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Photo detector using LED

2014-11-05 09:33  
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Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. visit page.Photo detector using LED - schematic
The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light. visit page.