Open Source Multimeter

[David Hess]

I wish he would comment in the text on why he used the base collector junction in the picture, the text only deals with the use of the base emitter junction.

He mentions the differences between BE and BC junctions when used in this type of application but I do not know why he used the BC junction here either.  The breakdown voltage will be higher but that does not matter and it will have slower recovery which seems like it would be a disadvantage.

[Marco]

He mentions the differences between BE and BC junctions when used in this type of application but I do not know why he used the BC junction here either.  The breakdown voltage will be higher but that does not matter and it will have slower recovery which seems like it would be a disadvantage.

I couldn't see those pages of the book ... but he does talk a bit more about it in this article EDN was nice enough to dig from their archives :

http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques

[mrflibble]

I couldn't see those pages of the book ... but he does talk a bit more about it in this article EDN was nice enough to dig from their archives :

http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques

Thanks, that indeed had interesting tidbits in it.  Pity the links to the (presumably) better images are dead, the EDN inlined jpg's were not super duper. But still readable enough.

[David Hess]

Thanks, that indeed had interesting tidbits in it.  Pity the links to the (presumably) better images are dead, the EDN inlined jpg's were not super duper. But still readable enough.

That is common with EDN and related online trade magazines.  I expect it more often than not.

Their comment system is even less reliable than the EEVBlog forum.

[mrflibble]

That is common with EDN and related online trade magazines.  I expect it more often than not.

And the sad part is that the machine on which those jpg's are still exists. They just decided (or probably didn't even decide anything) to not maintain those linked images. From which you can usually extrapolate amusing characteristics about the CMS & backup solutions they use.

[EEVblog]

Their comment system is even less reliable than the EEVBlog forum.

The EEVblog forum is not reliable? 
Haven't lost a single attachment or post since it's been running...

[Marco]

Long term reliable, with more than a few service interruptions though

[Bloch]

I think he means links to external jpg/pdf.


Sometime the https://archive.org/web/ can help getting old stuff.


Quote from: EEVblog on Today at 01:11:50 AM

>Quote from: David Hess on Yesterday at 12:58:50 PM

Their comment system is even less reliable than the EEVBlog forum.

The EEVblog forum is not reliable? 
Haven't lost a single attachment or post since it's been running...

[mrflibble]

Sometime the https://archive.org/web/ can help getting old stuff.

Agreed. Unfortunately linked images is not the wayback machine's strongest suit. It's rather hit & miss ... mostly miss. Case in point, the hi-res images from that EDN article where not to be found that way.

[chickenHeadKnob]

The first time I glanced at that EDN article I gave up too soon. After reading mr.Flibble's recommendation  I went back and downloaded and magnified. Well well worth it! But one thing disturbed me, In the section marked " So you say you need a diode" Pease writes:

"For extremely low leakage .. consider using collector-base junctions. If, for instance, you need leakage lower than 100pA,  then it's often much less costly to test transistors with a 98% yield to this spec ....

Some low leakage transistors to consider are the 2N930, 2N3707 and 2N4250. However most other small signal transistors have an excellent yield to a leakage spec of 30 pA max at 5V, even though the spec sheet guarantees 10nA."

edited for brevity and all transcription errors mine.

Now if someone dropped a bag of transistors in my lap I would have no clue as to how to characterize their leakage. Do you need a  pico-Ammeter? or can it be done some sneaky cheap way with a bridge and some op amps?

[SeanB]

Simple, just use your 10M input impedance DVM and put the transistor in series with the positive lead, and apply a voltage that is equal to Vceo of the transistor to the whole lot. Then simply bin according to the measured voltage, the lower the voltage the lower the leakage.

[David Hess]

Their comment system is even less reliable than the EEVBlog forum.

The EEVblog forum is not reliable? 
Haven't lost a single attachment or post since it's been running...

Every couple weeks I have to erase the EEVblog cookies (there is a forum thread discussing this remedy) and I have lost posts often enough that I sometimes remember to save long ones locally before pressing post just in case.  Usually Firefox allows recovery of the post text but it only takes losing it once.  Preview and post occasionally return an error requiring the thread to be reloaded.

Given the choice, I prefer email based forums because they are both faster and more reliable.

Update:  It was unable to access the forum for hours not long after I posted this.  Instead I got this:

Lost connection to MySQL server during query
Connection Problems
Sorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.


Connection Problems
Sorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.


Error establishing a database connection

[David Hess]

Now if someone dropped a bag of transistors in my lap I would have no clue as to how to characterize their leakage. Do you need a  pico-Ammeter? or can it be done some sneaky cheap way with a bridge and some op amps?

Simple, just use your 10M input impedance DVM and put the transistor in series with the positive lead, and apply a voltage that is equal to Vceo of the transistor to the whole lot. Then simply bin according to the measured voltage, the lower the voltage the lower the leakage.

This yields 10 microvolts per picoamp which is good enough for most applications but many transistors will have a leakage low enough to require either an electrometer or some type of charge measurement to be made with something like an integrator.

You also have to be careful because higher resolution voltmeters usually lack a 10 MOhm shunt on their lower voltage ranges so the shunt has to be added externally.

The integration method is preferred at the highest sensitivities because it has lower noise.  It can be low enough to pick up cosmic rays if the integration capacitor has too great a volume.

[ToddBMarshall]

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

[codeboy2k]

Todd, check this thread out. It's not a multimeter, but it has features like what you describe, but not designed for in-circuit testing.

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/

Todd's post brought this thread to life again, and reading back in the thread I realized I actually have the 1983 article referenced here from EDN that some people could not find. I squirrelled it away back in 2011 when the image links still worked and I made a PDF from the images in the article.

So here it is.

 (There was always an error when attaching files to the post today, so I put it on my dropbox)

https://www.dropbox.com/s/nttegd9zwfxh5j3/1983-11-10_pease_clamping_EDN.pdf

Cheers!

[mrflibble]

(There was always an error when attaching files to the post today, so I put it on my dropbox)

https://www.dropbox.com/s/nttegd9zwfxh5j3/1983-11-10_pease_clamping_EDN.pdf

Cheers!

Nice, thanks! Definitely better than the low res images.

[ToddBMarshall]

Codeboy2k:

Todd, check this thread out. It's not a multimeter, but it has features like what you describe, but not designed for in-circuit testing.

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/

I have one. Use it all the time. $17 kit. Amazing!
http://www.amazon.com/Capacitance-Multi-meter-Capacitor-Inductance-Transistor/dp/B00OFQGZH2

P.S. I'm new here. Does this forum app have a threaded message option?

[zapta]

P.S. I'm new here. Does this forum app have a threaded message option?

Tapatalk works we with eevblog forums.

[MAntunes]

Hello!
I'm considering building a multimeter as my first serious project.
Something simple at first, but I think it is had a good analog/digital mix. After searching a bit I didn't find many information, do you know about some classes, books, articles that could help me?
Best regards!

[MAntunes]

Hello!
I'm considering building a multimeter as my first serious project.
Something simple at first, as I think it is had a good analog/digital mix. After searching a bit I didn't find many information, do you know about some classes, books, articles that could help me?
Best regards!

[jaromir]

Oh well, 29 pages and yet not that much of finished projects.

Just for lulz and for the sake of cramming a few parts to 1x1 inch PCB I created this tiny "multimeter" - it was not intended as serious test device, but it works quite acceptably.
It is open sourced, released under MIT license. Sources are intended to use with XC8 or open-source SDCC compiler. There are complete details, drawings, source files and build tutorials here https://hackaday.io/project/7988-micro-progmeter leading to here https://github.com/jaromir-sukuba/micro_progmeter
If you wish, you can build your open source programmer https://hackaday.io/project/8559-pic16f1xxx-arduino-based-programmer to FLASH the PIC on board ;-)

[John Heath]

My friends and I have been developing an open source multimeter. I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.

I am liking it. Why not kick it up and go for a full android cell phone as a base. This leaves the door open for many bright minds around the world to contribute software with common hardware and operating system. For an example Dr Owen Thomas from the UK , keuwlsoft , would have the software for frequency counter and jitter measurements covered. Someone else contributes software for AC DC Ohms with smart auto select. With a sim card one could make a phone call on their DMM. And lets not forget voice commands " what is the value of this inductance and its Q" , ".  "FFT for this wave form please" , " record AC values over 8 hours and email results to myself ". The possibilities are endless once the software is open to science nerds around the world with a common operating system and hardware. The DMM only needs to deal with new standards for sound I.C and high voltage protection. The rest is already in place with a standard android cell phone. I would shell out some bucks if such a DMM came on the market.
 

[SaabFAN]

Reminds me of the TNG-Tricorder

[EEVblog]

http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques

This is gold:

[John Heath]

Reminds me of the TNG-Tricorder

I see the similarity. Beam me up Scotty. Did they move actual atoms to do this or just use information and atoms that are already on the Enterprise , somewhat like a 3d printer. From a philosophical point of view it makes a big difference if you are the one that is being transported.