Electronic Design

Bob's Mailbox

Dear Mr. Pease:
In the Aug. 3 issue of Electronic Design, you mention the Heathkit C.D. ignition system. I believe it was the same as the Delta unit that I have been using for many years. I have one installed in my '69 Bronco, and another in my '71 Ford F-250. Both were installed sometime around 1972, and have been functioning with no failures. I recently came across a box full of the same at an auction—some working and some not—cheap. My experience with these is that the usual failure is the SCR, and second the inverter transistors. The whole system is fairly simple. The inverter supplies the high voltage to charge a capacitor. There's a trigger circuit, and that's about it.

Now, on another subject, Home Circuits: I have a front and rear entrance. The front has a motion detector, but I normally park in front and use the rear entrance. Being in a rural area, it gets black out here. I didn't want a motion detector in the rear, as I didn't want it on at times.

What I did was wire a relay to "Blip the motion detector," which would cycle it. The motion detector lights also turn on the side and rear lights at the same time. So, I have three minutes to park, unload, and walk to the rear—under lights. The reverse is the neat part.

I rewired the the rear doorbell with an SPDT switch. I charge a large (2000 µF) capacitor through a resistor. The switch grounds the doorbell and Blips the motion detector relay by discharging the capacitor through the relay to the ground. The resistor controls the rate the capacitor charges (to prevent anyone from holding the switch in and keeping the lights off). Now, on leaving the rear door, I can cycle the motion detector by hitting the doorbell, and visitors are greeted by the lights coming on. Or, I have the lights for my normal exit and they turn themselves off. The system works quite well, and I had a similar setup in a house I used to own.
North Fork, Idaho

Isn't it amazing how a study of our different "consumer needs"—and a little customizing of circuits, delays, interlocks, and interactions—can lead to some very versatile applications? And surprise the heck out of the deer and raccoons, too!—RAP

You learned to type the HARD way. I took a typing and shorthand class (only two males in our class!) when I was in the 11th grade of high school. (No, because I learned in the 4th or 5th grade. Learning skills there are better than in the 11th grade. /rap) I was thinking those two skills would come in handy when I entered Ohio State University (taking notes during lectures, typing English essays, etc.).

Well, I did quite well in both typing AND shorthand, being "certified" at 125 wpm in both (mechanical typewriters, I might add!). I made one big mistake, however. I didn't continue with the typing and shorthand classes during my Senior year. So, by the time I entered university the following fall, I'd TOTALLY lost my shorthand skills. I DID manage to keep my typing speed up.

Now that I'm much older, I can still do a respectable 80 to 90 wpm in "straight text" on a decent keyboard. I come to a screeching halt, however, when numbers are thrown in.

Thank you, Robert, for all your erudite writing(s). Please don't ever stop!
via e-mail

Hey, I'm happy with 30 wpm.—RAP

All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
Please note NEW e-mail address:
[email protected] The older one at "webteam" seems to be broken. Sorry. /rap—or:

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

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