1. • SUBMITTED TO:
MR. J. Sreedhar Sir
• SUBMITTED BY:
Names & Roll no’s:
A .Srikanth Reddy & 402
Abhilash & 425
Shiva teja & 408
Jaydeep &LE 404
Automatic Street Light 1
PARTICIPATORY REPORT AND ASSESSMENT(PRA)
The Automatic Street Light System Electronics is a simple and
powerful concept that uses transistor (2222A) as a switch to
automatically switch ON and OFF the light & a light-dependent
resistor (LDR) that senses the light, made of a piece of exposed
semiconductor material, i.e. cadmium sulphide, that changes its
electrical resistance from several thousand Ohms in the dark to
just a few hundred Ohms when light hits the device, the
photographic resistor. This makes them jump into the
conductive band and conduct electricity as a result. When the
light goes below the visible region, the circuit switches ON
lights automatically and switches OFF lights automatically when
light falls on it, using a sensor that senses the light just like our
eyes. The circuit also has a long response time that requires
several seconds to respond to a light intensity change.
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• LDR(Light dependence Resistor)
• Transistor 2N2222A
• PCB Board
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About the Components
• What is a LDR?
LDRs are made from semiconductor materials to enable them
to have their light sensitive properties. There are many types
but one material is popular and it is cadmium sulphide (CdS).
These LDRs or PHOTO REISTORS works on the principle of
“Photo Conductivity”. Now what this principle says is,
whenever light falls on the surface of the LDR (in this case)
the conductance of the element increases or in other words the
resistance of the LDR falls when the light falls on the surface
of the LDR. This property of the decrease in resistance for the
LDR is achieved because it is a property of semiconductor
material used on the surface
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• Working Principle of LDR
It works on the principle of photoconductivity whenever the
light falls on its photoconductive material, it absorbs its energy
and the electrons of that photoconductive material that is in the
valence band get excited and go to the conduction band and
thus increasing the conductivity as per the increased in light
Also, the energy in incident light should be greater than the
bandgap gap energy so that the electrons from the valence
got excited and go to the conduction band.
The LDR has the highest resistance in dark around 1012 Ohm
and this resistance decreases with the increase in Light.
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• Transistor 2222A
The 2N2222 transistor is an NPN bipolar junction transistor
used for general purpose applications like low-power amplifying
or switching applications. It is designed for low to medium
current, low power, medium voltage and can operate at
moderately high speeds.
The flow of current across the resistor device adjustable are
refers to as potentiometers.
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A battery is a device that is able to store electrical energy.
• PCB Board(Printed Circuit Board)
Mechanically supports and electrically electronic connects components
using conductive tracks.
• LED(Light Emitting Diode)
The switching of LED is controlled by LDR sensor depending
on day and night.
• Relay switch opens or closes electrically and automatically. Which is
energized or de-energized by the Darlington pair.
Automatic Street Light
• A relay is an electrically controllable switch
widely used in industrial controls, automobiles
• The relay allows the isolation of two separate
sections of a system with two different voltage
Automatic Street Light
Operation of Relay:
• 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 armature’s
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
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➢In this project, we have used an LDR (Light Dependent
Resistor) which is responsible for detecting light and darkness.
The resistance of LDR increases in darkness and reduces in
presence of light.
➢Now whenever LDR senses Darkness, mean no light, then
transistor Q1 turned ON due to increase in the resistance of LDR
which is responsible for voltage drop at the base of Q1. Due to a
LOW signal at the Q1 base, Q2 transistor gets a HIGH signal
from the collector of Q1 and turns ON the relay. Relay turned
ON the AC load that is connected to relay. A 10K pot is also
used for setting up the sensitivity of the circuit
• In this project we made an attempt to design Automatic Street
Light System. When in light it works as a Light Sensor with
Low Resistance and more brightness to Switch on Led. When is
dark it works as a dark Sensor with high Resistance and more
darkness to Switch on LED Our circuit has detected both the
presence of Light and darkness. Finally, the project has been
successfully implemented & tested.
Automatic Street Light