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Electronic Design


Re-Read Reveals Growth
I particularly enjoyed \[Steve Scrupski's\] contributions in the Sept. 5 issue \["Firms Seek Ultrareliability For Minuteman Missile Program," p. 82\]. They brought back a flood of memories.

In June of '62, I started as a junior engineer at Motorola. One of the first things I worked on was teleprinters that were going into the Minuteman missile silos. At the time, we were using core rope memories to convert ASCII to 5- by 7-dot matrices. The print was produced on a coated carbon-impregnated paper. This paper was selectively zapped with high voltages to blast away the coating to form dots on it. Our circuits included a smattering of the logic family that had been introduced not long before, emitter-coupled logic (ECL). We marveled then at the prospect of someday obtaining memory for as little as a penny per bit.

Shortly thereafter, I generated a proposal meant to produce a research grant for us. I did considerable reading about bionics, including frogs' eyes, adaptive systems, self-organizing logic—that sort of thing. Much of the reading was from the proceedings of one of the Bionics Symposiums that had been held at the Wright-Patterson Air Force Base. For some reason, I even recall the name of one of the prominent authors in the field, Marvin Minsky.

Recently, I had the occasion to re-read my proposal and I believe that I understand why we didn't get the grant. Mostly, it was because a certain junior engineer was so wet behind the ears. In the re-read, I was embarrassed to discover how little I knew then, especially compared to what I have learned in the many years since. This sort of exercise isn't recommended for those who suffer from any lack of self-esteem.
Dick Merrell

Stainless Probes Are The Way To Go
Unfortunately, until you get into the real world and realize that water is corrosive (pure water is nonconductive), you can get away with circuitry like this \["Water-Level Sensor Uses Hysteresis," Aug. 21, p. 126\]. The dc potential applied to probes will promote corrosion. National builds a wonderful IC, the LM1830, which applies a low-level ac to the probes. I believe that they recommend, and I heartily agree, stainless (300 series) probes. Stainless passivates more readily than most other metals, and the ac doesn't give the liquid molecules time to polarize.

I once built a water-detection circuit for a fuel filter for my friend who went on a two-year sailing cruise. I was worried that the diesel fuel would contaminate the probes, or react with them, or whatever. Four years later, in Mexico, the alarm went off. My friend had forgotten that he had it and had to trace down the noise. There was water in the filter, but it was caught in time to save the injectors.
John Erskine

Sometimes, in our quest to identify articles that are unique in their simplicity and demonstration of useful principles, circuitry can be published that may only meet the needs of the narrow application requirements for which the author developed the circuit. Thanks to field-savvy readers like yourself, these shortcomings rarely go unnoticed. If you feel the circuitry that you developed adds a new twist to the application, please feel free to submit it to us at [email protected]—Jim Boyd, IFD Editor

What One Man Would Do
Thank you for your tribute to Bob Pease \["What's All This Perfect 10 Stuff, Anyhow?" Sept. 5, p. 182\]! Let me tell you another story to indicate what sort of person Bob is, although I'm sure that you know already. Within the last few days, I was having trouble finding a dual-voltage (110/220) battery charger for NiMH batteries. This is for my daughter to take on a long trip, initially going to Nepal. (That made me think of Bob.)

When I mentioned to a group of hardware engineers that I had sent an e-mail to Bob, it turned out that every one of them was familiar with his column. Several suggested that he was likely to respond by jotting a circuit down on a piece of paper and sending it to me.

Bob and I were only two classes apart at MIT, although we never met there. In fact, I've never met him, although he once did telephone me out of the blue when he got excited by something in an e-mail that I sent him. Nevertheless, when I mentioned to him, via e-mail, my difficulty finding what I was after, Bob wrote back and said he would check for me to see what was available at Fry's Electronics, and if he could find the right piece of equipment, he would buy it and mail it to me! Then, when he didn't find anything appropriate at Fry's, he checked at the San Francisco Airport, where he happened to be going over the weekend—all this for someone he had never met!

By the way, we did find the charger. My wife found it, using a search engine that I never use, "Ask Jeeves." It was mixed in with a bunch of hits on the San Diego Chargers (must be an electrifying team), but there it was.

Bob's a great guy! I won't be able to answer any return mail right away. I'm leaving tomorrow for Italy, and I won't be back until Oct. 5. I'm glad that I saw the article just before leaving, so I could get this message off. You'll notice that without much time to spare, the first thing I looked at when the magazine came in was Bob's column.
Larry Krakauer
via e-mail

Glad you liked the tribute. Yup. I've seen many a circuit that Bob scrawled on a sheet of paper to help out a reader. So, I'm not surprised that he went out of his way to look for a charger. Your wife sounds pretty resourceful, and the good news is that your daughter now has her charger. Thanks for yet another interesting anecdote about Bob.—Bob Milne

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