This receiver for a modulated light intercom was found in a 90s Elektor. The audio amplifier can be replaced by an equivalent. The sensor can be any phototransistor.
This is the traditional configuration of an unregulated bridge rectified power source. The circuit...
In the figure we have a circuit that produces interval pulses, reproduced in the piezoelectric...
Found in American documentation from the 90s, this circuit passes frequencies above 1 kHz. The...