit adc chip that they designed for very high precision measurements (ADS1282) while I personally would not even attempt to integrate this chip due to the LVDS signalling and need for a DSP to read it, they have a reasonably priced dev kit (http://focus.ti.com/lit/ug/sbau144b/sbau144b.pdf) that includes a USB interface and sample program to do voltage measurements ($170 from mouser, not CHEAP, but considering the cost of 6+ digit bench meters a bargain compared to commercial meters). This board would be an interesting basis for a 6+ digit meter that has all the analog backend and computer interfacing done and just needs the front end range switching and whatnot developed. I am still strongly considering this as I do a lot of very low level measurements from sensors.Anyway, I will be following this thread with interest as I think having more open source test equipment designs for hobby/small business electronics is a great idea. Computing power and precision measurement IC's are to a point now where there is not much test gear that can't be built on the cheap.-Aaron

author: Zad
author_rank: Super Contributor
timestamp: December 21, 2010, 02:15:39 am
content: No onboard ADC is 'precision' or 'low noise' no matter how many bits or nV of noise they claim. It just isn't possible. You might like to compare the data sheets for the TI 32-bit ADC to their 24-bit parts. The 32-bit parts are several bits worse than the best 24-bit ADCs.

author: Bloch
author_rank: Unknown
timestamp: December 21, 2010, 07:05:23 am
content: An onboard ADC will also lock the project to a single cpu.The more modular the better.Front endadccpuIO (to PC)Display

author: Neb
author_rank: Newbie
timestamp: December 22, 2010, 03:00:16 am
content: I don't see a need for a 31-bit adc since they are so expensive. I think a 24-bit adc would be more than enough and the saved money can be spent on better input circuitry. The real culprit will be getting the noise floor down and keeping it calibrated. Ideally it would not need calibration, the references should be accurate and not drift. If i try to calibrate it with a store bought DMM with 1% accuracy, i can't expect the device to produce better than 1% accuracy and the extra counts/adc bits are wasted.

author: firewalker
author_rank: Super Contributor
timestamp: December 27, 2010, 06:53:07 pm
content: Is this project dead?

author: Bored@Work
author_rank: Super Contributor
timestamp: December 27, 2010, 07:24:07 pm
content: Quote from: firewalker on December 27, 2010, 06:53:07 pmIt was dead right from the beginning. Becausea) It is difficult. Despite the wet dreams of some, a good meter can't be done with just cobbing together a cheap ADC with a cheap MCU.b) Because of a) it requires a good amount of work.c) Most people discussing here were after getting it without any own effort, in the hope all they had to do was to add to the wishlist. This behavior is not compatible with b).d) Most people discussing were just after getting something cheap. This won't happen. One can't beat the price of cheap multimeters, and one can't bet the price of expensive multimeters. The cheap ones are, well, just too cheap. The expensive ones require expensive parts and expensive equipment, e.g. to adjust them.e) There was and is no forceful project leader. Someone skilled enough and with enough time on his or her hands to push the project, to make decisions, to attract contributors, to guide contributors towards the common goal (heck, a common goal wasn't even defined), and keep contributors working for the project, even if their opinions are overruled.f) No one is or was willing to fund the effort. See d) and e).Realistically, it never had a chance of taking off.If you want a community project, fix a) ... f), and probably some more issues I forgot to mention. If you want an good chance of having a DIY meter, forget about the community project, do it completely on your own, and once done brag about it. The leechers at HackADay will welcome you with open arms and make you their hero (for a day).

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 27, 2010, 10:26:19 pm
content: It might not be worth the effort to build a high accuracy meter or an extra cheap meter, but there are some niche applications where it makes sense. Such as a meter that automatically calculates average and peak power. Or a datalogger that records voltages to a SD card at a sample rate of a few Hz or kHz. In any case, we'll make the assumption that the accuracy needed is comparable to or less than that of the under $20 meters and that the builder already owns a meter (and calibration reference) much more accurate than the one being built.One extremely high accuracy measurement that is relatively easy to make is time/frequency. Put a GPS in your homemade frequency counter and you'll very likely have more accuracy than you'll ever need.

author: Unknown
author_rank: Unknown
timestamp: December 27, 2010, 10:38:33 pm
content: I'm sort of interested in the idea of this, so, realistically, what is required to make a meter? I imagine that conceptually it is a pretty straightforward idea. A voltage reference and an ADC. Compare the incoming voltage with the reference. Use a DSP to analyze the input and do whatever you want with it, whether that's measuring the average of the input, p-p voltage, Fourier analysis, etc. Feed it to an mcu/mpu and display it on a nice little screen. Of course that's just voltage. I would think current could be measured in a similar manner. Really, as far as quality goes, what would be required to make it as high-quality as possible? I would think basically just an extremely accurate and precise voltage reference, high-quality ADC, and measures to minimize input noise. Is there anything (probably a lot) that I'm missing? Because it really sounds fairly simple to me. Simple idea, hard to pull off, I would imagine.

author: Bored@Work
author_rank: Super Contributor
timestamp: December 27, 2010, 10:49:49 pm
content: Quote from: NiHaoMike on December 27, 2010, 10:26:19 pmSo, you are volunteering to fix issues a) to f) above, or ...Quote... do you just want to add to the wish list?BTW, one can get low-quality datalogging multimeters for 120 € onwards (new), e.g.http://www.unisource21.com/tDM620.html(many people allegedly have problems with it, but they will have with a DIY meter, too). Can you build one for that price?And automatic calculation of averages and peak power can be done with any piece of rubbish that has a PC interface, plus some PC software. I never checked what the cheapest meter with a PC interface costs. I know a VA-18B can be had for 40 € (new).QuoteThat excludes all those who were after a high-precision meter for next to nothing.Quote1) What has that got to do with a bench multimeter?2) The guys on timenuts would disagree with "GPS in your homemade frequency counter and you'll very likely have more accuracy than you'll ever need".

author: Bored@Work
author_rank: Super Contributor
timestamp: December 27, 2010, 10:55:35 pm
content: Quote from: smindinvern on December 27, 2010, 10:38:33 pmThen do it. Don't talk, do it.

author: Unknown
author_rank: Unknown
timestamp: December 27, 2010, 11:01:29 pm
content: Quote from: BoredAtWork on December 27, 2010, 10:55:35 pmCould you be a little bit more helpful? I'm interested in learning as much as I can. This forum is a treasure trove of knowledge. That's why I asked. My education certainly isn't your responsibility, but any help you would like to offer would be appreciated.

author: Bored@Work
author_rank: Super Contributor
timestamp: December 27, 2010, 11:36:05 pm
content: Quote from: smindinvern on December 27, 2010, 11:01:29 pmWhy? I owe you nothing. Let me tell you a little story. It is the story of why I don't have a ham license.When I was a boy ((C) Dave Jones) I was at some point in time very interested in amateur radio. So I started to study for a ham license. I memorized all the abbreviations, operating procedures and stuff. I even started to learn morse code, taking a course. This was the time when you only got a serious license if you knew morse code. I was about to become better, almost to the point that I could do morse.And then, via the morse code course, I started to make contact with hams in the local amateur radio club. These OMs (see, I can still do the ham lingo) were all the same. They were always talking about the great things they plan to do, and what they would build and how great hams are, how special, because they build their own stuff. Yes, they do. Licensed by the government, no less.But when visiting their shacks it was always the same. There was just commercial equipment on their benches, and somewhere in a corner was a half-finished project. Often literally covered in cobwebs. They all had their unfinished alibi project, but nothing else. They just talked, often about things they didn't really understand, because their technical ham training was in fact poor.It was deeply disappointing. And I dropped the morse code course and stopped studying for a license, because I never wanted to be like them. Only talk, no do. Many years later, at some point in my EE career, I was operating RF equipment every ham would go apeshit about. Of course no ham license needed, and it gave me deep pleasure to remember these poor "we are so great, we are hams" guys with their cobweb projects.And since the days of my aborted attempt to get a ham license I despise people who always talk, but don't do. Who wank about how great some project could be - if just others would do the work. They are time wasters.Unfortunately, this type of people have become more ubiquitous in recent years. Scratching their private parts, grunting "uh, cool, eh, eh, eh", feeling entitled, and shouting "awesome" is all they do. I have seen many such "projects" like this one. Someone shoutsWouldn't it be great, if ...?, and the wanking croud respondsCool, you are awesome dude! You are the man! And it must have .... Of course non of them lifts a finger to actually do something.QuoteYou just got an education. Don't talk, do, especially if you thinkQuote

author: Unknown
author_rank: Unknown
timestamp: December 28, 2010, 12:59:15 am
content: Quote from: BoredAtWorkAm I detecting some animosity here? I certainly hope not; I haven't really done anything to deserve that.Quote from: BoredAtWorkThat doesn't really mean much coming from someone who just did a heck of a lot of talking, and a questionable amount of doing.To be honest, I probably never will build a bench meter; I have enough to keep me busy for quite a while, and not enough money to go spending on projects whenever I want. But it never hurts to procure another bit of knowledge, especially not about something which you'll probably use at some point in the future.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 28, 2010, 05:26:14 am
content: Quote from: BoredAtWork on December 27, 2010, 10:49:49 pmThat's true of steady DC, but not for AC or DC with significant AC ripple. For AC, you'll need to sample both the voltage and the current, then multiply them together and take the average. A normal multimeter would also sample too slowly to catch a brief inrush. (And if your supply voltage changes over the course of the measurements, you'll need a second meter to be able to read both voltage and current. It still won't work for AC measurements since you need instantaneous voltages and currents, not RMS.)

author: firewalker
author_rank: Super Contributor
timestamp: December 28, 2010, 08:20:50 pm
content: Maybe the project should divert to something more doable.E.g. Community Bench PSU &&, || a Community Bench Function Generator.

author: hans
author_rank: Super Contributor
timestamp: December 30, 2010, 11:08:52 pm
content: Quote from: smindinvern on December 27, 2010, 10:38:33 pmI've seen people talking about 24 or even crazy 32-bit devices (with an ENOB of 21.3 max). If you're designing such devices in practice, it's not the case of slamming some parts together with the highest specs, it's nicer if you can get the maximum specification that's still reliable from every part in your circuit.A 24-bit is really not necessary. If you want to design a 20,000 count multimeter it basically means the A/D converter needs a effective resolution of 20k steps. That's a resolution of about 14.288 bits. There are 16-bit A/D converters on the market that can get that resolution easily, even in bi-polar form to make things 'easier'. Remember these circuits are extremely low noise (anything from 14-bits is) which requires very well thought circuit design and prototyping.I also hear people talking about power measurement. I think it's a community challenge enough, as it is proven, to even choose a single set of measurements to be taken. Adding power to that is not sane. Furthermore, it would push the budget far because you will need to select a multi-channel A/D converter. On top of that, good power measurements are done by simultaneously sampling both channels (current and voltage readings) instead of sequential, and those parts are more expensive as well.What I think first is needed for a project always is a budget. I never saw people talking about prices, except it might become too expensive. Let's say we make it reasonable of 200$. I can tell you that is going to be really tight for an accurate meter, if you look up the specs below. MCU, A/D, 'basic parts', mechanical (PCB, casing, buttons) will cost >$125 easily for a small project. Then again, I guess a case wouldn't be required if it's not going to be markted product. People might be able to built it into their own casings.VDC: 20000 count (V), 2000 count (mV) in high ranges 0.25%VAC: 2000 count, 2%AAC: 2000 count, 2%ADC: 2000 count, 0.5%Ohms: 2000 count, 0.5%(Cap: 100 count, 2%)Diode test: 1mA test , up to 2V, 2000 countFrequency: 100kHz with a fast proccesor should be possible...Adjustable current sounds fun and useful, but I have some arguments in not incorpating that:1) When do you actually need to measure accurately the voltage of a LED?2) If you do, however, you can built a 'Diode tester' more easily. There are dozen schematics on the internet that do just that, with adjustable current (tenths of mA to several mA's) and respectable resolution.3) It sounds kinda cheap, but high currents drains battery.In my mind, the easiest solution on making a multimeter is to have a MCU with an external ADC linked together (SPI/Parallel). On the A/D is , ofcourse, some amplifying, protection, detection and range selection circuits. For a MCU it will has to be a 16 or 32-bit device for sure. MSP430 sounds reasonable because it's famous for mobile device operation, but microchip has some interesting controllers as well in their dsPIC, PIC24 and PIC32 ranges. I think Microchip, being a hobbyist community project, is more accessible. But the exact selection is not necessary now, as I will explain.Communication to outside world could be done with USB (FTDI chip to make a virtual COM port). Easy, always works. Add a digital isolator and it's a bit safer, but I still wouldn't want to measure the mains whilst having it connected to PC. Optical is best.Just to note something, it's funny that people are discussing ARMs, connection methods, but I haven't seen much attention to the analog part at all.How do you design overload protections? Surges, be able to handle high voltages on every input setting, etc.Determine required accuracy of the built electronics instead of gambling for high-spec-unaffordable-parts?Create ultra low noise pre amplifying circuits?Set up a reliable form of ranging that doesn't blow up components (i.e. 230V~ on mVdc)?Calibration, reliabality, accuracy, bandwith, noise levels, power supplies, bipolar measurements, diode/cap/resistance measurements..?etc.To me, the digital part of a multimeter is just a way of common sense on what microcontroller and A/D converter fits the bill the most. But you do this after you investigated what you want to capture from the analog frontend and at what degree. These kind of circuits has the A/D and MCU coupled tight together. If a project can get away with a 10-bit resolution, it might be fine to use onboard A/Ds. If a high speed measurements are in order, having a high speed A/D connected to a 16-bit wide PMP on a PIC32 might be necessary. The A/D converter is selected on the required speed, SNR or SINAD calculated from the desired ranges and resolutions, margins and stuff like that.I think we should discuss on getting those figures and schematic(!) idea's on table first, before adding anything else to the discussion on the 'digital section'. In my opinion a high-count multimeter is more about the analog circuitry, because that needs to be done well. A digital circuit is more like connecting the pins correctly when the right parts are chosen for the job.

author: 001
author_rank: Super Contributor
timestamp: December 05, 2018, 07:08:22 am
content: Quote from: hans on December 30, 2010, 11:08:52 pmYea! I see input circuits and signal path in 1980th gear are kind of artThe endless tell about diy bench meter is silly since everybody who REALLY need it know how it cost