LDR circuit diagram

LDR darkness sensor circuit

This is an Automatic Night Light circuit Without Transformer operated by Light Using Light Sensor LDR (Light-dependent resistor). This Transformerless Automatic Light operated Night Light circuit is very simple and easy. At DayThe Bulb is an automatic switch off and At night Automatic Switch ON Automatic Night Bulb Switch.

IN this circuit No transformer is used so it makes this very portable and small. Use a 9-12v Relay to connect the Bulb. Capacitor C1 must be 400v Rated. You can use one Rectifier ic MIC DB107 at the place of 4 IN4007 Diode. DB107 is a Small Package of 4 Rectifier diodes in a single IC. Resistor R1 should be of 1/2w.

Working

The working of this Automatic Night Light Bulb Switch Without a transformer is simple. When Light Fall on LDR in day then the resistance of Both LDR is Low and When the resistance is very than then all voltage passes the R2 is Dropped with a Negative supply and No sufficient voltage goes at the Base terminal of the transistor. When no voltage goes on Base the transistor Remains turned OFF and Relay is Not Activated and the bulb is switched off.

At Nighttime when No Light Fall on LDR the Resistance of LDR is Very High. At Resistance is high then a very Less amount of voltage passes through LDR and dropped with negative. And the Maximum amount of voltage comes on the Base of a transistor and it turns ON. When the transistor Turns on then the Relay Get Active and Bulb is switched ON.

So this works Automatically as a Night Bulb Switch system. It can be used as Street Light Switching or any other purpose where needs to Switch ON and OFF the AC Bulb Automatically.