This circuit uses a contactor having been found in a 1987 publication. More modern equivalent devices may be used. The circuit has neon indicator lamps.
The values of the capacitance between output A and ground can be programmed digitally in 18 steps...
This circuit is the traditional 555 oscillator that produces a hum in the piezoelectric...
This circuit activates an output, which can be a lock, only when a card containing the programmed code...