Simple DIY DVM Voltage Reference

[Nick]

That is an interesting article athough fig 5 seems to have some serious drafting errors around IC3's inputs, the 500 ohm zero trim resistor and Q3's emitter connection (or lack of it) to the LT1088. As it stands, it would not work.

The correct schematic and full article is in Linear Technology app note 83, appendix C. 


  an83f.pdf (Size: 528.81 KB / Downloads: 11)

[ppppenguin]

Even if you're not especially interested in the subject I urge you to look at that app note. There is a marvellous photo of "tin box technology". This is classic Jim Williams stuff. He was a true master of analogue techniques.

[Nick]

Many years ago I was building an ultra-low-distortion oscillator based on a Jim Williams design and was having some stabilty problems.

I emailed the great man and he replied the same day - we exchanged a few emails - he was unbelievably helpful. Great guy, terrific engineer, sadly missed.

[ppppenguin]

Back in 1991, long before I had email, I wrote (by fax) to Jim Williams. Got a snail mail reply which I have kept. Here's the first page of his reply.

JW was truly one of the greats. Along with Bob Pease and Barry Gilbert. There may be a couple I've missed but we're still talking of just a handful. These are the guys who created analogue ICs as we know them. Opamps, voltage regs, comparators and much more.

[Nick]

Bob Widlar? Brilliant, but mad as a box of frogs... Bob Dobkin of Linear Technology?

Seems that to be a great analogue designer you should probably be called "Bob" (or Jim).

[Radio Fixer]

Great app note, once upon a life I would have read it avidly but not now; the tin box was a fine (nothing posh like an Eddy box). Done a few myself similar or wrapped things up in tin foil.

thanks Gary

[Mark Hennessy]

That is an interesting article athough fig 5 seems to have some serious drafting errors around IC3's inputs, the 500 ohm zero trim resistor and Q3's emitter connection (or lack of it) to the LT1088. As it stands, it would not work.

The correct schematic and full article is in Linear Technology app note 83, appendix C. 

Thanks for the pointer to the source - EDN's PDF might have been better than the HTML (with a bunch of non-working links), but it was still obviously wrong.

I'm lucky enough to have hard copies of the LT app notes in 3 volumes of books that I got from LT back in the paper days. They are up there with "The Art of Electronics" in terms of how much you can learn in such an easy to digest writing style. My books are currently in a box - having been in this house for 10 years we've still not finished unpacking! - but I will endeavour to dig them out this weekend. The cellar workshop is dry enough for paper/books now, but that wasn't the case when we first moved here...

Last night I ordered a number of those Chinese AD584 references that were being discussed on UKVRRR, plus a couple of LM399 references (as used in many posh meters, including my Keithley). I can feel myself being dragged down the "Volt Nut" path! There is something addictive about precision analogue electronics, and it's very refreshing today, where so much of the world is digital: http://www.theamphour.com/a-widlar-poster-for-the-ages/

I still can't believe that Bob Pease died on the way home from Jim Williams's funeral

[Nick]

Technically, he was on his way home from a memorial service, not the funeral....

None-the-less, a strange and unwelcome coincidence....

Back on the subject of RMS measurement, here's - an article from the Hewlett Packard Journal, Jan 1964, about the design of the HP 3400A...

http://www.hparchive.com/Journals/HPJ-1964-01.pdf

Another good read

[Refugee]

EDIT: Has to be the absolute ugliest bench DMM I have ever seen ! Simply for aesthetic reasons, it's not going into my shack !

The earlier bench models were a little more conventional in the aesthetic design such as my only Fluke I own from the 1970s. It is an early example of an auto ranging instrument. It is an 8800A.

[Mark Hennessy]

Now I'd argue that those are even uglier. I picked up an 8000A at the last NVCF - just a basic 3.5 digit meter which needs new NiCad cells. It's hardly worth the expense - it's a collection piece. There's something about the green/blue and black that I can't warm to.

The 8050A is really nice - example here - http://electev.blogspot.co.uk/2013/07/fl...art-1.html

They are smaller than you'd expect from the pictures, and provided the case hasn't gone too off-colour, they are quite pretty. The battery option is quite convenient too. Main problem with meters of that vintage is the LCD, but a lot of people are hacking LEDs in place of the LCD, and the results look pretty nice IMHO. Here's an interesting TFT job: http://vondervotteimittiss.com/belfry/?p=180

The 8050A does dBm, and has a decent AC bandwidth. And it takes modern shrouded 4mm plugs, unlike a lot of that vintage.