The document describes a circuit project using an LDR (light dependent resistor) on a breadboard that acts as a dark sensor. The circuit uses two transistors, an LED, an LDR, resistors, a battery, and a buzzer. When light falls on the LDR, the LED and buzzer turn off, and when light is blocked from the LDR, the LED glows and buzzer sounds. The document provides details on the components used, breadboard connections, circuit diagrams, and the working of the circuit.

1. DARK SENSORUSING
LDR ON BREADBOARD
It spreads light in the dark and remains off in the light.
SUBMITTED BY:
SAQIBIQBAL (14-CS-07)
FAWAZ ALI (14-CS-09)
SUBMITTED TO:
Mr. JIBRAN
DATE OF SUBMISSION:
March 16, 2015

2. ABSTRACT
Thecircuit presented here is a project of a DARKSENSORusingLDR
(LightDependent Resistor)on BREADBOARD.
LDRs area particularlyconvenient electronics component touse. They
provide largechange in resistancefor changes in lightlevel.
In view of their low cost,easeof manufacture, and easeof useLDRs have
been used in a varietyof different applications.Atone timeLDRs were
used in photographiclightmeters, and even now theyare stillusedin a
variety of applications whereit is necessary todetect lightlevels.
We can usedarkor lightsensors instreetlightand we thelightsensorcan
give therobot visionand makeit easier for it to operateautonomously.

3. TABLE OF CONTENTS
1. Introduction……………………………………………………………………………………………………………………………….......................4
2. BreadBoard………………………………………………………………..…………………………………………………………………………………...5
3. Project…..………………………………………………………………………………………………………………………………………...................6
4. Components…………………………………………………………………………………………………………………………………………………….7
4.1. Transisitor……………….…………………….………………………………………….…………………………………..………………………..7
4.2. LED.…………………………………...…………….………………………….………………………………………………..………………………..7
4.3. LDR.……………….………………………………………………………..……………………………….…………………..…………………………8
4.4. Resistors……….……….……………………………………………….……………………………………………………………………………….8
4.5. Battery…………………………………………………………………………………………………………………………………………………....9
4.6. Buzzer………………………………………………………………………………………………………………………………………….………....9
5. Steps Of Construction And Working….…………………………………………………………………………………………………………….10
6. CircuitDiagram.…………………………………………….…………………………………………………….....................………………….....13
7. Schematic Diagram…………………………………………………………………………………………………………………………………………13
8. Acknowledgement ………………………………….……………………………………………………………………………………………………..14
9. Biblography…………………………………………….……………………………………………………………………………………………………..14
INTRODUCTION

4. Lighting can account for 10-38% of the total energy bill in typical cities
worldwide. The main consideration in the present field technologies are
Automation, Power consumption and cost effectiveness. Automation is
intended to reduce man power with the help of intelligent systems.
Power saving is the main consideration forever as the sources of the
power are getting diminished due to various reasons.
The main aim of this project is to saving system with LDR this is to save
the power. We want to save power automatically instead of doing
manual. So it’s easy to cost effectiveness. This saved power can be used
in some other cases. So in villages, towns etc. we can design intelligent
systems for the usage of light or we can also use this to reduce the
electricity bill of our home. This project can also be used for security of
the houses, banks, etc.
WHAT IS BREADBOARD

5. A breadboard is a device for testing temporary electronics projects. Components used to test a
circuit can be reused for other projects. None of the components are damaged.
Almost all people start to learn electronics using breadboard because it is the simplestway of
making circuit. The photograph shows a typical small breadboard which is suitable for beginners
buildingsimple circuits with one or two ICs (chips).
Connections on Breadboard
Breadboard has many tiny sockets or holes arranged on a 0.1’’ grid. The leads or terminals of most
of the components like resistors, diodes, transistors, etc. can be pushed straight into the holes.
A breadboard has 4 rows of holes at the top and 4 rows at the bottom and there are several
columns of holes in the middle.
There are two groups of vertical columns in the middle part, as you see in the picture below it has
been separated by a blue rectangular block.
None of the rows and columns are linked to one another.
The holes in rows are linked horizontally and column holes are linked vertically.

6. Converting a circuit diagram to a breadboard layout is not straight forward because the
arrangement of components on breadboard looks quite differentfrom the circuit diagram. When
putting parts on breadboard you must concentrate on their connections, not their positions on the
circuit diagram.
OUR PROJECT

7. COMPONENTS
1) 2 NPN Transistors (Code no: BC547)
A BC547 transistor is a negative-positive-negative (NPN) transistor that is used for many
purposes. Together with other electronic components, such as resistors, coils, and capacitors, it
can be used as the active component for switches and amplifiers.
2) 1 LED
A semiconductor diode that emits light when conducting current and is used in electronic
equipment

8. 3) 1 LDR (Light Dependent Resistor)
Light Dependent Resistor or Photoresistor, which is a passive electronic component, basically a
resistor which has a resistance that varies depending of the light intensity. A photoresistor is
made of a high resistance semiconductor that absorbs photons and based on the quantity and
frequency of the absorbed photons the semiconductor material give bound electrons enough
energy to jump into the conduction band. The resulting free electrons conduct electricity
resulting in lowering resistance of the photoresistor. The number of electrons is dependent of
the photons frequency.
4) 4 Resistors (330 ohms, 470 ohms, 1k ohms, 4.7k ohms)
A resistor is an electrical component that limits or regulates the flow of electrical current in an
electronic circuit. Resistors can also be used to provide a specific voltage for an active device
such as a transistor.

9. 5) 9 volts battery
A battery is an electrochemical cell (or enclosed and protected material) that can be charged
electrically to provide a static potential for power or released electrical charge when needed.
6) Buzzer
An electrical device, similar to a bell that makes a buzzing noise and is used for signaling.

10. STEPS OF CONSTRUCTION AND
WORKING
Step 1: Put first transistor Q1-BC547 on breadboard as shown in the picture.
Step 2: Put another transistor Q2- BC547 on breadboard as in step 1.
Step 3: Put wires across emitter pin of both transistors and -ve terminal of battery(lowest/
bottom row of breadboard.)

11. Step 4: Put a wire across Collector pin of transistor Q1 and Base pin of transistor Q2.
Step 5: Put a resistor 1K across positive terminal of battery (topmost row of breadboard) and
Collector pin of transistor Q1.
Step 6: Insert Light dependent resistor (LDR) across positive terminal of battery (topmost row of
breadboard) and base terminal of transistor Q1.

12. Step 7: Put a resistor- 330 Ohm across base pin of transistor Q1 and negative terminal of battery
(lowest bottom row of breadboard).
Step 8: Put a resistor 330R across positive terminal of battery (topmost row of breadboard) and
anode terminal of LED (Light emitting diode) & Connect the cathode terminal of LED to Collector
pin of transistor Q2. Do same to attach the buzzer
The circuit is ready for testing. Connect battery terminals and see the output. As you block light
fallingon LDR (Light dependent resistor), the LED glows and buzzer produces a sound.

13. Circuit Diagram:
Schematic Diagram

14. Acknowledgement
We wishtothank all our respectedteachersandfriendsfortheirexcellentcontributionandsupportfor
the completionof thisproject. Especiallywe are verymuchthankful toourclassfellow SyedMuhammad
Taha (D-14-CS-03) for hisguidance aswell asfor providingnecessaryinformationregardingthe project
& also forhissupportin completingthe project.
BIBLOGRAPHY
1) http://www.buildcircuit.com/dark-sensor-on-breadboard/
2) http://mjkcircuits.blogspot.com/2014/07/dark-sensor-using-ldr-on-breadboard.html
3) http://www.instructables.com/id/Dark-Sensor-with-LDR-transistor-and-a-LED/