night lighting using ldr and arduino uno

AUTOMATIC NIGHT 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 5 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 RELAY 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.
In this it has been replaced by the LED.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 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
second transistor. The LED lights

 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 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 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 .

night lighting using ldr and arduino uno

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