AUTOMA
AUTOMA
TIC
TIC
STREET
STREET
LIGHT
LIGHT
CONTROL USING LDR
INTRODUCTION:
INTRODUCTION:
Automatic Street Light Control System is a
Automatic Street Light Control System is a
simple yet powerful concept, which uses
simple yet powerful concept, which uses
transistor as a switch. By using this
transistor as a switch. By using this
system manual works are 100% removed.
system manual works are 100% removed.
By using this system energy consumption
By using this system energy consumption
is also reduced.
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.
Individual block explanation
:
1.Power supply
Block Diagram of Power Supply:
Regulator Filter Bridge Rectifier Step down transformer 230V AC 50Hz D.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 constant
Voltage 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 required
2.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.
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 SYMBOL
When 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
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.
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
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 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 applications
Relay 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 voltage is not sufficient to drive the
transistor into saturation region. Hence, the
transistor will be in cut-off region.
In cut-off region, I
C(Collector Current) is
zero. Because of this I
C, The relay will not
be energized, and the lamp will be in OFF
state only.
Diode is connected across the relay to
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.
