AUTOMATIC LIGHT SWITCHING SYSTEM

 

This is the basic project that switches the led on off on the basis of their requirement.

When there is dark in the room, the led switches on automatically, as soon as the room is bright the led automatically switches off.

This project works with the help of LDR sensor that sense the sensitivity of light.

ABOUT LDR

A Light Dependent Resistor (LDR) is also called a photo resistor or a cadmium sulphide (Cd S) cell. It is also called a photoconductor. It is a photocell that works on the principle of photoconductivity. The passive components are basically a resistor whose resistance value decreases when the intensity of light decreases. This device is mostly used in light varying sensor circuit, and dark and light activated switching circuits. Some of its applications include:

·       Camera light meters

·       Street lights

·       Clock radios

·       Light beam alarms

·       Reflective smoke alarms

·       Outdoor clocks.

The snake like track shown in the hardware of LDR is Cadmium Sulphide (Cd S) film which also passes through the sides, it is used as the photoconductor and contains very few electrons when not illuminated. On the top and bottom there are metal films which are connected to the terminal leads. It is designed in such a way that provide maximum possible contact area with the two metal films of the LDR. The structure is fixed in a clear plastic or resin case, to provide free access to external light. In the absence of light it is designed such to have a high resistance in the range of mega ohms. As soon as light falls on the sensor, the electrons are liberated out and the conductivity of the material increases. When the light intensity exceeds a certain frequency, the photons absorbed by the semiconductor give band electrons the energy required to jump into the conduction band of the material. This causes the free electrons or holes to conduct electricity and thus dropping the resistance dramatically i.e. (< 1 Kilo ohm).

Advantage of this project:

·        By using this Automatic system for light controlling, we can reduce energy consumption because the manually operated lights are not switched on and off at the correct instant on large scale for example manually controlled street lights.

Disadvantage of this project:

·        In sunny and rainy days, ON and OFF time differ which is one of the major disadvantage of using timer circuits or manual operation for switching street light system.

 

Requirements:

 

·       LDR (Light Dependent Resistor)

·       2 Transistors (BC545)

·       Resistors (1k, 2.2k,470 ohm)

·       1 Light Emitting Diode (any colour)

·       Connecting wires

·       Power supply 5v

 

Circuit Diagram

 

 

Procedure

·        Insert first transistor BC547 (NPN) on breadboard.

·        Connect another transistor BC547 (NPN) on breadboard.

·        Connect wires across emitter pin of both transistors to the negative terminal of the supply.

·        Connect a wire across Collector pin of transistor 1 and Base pin of transistor 2.

·        Connect a resistor 1K across positive terminal of supply and Collector pin of transistor 1.

·        Connect Light Dependent Resistor (LDR) across positive terminal of supply and base terminal of transistor 1.

·        Insert a resistor- 2.2 K across base pin of transistor 1 and negative terminal of supply.

·        Connect a resistor of 470ohm across positive terminal of supply and anode terminal of LED (Light emitting diode) & connect the cathode terminal of LED to Collector pin of transistor 2.

 

So here the circuit is completed and it can be used anywhere where instant ON, OFF of led is required.