AUTOMATIC SWICH CIRCUIT

Switch circuit which saves energy consumption by automatically turning off appliances connected to it either at day or at night. This switch circuit can be employed to reduce the energy consumption of fridges, air conditioners, lights, and many more appliances that you want to control their turn on time.

The circuit is based on light dependent resistor (LDR) popularly known as photo cell. The LDR is a type of resistor which reduces its resistance when light falls on it. The resistance value is directly proportional to the amount of light that falls on it. The more the light, the less the resistance of the LDR and the less the light, the high the resistance.

In this circuit, the LDR is our sensor which controls the relay U1 and also your connected load..

AUTOMATIC SWITCH CIRCUIT

Click to View

 

CIRCUIT OPERATION

When the circuit is connected to 220V or 110V  AC, transformer T1 steps down the input voltage to 12V AC which is fully rectified by D1 and D2. Filtering of the resulting ripples is done by 220uf capacitor C2. The LM358 is configured as as a comparator which compares the divider voltage  of LDR and U20 to a reference voltage from 4.7V zener and R16.

Any time that the voltage from the LDR and the variable on Pin 2  becomes higher than the zener voltage, Pin 1 which is the output of the op amp will go low and turn U1 off through Q1.

As the relay turns off, the appliances connected to the relay turns on. 

If you want The appliances to turn on during the day, then leave everything as it is.

If you want the appliances to turn on at night when there is no sunlight, then connect the appliance to the normally open part of the relay so that at night when the zener voltage has become higher than the divider voltage from the LDR, the Relay will energize and connect the appliances to power.

The sensitivity or operating point of the system is set using U20. Increase the value of R11 to reduce reactivating sensitivity.

NOTE DANGEROUS VOLTAGE INVOLVE PLEASE BE CAREFUL.