This very low frequency circuit was found in a 1964 Electronic Design. Transistors may be modern equivalents. The filter is low pass type.
This old receiver (1967) uses germanium transistors from the time and coupling transformers,...
This circuit can act as a shield being controlled by a microcontroller by pin 1 or 2. The...
A negative pulse applied to the input of the circuit shown in figure bellow turns on the relay....