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.
| 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 |
1. R1 Adjusts sensitivity