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 was obtained from an English publication from the 70's. The circuit is still current for...
This circuit makes use of an unusual Analog Devices component today. The circuit is from a 90's...
This circuit was found in a 1974 documentation. The bipolar transistor can be the BC548 and at the...