Automatic Street Light Controller

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  • Topic: Diode, P-n junction, Bipolar junction transistor
  • Pages : 16 (5204 words )
  • Download(s) : 1403
  • Published : January 6, 2013
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1. Introduction

Automatic Street Light Control System is a simple and powerful concept, which uses transistor as a switch to switch ON and OFF the street light automatically. By using this system manual works are removed. It automatically switches ON lights when the sunlight goes below the visible region of our eyes. It automatically switches OFF lights under illumination by sunlight. This is done by a sensor called Light Dependant Resistor (LDR) which senses the light actually like our eyes. By using this system energy consumption is also reduced because now-a-days the manually operated street lights are not switched off properly even the sunlight comes and also not switched on earlier before sunset. In sunny and rainy days, ON time and OFF time differ significantly which is one of the major disadvantage of using timer circuits or manual operation. This project exploits the working of a transistor in saturation region and cut-off region to switch ON and switch OFF the lights at appropriate time with the help of an electromagnetically operated switch. Automatic Streetlight needs no manual operation of switching ON and OFF. The system itself detects whether there is need for light or not. When darkness rises to a certain value then automatically streetlight is switched ON and when there is other source of light, the street light gets OFF. The extent of darkness at which the street light to be switched on can also be tailored using the potentiometer provided in the circuit. Moreover, the circuit is carefully designed to avoid common problems like overload, relay chattering and inductive kick back in relay.

2. 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. The central dogma of the circuit is that the change in voltage drop across the light dependent resistor on illumination or darkness switches the transistor between cut-off region or saturation region and switches OFF or ON the LED.

3. Block Diagram &
Circuit Diagram

3.1 Block Diagram

3.1.1 Individual Block Explanation
Power supply: AC power supply is stepped down, rectified and filtered to get almost ripple-free DC output for the operation of the circuit.

Light dependent resistor: LDR senses the illumination level and gives the input signal as voltage drop. Amplifier: Darlington circuit amplifies the input current to get maximum current gain. Switch: Relay switch closes or opens electrically and automatically, which is energized or de energized by the Darlington pair.

Street light: Street light is the output of the circuit. In this circuit, it has been replaced by LED

3.1.2 Amplification Unit
Darlington pair
In the Darlington configuration, the emitter current of one transistor becomes the base current of the second, so that the amplified current from the first is amplified further by the second transistor. This gives the Darlington pair a very high current gain such as 10000, since the Darlington configuration acts like one transistor with a beta which is the product of the betas of the two transistors. Darlington configuration can be used where high output currents are needed. The Darlington configuration has quite high input impedance. A Darlington pair can be sensitive enough to respond to the current passed by skin contact...
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