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.
Found in an Electronic Design from the 90s, this circuit modifies the phase of a signal in 8...
This shield circuit, from a documentation from the 70s, employs an optocoupler with two SCRs to...
This circuit has an automatic dynamic gain control in a range of 6 dB to 40 dB. We found it in...