AUTOMATIC STREET LIGHT CONTROL USING LDR

AUTOMATIC STREET LIGHT CONTROL USING LDR

INTRODUCTION:

Automatic Street Light Control System is a simple yet powerful concept, which uses transistor as a switch. By using this system manual works are 100% removed.By using this system energy consumption is also reduced.

Working Principle:

The automatic streetlight control system operates on 12 V DC supply. The automatic streetlight controller has a photoconductive device whose resistance changes proportional to the extent of illumination, which switches ON or OFF the LED with the use of transistor as a switch.

Light dependent resistor, a photoconductive device has been used as the transducer to convert light energy into electrical energy.

BLOCK DIAGRAM:

Individual block explanation:

1.Power supplyBlock Diagram of Power Supply:

RegulatorFilterBridge RectifierStep down transformer230V AC 50HzD.C Output

Power supply: The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V Transformer: Usually, DC voltages are required to operate various electronic equipment and these voltages are 5V, 9V or 12V. But these voltages can not be obtained directly.Rectifier: The output from the transformer is fed to the rectifier. It converts A.C. into pulsating D.C.Filter: In this capacitive filter is used. It removes the ripples from the output of rectifier and smoothens the D.C. Output received from this filter is constant until the mains voltage and load is maintained constantVoltage regulator: As the name itself implies, it regulates the input applied to it. A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. In this the power supply of 5V and 12V are required2.Light dependent resistor(LDR): LDR senses the illumination level and gives input signal as voltage drop.3. Amplifier: Darlington circuit amplifies the input current to get maximum current gain.4. Switch: Relay switch opens or closes electrically and automatically, which is energized or de-energized by the Darlington pair.5.Street light: Street light is the output of the circuit. In this it has been replaced by the LED.

LDR:

A Light Dependent Resistor (LDR) is special type of resistor that reacts to changes in light level. The resistance of the LDR changes as different amounts of light fall on the top 'window' of the device. This allows electronic circuits to measure changes in light level.

LIGHT DEPENDENT RESISTOR AND ITS CIRCUIT SYMBOLWhen the light level is low the resistance of the LDR is high. This prevents current from flowing to the base of the transistors. Consequently the LED does not light.However, when light shines onto the LDR its resistance falls and current flows into the base of the first transistor and then the second transistor. The LED lights

Top view and side view of LDR

Light sensitive material is arranged in the form of long stripped zigzagged across a disc shaped base with protective sides. For additional protection glass or plastic protection may be included. The two ends of the stripes are brought out to connecting pins below the base as shown above.

Light-emitting diode (LED)

Light-emitting diodes are elements for light signalization in electronics. They are manufactured in different shapes, colors and sizes. For their low price, low consumption and simple use, they have almost completely pushed aside other light sources- bulbs at first place. They perform similar to common diodes with the difference that they emit light when current flows through them.

Light emitting diode and circuit symbol RELAYS:

A relay is an electrically controllable switch widely used in industrial controls, automobiles and appliances.

The relay allows the isolation of two separate sections of a system with two different voltage sources.

Circuit symbol of a relay

Inductor

Operation:

When a current flow through the coil, a magnetic field is created around the coil i.e., the coil is energized. This causes the armature to be attracted to the coil. The armatures contact acts like a switch and closes or opens the circuit. When the coil is not energized, a spring pulls the armature to its normal state of open or closed. There are all types of relays for all kinds of applicationsRelay Operation and use of protection diodes

WORKING PROCEDURE:

LDR offers Very high Resistance in darkness. In this case the voltage drop across the LDR is more than 0.7V.This voltage is more sufficient to drive the transistor into saturation region.In saturation region, IC (Collector current) is very high. Because of this IC , The relay gets energized, and switches ON the lamp.LDR offers Very low Resistance in brightness. In this case the voltage drop across the LDR is less than 0.7V.This voltage is not sufficient to drive the transistor into saturation region. Hence, the transistor will be in cut-off region.In cut-off region, IC (Collector Current) is zero. Because of this IC , The relay will not be energized, and the lamp will be in OFF state only. Diode is connected across the relay to neutralize the reverse EMF generated.

CONCLUSION:

By employing this circuit, energy consumption can be reduced considerably as the light switches ON or OFF automatically in appropriate time.

Errors which occur due to manual operation can be eliminated completely.

The construction of the circuit is also simple .Thank You.