DESCRIPTION It is a simple and powerful concept, which uses transistor (BC 547) as a switch to switch ON and OFF the light automatically & a Light Dependent Resistors (LDR) which senses the light, made from a piece of exposed semiconductor material i.e cadmium sulphide, that changes its electrical resistance from several thousand Ohms in the dark to only a few hundred Ohms, when light hits the device, the photons give electrons energy by creating hole-electron pairs in the material. This makes them jump into the conductive band and thereby conduct electricity. The circuit automatically switches ON lights when the light goes below the visible region & automatically switches OFF lights when light fall on it, by using a sensor which senses the light just like our eyes. Also, the circuit has a long response time requiring many seconds to respond to a change in the light intensity. TEAM MEMBER SHAHRUKH JAVED MOHAMMED HASSAN M For more log on to: http://shahrukhjaved.webs.com/apps/blog/ E-mial: shahrukh.tjit14@gmail.com

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A Mini Project Report on
AUTOMATIC LIGHT & DARK SENSING SYSTEM WITH
MOSQUITO REPELLENT CIRCUIT
Submitted to
T JOHN INSTITUTE OF TECHNOLOGY
Bangalore.
Bachelor of Engineering
In
Electronics and Communication Engineering
By
Shahrukh Javed BEE141570
Mohammed Hassan M BEE141549
Session: 2016-2017
Date of submission 13th
Oct 2016
UNDER THE ESTEEMED GUIDANCE OF
PROF. BASAVANAGOUDA
DEPARTMENT OF ECE.
Department of Electronics and Communication Engineering
T JOHN INSTITUTE OF TECHNOLOGY
(Visvesvaraya Technological University)
(Approved by AICTE, Affiliated to VTU & Accredited by NAAC)
86/3, Gottigere, Bannerghatta Road, Bangalore - 560083

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PREFACE
This project provides complete information on the topic “AUTOMATIC
LIGHT & DARK SENSING SYSTEM WITH MOSQUITO REPELLENT
CIRCUIT” and maximum efforts have been taken to make the project more
comprehensive and lucid to understand.
This project covers a variety of sub topics like basic information, its working,
day to day uses in life and different aspects of mosquito repellent circuit. One
may notice a perceptible change in written in an easy dialogue style engaging
the readers constantly and included with more informatics comments.
I assure you to go through this project thoroughly to know a bit more and facts
about Light & Dark Sensing System.

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Declaration
I hereby declare that the project entitled “AUTOMATIC LIGHT & DARK
SENSING SYSTEM WITH MOSQUITO REPELLENT CIRCUIT” submitted
by us to T. John Institute of Technology, Visvesvaraya Technological
University during the degree of Bachelor of Engineering in Electronics &
Communication Engineering is a record of bonafide project work carried
out by us under the guidance of Mr. Basavanagouda.
I further declare that the work reported in this mini project has not been
submitted & will not be submitted either in part or in full for award of any
degree in this institute.
SHAHRUKH JAVED
MOHAMMED HASSAN M

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Acknowledgement
The satisfaction that accompanies the successful completion of the
task would be put incomplete without the mention of the people who made
it possible, whose constant guidance and encouragement crown all the
efforts with success.
It is my greatest pleasure to thank Dr. Arun Vikas Singh Head of
Department of Electronics and Communication, T.John Institute of
Technology for providing us heart full encouragement support and
allowing us to work in such a resourceful lab of this esteemed institute &
thereby fulfilling one of my dreams.
I whole heartedly thank my project guide Mr. Basavanagouda (Asst.
Professor Electronics & Communication Department) for his consistent
guidance, expert academic and support throughout the project, without his
great concepts & inspiration it would have been impossible.
I’m very much thankful to Mr.Chethan for his help in the laboratory for
practical guidance during this project.
I thank my parents for their emotional and financial support which they
provided during this project.
We show gratitude to our Honourable Principal Dr. H.N Thippeswamy,
for having provided all the facilities and support.
I thank to all faculties who directly and indirectly helped us in the
completion of this projects.

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INTRODUCTION
Here is my new simple Electronics project about Automatic Light & Dark sensing
system with mosquito repellent circuit.
It is a simple and powerful concept, which uses transistor (BC 547) as a switch to
switch ON and OFF the light automatically & a Light Dependent Resistors (LDR)
which senses the light, made from a piece of exposed semiconductor material i.e
cadmium sulphide, that changes its electrical resistance from several thousand Ohms
in the dark to only a few hundred Ohms, when light hits the device, the photons give
electrons energy by creating hole-electron pairs in the material. This makes them jump
into the conductive band and thereby conduct electricity.
The circuit automatically switches ON lights when the light goes below the visible
region & automatically switches OFF lights when light fall on it, by using a sensor
which senses the light just like our eyes.
Also, the circuit has a long response time requiring many seconds to respond to a
change in the light intensity.
Finally we designed a simple Light & Dark sensing along with mosquito repellent
circuit which can produce ultrasound in the frequency range of 20 kHz to 38 kHz,
which can scare away mosquitoes.

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COMPONENTS USED
SR.NO. COMPONENT NAME SPECIFICATION QUANTITY
1. INTEGRATED CIRCIUT NE555 IC 1
2. TRANSISTOR BC547 2
3. POTENTIOMETER 10K 1
4. LDR 1K 2
5. RESISTOR
220K Ω
750 Ω
330 Ω
220 Ω
2
1
1
1
6. CAPACITOR 0.01 μF 2
7. BUZZER
PIEZO
MAGNETIC
1
1
8. LED
RED
GREEN
1
1
9. SWITCH
ON/OFF 2
10. BATTERY
9V 1
Table 1. List of the Components Used.

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MAJOR COMPONENT DESCRIPTION
1. NE555 IC
Fig 1. Pin configuration of NE555 IC
The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation,
and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and
as a flip-flop element. Derivatives provide up to four timing circuits in one package.
These devices are precision timing circuits capable of producing accurate time delays or
oscillation.
In the time-delay or mono-stable mode of operation, the timed interval is controlled by a
single external resistor and capacitor network.
In the a-stable mode of operation, the frequency and duty cycle can be controlled
independently with two external resistors and a single external capacitor.
The threshold and trigger levels normally are two thirds and one-third, respectively, of VCC.
These levels can be altered by use of the control-voltage terminal. When the trigger input
falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger input
is above the trigger level and the threshold input is above the threshold level, the flip flop is
reset and the output is low. The reset (RESET) input can override all other inputs and can be
used to initiate a new timing cycle. When RESET goes low, the flip-flop is reset, and the
output goes low. When the output is low, a low-impedance path is provided between
discharge (DISCH) and ground. The output circuit is capable of sinking or sourcing current
up to 200 mA. Operation is specified for supplies of 5 V to 15 V. With a 5-V supply, output
levels are compatible with TTL inputs.

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Pin description
The connection of the pins for a DIP package is as follows:
PIN NAME PURPOSE
1 GND Ground reference voltage, low level (0 V)
2 TRIG
OUT will be high as long as the trigger is kept at low voltage.
Output of the timer totally depends upon the amplitude of the
external trigger voltage applied to this pin.
3 OUT This output is driven to approximately 1.7 V below +VCC, or
to GND.
4 RESET
A timing interval may be reset by driving this input to GND,
but the timing does not begin again until RESET rises above
approximately 0.7 volts. Overrides TRIG which overrides
THR.
5 CTRL Provides "control" access to the internal voltage divider (by
default, 2/3 VCC).
6 THR The timing (OUT high) interval ends when the voltage at THR
("threshold") is greater than that at CTRL (2/3 VCC if CTRL is
open).
7 DIS Open collector output which may discharge a capacitor
between intervals. In phase with output.
8 VCC Positive supply voltage, which is usually between 3 and 15 V
depending on the variation.
Table 2.
Features
1. Timing From Microseconds to Hours
2. Astable or Monostable Operation
3. Adjustable Duty Cycle
4. TTL-Compatible Output Can Sink or Source Up to 200 mA
Applications
• Fingerprint Biometrics.
• Iris Biometrics.
• RFID Reader.
• Pulse width modulation.
• Precision timing and pulse generation.

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2. LDR.
LDR means light dependent resistance also called a photoresistor or a cadmium
sulfide (CdS) cell is a light-controlled variable resistor.A photoresistor is made of a
high resistance semiconductor.
It is basically a photocell that works on the principle of photoconductivity.One of the
most commonly used symbol is shown in the figure below. The arrow indicates light
falling on it.
If LDR placed in darkness, the resistance of LDR increases and when light falls on it,
the resistance of LDR decreases and act as a conductor. Any LDR in the presence of
light and darkness changes its resistance is depends on the different types of LDR.
Fig 2. Light Dependent Resistor
TYPICAL CONSTRUCTION.
The snake like track shown above is the Cadmium Sulphide (CdS) film which also passes
through the sides. On the top and bottom metal film are connected to the terminal leads & the
sensitivity of a photo detector is the relationship between the light falling on the device and
the resulting output signal. Thus it is designed in such a way as to provide maximum possible
contact area with the two metal films, to provide free access to external light.
Applications: Photoconductive cells are used in many different types of circuits and
applications.

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Analog Applications Digital Applications
Camera Exposure Control. Automatic Headlight Dimmer.
Photocopy Machines - density of toner. Night Light Control.
Auto Slide Focus & Electronic Scales - dual cell. Oil Burner Flame Out.
Densitometer & Colorimetric Test Equipment. Street Light Control.
Automatic Gain Control – modulated light source. Absence / Presence (beam
breaker)
Automated Rear View Mirror. Position Sensor

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CIRCUIT DIAGRAM
Fig3.
How The Circuit Works?
Automatic Light & Dark sensing control system works like this:
When it’s dark, the LDR has high resistance. This makes the voltage at the base of the
transistor too low to turn the transistor ON. Therefore, no current will go from the collector to
the emitter of the transistor. All the current will instead pass through the LDR and the
potentiometer.
When it’s light, the LDR has low resistance. This makes the voltage at the base of the
transistor high enough to turn the transistor ON. Because the transistor is turned on, current
flows through the transistor. It flows from the positive battery terminal, through resistor and
the transistor down to the negative battery terminal. This makes the LED light up.
Principle behind Mosquito Repellent Circuit:
Human beings can hear sound in the range of 20 Hz to 20 kHz. Sound of any frequency
above 20 kHz is termed as ultrasonic sound. Insects like mosquitoes have the feature of being
able to hear this ultrasonic sound.
In mosquitoes, this feature is attributed to the presence of sensory structures in their antennae.
Usually ultrasound is transmitted by male mosquitoes and received by female mosquitoes.
The ultrasound produces a stress on the antennae of the mosquitoes and repels them away.

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Mosquito Repellent Circuit Operation:
Once the switch is closed, the 555 timer gets the power supply. As per the inner circuit,
initially the capacitor voltage will be zero and hence voltage at threshold and trigger pin will
be zero. As the capacitor charges through resistors, at a certain point voltage at threshold pin
is less than the capacitor voltage. This causes a change in timer output. The capacitor now
starts discharging through resistor i.e. the discharge pin and continues so until the output
voltage is back to the original.
Thus the output signal is an oscillating signal with frequency 38 KHz. The output from this
astable multivibrator circuit drives a 38 KHz piezo buzzer, producing ultrasound at regular
repetitions. On varying the value of potentiometer the output frequency can also be
varied.

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Advantage
 Easy to operate & Fast response.
 Smaller in size.
 Low power consumption very small voltage for its operation.
 Sensor (LDR) is cheap and is readily available in many sizes and shapes.
Disadvantages
 Highly inaccurate with a response time of about tens or hundreds of
milliseconds.
 It requires a lot of frequency setting & It shows effect for lesser mosquito
population.
Applications:
 Light intensity Control for Street Lights
 Lighting Switch from Sunset to Sunrise
 Needs no manual operation for switching ON and OFF.
 Circuit can be used as a mosquito repellent.

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CONCLUSION
In this project we made an attempt to design Automatic Light & Dark sensing system
with mosquito repellent circuit which can sense in light as well as in darkness.
When in light- Light Sensor.
Low Resistance –More Brightness to Switch on Led.
When is dark- Dark Sensor.
Low Resistance –More Darkness to Switch on Led.
Our circuit has detected both the presence of Light and darkness.
Mosquito Repellent.
A simple circuit is designed which can produce ultrasound in the frequency range of
20 kHz to 38 kHz, which can scare away mosquitoes.
Finally, the project has been successfully implemented & tested. It really persuades us
to do more and more perhaps in better way in future.
I am proud to express my delight as the project I embarked upon is successfully
finished in such a short span. The project gave us more confidence that we will be
able to put in practice, whatever the theoretical knowledge we gained during the
course of study till now.