19-06-2012, 04:46 PM
Automatic street light control
Automatic street light control.pptx (Size: 920.06 KB / Downloads: 326)
INTRODUCTION
Automatic Street Light Control System is a simple and powerful concept
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
PRINCIPLE
The automatic streetlight control system operates on 12 V DC supply.
LDR whose resistance changes proportional to the extent of illumination, which switches ON or OFF the LED with the use of transistor as a switch
The central dogma of the circuit is that the change in voltage drop across the LDR on illumination or darkness, switches the transistor between cut-off region or saturation region and switches OFF or ON the LED.
Light Dependent resistor
A light dependent resisitor is a resisitor whose resistance changes with the intensity of incident light
The working principle of light dependent resistor is photoelectric effect.
Advantages :
Errors which occur due to manual operation also can be eliminated
cost effective
high sensitivity
reproducibility
construction is simple with locally available components
The circuit is designed in such a way that the extent of darkness at which the light has to switch ON or OFF also can be tailored whenever it is needed
Applications:
Application 1:
The above circuit can be powered from a battery, which can be charged during day time by harvesting the solar energy through a solar cell as shown below: