Light-controlled/dark-controlled relay switch

A simple light/dark activated relay switch circuit suitable for many applications, such as automatically switching the lights in a shop window or room based on ambient light levels. The circuit uses a photoresistor (LDR) and includes a light/dark option. The term "light/dark" is used because there is a PCB-mounted switch on the board. In one switch position, the transition from light to dark activates the relay. In the other position, a transition from dark to light is required. Therefore, you can use the light reduction on the detector to open a normally open circuit or close a normally closed circuit. The relay is on when the LDR is not covered and off when the LDR is covered. Adjust VR1 to set the light sensitivity. The LED will light up simultaneously with the relay.

Power supply: 12 to 15V DC

Relay contact rating: 5A / 240V AC