Electronic Design

Bob's Mailbox

Dear Bob: There's an error in your recent "Mailbox."* What you "heard" about the 555 timer is a bit off the mark. Your story mixed up the 555 with my work on semicustom ICs, which happened about the same time. If you want the actual story, you can download my new book, Designing Analog Chips, from my Web site, www.arraydesign.com. It's free.

At Signetics (January 1968 through December 1970), I developed the first semicustom chip, used internally to get a new design onto silicon in about two weeks and then debug it. I have been using this approach since then to fabricate custom designs for quantities below a million/year.

I proposed the 555 timer when I left Signetics and developed it as an independent. It went from breadboard straight into layout--the same layout still used today, save for shrinking it once.

  • Hans Camenzind (via e-mail)
  • Pease: Okay Hans, so the 555 was really designed as a product, not just as a test pattern. Thanks for clearing this up. I've started to read your book. It looks great! I recommend that all engineers read it.
  • Dear Bob: Some of your comments about Spice simulation put me in mind of an engineer I knew in the early 1970s. Chris was fascinated with the possibilities of the digital world. I think he built an RCA 1602-based microcomputer, which could make lights flash, depending on how you set the switches. At the time, I really didn't get it.

    Anyway, Chris was a big proponent of digital simulation. He told me that breadboarding analog circuits was primitive, and you could never prove much by building a model. You could always "get one of anything to work." He insisted that I really needed to use RF-OPT and Spice. I eventually did, and I must say they did some good, if only by forcing me to sit down and analyze my circuits in detail to make a simulation model to plug into the program. (But I'll say, "You can always get a digitally simulated circuit to work." And after all that work, it is NOT automatic to say you can build them in production. That's my point. /rap)

    Chris loved tricks and illusions. One of his favorites was to hold a pencil mid-length between thumb and forefinger and wiggle it. It gave the illusion of bending--the "Rubber Pencil" illusion.

    I decided to go him one better. I took a white eraser rod for an electric drafting eraser, sharpened one end in a pencil sharpener, and decorated it with colored markers and the ferrule and eraser tip from a pencil. When I did the "Rubber Pencil" trick, he was flabbergasted! (Jolly good!! /rap) That is the difference between Spice and reality.

  • Roger Burchett (via e-mail)
  • Pease: Sometimes there is good correlation between Spice and reality. Jolly fine. But when the correlation is LOUSY, then you will waste a lot of time--and money.
  • Hi Bob: I enjoy reading your column very much. Thank you! However, I take exception to the snub you made at Disney in "What's All This Theme Park Stuff, Anyhow?" (electronic design, June 7, p. 18). As an engineer, I appreciate all the high-tech stuff they have designed. And as a kid at heart, I appreciate all the fun I have!

    I would argue that Disney's intent is not to diminish all of the wonders of the world, some of which you mentioned, but to have people enjoy them. By creating the incredible reproductions, they are in fact promoting some of these wonders to people that may never have the financial or time resources to see the real things.

  • Jon Kanter (via e-mail)
  • Pease: It still only costs a few tanks of gas to go see the nearest theme parks, such as New England, the Grand Canyon, New Orleans, or the Rock Museum in Cleveland.
  • Comments invited! [email protected] --or:
    Mail Stop D2597A, National Semiconductor
    P.O. Box 58090, Santa Clara, CA 95052-8090

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