This code key uses a PLL and an oscillator that generates two frequencies that must be recognized for the relay to be activated. The circuit is from an 80's Popular Electronics.
This circuit is from a 1968 publication. It uses germanium transistors from the time, having...
This circuit can be used as shield or to drive powerful loads from low current switches such as...
This is a 6-transistor transistor receiver manufactured in the 60s. The circuit is a...