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Electronic Design

Bob's Mailbox

Dear Bob:
I enjoyed reading about your innovative aspirin-triggered moisture detector in the March 3 issue, "What's All This FLOOBYDUST Stuff, Anyhow? (Part 5)." It reminded me of a freezer alarm I built about 20 years ago when my sons were Cub scouts.

The den meetings were held in my basement where the freezer was located. Anyone who has witnessed one of these meetings knows that about 80% of the time is occupied with the boys practicing their wrestling skills. Consequently, in my case, the freezer door would occasionally be left open after impact or the power cord would be jerked out of the wall outlet. I decided to design a cost-effective (cheap, that is) alarm to warn me before the freezer contents had a chance to thaw. No self-respecting engineer would spend $20 to buy one at the local hardware store.

I used an old copper-clad board that had separated etched pads to which I soldered wires. A 9-V battery and a beeper made up the rest of the circuit. I made a salt-water solution and froze it in a paper cup. Then, the frozen mass was inverted in another cup containing the copper-clad board.

If the temperature rose in the freezer, the mass would begin to melt and drip onto the board, completing the circuit and energizing the beeper. The beeper operated down to about 3 V, and the very-conductive salt water easily provided a low-resistance current path. The other advantage of using salt water is the melting point is well below 0°C, so the beeper sounds before the food thaws. If necessary, the melting point can be accurately set by using a calculated salt concentration.
Chief Engineer
Springfield, Ill.

Hi, Jack, I like your "solution"- elegant. But how do you prove that the salt water is adequately LOW-Z to ensure the beeper is loud? I guess you just gotta run it!-RAP

Dear Bob:
Regarding the letter from Anonymous in your Dec. 16, 1996 column asking "Why is our profession so poorly regarded?" The answer is in the immortal words of Pogo: "We have met the enemy and he is us!"

Unlike lawyers or doctors, no one I know becomes an engineer for the money or prestige. We are engineers because we enjoy it. That puts us at a professional disadvantage with our employers and the public.

Additionally, our public relations are very bad. Although engineers have created virtually everything around us in our modern world, no one realizes this. Everyone knows what doctors and lawyers do, and their value to society. But walk down the street and ask someone what an engineer does. You'll probably hear something that relates to Casey Jones.

If we want to change this, we will have to go against our grain and act like the respected professionals do, which I believe means licensing, professional standards with peer review, and self promotion. Of course, this will take all the creativity and fun out of it.
West Islip, N.Y.

Joseph, your comments are astute: Is it worth more to be professional, or to have fun? Or to be able to to make a living? No easy answers. One thing Adams? Dilbert has shown: engineers try to make sense, despite their managers? foolish moves.-RAP

All for now. / Comments invited!
RAP / Robert A. Pease / Engineer

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

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