Make: More Electronics

Chapter 3. Experiment 3: From Light to Sound

In this experiment you’ll get acquainted with a phototransistor. Its symbol is shown in Figure 3-1, looking very much like a bipolar NPN transistor. In fact, its collector and emitter serve the same functions. The big difference is that the base is energized by incoming light, indicated by one or two arrows pointing toward it.

Sometimes the circle around the symbol is omitted. Sometimes there may be a single zigzag arrow instead of two straight arrows. These variations don’t indicate any difference in operation. However, if a connection is shown protruding from the base, a base connection is available to supplement the effect created by the incoming light. I’m just mentioning this so that you’ll recognize ...