Description
ABSTRACT
This work is on a phototransistor which is a resistor whose resistance changes in response to light. A photoresistor resistance decreases with the strength of the light. In this study a simple circuit that demonstrates the operation of a photoresistor was drawn. The photoresistor circuit is all about when the photoresistor is exposed to darkness. When exposed to darkness, the photoresistor has very high resistance, so current cannot flow through the circuit. The LED receives no current and, thus, does not light up. The LED stays off as long as the photoresistor is exposed to darkness.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE PROJECT
- AIM/OBJECTIVE OF THE PROJECT
- ADVANTAGES OF PHOTORESISTOR
- DISADVANTAGES OF PHOTORESISTOR
- APPLICATIONS OF PHOTORESISTORS
CHAPTER TWO
LITERATURE REVIEW
- OVERVIEW OF PHOTORESISTOR
- TYPES OF PHOTORESISTORS
- PHOTORESISTOR SYMBOL
- LDR FREQUENCY DEPENDENCE
- PHOTORESISTOR / LIGHT DEPENDENT RESISTOR LATENCY
- LIGHT DEPENDENT RESISTOR SPECIFICATIONS
- TYPES OF LIGHT SENSORS
CHAPTER THREE
METHODOLOGY
- WORKING PRINCIPLE OF PHOTORESISTOR
- SYSTEM BLOCK DIAGRAM
- SYSTEM CIRCUIT DIAGRAM
- CIRCUIT OPERATION
CHAPTER FOUR
RESULT ANALYSIS
- RESULTS AND DISCUSSION
- HOW TO TEST AN LDR
- DESIGN CONSIDERATIONS
CHAPTER FIVE
- CONCLUSION AND RECOMMENDATION
- REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Light is a form of electromagnetic radiation. The electromagnetic spectrum is divided into many bands from which Light usually refer to the Visible Spectrum. But in physics gamma rays, X-rays, microwaves and radio waves are also considered as Light. The visible light spectrum has wavelengths in the range of 400-700 nanometers, lying between infrared ray spectrum and ultraviolet spectrum.
The name photoresistor is the combination of words: photon (light particles) and resistor. A photoresistor is a type of resistor whose resistance decreases when the intensity of light increases. In other words, the flow of electric current through the photoresistor increases when the intensity of light increases.
Photoresistors are also sometimes referred as LDR (Light Dependent Resistor), semiconductor photoresistor, photoconductor, or photocell. Photoresistor changes its resistance only when it is exposed to light.
A photoresistor can be applied in light-sensitive detector circuits and light-activated and dark-activated switching circuits acting as a resistance semiconductor. In the dark, a photoresistor can have a resistance as high as several megaohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within certain wavelength bands.
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device.
1.2 AIM OF THE STUDY
The main aim of this study is to carry out a research on a photoresistor which is a passive component that decreases resistance with respect to receiving luminosity (light) on the component’s sensitive surface. The objectives are:
- The description of photoresistor shall be known
- Applications, advantages, disadvantages and operating principle of the device shall also be known.
1.3 ADVANTAGES OF PHOTORESISTOR
- Small in size
- Low cost
- It is easy to carry from one place to another place.
1.4 DISADVANTAGES OF PHOTORESISTOR
- The accuracy of photoresistor is very low.
1.5 APPLICATIONS OF PHOTORESISTORS
- Photoresistors are used in streetlights to control when the light should turn on and when the light should turn off. When the surrounding light falls on the photo resistor, it causes the streetlight to turnoff. When there is no light, the photoresistor causes the street light to turn on. This reduces the wastage of electricity.
- They are also used in various devices such as alarm devices, solar street lamps, night-lights, and clock radios.
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