Simple Light Sensor Circuit

Preview

If you need to turn on any device at morning, then you can use this circuit.

This is a light sensor and you can control any device by connecting it through the relay. The relay was activated when the around is light or when we focus a light to the surface of the LDR.The circuit is very simple and you can use a dot board to assemble it and use any power supply to give power.

If you have a 9v or 6v relay then decrease the input voltage according to the voltage of relay. Use
RV1 to change the sensitivity of this circuit.

Light Sensor Circuit

Operation

In dark condition impedance of LDR is very high. Q1 transistor is in off state. because bias voltage coming to the base of Q1 is low due to high impedance of LDR.

At light condition impedance of LDR is goes down and therefore voltage of Q1 base is goes high and after it reach its saturation voltage Q1 activated and bias voltage for Q2 is start to going through R1 and Q1. then Q2 activated and also relay was activated.

If you connect you device across the NC and Com pin of relay then you can also use this as dark activated switch.