Electronic Design

Bob's Mailbox

Dear Bob: I have enjoyed your writings and presentations for years. Please keep up the good work. I've learned a lot from you even though my technicians have named me the SandMan for all the ICs I've returned to their native state of sand. I'm trying to find the name of the circuit designer of the Signetics SE555/NE555 timer. Can you point me to someone who might know?


  • Mike Turner (via e-mail)

  • Pease:
  • We were just talking about that the other day. The inventor was Hans Camenzind, who has (had?) a lab on Virginia Street in San Francisco, on Bernal Heights. I heard that the 555 was originally just a feasibility test chip for various features (current mirrors, comparators, etc.) that might be used in future ICs. When customers found it useful, it took some work to redesign it hurriedly into a real IC. I'm not sure if that's true.


    Hi Bob: Re your "Cruise Control Stuff" (electronic design, May 10, p. 18). It started when I ended up with a Lincoln Town Car from a friend's estate. The car was so quiet that you couldn't sense engine or transmission malfunctions until they became gross and expensive.

    What I came up with was entirely passive—a small loudspeaker driven through a series capacitor and low-pass filter from an arm of the wye stator winding of the alternator. The alternator has a unipolar 15-V square wave that Ford brings to an external terminal. (How odd! /rap) The frequency is high compared to the exhaust note, but I adjusted it so that its level just exceeds cabin noise, and it's completely unobtrusive. If I get the time, I'll divide it down by eight or so. (If it works now, changing it might do harm, not good! /rap)

    What you get is a precise sense of how well or poorly the transmission is shifting. And you can even hear an intermittent single-cylinder miss, something you'll never notice otherwise in a big V-8 under light load. (REALLY! /rap) It probably helps if you don't have a tin ear, but the tone helps you maintain a constant speed without the other noise clues you get from a lighter car—as long as the torque converter is locked up. (Interesting. I never would have thought of it, but I guess you had to try it. I had to try MY scheme. /rap)

    This signal is also available at the cigarette lighter, but it's only millivolts and you'll have to amplify it. This is worth doing when test driving a used car. A small PC speaker that is happy with 12 V does the trick. On a recent BMW, you will also hear the chorus of the dozens of microprocessors that you hope are your friends.


  • Bill Schmitt (via e-mail)

  • Pease:
  • Thanks for the interesting comments on your "Cruise Control" circuit. All of the microprocessors in my car are my friends—all ZERO of them.


    Dear Bob: An old geezer like you driving at 68 mph? You should have your license revoked. You're endangering people's lives, you know.


  • C.M.W. (via e-mail)

  • Pease:
  • I am NOT old, and my reflexes and eyesight are perfect. 68 mph is NOT speeding. The only thing unsafe about driving at 68 is that the median speed out on I-280 is about 78 mph. At 68 mph, 95% of the cars are passing me, and I'm passing 5%. I will not drive at 78 mph, in my car, just to be closer to the median speed. I am not endangering anybody else, nor myself, at 68 mph. I just got back from South Africa where I was driving between 75 and 85 mph, and I was still down at the 20th percentile. When in Germany, I drive 85, 95, 105, or 125. That is miles/hour, not kph. And I am DAMN careful at ALL speeds, fast and slow. I'm STILL not usually above the 50th percentile. Best regards, and thanks for the silly comment.


    Comments invited!
    [email protected] —or:

    Mail Stop D2597A, National Semiconductor
    P.O. Box 58090, Santa Clara, CA 95052-8090

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