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.
We found this simple transistor tester in a French publication in 1981. It uses a common analog...
Who is faster? or reaction game are other names for this circuit that we find in old...
This circuit is from an 80's component manual. The components are from the time, but the circuit...