phy1020.DVI

+ Xtal Osc.

GND

PWR OUT

Mic. Transformer

Figure 43.5: Simple transmitter with a microphone.

A more sophisticated transmitter can be built by replacing the telegraph key with a microphone (Figure
43.5). The microphone is coupled to the transmitter circuit via atransformer, which consists of two separate
coils of wire wrapped around a common core. The transformer also serves to amplify the microphone’s signal
as it is sent to the the rest of the transmitter circuit.