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Reflected Infrared Light Switch
designed by David Johnson, P.E.

This hobby circuit has been used in some museum displays and exhibits when the electronics needed to trigger an audio/visual presentation is behind a plastic or glass panel.  A finger pressed against the glass, over a designated area triggers the switch. 

Infrared light reflected off a finger is used to activate this switch circuit. Drawing only 30uA from a 3v supply, this electronic circuit will detect a human finger with a range of about 1 inch.  The sensor uses an inexpensive infrared LED and a matching photo diode.  The circuit is immune to ambient light.

Click on Drawing Below to view PDF version of Schematic

Circuit Reflected Infrared Light Switch Circuit


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