A Jim Williams barometer schematic from 1992
Fran Hoffart was wise enough to take this picture of a Jim Williams schematic back in 1992. It is a design for a barometer. I was at the Computer History Museum today to record a video interview of my memories of Jim. That got me a little bummed out. I wrote up an editorial for the next EDN issue. The Museum is doing a display about Engineers at Work” and Jim’s bench is going to be a part of it. I took a picture of Jim’s bench at the meuseam’s loading dock. Then I went through a ton of my Jim Williams pictures, looking for a good picture of his bench for the editorial. While looking I came across this picture of one of his schematics.
A barometer circuit Jim Williams designed in 1992 (courtesy Fran Hoffart).
Andy T commented:
The use of the 12AX7 is a clear indication of a lack of adult supervision over Williams. Like any kid, it's obvious he got off on testing the limits of managerial stupidity and ignorance - a hobby of mine as well.
That said, what a frickin mess. His lack of formal education shows in his schematic. Don't confuse that with brilliant understanding or insight.
Bill Franks commented:
"Ah.. Too hard to find a 12AX7 these days."
Not so! 12AX7's are commonly used as preamp tubes in many guitar amps to this day, and are readily available, so have at it!
S.A. commented:
Surprisingly each and every available technology domain of that time was used in this schematic, active, passive, resistors, capacitors, tube, semiconductors, diode, transistors, FETs, analog & digital ICs, etc etc etc ..... except ..... microprocessor!
Jim Harvey commented:
Ah.. Too hard to find a 12AX7 these days.
Paul Baltrunas commented:
Seeing many of the previous comments forces me to grin. As an electronic engineering technician in the r&d lab at General Instrument in the early 1980's I was more than once handed schematics scrawled on a piece of paper for prototyping. Drawn up with CAD! Some one needs to learn what a pencil is used for. I currently use Bentley Microstation for final drawings, and still draw the prelims by hand.
pfb
William Ketel commented:
Now the challenge is to produce an accurate copy of this schematic using some current cad program, so that others can study it. What it shows in it's present form is the degree of brilliance of the creator. Jim Williams was truly a genius.
A guy in back.. commented:
Different parts, different function, but same style in 1975 at UC Irvine..and you built it and it translated well to the breadboard and to troubleshooting and it worked and was understandable and FUN...what a concept!
JJ commented:
Anybody come across the Verilog for it?
Mirko commented:
Cool!!
Tony Bonte commented:
I can verify that Jim built this barometer schematic. He and I wold routinely check its reading in the LTC lab against that available from the San Jose Airport.
Ryan commented:
I thought he had a "Big Digit Barometer" in his office last time I was up there...
Jim Burke commented:
Does anyone know the whereabouts of the prototype Jim built or any other attempts to construct a working example of this circuit?
Brian Barnett commented:
After attending a few useless seminars in the late 70's, I stopped going until I decided to try one again in the early 90's put on by LT. To my surprise Jim Williams and Bob Dobkins showed up and did a great job. Jim brought a barometer he had built, presumably the circuit here, and gave it away as a door prize. I think he said it would measure the pressure difference between ground level and an overpass across the Central Expressway. It was an interesting day.
jazz commented:
its brilliant , I can imagine the situation, this idea just popped up in mind and he wrote it down for future reference, i think it is common for creative people independent of what art. Jim was a great artist
dougspair commented:
..well...you have to start somewhere....in the 1070's, I was an elec-tech working on TTL numerical controls (before the micro-processors were here)...and often I/we had to design and mock-up something on a 'bread-board'....this was not an unusual type of place to start from....
Plenty of mechanical engineering was also started this way.
12AX7...they were everywhere...
k.cotton commented:
can we say Jim Williams, 'Mozart' of the electronic
IABoy commented:
Feel sorry for the poor tech who had to build this, if indeed it was. Or maybe this was just a "back of napkin" schematic.
Still interesting to study as to what Jims thinking was and why he designed it as he did.
JSTCanuck commented:
Looks just the schematic that you get with the purchase of a $5000 audiofool tube amplifier too.
Vincent Rheaume commented:
That is a nice schematic.
From looking at it you can see the sequence in which elements were drawn by Jim; he started off with the sensor conditioning, then the ADC/display, then the clocks, and the power supply at the very last (it looks like he underestimated the schematic space it would take up!). The exact value for the 100-ohm resistor acting as bridge current sense has been measured (100.34 ohms), which confirms that the circuit was built and could still exist...
I like the ADC and the high voltage regulator at the bottom, you never see stuff like that...
Kevin Szabo commented:
Tubes :-) !? It is always interesting to see a design by an expert and try to decipher the design decisions. It looks like the 12AX7 is being used as part of a level shifter to drive a high side switch on the 175v line. Looks like the output is a bunch of nixie-glow discharge seven segment displays (driven by 7446 and MPSA42 drivers. I guess the 12AX7 is part of the display blanking while the count is being updated. Cool. And a bit scary.
