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 was found in documentation from the 1980s. It is powered by the audio signal that must...
Damped oscillators can be used to produce sound from percussion instruments such as the triangle, bell,...
Found in Radio Electronics from the 90s, this circuit produces pulses to test an infrared...