This circuit triggers a buzzer or other warning device when the light falling on the sensor is cut off. We found it in the Encyclopedia of Electronic Circuits Volume 5 of 1995.
In the figure we have three voltage doubler configurations that can be used in high and low...
In this application, from English documentation, we have the way to activate an AC load up to 10 W...
This 1-transistor reflex receiver was found in a 1963 publication. The coil is for the mid wave...