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?
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.
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.
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