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.
The load controlled by this circuit depends on the triac used. The circuit is from Electronics Now magazine...
Suggested by a 90s Radio Elecrtronics, this circuit is intended to supply mobile equipment of the time....
This circuit is from a 1966 NASA documentation. The circuit uses a photodiode as a sensor. The other...