Cover by David Erik Nelson

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Building It

Start by examining the schematic in Figure 7-3. If the heart of the Ticklebox is the step-up transformer, then the brain is the relay, represented by the dashed box containing squares and little pennants. This is an electromagnetically controlled switch: When you power up the coil, it creates an electromagnetic field that pulls the switch closed, thus completing a circuit and turning your gadget on. When the coil loses power, the magnetic field dissipates, the switch opens, and the gadget turns off. Like other switches, relays come in SPST, DPDT, and other varieties (for a full discussion of different kinds of switches, see Types of Switches in Building It).

Figure 7-3. The Ticklebox’s full circuit diagram at the top (it is a very simple ...

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