Automatic Light Control Switch Circuit using IC 555

This article is for Automatic Light Control Switch Circuit using IC 555

When light fall on LDR its resistance changes.

That resistance change is converted by IC 555 and used to drive a relay.

With relay we can connect lamp, fan, motor or other load.

It is useful for automatic street light, garden light, dark sensor lamp or security alarm.

Circuit Working:

This circuit is easy to build.

LDR sense the light and potentiometer sets the light level.

555 IC and two transistors do the switching and relay is used for output load.

When light is low the voltage on LDR is small and output of IC1 555 is high.

Q1 turns ON, Q2 stays OFF and relay is OFF.

When light become strong the voltage on LDR goes above a limit and a output of IC1 change with Q2 turns ON and relay gets power.

So relay work according to light on LDR.

This Light Control Switch Circuit is useful for home and industry for automatic light control.

LDR resistance in dark means few hundred kilo ohm.

LDR resistance in light means few hundred ohm.

Divider voltage = Vcc × (Rldr / (Rldr + Rpot))

where,

IC 555 trigger point is at 1/3 Vcc and threshold point is at 2/3 Vcc.

So design is done by adjusting Rpot so that divider crosses these points when light condition changes.

Example:

If Vcc is 12V then 1/3 Vcc is 4V and 2/3 Vcc is 8V.

So if LDR divider voltage crosses these levels then output toggles and relay changes state.

To build a Automatic Light Control Switch Circuit using IC 555 follow the below steps:

Take all the parts as shown in circuit diagram
Connect pin 1 of IC1 555 to ground
Pin 2 and pin 6 of IC1 555 connect between LDR, potentiometer VR1 and resistor R2
Connect pin 3 of IC1 555 to the base pin of transistor Q1 through resistor R3
Pin 4 and pin 8 of IC1 555 connect to positive supply of 12V
Connect pin 5 of IC1 555 to GND through capacitor C1
Connect collector of transistor Q1 to positive supply through resistor R3
Connect emitter of transistor Q1 to GND
Base pin of Q2 transistor connect to collector pin of Q1 transistor through resistor R4
Connect collector pin of of transistor Q2 to coil pin of 12V relay
Connect emitter pin of transistor Q2 to GND
Connect anode of diode D1 to coil pin of relay and cathode of D1 to positive supply

This is a simple project for Automatic Light Control Switch Circuit using IC 555

It uses only one 555 IC, two transistors, one relay and few more components.

It can control any electrical load automatically depending on light or dark.

By changing potentiometer value we can set sensitivity.

This type of circuit is good for automatic lights, alarms and energy saving projects.