Light/Dark Detector

This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100K Pot Q1 1 2N3904 NPN Transistor 2N2222 Q2 1 NPN Phototransistor RELAY 1 9V Relay MISC 1 Board, Wire, 9V Battery Snap (if battery used), Knob For R1

Notes

1. R1 Adjusts sensitivity