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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. |
