A Word About Switches

All three robot projects use toggle switches for power. For the newbie, the terminals on switches may be befuddling. Many switches, like the kind you buy at your local Radio Shack, or the ones you yanked out of your mouse, have three terminals protruding from the package. In the book, we don't really address this until a side Note in Chapter 9, Project 3 (on page 280).

So, if you're confused, here's the dealio: If your switch only has two terminals, to control a circuit, all you have to do it solder one positive wire coming from your power source to one switch terminal and solder another positive wire going to your circuit to the other terminal. Easy.

If your switch has three terminals, look closely on the switch package (no, not the product package Einstein, the plastic case that houses the switch!). Most switches with more than two terminals have the functions of the terminals stamped on the package in teeny-tiny letters. You'll usually see the letters C, NO and NC. "C" stands for Common. One of your wires will always go to this. "NO" stands for Normally Open. This means that, if you attach your wire to this terminal, the circuit will remain open (not connected) until you throw the switch. "NC," Normally Closed, means the exact opposite. If you attached your wire to that terminal, the power will be delivered to your circuit until you engage the switch. So, in all three of our projects, for both the power switches and our bump switches, we want to use the NO terminals.