Ultimate Bench meter project - Page 1
Forum section: electronics / projects

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 07, 2010, 10:37:14 pm
content: Not quite sure where to post this, but this thread seams as good as any.Having read Daves archive of his test equipment he built when he was a lad and made a very useful probe from a design by Mondo Technology the superprobehttp://mondo-technology.com/super.htmlI got to thinking what could be done as a hobbyist to make the ultimate bench meter/probe.What would you like to see it be able to do?Logic analyzer, dso, fft, etc.Bandwidth would be a consideration but just how far could a pic or similar be pushed and what features could be shoehorned in?Cost should be a prime consideration too and manufacturability for a hobbyist.So my Idea would be to create a thread for people to kick ideas around with a view building a working prototype, all software used should be free, ie eagle, design spark etc and all files open source, may all come to nothing but I feel it might be a good idea.Then again they do say that a camel is a racehorse designed by a committee

author: tyblu
author_rank: Frequent Contributor
timestamp: December 07, 2010, 11:27:00 pm
content: You mean like this?http://members.cox.net/berniekm/super.html

author: armandas
author_rank: Frequent Contributor
timestamp: December 07, 2010, 11:35:10 pm
content: https://www.eevblog.com/forum/index.php?topic=173.0Too many ideas, too little action. IMO, unless a BDFL steps up, there is no way such a project can go anywhere. The design could be done by the community, but someone needs to:Organise everything (transform chaos into order)Make final decisions if there is a disagreement in the community???Someone with authority would make things easier, since people would be less likely to revolt.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 08, 2010, 12:44:39 am
content: Quote from: armandas on December 07, 2010, 11:35:10 pmAgreed. All I have is a woolly idea at the moment. This should be viewed as a request for comments.I have NO experience of design, I'm a service Tech and have to repair stuff.This is (sometimes) a bit of a black art, But I build things - some work some don't.None are professional products, in truth lashups at best.However I think the IDEA has merit and could be a great tutorial of a design process.Needs a lot of thought and organization but that is also part of the design cycle.As for a BDFL you're right.I would expect a small design team to be formed and that they would report every step of the design process BUT WOULD NOT BE challenged on any design decisions outside of the design team, we would be 'viewers' who could observe the process but NOT comment.Once the final design requirement was hammered out it would be up to the design team to complete the project and publish the final files for all.As I said earlier it may not be feasible but that is no reason not to discuss it

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 08, 2010, 01:27:24 am
content: Quote from: tyblu on December 07, 2010, 11:27:00 pmYep! That is the link I was pointing to

author: joelby
author_rank: Frequent Contributor
timestamp: December 09, 2010, 01:23:42 pm
content: There was some discussion about this a while back:https://www.eevblog.com/forum/index.php?topic=173.0

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 09, 2010, 02:49:09 pm
content: Quote from: armandas on December 07, 2010, 11:35:10 pmagreed, maybe because the busy'ness. so i'm thinking if we want to do something seriously, we may start googling the net for the keyword, there are alot of useful info out there, some links has been provided above (mainly in non-forum style, just a typed plain fix webpage report, congrats to them for their effort). and then if we got stucked we may start "threading" here and make the progress bit by bit until we got a fully working unit... and then possibly the OP can sell that to the forum members at a half pricedps: i'm thinking i'm the one who talked alot eeey? maybe its time for lurk more talk less, just for me.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 09, 2010, 03:04:26 pm
content: Quote from: FreeThinker on December 07, 2010, 10:37:14 pmwhere is the description for working principle? none?

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 09, 2010, 04:24:20 pm
content: Quote from: joelby on December 09, 2010, 01:23:42 pmExactly what I had in mind!Seems to have come to a halt, but there was a lot of interest at the time.I think Dave has a few open source projects in the pipe line, maybe he could draw together a (possibly closed ) group together to draw up some firm ideas so that the next month is not spent on arguing about pic, arm, arduino etc.Once a basic spec was drawn up a poll could gauge interest before any major work was undertaken.I for one like the modular idea and Daves spechttps://www.eevblog.com/forum/index.php?topic=173.msg1699#msg1699seems spot on.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 09, 2010, 04:28:17 pm
content: Quote from: shafri on December 09, 2010, 03:04:26 pmHe never intended it to be a tutorial only an exercise to demonstrate the principle.None the less an Excellent piece of kit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 09, 2010, 04:41:07 pm
content: Quote from: FreeThinker on December 09, 2010, 04:28:17 pmdemo the principle? where? i only see a hardware circuit, places to buy parts, and hex program (never click that either). o well, at least he provided the real implementation, thank him!... the theory and algorithm are left for us as a homework. saved the web into my HD for later reference. interestingly he never use an op-amp there, just bunch of resistors and a v-reg. osc is pretty much standard there. could use int osc i think.

author: saturation
author_rank: Super Contributor
timestamp: December 09, 2010, 08:20:34 pm
content: In my mind, an ultimate bench meter must be extremely accurate and stable measuring voltage, current and resistance; that would mean beat or meet the specifications of the Agilent 3458a meter or its competition, entered into the HP catalog in 1989; it defines ultimate, there is nothing above it in terms of measuring capacity. If you can do this fairly cheaper than $10,000, that would be marvelous. In voltage, meter have not gone beyond 8.5 digits, or about 1nV resolution. The US standard volt is accurate to this level using a Josephson junction method.If you're looking at ultimate in terms of the biggest Swiss-army knife type DMM, its hard to pin down because a reason many different devices exists in electrical measurement is that many in electronics work in a niche, so one size doesn't fit all. Makers define types of DMM based on what likely the user works on: electronics versus electrical, industrial versus automotive etc., and what functions can be added to speed up the workers time by adding such functions into one device.As hobbyists focus can be in so many areas, it'll be hard to pin down, but as more devices are crammed into a space, the device also gets bigger and the quality of the device's measuring capacity may likely too, just like with big swiss army knives versus the simpler ones. My 2c.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 11, 2010, 09:43:38 pm
content: Quote from: saturation on December 09, 2010, 08:20:34 pmYep I was thinking more along the lines of a combined meter rather than ultimate performance.With todays mcu's you can get a whole raft of functionality in a few chips, the question is what functionality you want at what performance..... which is the question I was asking what spec features would (could) be built into a reasonable cost universal bench meter/lab?PS Where could i get the knife from?

author: saturation
author_rank: Super Contributor
timestamp: December 12, 2010, 12:29:51 am
content: For the knife, see Swiss Army:http://www.swissknifeshop.com/shop/swiss-army/executive-swiss-army-knives/swiss-army-giant-by-wengerIts called 'the giant', almost $1000!

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 12, 2010, 06:23:23 pm
content: Quote from: saturation on December 12, 2010, 12:29:51 amAhh! Just to late.Sent my list to santa yesterday, maybe next year.

author: Balaur
author_rank: Unknown
timestamp: December 12, 2010, 06:44:19 pm
content: That knife is as useful in real life as the ultimate bench is in ... well, in real life too.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: December 12, 2010, 07:10:43 pm
content: Quote from: Balaur on December 12, 2010, 06:44:19 pmWell as we do not have a spec for the ultimate bench meter this is a hard one to answer but with a little thought it could be a little more practical.Perhaps it would use some of Daves lcds to good effect

author: Unknown
author_rank: Unknown
timestamp: December 12, 2010, 08:00:29 pm
content: The analog part of any DIY design is probably not even close to a low-mid-end model like the Agilent 34401A: 6.5digits, 30ppm or so, 1kS/s (not all at the same time). Getting even close to them will probably be really expensive, even just an LTZ1000 reference will be something like $40. To keep with the knife analogy, your knife will probably be less sharp and edge retention will be worse.You may be able to compete by offering bells and whistles, some ideas:Don't try to match analog performance of current commercial models, something like 4.5 digits would be plenty for most work. This is similar to what high-end handhelds can do, so less will be pointless, and better is probably hard (but if you think you can pull off 6.5 digits 30ppm, I'm not going to stop you).I like fast updates, especially when doing things like adjusting trimmers.Option for multiple channels, just plugging in multiple PCB's (with front-end and ADC) will require little effort.Put something like an embedded Linux OS on it, with large, bright gLCD and nice controls (not sure about touch screens, they can be annoying). Allow math and graphing on the DMM. Sure, you can always do this on your computer, but it's sometimes convenient to have instant feedback, for example you could show the efficiency of a power supply by measuring input and output I/V. You could even calculate real (as opposed to apparent) power if the sample rate is fast enough.You need to pay some attention to safety. Will you design it to IEC61010 requirements? How do you verify this? Do you expect it to be able to measure mains?Significant competition for hobbyists would be used bench meters from 20+ years ago for free-$400 or so. They're usually worse at communication (no chance of USB host or ethernet, which are almost free with any contemporary micro), but likely to be much better at the nitty gritty analog stuff.My suggestion would be to design a front-end / ADC that can do say (+/-)100mV-1000V full-scale at 4.5 digits (0.025% accuracy or so) first, I think this is where the previous project stranded. Everything else will be useless without a good front-end, and will be much easier (hooking up an ADC to a micro and displaying results has been done thousands of times).

author: saturation
author_rank: Super Contributor
timestamp: December 12, 2010, 10:01:14 pm
content: Here are some articles about DMM which shows you how they evolved and ideas for functions for them to do:http://www.evaluationengineering.com/index.php/solutions/instrumentation/dmm-is-an-understatement.htmlhttp://www.evaluationengineering.com/index.php/solutions/instrumentation/powerful-and-portable-dmms-for-2008.htmlhttp://www.evaluationengineering.com/index.php/solutions/instrumentation/6-digits-is-quite-a-handful.htmlhttp://www.evaluationengineering.com/index.php/solutions/instrumentation/reading-the-fine-print-in-a-dmm-specification.htmlhttp://www.evaluationengineering.com/index.php/solutions/instrumentation/how-much-meter-is-enough.html