In this circuit of an American documentation of the 90s, when the light is cut, we have the production of a pulsating tone. R3 determines the trigger sensitivity.
This circuit, found in 2002 documentation, generates a strong audio tone when the light in the...
This circuit uses a variable transformer available at the time. This turns of the windings were...
This is one of the many 7400 oscillators we have in our circuit bank. It is crystal controlled and must be...