MAJOR PROJECT REPORTOn

Design and Implementation of Maximum Solar Power Tracking System

Submitted by

Gaurav Sharma(109755)Sukrit Mehta(109760)

Rohit Kumar Vidhuri(109488)Pooja Singh(109459)Harsh Goyal(109508)

Vinod Kumar Meena(109468)

Under the guidance of

Dr. Ratna Dahiya,Associate Professor,

In the partial fulfillment for the 8th semesterB. Tech in Electrical Engineering

Department of Electrical Engineering,National Institute of Technology,

Kurukshetra

CERTIFICATE

This is to certify that major project titled Design and Implementation of Maximum Solar Power Tracking System in partial fulfillment of B.Tech. (Electrical Engineering) VIII semester has been carried out under the guidance of Dr. Ratna Dahiya, Associate Professor, Department of Electrical Engineering, NIT Kurukshetra and to the best of our knowledge is an original work and has not been submitted as project/thesis in any other university or institute.

Gaurav Sharma(109755)

Sukrit Mehta (109760)

Rohit Kumar Vidhuri (109488)

Pooja Singh(109459)

Harsh Goyal(109508)

Vinod Kumar Meena(109468)

Certified that above information is correct to the best of my knowledge.

Date : Dr. Ratna Dahiya Associate Professor

Department of Electrical Engineering NIT, Kurukshetra

ACKNOWLEDGEMENT

The satisfaction that accompanies the successful completion of any task would be incomplete without the mention of the people who made it possible and whose constant guidance and encouragement crown all the efforts with success.First and foremost we would hereby like to express our deepest gratitude to Dr. Ratna Dahiya for being an erudite project guide. We are thankful to him for providing the right direction for the conduct of the project and also for his enlightening guidance that was vital to the success of the project. He exuded in us tremendous faith and confidence which inspired us to conquer all the challenges that we faced during the project. Even the present project report would not have been possible without his valuable guidance.Without any dilution, we would also like to thank all the staff members of the Computer labs since their co-operation and help to arrange the entire necessary infrastructure for the carrying out the project was invaluable. Last but not the least, we offer our deepest gratefulness and thus owe a large amount of credit for this success to our respected parents for being our support throughout our ups and downs, sharing the most precious bond of love and affection we have ever known in this life.

Gaurav Sharma(109755)Sukrit Mehta(109760)

Rohit Kumar Vidhuri(109488)Pooja Singh(109459)Harsh Goyal(109508)

Vinod Kumar Meena(109468)

CONTENTS

1. Abstract2. Chapter 1

a. Introductionb. Classification of Energy Resourcesc. Solar Energyd. Application of Solar Energye. Solar Cellf. Motivation for the projectg. Justification for the projecth. Sun Tracking Techniques

3. Chapter 2 (Project Overview and Designing)a. The Working Principlesb. Block Diagram/Pictures of Modelc. Design of Solar Tracking Systemd. Workinge. Flow Chart

4. Chapter 3a. Hardware Descriptionb. Software Description

5. Experimental Observations6. Conclusion7. References

ABSTRACT

The following report documents the design, development and production of a Sun-

Tracking System. The primary purpose of this system is to maximize the amount of solar

energy that can be received from the sun.

Due to the negative environmental effects that conventional energy production cause, an

alternative source of energy has to be developed. This new source has to be pollution and

hazardous by-product free. One of the few energy options that meet these criteria is solar

energy. However, for solar energy to be a viable source the efficiency of present

collection methods has to be increased. This is where the importance of a sun-tracking

system comes into play. By tracking the sun, such that the suns rays always strike

normal to the arrays surface, more energy can be received. The system outlined in this

report proved to be successful in maximising the energy received from the sun. Although

it is not the only solution available, it is however, the most efficient given the time, budget

and material restrictions involved with an undergraduate thesis.

CHAPTER 1

Introduction

Energy is a crucial input in the process of economic, social and industrial development. Energy plays a vital role in our present day life. The degree of development and civilization of a country is measured by the utilization of energy by human beings for their needs.Being the most important form in this universe is required in almost all the things we do. Whether we walk or we rest it is the energy which is always and continuously getting transformed.Energy is available in different forms like Electrical energy, Mechanical energy, Chemical energy, Heat energy and Nuclear energy etc.Day by day, the energy consumption increase. The worlds fossil fuel supply coal, petroleum and natural gas will be depleted in few hundred years. The rate of energy consumption increasing, supply is decreasing resulting in inflation and energy shortage.

Classification of energy resources

Energy classification may be based on its nature, quality, availability and storing capacity.

Commercial and non commercial energy resources

These are also called primary energy resources. These are available in nature in raw form e.g. coal, natural gas, wind and water etc. The other resources which are freely available like, Solar energy, agricultural wastes etc. are known as non commercial energy resources. Hydro electric power and Nuclear power also comes under commercial resources.

Renewable and non-Renewable energy resources

Renewable resources are those resources which can be used to produce energy again and again e.g. Solar energy, Geothermal energy, Tidal energy etc.Non Renewable resources cannot be replaced once they are used e.g. Coal, Oil, Gas etc. These energy resources are liimited and would get exhausted within a period of time.

Conventional and non- conventional energy resources

Coal, oil and gas are commonly known as conventional energy resources. As the population is increasing and standard of living is rising, more energy needs will be in future. The scope of meeting these energy demands through conventional resources is limited due to their insufficient availability. Therefore, large amount of energy can be derived from non commercial resources like Agricultural waste, firewood, solar, wind etc. These resources are known as non- conventional energy resources. Conventional

energy resources are used conventionally and can be stored. The non- conventional energy resources cannot be easily stored.

SOLAR ENERGY

The most abundant form of energy which the earth receives is the SOLAR ENERGY.The earth receives the energy of sun in the form of electromagnetic radiations. Solar energy is cheap and free from pollution. In India, most of the parts receive 4 to 7 Kwh of solar radiations per sq. km per day. India receives solar energy equivalent to more than 5000 trillion Kwh per year, which is far more than its total annual consumption. Though the energy density is low and the availability is not continuous, it has now become possible to harness this abundantly available energy very reliably for many purposes by converting to heat or through direct generation of electricity.

Solar energy can be used in the following ways:

1) Convert the solar energy into electricity2) Convert the solar energy into thermal energy3) Photosynthesis

The main applications of solar energy are:

1) Heating of buildings2) Cooling of buildings3) Photo-voltaic conversion4) Solar cookers5) Solar water heaters6) Solar air heaters

Solar energy is collected by a device called solar collectors. Solar collectors collect the radiations and transfer the energy to a fluid passing in contact with it. For home heating, water heating flat plate collectors are used. Concentrating collectors are used to concentrate the energy on absorbing surface by reflections. Parabolic collectors are used in solar power plants. The energy collected by these collectors is used to heat the water which is converted into steam. This steam is used to run turbine which is coupled with alternators.

THE SOLAR CELL

Solar cell

A solar cell (also called a energy of light directly into photoelectric cell (in that its electricaresistancevary when light is incident upon it) which, when exposed to light, can generate and support an electric current without being attached to any external voltage source.

The term "photovoltaic" comes fro"Volt", the unit of electro-motive force, the of the Italian physicist Alessandro VoltaThe term "photo-voltaic" has be

Theory

The solar cell works in three steps:

1. Photons in sunlightmaterials, such as silicon.

2. Electrons (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this elecsolar cells, the electrons are only allowed to move in a single direction.

3. An array of solar cells converts solar energy into a usable amount of (DC) electricity.

THE SOLAR CELL

(also called a photovoltaic cell) is an electrical device that converts the directly into electricity by the photovoltaic effect. It is a form of

(in that its electrical characteristicse.g. current, voltage, or vary when light is incident upon it) which, when exposed to light, can

generate and support an electric current without being attached to any external voltage

The term "photovoltaic" comes from the Greek (phs) meaning "light", and from motive force, the volt, which in turn comes from the last name

Alessandro Volta, inventor of the battery (electrochemical cellvoltaic" has been in use in English since 1849.

The solar cell works in three steps:

hit the solar panel and are absorbed by semiconducting materials, such as silicon.

(negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.An array of solar cells converts solar energy into a usable amount of

) is an electrical device that converts the . It is a form of

e.g. current, voltage, or vary when light is incident upon it) which, when exposed to light, can

generate and support an electric current without being attached to any external voltage

) meaning "light", and from from the last name

electrochemical cell).

hit the solar panel and are absorbed by semiconducting

(negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel

tricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.An array of solar cells converts solar energy into a usable amount of direct current

Building block of a solar panel

Assemblies of photovoltaic cells are used to make solar modules which generate electrical power from sunlight. Multiple cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or "solar photovoltaic module," as distinguished from a "solar thermal module" or "solar hot water panel." The electrical energy generated from solar modules, referred to as solar power, is an example of solar energy. A group of connected solar modules (such as prior to installation on a pole-mounted tracker system) is called an "array."

Manufacture

Because solar cells are semiconductor devices, they share some of the same processing and manufacturing techniques as other semiconductor devices such as computer and memory chips. However, the stringent requirements for cleanliness and quality control of semiconductor fabrication are more relaxed for solar cells. Most large-scale commercial solar cell factories today make screen printed poly-crystalline or single crystalline silicon solar cells.

Poly-crystalline silicon wafers are made by wire-sawing block-cast silicon ingots into very thin (180 to 350 micrometer) slices or wafers. The wafers are usually lightly p-typedoped. To make a solar cell from the wafer, a surface diffusion of n-type dopants is performed on the front side of the wafer. This forms a pn junction a few hundred nanometers below the surface.

Anti-reflection coatings, to increase the amount of light coupled into the solar cell, are typically next applied. Silicon nitride has gradually replaced titanium dioxide as the anti-reflection coating, because of its excellent surface passivation qualities. It prevents carrier recombination at the surface of the solar cell. It is typically applied in a layer several hundred nanometers thick using plasma-enhanced chemical vapor deposition (PECVD). Some solar cells have textured front surfaces that, like anti-reflection coatings, serve to increase the amount of light coupled into the cell. Such surfaces can usually only be formed on single-crystal silicon, though in recent years methods of forming them on multicrystalline silicon have been developed.

The wafer then has a full area metal contact made on the back surface, and a grid-like metal contact made up of fine "fingers" and larger "bus bars" are screen-printed onto the front surface using a silver paste. The rear contact is also formed by screen-printing a metal paste, typically aluminium. Usually this contact covers the entire rear side of the cell, though in some cell designs it is printed in a grid pattern. The paste is then fired at several hundred degrees Celsius to form metal electrodes in ohmic contact with the silicon. Some companies use an additional electro-plating step to increase the cell efficiency. After the metal contacts are made, the solar cells are interconnected by flat

wires or metal ribbons, and assembled into modules or "solar panels". Solar panels have a sheet of tempered glass on the front, and a polymer encapsulation on the back.

Efficiency

The efficiency of a solar cell may be broken down into reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. The overall efficiency is the product of each of these individual efficiencies.

A solar cell usually has a voltage dependent efficiency curve, temperature coefficients, and shadow angles.

Due to the difficulty in measuring these parameters directly, other parameters are measured instead: thermodynamic efficiency, quantum efficiency, integrated quantum efficiency, VOC ratio, and fill factor. Reflectance losses are a portion of the quantum efficiency under "external quantum efficiency". Recombination losses make up a portion of the quantum efficiency, VOC ratio, and fill factor. Resistive losses are predominantly categorized under fill factor, but also make up minor portions of the quantum efficiency, VOC ratio.

The fill factor is defined as the ratio of the actual maximum obtainable power to the product of the open circuit voltage and short circuit current. This is a key parameter in evaluating the performance of solar cells. Typical commercial solar cells have a fill factor > 0.70. Grade B cells have a fill factor usually between 0.4 to 0.7. Cells with a high fill factor have a low equivalent series resistance and a high equivalent shunt resistance, so less of the current produced by the cell is dissipated in internal losses.

Materials

Various materials display varying efficiencies and have varying costs. Materials for efficient solar cells must have characteristics matched to the spectrum of available light. Some cells are designed to efficiently convert wavelengths of solar light that reach the Earth surface. However, some solar cells are optimized for light absorption beyond Earth's atmosphere as well. Light absorbing materials can often be used in multiple physical configurations to take advantage of different light absorption and charge separation mechanisms.

Materials presently used for photovoltaic solar cells include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide.

Many currently available solar cells are made from bulk materials that are cut into wafersbetween 180 to 240 micrometers thick that are then processed like other semiconductors.

Other materials are made as thin-films layers, organic dyes, and organic polymers that are deposited on supporting substrates. A third group are made from nanocrystals and used as

quantum dots (electron-confined nanoparticles). Silicon remains the only material that is well-researched in both bulk and thin-film forms.

Crystalline silicon

By far, the most prevalent bulk material for solar cells is crystalline silicon (abbreviated as a group as c-Si), also known as "solar grade silicon". Bulk silicon is separated into multiple categories according to crystallinity and crystal size in the resulting ingot, ribbon, or wafer.

1. Monocrystalline silicon (c-Si): often made using the Czochralski process. Single-crystal wafer cells tend to be expensive, and because they are cut from cylindrical ingots, do not completely cover a square solar cell module without a substantial waste of refined silicon. Hence most c-Si panels have uncovered gaps at the four corners of the cells.

2. Polycrystalline silicon, or multicrystalline silicon, (poly-Si or mc-Si): made from cast square ingots large blocks of molten silicon carefully cooled and solidified. Poly-Si cells are less expensive to produce than single crystal silicon cells, but are less efficient. United States Department of Energy data show that there were a higher number of polycrystalline sales than monocrystalline silicon sales.

3. Ribbon silicon is a type of polycrystalline silicon: it is formed by drawing flat thin films from molten silicon and results in a polycrystalline structure. These cells have lower efficiencies than poly-Si, but save on production costs due to a great reduction in silicon waste, as this approach does not require sawing from ingots.

4. Mono-like-multi silicon: Developed in the 2000s and introduced commercially around 2009, mono-like-multi, or cast-mono, uses existing polycrystalline casting chambers with small "seeds" of mono material. The result is a bulk mono-like material with poly around the outsides. When sawn apart for processing, the inner sections are high-efficiency mono-like cells (but square instead of "clipped"), while the outer edges are sold off as conventional poly. The result is line that produces mono-like cells at poly-like prices.

Thin films

Thin-film technologies reduce the amount of material required in creating the active material of solar cell. Most thin film solar cells are sandwiched between two panes of glass to make a module. Since silicon solar panels only use one pane of glass, thin film panels are approximately twice as heavy as crystalline silicon panels. The majority of film panels have significantly lower conversion efficiencies, lagging silicon by two to three percentage points. Thin-film solar technologies have enjoyed large investment due to the success of First Solar and the largely unfulfilled promise of lower cost and flexibility compared to wafer silicon cells, but they have not become mainstream solar products due to their lower efficiency and corresponding larger area consumption per watt production. Cadmium telluride (CdTe), copper indium gallium selenide (CIGS) and

amorphous silicon (A-Si) are three thin-film technologies often used as outdoor photovoltaic solar power production. CdTe technology is most cost competitive among them. CdTe technology costs about 30% less than CIGS technology and 40% less than A-Si technology in 2011.

Cadmium telluride solar cell

A cadmium telluride solar cell uses a cadmium telluride (CdTe) thin film, a semiconductor layer to absorb and convert sunlight into electricity. Solarbuzz has reported that the lowest quoted thin-film module price stands at US$0.84 per watt-peak, with the lowest crystalline silicon (c-Si) module at $1.06 per watt-peak.

The cadmium present in the cells would be toxic if released. However, release is impossible during normal operation of the cells and is unlikely during res in residential roofs. A square meter of CdTe contains approximately the same amount of Cd as a single C cell Nickel-cadmium battery, in a more stable and less soluble form.

Copper indium gallium selenide

Copper indium gallium selenide (CIGS) is a direct band gap material. It has the highest efficiency (~20%) among thin film materials (see CIGS solar cell). Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. Recent developments at IBM and Nanosolar attempt to lower the cost by using non-vacuum solution processes.Gallium arsenide multijunction High-efficiency multijunction cells were originally developed for special applications such as satellites and space exploration, but at present, their use in terrestrial concentrators might be the lowest cost alternative in terms of $/kWh and $/W. These multijunction cells consist of multiple thin films produced using metalorganic vapour phase epitaxy. A triple-junction cell, for example, may consist of the semiconductors: GaAs, Ge, and GaInP2. Each type of semiconductor will have a characteristic band gap energy which, loosely speaking, causes it to absorb light most efficiently at a certain color, or more precisely, to absorb electromagnetic radiation over a portion of the spectrum. Combinations of semiconductors are carefully chosen to absorb nearly all of the solar spectrum, thus generating electricity from as much of the solar energy as possible.

Light-absorbing dyes (DSSC)

Dye-sensitized solar cells (DSSCs) are made of low-cost materials and do not need elaborate equipment to manufacture, so they can be made in a DIY fashion, possibly allowing players to produce more of this type of solar cell than others. In bulk it should be significantly less expensive than older solid-state cell designs. DSSC's can be engineered into flexible sheets, and although its conversion efficiency is less than the best thin film cells, its price/performance ratio should be high enough to allow them to compete with fossil fuel electrical generation.

Quantum Dot Solar Cells (QDSCs)

Quantum dot solar cells (QDSCs) are based on the Gratzel cell, or dye-sensitized solar cell, architecture but employ low band gap semiconductor nanoparticles, fabricated with such small crystallite sizes that they form quantum dots (such as CdS, CdSe, Sb2S3, PbS, etc.), instead of organic or organometallic dyes as light absorbers. Quantum dots (QDs) have attracted much interest because of their unique properties. Their size quantization allows for the band gap to be tuned by simply changing particle size. They also have high extinction coefficients, and have shown the possibility of multiple exciton generation.

Organic/polymer solar cells

Organic solar cells are a relatively novel technology, yet hold the promise of a substantial price reduction (over thin-film silicon) and a faster return on investment. These cells can be processed from solution, hence the possibility of a simple roll-to-roll printing process, leading to inexpensive, large scale production.

Organic solar cells and polymer solar cells are built from thin films (typically 100 nm) of organic semiconductors including polymers, such as polyphenylene vinylene and small-molecule compounds like copper phthalocyanine (a blue or green organic pigment) and carbon fullerenes and fullerene derivatives such as PCBM. Energy conversion efficiencies achieved to date using conductive polymers are low compared to inorganic materials.

Silicon thin films

Silicon thin-film cells are mainly deposited by chemical vapor deposition (typically plasma-enhanced, PE-CVD) from silane gas and hydrogen gas. Depending on the deposition parameters, this can yield

1. Amorphous silicon (a-Si or a-Si:H)2. Protocrystalline silicon or3. Nanocrystalline silicon (nc-Si or nc-Si:H), also called microcrystalline silicon.

Indium Gallium Nitride

The ability to perform bandgap engineering with Indium gallium nitride (InGaN) over a range that provides a good spectral match to sunlight, makes InGaN suitable for solar photovoltaic cells. It is possible to grow multiple layers with different bandgaps, as the material is relatively insensitive to defects introduced by a lattice mismatch between the layers. A two-layer multijunction cell with bandgaps of 1.1 eV and 1.7 eV can attain a theoretical 50% maximum efficiency, and by depositing multiple layers tuned to a wide range of bandgaps an efficiency up to 70% is theoretically expected.

Motivation for the Project

Probably the biggest concern with conventional energy sources is the amount of pollutants that are released into the atmosphere. These growing concerns over the environmental changes caused by power generation with conventional energy sources has lead to the need for developing an alternative energy source; one that is highly efficient and pollution free.The most common method of electrical power generation uses fossil fuels such as coal. However, the burning of fossil fuels releases CO2 gas which has been directly associated with global warming due to the greenhouse effect. Photovoltaics represent one of the few energy generation options that do not create pollutants or hazardous wastes .Other factors that increase the appeal of solar energy as an alternative energy source are the high reliability of solar cells, the steadily improving performance and decreasing manufacturing costs of solar cells, and the fact that there is no fuel cost for the cells.

Justification for the Project

Before solar energy can be used as an alternative source of energy for the worlds ever increasing requirements, the efficiency of solar cells must be increased. Currently the average efficiency of a normal sized solar (photovoltaic) cell is only adequate enough to power small commercial devices, eg. calculators and toys. In order to supply enough power to operate larger devices, larger solar cell arrays are required. These are typically too large, and therefore unfeasible, for the application.Instead of increasing the size of the array, it is more beneficial to increase the performance of the solar cell.

The overall performance (amount of solar power that can be collected) of solar cells can be attributed to these two main factors:

1) The efficiency of the cell and2) The intensity of the source radiation on the cell.

The materials used in the manufacture of solar cells are the biggest factors that limit the cell efficiency. This makes it difficult to improve the efficiency of the cell, and hence restricts the overall performance of the cell. However, it is an easier process to increase the amount of source radiation that is received at the cell.

There are three methods that can be implemented to increase the intensity of solar radiation received by a solar array. These are:

Focusing the suns incident rays onto a rigid array Tracking the suns path using fixed control algorithms Tracking the suns path using a dynamic tracking system

Sun-Tracking Techniques

When tracking objects, which are movintechniques that can be used.

The two most common techniques which can be used forsun, are the:

Fixed control algorithm method Dynamic method

The main difference between these twodetermined. The fixed control algorithm method determines the path of the sun by referencing an algorithm that calculates, for each time period, the position of the sun. This method does not actually find thposition of the sun from specific, given data. This data is usually the current time, day, month and year.

The dynamic method is a system that actually finds the position of the sun based on sensory input. That is, data from light sensitive sensors is used such that the system can actively find the sun. Since the sensory data is continuous, the system can follow (track) the suns movement across the sky.

Tracking Techniques

When tracking objects, which are moving in the sky, there is a number of tracking

The two most common techniques which can be used for tracking objects, such as the

Fixed control algorithm method

The main difference between these two methods is the way the position of the sun is determined. The fixed control algorithm method determines the path of the sun by referencing an algorithm that calculates, for each time period, the position of the sun. This method does not actually find the sun in the sky, but instead works out the position of the sun from specific, given data. This data is usually the current time, day,

The dynamic method is a system that actually finds the position of the sun based on is, data from light sensitive sensors is used such that the system can

actively find the sun. Since the sensory data is continuous, the system can follow (track) the suns movement across the sky.

g in the sky, there is a number of tracking

tracking objects, such as the

methods is the way the position of the sun is determined. The fixed control algorithm method determines the path of the sun by referencing an algorithm that calculates, for each time period, the position of the sun.

e sun in the sky, but instead works out the position of the sun from specific, given data. This data is usually the current time, day,

The dynamic method is a system that actually finds the position of the sun based on is, data from light sensitive sensors is used such that the system can

actively find the sun. Since the sensory data is continuous, the system can follow

CHAPTER 2

THE WORKING PRINCIPLE

This project deals with controlling the solar panel at a single axis (or single angle) by using LDRs as sensors, stepper motors as actuators (SM1, SM2) and microcontroller as a controller. In order to keep the design as simple and cheap we have chosen 89c51 as a micro-controller-unit (MCU).

The panels are the fundamental solar-energy conversion component. Conventional solar panels, fixed with a certain angle, limit their area of exposure from the sun during the course of the day. Therefore, the average solar energy is not always maximized. In order to collect the greatest amount of energy from the sun, solar panels must be aligned orthogonally to the sun.The change in suns position is monitored, and the system always keeps that the plane of the panel is normal to the direction of the sun. By doing so, maximum irradiation and thermal energy would be taken from the sun. The elevation angle of the sun remains almost invariant in a month and varies little (latitude 10) in a year. Therefore, a single axis position control scheme may be sufficient for the collection of solar energy in some applications.

Fig. Two axis control of solar panel

Efficient collection of maximum solar irradiation on a flat panel requires adjustments of two parameters of the energy collecting surface namely the angle of azimuth, and the angle of tilt, , of the surface to be illuminated in Figure. This project deals with controlling the solar panel by using LDRs as sensors, stepper motors as actuators (SM1, SM2) and microcontroller as a controller. In addition to this, to observe position of the solar panel, PC based system monitoring facility is included in the design. Block diagram of the proposed solar-tracking system is given in Figure.

BLOCK DIAGRAM

DESIGN OF THE SOLAR TRACKING SYSTEM

The tracker control system contains a control board, a control program, a power supply board, one motor interface board and a set of sensors. The main idea of design of the solar-tracking system is to sense the sun light by using four light dependent resistors (LDRs). Each LDR is fixed inside the hollow cylindrical tubes. A pair of them, controlling the angle of azimuth, is positioned East-West direction and the two of them, controlling the angle of tilt, are positioned South-North direction. The LDR assembly is fixed onto the flat-solar panel. The tubes are making a degree of 45 with the plane of panel; so, the angle between the tubes is 90. The differential signals of each pair of LDRs representing the angular error of the solar panel are employed to re-position the panel in such a way that the angular errors are minimized.

The signals, taken from voltage divider consisting of resistors and LDRs (S1, S2, S3, S4), are applied to I/O port lines of MCU (RA0, RA1, RA2, RA3) respectively. These analog signals are converted to digital signals and compared with each others (S1-S2, S3-S4). If the difference between S1 and S2 (or S3 and S4), error signal, is bigger than a certain value (tolerance), MCU generates driving signals for stepper motors. If the error signals are smaller than or equal to the value of tolerance, MCU generates no signal; which means that the solar panel is facing the sun and the light intensities falling on the four LDRs are equal or slightly different.

Actual Images of the Model

WORKING

1) The power is switched ON.2) The system is initialized and the ports of microcontroller are reset.3) The light as sensed by both the LDRs is routed through the OP-APMs to the

transistors (where the signal is amplified) and then to the Microcontroller.4) The Microcontroller performs the following tasks:

If the light sensed by both the LDRs is equal, then there is no movement of the stepper motors and the solar panel remains stationary.

If the light sensed by both the LDRs is not equal, then the Microcontroller sends a signal which in-turn sends a control signal, which drives the Stepper motors in the direction of that LDR which senses greater intensity of light.

5) Now, the Stepper motors stops when the light sensed by both the LDRs becomes equal.6) The process continues and the system tracks the moving SUN.

Fig. Solar panel tracking the Sun

FLOW CHART

Convert the data from analog to digital form

Read data from the LDRs

START

Initialize the system

Generate driving signal for SM1 & SM2

Compare the data

IfL1L2

STOP

CHAPTER 3

HARDWARE DESCRIPTION

3.1 CHOICE OF DRIVING MOTOR

For both of the tracking techniques discussed in the previous chapter, the control methods for positioning the solar array are similar. Both tracking systems would need to consist of two motors, which control the position of the array, and a control circuit (either analog or digital) to direct these motors. The following sections discuss some possible types of motors that could be used for this type of application.

3.1.1 DC Motors

The above figure shows the inner workings of a basic DC motor. The outside section of the motor is the stator (stationary part), while the inside section is the rotor (rotating part).The stator is comprised of two (or more) permanent magnet pole pairs, while the rotor is comprised of windings that are connected to a mechanical commutator. The opposite polarities of the energized winding and the stator magnet attract each other. When this occurs the rotor will rotate until perfect alignment with the stator is achieved. When the rotor reaches alignment, the brushes move across the commutator contacts (middle section of rotor) and energize the next winding. There are two other types of dc motors: series wound and shunt wound. These motors also use a similar rotor with brushes and a commutator. However, the stator uses windings instead of permanent magnets. The basic principle is still the same. A series wound dc motor has the stator windings in series with the rotor. A shunt wound dc motor has the stator windings in parallel with the rotor winding.

3.1.2 Stepper Motors

The main difference between stepper motors and standard DC motors is that they cannot run freely by themselves. The basic operational characteristic of stepper motors is that they do as their name suggests; they "step" a little bit at a time. Also, the torque-speed

relationship for stepper motors is different to that of DC motors. DC motors are not very

good at producing high torque at low speeds, whereas, stepper motors produce the highest torque at low speeds. Stepper motors also have a characteristic known as holding torque. Holding torque allows a stepper motor to hold its position firmly when not turning. In applications where the motor is not constantly running (ie. starting/stopping) this is very beneficial, as it eliminates the need to incorporate a braking device.

Stepper motors fall into two basic categories: permanent magnet and variable reluctance. Permanent magnet stepper motors are available in a wide variety: Unipolar, Bipolar, and Multiphase. There are also hybrid motors, which are controlled in the same manner as permanent magnet motors. Variable reluctance motors usually have three (sometimes four) windings, with a common return. Permanent magnet motors however, have two independent windings with or without centre taps. Centre-tapped windings are used in unipolar permanent magnet motors. These windings need to be energised in the correct sequence in order for the motor's shaft to rotate clockwise. Reversing the orderof the sequence will cause the motor to rotate counter-clockwise. When choosing stepper motors for specific applications the following motor characteristics should be considered:

Voltage

Stepper motors usually have a voltage rating. This is either printed directly on the unit, or is specified in the motor's datasheet. Exceeding the rated voltage is sometimes necessary to obtain the desired torque from a given motor, but doing so may produce excessive heat and/or shorten the life of the motor.

Resistance

Resistance-per-winding is another characteristic of a stepper motor. This resistance will determine current draw of the motor, as well as affect the motor's torque curve and maximum operating speed.

Degrees-per-step

This is often the most important factor in choosing a stepper motor for a given application. This factor specifies the number of degrees the shaft will rotate for each full step. Half step operation of the motor will double the number of steps/revolution, and cut the degrees-per-step in half. For unmarked motors, it is often possible to carefully count, by hand, the number of steps per revolution of the motor. The degrees per step can be calculated by dividing 360 by the number of steps in 1 complete revolution.Common degree/step numbers include: 0.72, 1.8, 3.6, 7.5, 15, and even 90. Degrees per-step is often referred to as the resolution of the motor. As in the case of an unmarked motor, if a motor has only the number of steps/revolution printed on it, dividing 360 by this number will yield the degree/step value.

Stepper motors translate digital switching sequences into motion. They are used in printers, automated machine tools, disk drives, and a variety of other applications requiring precise motions under computer control. Unlike ordinary dc motors, which spin freely when power is applied, steppers require that their power source be continuously pulsed in specific patterns. These patterns, or step sequences, determine the speed and direction of a steppers motion. For each pulse or step input, the stepper motor rotates a fixed angular increment; typically 1.8 or 7.5 degrees. The fixed stepping angle gives steppers their precision. As long as the motors maximum limits of speed or torque are not exceeded, the controlling program knows a steppers precise position at any given time. Steppers are driven by the interaction (attraction and repulsion) of magnetic fields. The driving magnetic field rotates as strategically placed coils are switched on and off. This pushes and pulls at permanent magnets arranged around the edge of a rotor that drives the output shaft.

A stepper motor is a special type of electric motor that moves in increments, or steps, rather than turning smoothly as a conventional motor does. The size of the increment is measured in degrees and can vary depending on the application. Typical increments are 0.9 or 1.8 degrees, with 400 or 200 increments thus representing a full circle. The speed of the motor is determined by the time delay between each incremental movement.

Inside the device, sets of coils produce magnetic fields that interact with the fields of permanent magnets. The coils are switched on and off in a specific sequence to cause the motor shaft to turn through the desired angle. The motor can operate in either direction

(clockwise or counterclockwise). When the coils of a stepper motor receive current, the rotor shaft turns to a certain position and then stays there unless or until different coils are energized. Unlike a conventional motor, the stepper motor resists external torque applied to the shaft once the shaft has come to rest with current applied. This resistance is called holding torque.

Unipolar Stepper Motors

Unipolar motors are straightforward to control. A simple counter circuit can generate the proper stepping sequence, and drivers as simple as 1 transistor per winding are possible. Unipolar stepper motors are characterized by their centre-tapped windings. In use, the centre taps of the windings are typically wired to the positive supply, and the two ends of each winding are alternately grounded to reverse the direction of the field provided by that winding. Since the number of phases is twice the number of coils (each coil is divided in two), the diagram below, which has two centre tapped coils, represents the connection of a 4-phase unipolar stepper motor.

To rotate the motor continuously, power is applied to the two windings in sequence. Positive logic is assumed, ie. 1 means turning on the current through a motor winding. It should also be observed that the two halves of each winding are never energized simultaneously. In addition to the standard drive sequence, high-torque and half-step drive sequences are also possible. In the high-torque sequence, two windings are active at a time for each motor step. This two-winding combination yields around 1.5 times more torque than the standard sequence, but it draws twice the current. Half-stepping is achieved by combining the two sequences. First, one of the windings is activated, then two, then one, etc. This effectively doubles the number of steps the motor will advance for each revolution of the shaft, and it cuts the number of degrees per step in half. Even simple transistor circuits can drive unipolar stepper motors.

Bipolar Stepper Motors

Bipolar permanent magnet and hybrid motors are constructed with exactly the same mechanism as is used on unipolar motors, but the two windings are wired more simply, with no centre taps. Thus, the motor itself is simpler but the drive circuitry needed to reverse the polarity of each pair of motor poles is more complex. Bipolar stepper motors use the same binary drive pattern as a unipolar motor, but this time it is the polarity of the voltage applied to the coils, not simply 'on-off' signals.

To physically position the solar cell array two motors are required. After careful consideration of the motors discussed in Chapter 3, unipolar stepper motors were chosen. Stepper motors were chosen over DC motors since they are more effective in situations where controlled movement (ie. accurate positioning) is needed. Stepper motors also have a holding torque which meant that complex motor circuitry, such as in the case of servomotors, did not have to be developed. Finally, stepper motors are known to be more reliable as they do not have contact brushes like DC motors.

Once the decision had been made to use stepper motors, it was now a matter of choosing which type of stepper motor would best suit the projects needs. Unipolar stepper motors were chosen because they do not require complex drive circuitry to control them, and because of their high reliability and robustness.

Since the aim of this project is to design a highly efficient and accurate sun-tracking system, it was required that the stepper motors have a reasonably small degree-per-step ratio. However, the project is also required to be a cost-effective solution. The smallest degree-per-step motor (0.720) seemed to be an unnecessary expense when a wide range of motors were already available.

. Fig 1. Five-wire stepper motor

Fig 2. Six-wire stepper motor

Fig 3. Eight-wire stepper motor

A stepper motor has no brushes or contacts. It is basically a synchronous motor with the magnetic field electronically switched to rotate the armature magnet around.

3.1.3 BASIC WIRING DIAGRAM

3.1.4 Working of a Stepper Motor

Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and electromagnets on the stationary portion that surrounds the motor, called the stator At position 1, we can see that the rotor is beginning at the upper electromagnet, which is currently active (has voltage applied to it). To move the rotor clockwise (CW), the upper electromagnet is deactivated and the right electromagnet is activated, causing the rotor to move 90 degrees CW, aligning itself with the active magnet. This process is repeated in the same manner at the south and west electromagnets until we once again reach the starting position.

Fig. Activation pattern of the Electromagnets

In the above example, we used a motor with a resolution of purposes. In reality, this would not be a very practical motor for most applications.average stepper motor's resolution higher than this. For example, a motor with a rotor 5 degrees per step, thereby requiring 72 pulses (steps) to complete a full 360 degree rotation.

The resolution of some motors can be doubled by a process known as "halfInstead of switching the next stepping we turn on both electromagnets, causing an equal attraction between, thereby doubling the resolution. As we can see from below figure, in the first position only the upper electromagnet is active, and the rotor is drawn completely to it.the top and right electromagnets are active, causing the rotor to position itself between the two active poles. Finally, in position 3, the top magnet is deactivated and the rotor is drawn all the way right. This process can then be repeated for the entire rotation.

Activation pattern of the Electromagnets

In the above example, we used a motor with a resolution of 90 degrees or demonstration In reality, this would not be a very practical motor for most applications.

average stepper motor's resolution -- the amount of degrees rotated per pulse For example, a motor with a resolution of 5 degrees would move its

rotor 5 degrees per step, thereby requiring 72 pulses (steps) to complete a full 360 degree

he resolution of some motors can be doubled by a process known as "halfInstead of switching the next electromagnet in the rotation on one at a time, with half stepping we turn on both electromagnets, causing an equal attraction between, thereby

As we can see from below figure, in the first position only the active, and the rotor is drawn completely to it. In position 2, both

the top and right electromagnets are active, causing the rotor to position itself between Finally, in position 3, the top magnet is deactivated and the rotor is

This process can then be repeated for the entire rotation.

90 degrees or demonstration In reality, this would not be a very practical motor for most applications. The

the amount of degrees rotated per pulse -- is much resolution of 5 degrees would move its

rotor 5 degrees per step, thereby requiring 72 pulses (steps) to complete a full 360 degree

he resolution of some motors can be doubled by a process known as "half-stepping".electromagnet in the rotation on one at a time, with half

stepping we turn on both electromagnets, causing an equal attraction between, thereby As we can see from below figure, in the first position only the

In position 2, both the top and right electromagnets are active, causing the rotor to position itself between

Finally, in position 3, the top magnet is deactivated and the rotor is This process can then be repeated for the entire rotation.

Fig. movement of the rotor in the Stepper motor

There are several types of stepper motors.electromagnets; however the magnets, because the driving circuit must be able to reverse the current after each step.For example motors which rotated 90 degrees per step, realof mini-poles on the stator and rotor to increase resolution.add more complexity to the process of driving the motors, the operation is identical to the simple 90 degree motor we used in our example.be seen in figure below. In position 1, the north pole of the rotor's permanent magnet is aligned with the south pole of the stator's electromagnet.aligned at once. In position 2, the upper electromagnet is deactivated and the its immediate left is activated, causing the rotor to rotate a precise amount of degrees.this example, after eight steps the sequence repeats.

Fig

movement of the rotor in the Stepper motor

There are several types of stepper motors. 4-wire stepper motors contain only two electromagnets; however the operation is more complicated than those with three or four magnets, because the driving circuit must be able to reverse the current after each step.For example motors which rotated 90 degrees per step, real-world motors employ a series

the stator and rotor to increase resolution. Although this may seem to add more complexity to the process of driving the motors, the operation is identical to the simple 90 degree motor we used in our example. An example of a multi-pole motor can

in figure below. In position 1, the north pole of the rotor's permanent magnet is aligned with the south pole of the stator's electromagnet. Note that multiple positions are

In position 2, the upper electromagnet is deactivated and the its immediate left is activated, causing the rotor to rotate a precise amount of degrees.this example, after eight steps the sequence repeats.

Fig. An example of a multi-pole motor

wire stepper motors contain only two operation is more complicated than those with three or four

magnets, because the driving circuit must be able to reverse the current after each step.world motors employ a series

Although this may seem to add more complexity to the process of driving the motors, the operation is identical to the

pole motor can in figure below. In position 1, the north pole of the rotor's permanent magnet is

Note that multiple positions are In position 2, the upper electromagnet is deactivated and the next one to

its immediate left is activated, causing the rotor to rotate a precise amount of degrees. In

In the electrical equivalent of the stepper motor, we can see that 3 wires go to each half of the coils, and that the coil windings are connected in pairs

3.1.5 COMPARISON OF A STEPPER MOTOR WITH A DC MOTOR

Stepper motors are operated open loop, while most DC motors are operated closed loop.

Stepper motors are easily controlled with microprocessors, however logic and drive electronics are more complex.

Stepper motors are brushless and brushes contribute several problems, e.g., wear, sparks, electrical transients.

DC motors have a continuous displacement and can be accurately positioned, whereas stepper motor motion is incremental and its resolution is limited to the step size.

Stepper motors can slip if overloaded and the error can go undetected. (A few stepper motors use closed-loop control.)

Feedback control with DC motors gives a much faster response time compared to stepper motors.

3.1.6 ADVANTAGES OF STEPPER MOTORS

Position error is non cumulative. A high accuracy of motion is possible, even under open-loop control.

Large savings in sensor (measurement system) and controller costs are possible when the open-loop mode is used.

Because of the incremental nature of command and motion, stepper motors are easily adaptable to digital control applications.

No serious stability problems exist, even under open-loop control. Torque capacity and power requirements can be optimized and the response can

be controlled by electronic switching. Brushless construction has obvious advantages.

3.1.7 DISADVANTAGES OF STEPPER MOTORS

They have low torque capacity (typically less than 2,000 oz-in) compared to DC motors.

They have limited speed (limited by torque capacity and by pulse-missing problems due to faulty switching systems and drive circuits).

They have high vibration levels due to stepwise motion. Large errors and oscillations can result when a pulse is missed under open-loop

control.

3.2.1 THE STEPPER MOTOR DRIVER

Fig. ULN2803

The ULN2801A-ULN2805A, each contains eight Darlington transistors with common emitters and integral suppression diodes for inductive loads. Each Darlington features a peak load current rating of 600mA (500mA continuous) and can withstand at least50V in the off state. Outputs may be paralleled for higher current capability. Five versions are available to simplify interfacing to standard logic families: the ULN2801Ais designed for general purpose applications with a current limit resistor; theULN2802Ahas a 10.5kW input resistor and zener for 14-25VPMOS; theULN2803A has a 2.7kW input resistor for 5V TTL and CMOS; the ULN2804A has a 10.5kW input resistor for 6-15V CMOS and the ULN2805A is designed to sink a minimum of 350mA for standard and Schottky TTL where higher output current is required. All types are supplied in a 18-lead plastic DIP with a copper lead from and feature the convenient input opposite-output pinout to simplify board layout.

3.3.1 THE MICROCONTROLLER 8051

The MICROPROCESSOR based system design, one may note that a stand alone microprocessor is not a self sufficient device. It requires other components like memory and input/output devices to form a minimum workable system configuration. Rather, one may infer that in addition to a microprocessor, the memory and I/O ports are unavoidable parts of a practical useful system. To have all these components in discrete form and to assemble them on a PCB, most of the times, is not an affordable solution for the following reasons:

1) The overall system cost of microprocessor based systems built around a CPU, memory and other peripherals is high as compared to microcontroller based system.

2) A large sized PCB is required for assembling all these components, resulting in an enhanced cost of the system.

3) Design of such PCBs requires a lot of effort and time and thus the verall product design requires more time.

4) Due to large size of the PCB and the discrete components used, physical size of the product is big and hence not handy.

5) As discrete components are used the system is not reliable nor it is easy to troubleshoot such a system.

Considering all these problems, INTEL decided to integrate a microprocessor alongwith a I/O ports and minimum memory in a single package. Another frequently used peripheral, a programmable timer, was also integrated to make this device a self sufficient one. This device which contains a microprocessor and the above mentioned components has been named MICROCONTROLLER. Thus a microcontroller, a microprocessor with integrated peripherals. The introduction of microcontrollers drastically changed the microprocessor based system design concepts, specially in case of small dedicated systems.

Design with microcontrollers has the following advantages:

1) As the peripherals are integrated into a single chip, the overall system cost is very low.

2) The product is of small size as compared to the microprocessor based system and thus very handy.

3) The system design now requires very little efforts and easy to troubleshoot and maintain.

4) As the peripherals are integrated with a microprocessor, the system is more reliable.

5) Though a microprocessor may have on-chip RAM, ROM and I/O ports, additional RAM, ROM and I/O ports may be interfaced externally, if required.

6) The Microcontroller with on-chip ROM provide a software security feature which is not available with microprocessor based system using ROM/EPROM.

7) All these features are available in a 40 pin package as in an 8-bit processor.

Fig. Microcontroller internal block diagram

3.3.2 THE 8051 PIN CONFIGURATION AND CIRCUITRY

Fig. Pin configuration of the Microcontroller

Microprocessor

RAM/ROMMEMORY

I/O ports

Peripherals like Timers etc.

3.3.3 SIGNAL DESCRIPTION OF 8051

8051 is available in a 40 pin plastic and ceramic DIP packages. Here we discuss the description of the pins:

VCC This is a +5V supply voltage pin.

VSS This is a return pin for the supply.

RESET The reset input pin resets the 8051, only when it goes high for two or more machine cycle. For a proper reinitialization after reset, the clock must be running.

ALE/PROG The address latch enable output pulse indicates that the valid address bits are available on their respective pins. This ALE signal is valid only for external memory access. Normally the ALE pulses are emitted at the rate of one-sixth of the oscillator frequency. This pin acts as program pulse input during on-chip EPROM programming. ALE may be used for external timing or clocking purpose. One ALE pulse is skipped during each access to external data memory.

EA/Vpp External access enable pin, if tied low, indicates that the 8051 can address external program memory. In other words, 8051 can execute a program in external memory, only if this pin is tied low. For execution of program in external memory, this pin should be tied high.

PSEN Program store enable is an active-low O/P signal that acts as a strobe to read the external program memory accesses.

PORT 0(P0.0-P0.7) Port 0 is an 8 bit bi-directional bit addressable I/O port. This has been allotted an address in the SFR address range. Port 0 acts as multiplexed address/data lines during external memory access, that is when EA is low and ALE emits a valid signal. In case of controllers with on-chip EPROM, port 0 receives code bytes during programming of the external EPROM.

PORT 1(P1.0-P1.7) Port 1 acts an 8 bit bi-directional bit addressable port. This has been allotted an address in SFR address range.

PORT 2(P2.0-P2.7) Port 2 is an 8-bit bi-directional bit addressable I/O port. This has been allotted an address in the SFR address range. During external memory accesses, port2 emits higher 8 bits of address (A8-A15) which are valid if ALE goes high and EA goes low. P2 also receives higher order address bits during programming of the on-chip EPROM.

PORT 3(P3.0-P3.7) Port 3 is an 8-bit bi-directional bit addressable I/O port. This has been allotted an address in the SFR address range. The port 3 pins also serve the alternative functions

PORT 3 PINS ALTERNATIVE FUNCTION

P3.0 Acts as serial input data pin (RXD)

P3.1 Acts as serial output data pin (TXD)

P3.2 Acts as external interrupt pin 0 (INT0)

P3.3 Acts as external interrupt input pin 1 (INT1)

P3.4 Acts as external input to timer 0 (T0)

P3.5 Acts as input to timer 1 (T1)

P3.6 Acts as write control signal for external data memory (WR)

P3.7 Acts as read control signal for external data memory read operation (RD)

Table. Alternative functions of Port 3 pins

XTAL1 and XTAL2 There is an in-built oscillator, which derives the necessary clock frequency for the operation of the controller. XTAL1 in the input amplifier and XTAL2the output amplifier.

3.3.4 Some Assembler Directives

The assembler directives are special instruction to the assembler program to define some specific operations but these directives are not part of the executable program. Some of the most frequently assembler directives are listed as follows:

ORG Originate, defines the starting address for the program in program (code) memory

EQU Equate, assigns a numeric value to a symbol identifier so as to make the program more readable.

DB Define a Byte, puts a byte (8-bit number) number constant at this memory location

DW Define a Word, puts a word (16-bit number) number constant at this memory location

DBIT Define a Bit, defines a bit constant, which is stored in the bit addressable section if the Internal RAM.

END This is the last statement in the source file to advise the assembler to stop the assembly process.

Program Control Instructions

The 8051 supports three kinds of jump instructions:

LJMP SJMP AJMP

LJMP

LJMP (long jump) causes the program to branch to a destination address defined by the 16-bit operand in the jump instruction. Because a 16-bit address is used the instruction can cause a jump to any location within the 64KByte program space (216

= 64K). Some example instructions are:

LJMP LABEL_X ; Jump to the specified label

LJMP 0F200h ; Jump to address 0F200hLJMP @A+DPTR ; Jump to address which is the sum of DPTR and Reg. A

SJMP

SJMP (short jump) uses a single byte address. This address is a signed 8-bit number and allows the program to branch to a distance 128 bytes back from the current PC address or +127 bytes forward from the current PC address. The address mode used with this form of jumping (or branching) is referred to as relative addressing, introduced earlier, as the jump is calculated relative to the current PC address.

AJMP

This is a special 8051 jump instruction, which allows a jump with a 2KByte address boundary (a 2K page)

There is also a generic JMP instruction supported by many 8051 assemblers. The assembler will decide which type of jump instruction to use, LJMP, SJMP or AJMP, so as to choose the most efficient instruction.

Subroutines and program flow control

A subroutine is called using the LCALL or the ACALL instruction.

LCALL

This instruction is used to call a subroutine at a specified address. The address is 16 bits long so the call can be made to any location within the 64KByte memory space. When a LCALL instruction is executed the current PC content is automatically pushed onto the stack of the PC. When the program returns from the subroutine the PC contents is returned from the stack so that the program can resume operation from the point where the LCALL was made

The return from subroutine is achieved using the RET instruction, which simply pops the PC back from the stack.

ACALL

The ACALL instruction is logically similar to the LCALL but has a limited address range similar to the AJMP instruction.

CALL is a generic call instruction supported by many 8051 assemblers. The assembler will decide which type of call instruction, LCALL or ACALL, to use so as to choose the most efficient instruction.

3.4 PCB

A Printed circuit board is a piece of Bakelite insulating board. It defines all the details of the circuit & partly also final equipment. Copper or silver layer covers one side or both side of PCB. The metallic conductive path for the electronic component, which are mounted on the other side of PCB.

Printed circuit boards are exclusively used for assembling electronics circuit due to its advantage which is given below:-

1. Easy adaptability to manufacture & modular design.2. Provide uniformity in production.3. Lower cost.4. Virtually eliminate wiring error & complexity.5. Minimize assembly & inspection time.

3.4.1 Types of PCB

Single sided PCB

Single sided PCB is mostly used where manufacturing cost have to be the kept minimum. To jump over conductors tracks, component have to be utilize if this is a not feasible, jumper wire are restricted by economic reason.

Flexible PCB application

Flexible PCB are mainly used in military &aero space but now they are incorporated in many other fields like computer industry etc. this may have the function of broadness or similar to a single PCB or a combination of both.

Metal core PCB

In metal core board the typical resin or fuller laminated of ordinary PCB replaced by sheet or metal covered with insulating material.

3.4.2 Material of PCB

The number of different printed circuit board material in common use infinite, the problem of material selection & quality control are always arises.

A laminate can be obtained by pressing layer of fillers material impregnated with resin under heat and pressure.

The basic required material of copper laid board is fillers, resin & copper foils.

Fillers

Fillers are variety of paper, glass in various forms such as cloth and continues filament & are used as reinforcing agent. The paper used is Kraft, alpha cellulose rag or their combination the rag paper provides an electrically better Lamination than the alpha cellulose paper.

Resin

The fillers are embedded in a matrix of a resin when laminated. Matrix material is phenol formaldehyde resin. Epoxy is much costlier. Polyester has good electrical & mechanical properties. They also have a low chemical resistance.

Copper coils

Copper coils form the surface of copper clad laminate & is manufacture by the process of electrode position. A thin film of copper metal is deposited on to a slowly rotating corrosion resistant metal cylinder. Whose lower portion is immersed in a copper rich electrolytic both.

3.4.3 Design of PCB

The designs PCB can be considered as well as first Mayer step in the production of PCBs.

The designing of PCB consist of the designing of the layout by the preparation ofartwork. The fabrication of PCB layout consists if following step.

1. Layout planning.2. Drawing of layout one PCB.3. Etching

3.5 RESISTANCE

Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. It is the ratio of the potential difference (i.e. voltage) across an electric component (such as a resistor) to the current passing through that component. A resistor is an electronic mechanism that is used to control electrical current through the use of electrical resistance. Resistors limit the flow of electrical current so that higher incoming voltage is reduced to a lower one that the component uses to operate. Electrical resistance or the resistance value, which is the ratio of voltage to current, is measured in ohms or mega ohms, which is the equivalent of 1,000,000ohms.

3.5.1 Types of Resistor

There are two types of resistors, fixed and variable. Fixed resistors have a fixed resistance value while variable resistors have an adjustable resistance value. Variable resistors are quite common and are represented as a knob to control volume and brightness on a television set or in the case of a heater, warm to cool settings.

Resistors are made in one of several ways, a carbon rod, carbon or metal film on a ceramic rod, or wire-wound. Carbon rods are most common because they are less expensive and can be used for multiples purposes. When a carbon or metal film is used, parts of it are removed to give the resistor its resistance value. Wire wound resistors consist of wire wrapped around a ceramic rod. Again, the amount of wire used depends on the required resistance level for the resistor.

3.5.2 How Are Resistors Used?

Resistors are used in electronic circuitry for numerous telecommunications devices as well as computers, stereos and amplifiers. A typical use for resistors is in light emitting diode (LED) applications such as the lighted numbers on a clock radio. Resistors prevent too much electrical current from reaching the LED components and damaging them.

Wire wound resistors are used when dissipation of heat is required, for example in heaters or toasters. When the electrical current flows through the resistor, energy in the form of heat is released. The metal coils do not conduct heat well, but when electric current passes through them the elements themselves give off heat.

3.5.3 Determining Resistance Value

Resistors are color coded with each color representing a different standardized resistance value as well as the tolerance, or how accurate the value really is. When selecting a resistor for a circuit it is essential to look at the color coded bands. Most resistors have 4 colored bands. The first two bands are keyed to the resistance value. The third is called a multiplier and indicates how many zeros to add after the first two numbers. The fourth band is the tolerance. Wire wound resistors usually have a more precise tolerance value than ceramic rods.

Resistor Color Code Guide

Fig. Resister color coding technique

Fig. Color chart

The five band resistor color code is more likely to be associated with the more precision V can either be measured directly across the component or calculated from a subtraction of voltages relative to a reference point. The former method is simpler for a single component and is likely to be more accurate. The latter method is useful when analysing a larger circuit or if you want to work one handed with one lead clipped (which can be a useful safety precaution on systems using dangerous voltages).

There may also be problems with the latter method if the system is AC and the two measurements from the reference point are not in phase with each other.

Resistance is thus a measure of the component's opposition to the flow of electric charge. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage. This means that voltage is proportional to current and the proportionality constant is the electrical resistance. This case is described by Ohm's law and such materials are known as ohmic devices.

3.6 LIGHT DEPENDENT RESISTANCE

A photoresistor is an electronic component whose resistance decreases with increasing incident light intensity. It can also be called a light-dependent resistor(LDR), or photoconductor.

A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. 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 added, which have a ground state energy closer to the conduction band - since the electrons don't have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device.

Some photosensitive element like cadmium sulphide, cadmium selenide etc. Emits electrons when receive light. The resistance of these elements in dark is in mega ohm but remains in few ohms when they get light. Light dependent Resistance are made by stiking photo sensitive strip on the base of the insulating material. In this two strips of cedmium sulphide are separated by a small gap, this appears as if two combs are joined. This type of resistance is used in some television receivers for

automatic brightness and contrast control. Besides, this, these are mainly used in the flash system of camera. In this type of camera there is small hole near the lens through which light comes on the LDR.

Whenever the light is dim, the value of LDR became high, as a result capacitor charges due to high value load resistance in the charging circuit thus flash does it work. But when there is enough light than LDR get the light so the value of load resistance become low and charging circuit does not works so flash does not works because capacitor does not charges. Besides this LDR is used in many other devices.

3.6.1 Applications

Photoresistors come in many different types. Inexpensive cadmium sulfide (CdS) ones can be found in many consumer items such as camera light meters, clock radios, security alarms and street lights. At the other end of the scale, Ge:Cuphotoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscopy.

3.7 LCD

A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices.

Each pixel consists of a column of liquid crystal molecules suspended between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. Without the liquid crystals between them, light passing through one would be blocked by the other. The liquid crystal twists the polarization of light entering one filter to allow it to pass through the other.

The molecules of the liquid crystal have electric charges on them. By applying small electrical charges to transparent electrodes over each pixel or subpixel, the molecules are twisted by electrostatic forces. This changes the twist of the light passing through the molecules, and allows varying degrees of light to pass (or not to pass) through the polarizing filters.Before applying an electrical charge, the liquid crystal molecules are in a relaxed state. Charges on the molecules cause these molecules to align themselves in a helical structure, or twist (the "crystal"). In some LCDs, the electrode may have a chemical surface that seeds the crystal, so it crystallizes at the needed angle. Light passing through one filter is rotated as it passes through the liquid crystal, allowing it to pass through the second polarized filter. A small amount of light is absorbed by the polarizing filters, but otherwise the entire assembly is transparent.

When an electrical charge is applied to the electrodes, the molecules of the liquid crystal align themselves parallel to the electric field, thus limiting the rotation of

entering light. If the liquid crystals are completely untwisted, light passing through them will be polarized perpendicular to the second filter, and thus be completely blocked. The pixel will appear unlit. By controlling the twist of the liquid crystals in each pixel, light can be allowed to pass though in varying amounts, correspondingly illuminating the pixel.Many LCDs are driven to darkness by an alternating current, which disrupts the twisting effect, and become faint or transparent when no current is applied.

To save cost in the electronics, LCDs are often multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together, and each group gets its own voltage source. On the other side, the electrodes are also grouped, with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink.Important factors to consider when evaluating an LCD monitor include resolution, viewable size, response time (sync rate), matrix type (passive or active), viewing angle, color support, brightness and contrast ratio, aspect ratio, and input ports (e.g. DVI or VGA).

3.7.1 Transmissive and reflective displays

LCDs can be either transmissive or reflective, depending on the location of the light source. A transmissive LCD is illuminated from the back by a backlight and viewed from the opposite side (front). This type of LCD is used in applications requiring high luminance levels such as computer displays, televisions, personal digital assistants, and mobile phones. The illumination device used to illuminate the LCD in such a product usually consumes much more power than the LCD itself.

Reflective LCDs, often found in digital watches and calculators, are illuminated by external light reflected by a (sometimes) diffusing reflector behind the display. This type of LCD can produce darker 'blacks' than the transmissive type since light must pass through the liquid crystal layer twice and thus is attenuated twice, however because the reflected light is also attenuated twice in the translucent parts of the display image contrast is usually poorer than a transmissive display. The absence of a lamp significantly reduces power consumption, allowing for longer battery life in battery-powered devices; small reflective LCDs consume so little power that they can rely on a photovoltaic cell, as often found in pocket calculators.Transflective LCDs work as either transmissive or reflective LCDs, depending on the ambient light. They work reflectively when external light levels are high, and transmissively in darker environments via a low-power backlight.

3.7.2 Color displays

In color LCDs each individual pixel is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters. Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel. Older CRT monitors employ a similar method for displaying color. Color components may be arrayed in various pixel geometries, depending on the monitor's usage.

3.7.3 Passive-matrix and active-matrix

Fig. LCD

A general purpose alphanumeric LCD, with two lines of 16 characters.LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have a single electrical contact for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive-matrix structure employing supertwist nematic (STN) or double-layer STN (DSTN) technology (DSTN corrects a color-shifting problem with STN). Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called a passive matrix because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes increasingly less feasible. Very slow response times and poor contrast are typical of passive-matrix LCDs.

For high-resolution color displays such as modern LCD computer monitors and televisions, an active matrix structure is used. A matrix of thin-film transistors (TFTs) is added to the polarizing and color filters. Each pixel has its own dedicated transistor, which allows each column line to access one pixel. When a row line is activated, all of the column lines are connected to a row of pixels and the correct

voltage is driven onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the row lines are activated in sequence during a refresh operation. Active-matrix displays are much brighter and sharper than passive-matrix displays of the same size, and generally have quicker response times.

3.7.4 Active matrix technologies

3.7.4.1 Twisted Nematic (TN)

Twisted Nematic displays contain liquid crystal elements which twist and untwist at varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, the light is polarized to pass through the cell. In proportion to the voltage applied, the LC cells twist up to 90 degrees changing the polarization and blocking the light's path. By properly adjusting the level of the voltage most any grey level or transmission can be achieved.

3.7.4.2 In-Plane Switching (IPS)

In-plane switching is an LCD technology which aligns the liquid crystal cells in a horizontal direction. In this method, the electrical field is applied through each end of the crystal, but this requires the need for two transistors for each pixel instead of the one needed for a standard thin-film transistor (TFT) display. This results in blocking more transmission area requiring brighter backlights, which consume more power making this type of display undesirable for notebook computers.

3.7.4.3 Vertical Alignment (VA)

Vertical Alignment displays are a form of LC displays in which the liquid crystal material naturally exists in a horizontal state removing the need for extra transistors (as in IPS). When no voltage is applied the liquid crystal cell, it remains perpendicular to the substrate creating a black display. When voltage is applied, the liquid crystal cells shift to a horizontal position, parallel to the substrate, allowing light to pass through and create a white display. VA liquid crystal displays provide some of the same advantages as IPS panels, particularly an improved viewing angle and improved black level.

3.7.5 Quality control

Some LCD panels have defective transistors, causing permanently lit or unlit pixels. Unlike integrated circuits, LCD panels with a few defective pixels are usually still usable. It is also economically prohibitive to discard a panel with just a few bad pixels because LCD panels are much larger than ICs. Manufacturers have different

standards for determining a maximum acceptable number of defective pixels. The following table presents the maximum acceptable number of defective pixels for IBM's ThinkPad laptop line.

Resolution Bright

Dots

Dark dots Total

20481536

(QXGA)

15 16 16

16001200

(UXGA)

11 16 16

14001050

(SXGA+)

11 13 16

1024768

(XGA)

8 8 9

800600

(SVGA)

5 5 9

Table. maximum acceptable number of defective pixels

LCD panels are more likely to have defects than most ICs due to their larger size. In this example, a 12" SVGA LCD has 8 defects and a 6" wafer has only 3 defects. However, 134 of the 137 dies on the wafer will be acceptable, whereas rejection of the LCD panel would be a 0% yield. The standard is much higher now due to fierce competition between manufacturers and improved quality control. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. The location of defective pixels is also important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other. Manufacturers may also relax their replacement criteria when defective pixels are in the center of the viewing area.

3.7.6 Zero-power displays

The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can retain an image without power. The crystals may exist in one of two stable orientations (Black and "White") and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufacture both grayscale and colour ZBD devices.

A French company, Nemoptic, has developed another zero-power, paper-like LCD technology which has been mass-produced in Taiwan since July 2003. This technology is intended for use in low-power mobile applications such as e-books and wearable computers. Zero-power LCDs are in competition with electronic paper.Kent Displays, has also developed a "no power" display that uses Polymer Stabilized Cholesteric Liquid Crystals(ChLCD). The major drawback to the ChLCD display is slow refresh rate, especially with low temperatures.

3.7.7 Drawbacks

LCD technology still has a few drawbacks in comparison to some other display technologies:

While CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCD displays usually produce only crisp images in their "native resolution" or even fractions of it. LCD displays generally have a lower contrast ratio than that on a plasma

display or CRT. This is due to their "light valve" nature: some light always leaks out making black grey.

LCDs have longer response time than their plasma and CRT counterparts, creating ghosting and mixing when images rapidly change; this caveat however is continually improving as the technology progresses.

The viewing angle of a LCD is usually less than that of most other display technologies thus reducing the number of people who can conveniently view the same image. However, this negative has actually been capitalised upon in two ways. Some vendors offer portables with intentionally reduced viewing angle, to provide additional privacy for example when using the PC in airplanes. Secondly, it allows multiple TV outputs from the same LCD screen just by changing the angle from where the TV is seen. Such a set can also show two different images to one viewer, providing 3-D.

Many users of older (around pre-2000) LCD monitors get migraines and other severe eyestrain problems from the flicker nature of the fluorescent backlights. If you experience eyestrain issues with LCDs, consider these possibilities: using a small resolution for reading text, on a >=15 inch LCD, glare from another light, brightness is set too low or high, defective backlight, LCD monitor is too close, or too far away,

3.8 CAPACITOR

A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. Intentional capacitors have thin metal plates stacked or rolled to form a compact device, but every multi-conductor geometry has capacitance.

Typical designs consist of two electrodes or plates, each of which stores an opposite charge. These two plates are conductive and are separated by an insulator or dielectric. The charge is stored at the surface of the plates, at the boundary with the dielectric. Because each plate stores an equal but opposite charge, the total charge in the device is always zero.

Capacitance

The capacitor's capacitance (C) is a measure of the potential difference or voltage(V), which appears across the plates for a given amount of charge (Q) stored on each plate:

C = \frac{Q}{V}

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge causes a potential difference of one volt across the plates. Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (F), nanofarads (nF) or picofarads (pF). The capacitance is proportional to the surface area of the conducting plate and inversely proportional to the distance between the plates. It is also proportional to the permittivity of the dielectric (that is, non-conducting) substance that separates the plates.

The impedance of a capacitor is: