Automatic night lamp circuit using LDR and IC 555

This circuit can be used for different automatic light sensing projects, including automatic night lamp, automatic street light controller circuits, etc.

An automatic night light circuit controls the switching of light by sensing the surrounding light intensity. The circuit ON the LED light, when the incident light intensity falls below a particular limit. And OFF the light when the incident light is above the limit.

automatic night lamp, LDR night light

In the circuit, the threshold and trigger pin of the NE555 has connected with a voltage divider network. It can obtain a trigger voltage which is half of the voltage at threshold pin. In a 555 IC, when the threshold pin has a voltage above 2/3Vcc, the output switches to a low state. And output switches to a high state when the voltage at trigger pin falls below 1/3Vcc.

The LDR (Light dependent resistor) has a negative co efficient of resistance with the light intensity. So, when the intensity of the incident light is high, the voltage drop across the LDR decreases. Thus, the voltage across the threshold pin reaches the threshold value and the Light OFF. Similarly, with the decrease in light intensity, the voltage across the threshold pin and the trigger pin decreases and the Light ON.

The light sensitivity of the circuit can be adjusted by the varying the potentiometer R1.

Components Required

IC – NE555

Resistor – R1 – pot 407k, R2,R3 – 82K, R4, R5, R6- 220Ω

LDR

Capacitor – C1 – 0.01uf

Diode – D1 – D9 – LED

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