This circuit was found in the August 1971 Radio Electronics magazine. The SCR admits equivalents and instead of the buzzer a sensitive relay can be used.
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
Found in a Popular Electronics from the 9s, this circuit has output for RS-232 interfaces and current...
Photodiodes can be used to sense moving objects, such as optical switches and encoders. In the...