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This circuit does the following:
1) Switches on triggered by an LDR (when there is no ambient light) (turn up the upper opamp "+" leg potentiometer wiper to exceed 30% to trigger). Use the upper left potentiometer to adjust the light level to trigger the LDR.
2) Runs for 5 seconds (tune the 555 potentiometer for higher values), keeping the LED on, then automatically turns off. Even if the light level changes during this time, the 555 will not trigger again because of the 10uF capacitor in between the two 100 kohm resistors.
3) If you switch to the output of the bottom opamp to drive the LED and relay, the circuit becomes a night switch without a timer.
It draws 80-90 mA at 12 V power supply when the light is lit.
I am open to constructive criticism, tips, comments, etc.
(Credit:
http://discuss.littlebits.cc/t/how-can-i-send-a-single-pulse-when-the-input-is-a-constant-on/23894/18)
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