Electronics > Projects, Designs, and Technical Stuff
Community Bench Meter
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GeekGirl:
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 debate :)

Battery / Mains powered.
Back light LCD Graphics ???
5000 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 OHMS
Lightning fast continuity range ;)
RMS AC
Graphing function
Data Logging

I would like a retro push button range switch ;)

What 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 ?


joelby:
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.
GeekGirl:
Yeah, I have seen the Jaycar Kit, But the specifications are not shown (maybe they are that bad ;)

I 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).

SockThief:
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!
Andrew:
German computer magazin c't did a whole series about building a modular DIY measurement and control lab http://www.heise.de/ct/projekte/machmit/ctlab/wiki

It 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 at http://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 at http://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.

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