Found in a Motorola documentation from the 70s, this circuit makes use of transistors of the time. Modern equivalents can be used. The diode also supports an equivalent.
This simple circuit allows the monitoring of both audio and RF signals. With the switch in one...
This circuit was found in documentation from the 1980s. The integrated circuit used is uncommon today...
With a light pulse on the Q1 sensor the circuit turns on and locks. To switch off, a light pulse...