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 old documentation, but as it uses the 555 it can still be easily...
This is the radio receiver for the previous infrared alarm radio transmitter. It contains the...
This circuit was found in an old European documentation. When R2 is cut off the circuit triggers...