This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used over short distances with a lens system. The circuit is from a 1967 Japanese publication.
This circuit is from the 1993 Motorola Linear Interface ICs. Equivalent operating may be used and...
Through the TTL output this circuit can be used as a shield. The sensor is a platinum probe, and...
This alarm with sensors in series and parallel was found in the 1995 Encyclopedia of Electronic...