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 obtained in a 1975 documentation. It is intended for old vehicles that still use...
A Schmitt trigger inverter can be obtained from each gate of the 4093 with the connection shown in the...
In the figure we have a typical voltage follower. In a voltage follower the voltage gain is...