Preface
The first electrical circuit I built was a headlight for a homemade soapbox racer. The lamp was soldered inside a tin can. The switch was made from a bent nail. The light turned on just fine, but it didn’t turn off completely. When the batteries lasted only a short time, I checked the circuit and found the problem. Instead of connecting the switch between the battery and lamp, I had connected it across the lamp. So when I thought the switch was in the off position, it was really short circuiting the battery.
I was 11 years old when I built that soapbox racer. The lesson learned from that improperly wired “switch” has stayed with me ever since. Even today I never apply power to a circuit I’ve built until checking and rechecking every ...
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