This circuit, to control air conditioning systems, was found in July 1984 Radio Electronics magazine. The circuit is for old types of the time that did not have microcontroller control.
This circuit, found in a 1988 documentation consisting of an audio switch that turns off the load...
This stabilized source can supply currents up to 200 mA with the indicated transistor or 500 mA...
With the shadow over the sensor, it is possible to interrupt the sound of your amplifier using this...