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. 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.
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. 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.
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