Automatic night light cheap and simple with few transistors and the NE555 timer is shown here. The circuit automatically turns on AC lamp after dark and the light turns off automatically after a preset time.
The operation of this circuit very simple night light. A LDR is used as the sensor here. At the time of day of the LDR resistance will be low as the voltage drop across it, the transistor Q1 will be on how to carry out. When darkness falls the resistance of LDR increases, so does the voltage across it. This causes the transistor Q1 OFF. Base of Q2 is connected to the emitter of Q1 and Q2 which is biased in that turn, the powers of IC1. NE555 is wired as monostable multivibrator which is activated automatically when the power is.
This automatic release is achieved with the help of the capacitor C2. The output of IC1 remains high for a time determined by resistor R5 and capacitor C4. When the output of IC1 goes high transistor Q3 is turned on which activates triac T1 and lit the lamp. A 9V battery is included in the circuit to power the timing circuit during power failures. Resistor R1, diode D1, capacitor C1 and Zener D3 is the feed section of the circuit. R7 and R8 are current limiting resistors.
