This circuit was found in a 80's Popular Electronics. The sensor can be any phototransistor. The circuit is indicated for an audio link modulated in pulses.
This circuit for vehicular use is from an 80's American publication. The circuit has a light...
You can change the output voltage of a fixed 3-terminal regulator using a zener diode. The voltage of...
This circuit was found on a Radio Elettronica (Italy) from April 1974. The circuit can still be...