This touch switch uses components that have easy-to-obtain current equivalents. The power supply must be isolated and the cable to the sensor must be short.
This circuit is for collectors. It is the circuit of one of the most popular transistor radios of the...
This circuit, from a 1978 publication, emits a modulated signal when the fine sensor is...
This simple amplifier uses a microphone attached to the telephone. The 3-transistor circuit was...