Tulley Family Tinkering Lab Website

Magic Smoke! – Science Fair Project progress

by on Apr.04, 2010, under science fair

No electronics project is complete without Magic Smoke!

The backstory:

We realized we needed to build all of our logic gates by hand (reference the last post), so we got to work creating OR and NOT gates. We double and triple-checked our circuit, held our breath, and plugged in the batteries.

MAGIC SMOKE! I don’t recall if it happened immediately, or only after we triggered the circuit, but some transistor somewhere wasn’t happy.

After frantically pulling all power to the circuit, I had the presence of mind to test each transistor’s temperature. It was a transistor on one of the NOT gates. That didn’t make much sense, since that is the one circuit I had already built successfully.

Now you have to wonder — are all the circuits fried? What does and doesn’t work? We started pulling wires so that each individual circuit was isolated from others, testing each part along the way. 556 chip is still good (yay!) OR gates working. NOT gates are wired correctly according to everything I know and am reading about on the Internet. Hmm… In the end, we concluded that it was probably just a bad transistor, and rewired everything. I also got a working circuit (a NOT?) and tried each of my transistors in turn in that circuit, to make sure that there would be no surprises from any of the rest.

After putting it all back together and plugging in the batteries, we tried again. Trigger…click….2 second pause….click. Not only that but with repeated attempts at triggering the circuit were ignored for 10 seconds, one of our design goals (and the reason for the 2nd 555 circuit and most of the logic gates).

Now that we are high on magic smoke, we are ready to complete the circuit!

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