CHAPTER-1
INTRODUCTION
1.1 INTRODUCTION TO SOLAR ENERGY

Fig. 1.1(a) Block Diagram of Photovoltaic System
Renewable energy is rapidly gaining importance as an energy resource as fossil fuel prices fluctuate. At the educational level, it is therefore critical for engineering and technology students to have an understanding and appreciation of the technologies associated with renewable energy. One of the most popular renewable energy sources is solar energy. Many researches were conducted to develop some methods to increase the efficiency of Photo Voltaic systems (solar panels). One such method is to employ a solar panel tracking system. This project deals with a microcontroller based solar panel is always able to maintain a perpendicular profile to the sun’s rays. Development of solar panel tracking systems has been ongoing for several years now.
As the sun moves across the sky during the day, it is advantageous to have the solar panels track the location of the sun, such that the panels are always perpendicular to the solar energy radiated by the sun. This will tend to maximize the amount of power absorbed by the PV systems. It has been estimated that the use of a tracking system, over a fixed system, can increase the power output by 30%-60%. The increase is significant enough to make tracking a viable preposition despite of the enhancement in system cost. It is possible to align the tracking heliostat normal to sun using electronic control by a microcontroller.

Fig 1.1(b) Working of Solar Energy System

Solar energy is the energy force that sustains life on earth for all plants, animals, and people. It provides a compelling solution for all the societies to meet their needs for clean, abundant sources of energy in the future. The source of solar energy is the nuclear interactions at the core of the Sun where the energy comes from the conversion of hydrogen into helium. Sunlight is readily available, secure from the geopolitical tensions, and poses no threat to environment and our global climate systems from pollution emissions. Solar energy is primarily transmitted to the earth by electromagnetic waves, which can also be represented by particles (photons). Although the earth receives about 10 times as much energy from sunlight each year as that contained in all the known reserves of coal, oil, natural gas, and uranium combined, renewable energy has been given a dismally low priority by most political and business leaders.

1.2 ORGANIZATION OF PROJECT
A solar panel is mounted on a wooden board along with a stepper motor, which is capable of changing to its position corresponding to the changes in the position of the sun. The solar panel thus moves along with the sun and thereby absorbs maximum solar energy. So this project aims to seek the position of the sun and hence the name, automated sun tracker. Thus when the sun is there during the day, the automated sun tracker absorbs energy maximum energy). Hence the system converts the non-conventional solar energy source into the electrical energy that can be used for various household purposes. The whole arrangement operates as follows: The computer is interfaced with connector with the stepper motor control card IC ULN 2803. The interfacing is done at a parallel printer port of the computer. The connector is connected at the other end to the stepper motor control card. The ULN 2803 IC drives the 12V stepper motor.
The stepper motor drives the solar panel rotationally. The whole movement is of the order of 180. Once the solar panel has moved a distance of 180, the stepper motor control card drives the solar panel in reverse direction and resets it for the next day. The same process is repeated again. Power supply circuit drives the stepper motor.
Thus the whole arrangement achieves the primary object of rotating the panel clockwise or anti clockwise, thereby changing the position of the solar panel with respect to the position of sun in earth’s orbit. The 180 movement is achieved in a span of 12 hours and then as the sun sets, the solar panel is reset to its original position for the next day.

CHAPTER-2
AUTOMATED SUN TRACKER
2.1 OBJECTIVE
The objective of this project is to control the position of a solar panel in accordance with the motion of the sun. This project is designed with the solar panels, LDR, Comparator, Microcontroller, Stepper Motor and driving circuit.
In this project three LDRs are fixed on the solar panel at three distinct points. LDR (Light Dependent Resistor) varies with the resistance depending upon the light fall. The varied resistance is converted into analog voltage signal. The analog voltage signal is then fed to the comparator. Comparator receives the three LDR voltage signals, compares them and converts them to corresponding digital signal. Then the converted digital signal is given as the input of the microcontroller.
Microcontroller receives the digital signal and generates an output which is fed to the driving circuit. The driving circuit drives the steeper motor and amplifies the value of current. An interfacing is provided between microcontroller and stepper motor. The stepper motor thus generates a mechanical output which rotates the panel.
When the LDR senses the position of the maximum sunlight, the panel is rotated in that direction and thus in this direction solar panel will convert the solar energy into the corresponding electrical which charges the battery and thus the process continues.

Fig 2.1(a) Automated Sun Tracker

2.2 CIRCUIT DIAGRAM

Fig 2.2(a) Circuit Diagram

CHAPTER-3
COMPONENTS OF AUTOMATED SUN TRACKER

3.1 LIST OF COMPONENTS 1. Solar panel 2. Stepper motor, 12V, Unipolar 3. Light Dependent Resistor (LDR) 4. Voltage regulator: LM7805 5. Microcontroller: 89S52 (8051 Family) 6. Driver IC: ULN 2803 chip 7. Comparator: LM358 8. Electrolytic capacitor 9. Variable resistor 10. Complimentary resistor: 4.7KΩ 11. Battery: 9V each 12. LED

3.2 DETAILED STUDY

3.2.1 LIGHT SENSOR (OR LIGHT DEPENDENT RESISTOR)
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. Sensor can also be defined as a device which receives a signal and converts it into electrical form which can be further used for electronic devices. A sensor differs from a transducer in the way that a transducer converts one form of energy into other form whereas a sensor converts the received signal into electrical form only. The sun’s position is required to be sensed continuously. The presence of the solar panel is required to be sensed at the extreme ends.

Fig 3.2.1 (a) CDS photocell and circuit diagram
Types of sensors used:
A photo resistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. It can also be referred to as a photoconductor or CDS device, from "cadmium sulfide," which is the material from which the device is made and that actually exhibits the variation in resistance with light level. Note that although CDS is a semiconductor, it is not doped silicon.
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.
The light dependent resistors are used in the circuit to sense the change in the sun’s position. The Proximity sensor is used at one corner in order to sense the presence of the solar panel while rotating. A photo resistor or light dependent resistor or cadmium sulphide (CDS) cell is a resistor whose resistance decreases with increasing incident light intensity. A photo resistor requires a power source because it does not generate Photocurrent; a photo effect is manifested in the change in the material‟s electrical Resistance. Construction and Characteristics of LDR
This is an example of a light sensor circuit:

Fig 3.2.1 (b) LDR structure and symbol

Fig 3.2.1 (c) Working of LDR
When the light level is low the resistance of the LDR is high. This prevents current from flowing to the base of the transistors. Consequently the LED does not light. However, when light shines onto the LDR its resistance falls and current flows into the base of the first transistor and then the second transistor. The LED lights. The preset resistor can be turned up or down to increase or decrease resistance, in this way it can make the circuit more or less sensitive.

3.2.2 SOLAR CELLS
A solar cell (also called photovoltaic cell or photoelectric cell) is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect. Assemblies of solar cells are used to make solar modules which are used to capture energy from sunlight. When multiple modules are assembled together (such as prior to installation on a pole-mounted tracker system), the resulting integrated group of modules all oriented in one plane is referred to in the solar industry as a solar panel. The electrical energy generated from solar modules, referred to as solar power, is an example of solar energy. Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.

Fig 3.2.2 (a) Construction of Solar Panel

Cells are described as photovoltaic cells when the light source is not necessarily sunlight (lamplight, artificial light, etc.). These are used for detecting light or other electromagnetic radiation near the visible range, for example infrared detectors, or measurement of light intensity.
A solar cell or photovoltaic cell is a device which generates electricity directly from visible light by means of the photovoltaic effect. In order to generate useful power, it is necessary to connect a number of cells together to form a solar panel, also known as a photovoltaic module. There is more about the the different types of solar cell here. The nominal output voltage of a solar panel is usually 12 Volts, and they may be used singly or wired together into an array. The number and size required is determined by the available light and the amount of energy required. Solar cells are often electrically connected and encapsulated as a module. Photovoltaic modules often have a sheet of glass on the front (sun up) side, allowing light to pass while protecting the semiconductor wafers from abrasion and impact due to wind-driven debris, rain, hail, etc. Solar cells are also usually connected in series in modules, creating an additive voltage. Connecting cells in parallel will yield a higher current; however, very significant problems exist with parallel connections. To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected photovoltaic systems); in stand-alone systems, batteries are used to store the energy that is not needed immediately. Solar panels can be used to power or recharge portable devices.
Solar cells are used to generate energy using the sun, which is a renewable source of energy, in place of using non-eco friendly methods like burning fuel. The increasing use of Solar cell technology to produce energy gives a clear indication of the increasing awareness about the declining level of fossil fuels and their impact on the environment. Today, the electricity produced through solar technology is being used to power homes, cars and appliances. This has made solar technology to be one of the most important advances in technology in recent times.

Structure
Modern solar cells are based on semiconductor physics -- they are basically just P-N junction photodiodes with a very large light-sensitive area. The effect, which causes the cell to convert light directly into electrical energy, occurs in the three energy-conversion layers.

Fig 3.2.2 (b) Construction of Photovoltaic Cell The first of these three layers necessary for energy conversion in a solar cell is the top junction layer (made of N-type semiconductor). The next layer in the structure is the core of the device; this is the absorber layer (the P-N junction). The last of the energy-conversion layers is the back junction layer (made of P-type semiconductor).
As may be seen in the above diagram, there are two additional layers that must be present in a solar cell. These are the electrical contact layers. There must obviously be two such layers to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such diametrically opposed restrictions. It need simply function as an electrical contact and thus covers the entire back surface of the cell structure. Because the back layer must be a very good electrical conductor, it is always made of metal.
Operation

Fig 3.2.2 (c) Working of Solar Panel
Solar cells are characterized by a maximum Open Circuit Voltage (Voc) at zero output current and a Short Circuit Current (Isc) at zero output voltage. Since power can be computed via this equation:
P = I * V
Then with one term at zero these conditions (V = Voc / I = 0, V = 0 / I = Isc ) also represent zero power. As you might then expect, a combination of less than maximum current and voltage can be found that maximizes the power produced (called, not surprisingly, the "maximum power point"). Many BEAM designs (and, in particular, solar engines) attempt to stay at (or near) this point. The tricky part is building a design that can find the maximum power point regardless of lighting conditions.
3.2.3 SOLAR PANEL
Solar Panels, generally comprising of arrays of Photovoltaic Cells, use the solar energy directly from the Sun to generate electricity for our daily use. Being environment friendly in nature, they collect the solar energy which is available in abundance on our planet and convert it using the advanced technology developed by human beings.

` Fig 3.2.3 (a) Solar Panel

This invention of humans has led to a great achievement in world’s history of conserving non-renewable resources and saving the planet as well as the natural resources from depletion. This concept is already famous in countries like Australia, United Kingdom and United States of America etc. and is becoming very popular in the Indian market as well. Even used solar panels are being used in these countries so that the installation solar panels cost reduces further and it is easy for the people to generate green energy. A large number of factories in the global markets are now using solar panels for their daily electricity usage.

Advantages of Solar Cell Panels 1. Solar cell panels provide a large amount of electricity than a single cell. The electricity provided by it is used to run electric motors and lift water from deep wells. 2. The electric power required for working of artificial satellites stationed in outer space. Street lightning in remote areas and running of irrigation water pumps, etc, is obtained with the help of a solar cell panel.

3.2.4 MICROCONTROLLER

Description
Low-voltage, high-performance CMOS 8-bit microcontroller with 8KB of ISP flash memory. The device uses Atmel high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pin out. On-chip flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU provides a highly-flexible and cost-effective solution for many embedded control applications. The AT89LS52 provides the following standard features: * Compatible with MC-51 products * 8K Bytes of in-system programmable (ISP) Flash memory: Endurance: 1000 Write/Erase cycles * 2.7V to 4.0V operating range * Fully static operation: 0 Hz to 16 Hz * Three level program memory stock * 256*8-bit internal RAM * 32 programmable I/O lines * Three 16-bit timer/counters * Eight interrupt sources * Full duplex UART serial channel * Low-power idle and power-down mode * Watchdog timer * Dual data pointer * Power off flag * Flexible ISP programming (Bytes and page modes)
In addition, the AT89LS52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning.

Fig 3.2.4 (a) 40-lead PDIP
Pin Description (a) VCC-Supply voltage. (b) GND-Ground. (c) Port 0-Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs. Port 0 can also be configured to be the multiplexed low order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification. (d) Port 1-Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in the following table. Port 1 also receives the low-order address bytes during Flash programming and verification.

Table 3.2.4 (a) Alternate Pin Function (e) Port 2-Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external data memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification. (f) Port 3-Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull ups.
Port 3 also serves the functions of various special features of the AT89S52, as shown in the following table. Port 3 also receives some control signals for Flash programming and verification.
Block Diagram Fig 3.2.4 (b) Block Diagram
3.2.5 ULN 2803 IC

Fig 3.2.5 (a) Pin Diagram
The ULN 2803A is a high voltage, high current darlington transistor array. The device consists of eight npn Darlington pairs that features high voltage outputs with common –cathode clamp diodes for switching inductive loads. The collector-current rating of each Darlington pair is 500mA. The darlington pair may be connected in parallel for higher current capability.
Application include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers and logic buffers. The ULN2803A has a 27kΩ series base resistor for each Darlington pair for operation directly with TTL or 5-VCMOS devices.

3.2.6 VOLTAGE REGULATOR
(LM 7805-3-Terminal 1A Positive Voltage Regulator)
Description
The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators are available in the TO-220/D-PAK package and with several output voltages, making them useful in a wide range of applications. Depending upon the current requirement, a reasonable load regulation can be achieved. Line regulation in all cases is equal to that of the voltage regulator used.
Though high voltage can be obtained with suitable voltage boost circuitry using ICs like LM 723, some advantages of the circuits presented below are: simplicity, low cost, and practically reasonable regulation characteristics. For currents of the order of 1A or less, only one zener and some resistors and capacitors are needed. For higher currents, one pass transistor such as ECP055 is needed.

Fig 3.2.6 (a) Voltage Terminal Regulator
Rectified and filtered unregulated voltage is applied at VIN and a constant voltage appears between pins 2 and 2 of the voltage regulator. The distribution of two currents in the circuit (IBIAS and ILOAD) is as shown.
Electrically regulator will be at a distance from the rectifier supply. Thus, a tantalum grade capacitor of 5mf and rated voltage is good. Electrolytic capacitor is not suitable for it is poor in response to load transients, which have high frequency components. At the output side a 0.22mf disc ceramic capacitor is useful to eliminate spurious oscillations, which the regulator might break into because of its internal high gain circuitry.
These voltage regulators have a typical bias current of 5 mA, which is reasonably constant. By inserting a small resistor Rx between pin 2 and ground, the output voltage in many cases. By this method voltage increment of 5 to 10 per cent is practically feasible. However, if a high-value resistance is used to obtain a higher output voltage, a slight variation in bias current will result in wide variation of the output voltage.
If to the circuit resistor RY and zener Vz are added the output voltage is now given by:-
VOUT=VR+VZ + IBIAS RX
A constant current flows through RY because VOUT is constant, and small variations in IBIAS do not change practically the operating point of Vz. This situation is like constant current biasing of zener, which results in a very accurate setting of the zener voltage.
As long as VIN>VOUT+2 volts, VOZ is constant from the reasoning and thus current through RY is constant.
VOZ=VR + IBIAS Rx
Here the pin 2 of the regulator is raised above ground by Vz + IBIAS Rx. Thus, any combination of zener with a proper selection of RY can be used.
For example, Let VR=+15 V for 7815
IBIAS=5mA
VZ=39V (standard from ECIL)
For a standard 400mW zener of ECIL make, IZ MAX=10 mA. Thus, if we let pass 5mA through RY, to make a 55-volt supply.

Fig 3.2.6 (b) Current Directions
Schematic for constant high-voltage power supplies
The maximum input voltage allowed for 78XX regulators is 35V between pins 1 and 2.
Thus, from no-load to full-load condition, the unregulated input voltage-including peak ripple-should be within these limits.

3.2.7 STEPPER MOTOR
Stepper Motors convert electrical pulses into discrete mechanical rotational movement or steps. Typical stepper motors consists of two coils with two stator cups formed around each coil. Pole pairs are mechanically displaced by one-half each pole pair. When current is applied, the pole pairs become alternatively energized north and south poles. Between the stator coil pairs, there is a displacement of one quarter of each pole pitch. Fig 3.2.7 (a) Construction of stepper motor
Stepper motor operating performance specifications may be as follows: Holding torque, step angle (Degrees), steps/rev, DC operating voltage, resistance/windings (ohms) for a given applied voltage. Length, diameter, shaft size, and interface are other mechanical specifications available from the manufacturer.

Types of Stepper Motors:
There are three basic types of stepping motors:
Unipolar Stepper Motor
A unipolar stepper motor has one winding with center tap per phase. Each section of windings is switched on for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching the direction of current, the commutation circuit can be made very simple (e.g. a single transistor) for each winding. Typically, given a phase, the center tap of each winding is made common: giving three leads per phase and six leads for a typical two phase motor. Often, these two phase commons are internally joined, so the motor has only five leads.
A microcontroller or stepper motor controller can be used to activate the drive transistors in the right order, and this ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements. Bipolar stepper motor
The bipolar stepper motor usually has four wires coming out of it. Unlike unipolar steppers, bipolar steppers have no common center connection. They have two independent sets of coils instead. You can distinguish them from unipolar steppers by measuring the resistance between the wires. You should find two pairs of wires with equal resistance. If you've got the leads of your meter connected to two wires that are not connected (i.e. not attached to the same coil), you should see infinite resistance (or no continuity).

A simple example of 6 lead step motor is given below and in 5 lead step motor wire 5 and 6 are joined together to make 1 wire as common.

Fig 3.2.7(b) stepper-coils

Working of Stepper Motor
Now let’s discuss the operation principle of a stepper motor. When we energize a coil of stepper motor, the shaft of stepper motor (which is actually a permanent magnet) align itself according to poles of energized coil. So when motor coils are energized in a particular sequence, motor shaft tend to align itself according to pole of coils and hence rotates. A small example of energizing operation is given below.

Fig 3.2.7 (c) Working of Stepper Motor

When coil "A" is energized, a north-south polarity is generated at "A+A\" as shown in the figure above and magnetic shaft automatically align itself according to the poles generated. When the next coil is energized the shaft again aligns itself and takes a step.

Fig 3.2.7 (d) To make the stepper motor work, we need to energize coil in a sequence. Stepper motors can be driven in two different patterns or sequence namely,
1. Full Step Sequence
2. Half Step Sequence
Full Step Sequence
In the full step sequence, two coils are energized at the same time and motor shaft rotates. The order in which coils has to be energized is given in the table below.

Table 3.2.7 (a) Full Step Sequence

The working of the full mode sequence is given in the figure below.

Fig 3.2.7 (e) Working of 6 Lead Unipolar Driver

Half Step Sequence
In Half mode step sequence, motor step angle reduces to half the angle in full mode. So the angular resolution is also increased i.e. it becomes double the angular resolution in full mode. Also in half mode sequence the number of steps gets doubled as that of full mode. Half mode is usually preferred over full mode. Table below shows the pattern of energizing the coils.

Table 3.2.7 (b) Half mode Sequence

The working of the half mode sequence is given in the figure below.

Fig 3.2.7 (f) Half-Step Stepper Motor

Step Angle
Step angle of the stepper motor is defined as the angle traversed by the motor in one step. To calculate step angle, simply divide 360 by number of steps a motor takes to complete one revolution. As we have seen that in half mode, the number of steps taken by the motor to complete one revolution gets doubled, so Step Angle reduces to half.

As in above examples, Stepper Motor rotating in full mode takes 4 steps to complete a revolution.
So, step angle can be calculated as given below:-

Step Angle ø = 360° / 4 = 90°
And in case of half mode step angle gets half so 45°.
So this way we can calculate step angle for any stepper motor. Usually step angle is given in the spec sheet of the stepper motor you are using. Knowing stepper motor's step angle helps you calibrate the rotation of motor also to helps you move the motor to correct angular position.

.

3.2.8 RESISTOR, CAPACITOR AND DIODE
RESISTOR
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals to the intensity of current through the circuit is called resistance.

Fig 3.2.8 (a)
Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.

Fig 3.2.8 (b) Color Coding

CAPACITOR
It is an electronic component whose function is to accumulate charges and then release it.

Fig 3.2.8 (c) Symbol of Capacitor
To understand the concept of capacitance, consider a pair of metal plates which all are placed near to each other without touching. If a battery is connected to these plates the positive pole to one and the negative pole to the other, electrons from the battery will be attracted from the plate connected to the positive terminal of the battery. If the battery is then disconnected, one plate will be left with an excess of electrons, the other with a shortage, and a potential or voltage difference will exists between them. These plates will be acting as capacitors.
Capacitors are of two types: -

(1) Fixed type like ceramic, polyester, electrolytic capacitors-these names refer to the material they are made of aluminum foil.
(2) Variable type like gang condenser in radio or trimmer. In fixed type capacitors, it has two leads and its value is written over its body and variable type has three leads.

Fig 3.2.8 (d) Types of Capacitor

Unit of measurement of a capacitor is farad denoted by the symbol F. It is a very big unit of capacitance. Small unit capacitor are pico-farad denoted by pf (Ipf=1/1000,000,000,000 f) Above all, in case of electrolytic capacitors, it's two terminal are marked as (-) and (+) so check it while using capacitors in the circuit in right direction. Mistake can destroy the capacitor or entire circuit in operational.

DIODE A diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p-n junction connected to two electrical terminals. A vacuum tube diode, now rarely used except in some high-power technologies and by enthusiasts, is a vacuum tube with two electrodes, a plate (anode) and cathode.

Fig 3.2.8 (e) Diode
The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, including extraction of modulation from radio signals in radio receivers—these diodes are forms of rectifiers.
However, diodes can have more complicated behavior than this simple on–off action. Semiconductor diodes do not begin conducting electricity until a certain threshold voltage is present in the forward direction (a state in which the diode is said to be forward-biased). The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or voltage reference.
Semiconductor diodes' nonlinear current–voltage characteristic can be tailored by varying the semiconductor materials and introducing impurities into (doping) the materials. These are exploited in special purpose diodes that perform many different functions. For example, diodes are used to regulate voltage (Zener diodes), to protect circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit negative resistance, which makes them useful in some types of circuits.
Diodes were the first semiconductor electronic devices. The discovery of crystals rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

3.2.9 RELAY
Relay is a common, simple application of electromagnetism. It uses an electromagnet made from an iron rod wound with hundreds of fine copper wire. When electricity is applied to the wire, the rod becomes magnetic. A movable contact arm above the rod is then pulled toward the rod until it closes a switch contact. When the electricity is removed, a small spring pulls the contract arm away from the rod until it closes a second switch contact. By means of relay, a current circuit can be broken or closed in one circuit as a result of a current in another circuit.
Relays can have several poles and contacts. The types of contacts could be normally open and normally closed. One closure of the relay can turn on the same normally open contacts; can turn off the other normally closed contacts.
Relay requires a current through their coils, for which a voltage is applied. This voltage for a relay can be D.C. low voltages upto 24V or could be 240V a.c.

Fig 3.2.9 (a) Relay
A relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by the electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control the output circuit of higher power than the input circuit, it can be considered, in a broad sense, to be a form of electrical amplifier. These contacts can be either Normally Open (NO), Normally Closed (NC), or change-over contacts. * Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact. NO contacts can also be distinguished as "early-make" or NOEM, which means that the contacts will close before the button or switch is fully engaged. * Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact. NC contacts can also be distinguished as "late-break" or NCLB, which means that the contacts will stay closed until the button or switch is fully disengaged. * Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact ("break before make"). If this type of contact utilizes “make before break" functionality, then it is called a Form D contact.
Operation:
When an electric current is passed through the coil it generates a magnetic field that activates the armature and the consequent movement of the movable contact either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components. Some automotive relays include a diode inside the relay case. Alternatively, a contact protection network consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil is designed to be energized with alternating current (AC), a small copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase current which increases the minimum pull on the armature during the AC cycle.
.

Fig 3.2.9 (b)
Relays are used for: (A) Amplify a digital signal, switching a large amount of power with a small operating power. Some special cases are: * A telegraph relay, repeating a weak signal received at the end of a long wire * Controlling a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers, * Controlling a high-current circuit with a low-current signal, as in the starter solenoid of an automobile, (B) Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays), (C) Isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors to conserve energy, (D) Logic functions. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using normally closed contacts. The Ladder programming language is often used for designing relay logic networks. * Safety-critical logic. Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery. (E) Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed. (F) Vehicle battery isolation. A 12v relay is often used to isolate any second battery in cars, 4WDs, RVs and boats. (G) Switching to a standby power supply.
CHAPTER-4
INTERFACING WITH STEPPER MOTOR
This chapter discusses the motor control and shows interfacing with stepper motor. It begins with an overview of the basic operation of stepper motor then we describe how to interface a stepper motor to the 8051. Finally, we use Embedded C to demonstrate control of the angle and the direction of stepper motor rotation. 4.1 Connections of Unipolar Stepper Motor
There are actually many ways we can interface a stepper motor to your controller, out of them the most used interfaces are: 1. Interface using L293D - H-Bridge Motor Driver 2. Interface using ULN2803 - Darlington Arrays
The above mentioned methods need 4 controller pins for interface.
Connecting Unipolar stepper using ULN2803

Fig 4.1 (a) Pin Diagram ULN2803-Stepper Motor

As already discussed in case of L293D, Here in this circuit too the four pins "Controller pin 1",2,3 and 4 will control the motion and direction of the stepper motor according to the step sequence sent by the controller.
The electronics for controlling a stepper motor with a parallel port is very simple. We will be making use of the ULN2803 driver IC, which contains an array of 7 Darlington transistors with integrated diode protection, each capable of driving 500mA of current.

CHAPTER-5
SOFTWARE DEVELOPMENT
5.1 PROGRAMMING IN EMBEDDED C

Include<REGX51.H>//header file for microcontroller
Void MSDelay (unsigned int);//delay function
Void start_motor(bit);//if bit=0 then motor rotation is CCW //if bit=1 then motor rotation is CCW
Unsigned char steps=0;
Void main ()//start program
{
P2_0=1; // configure pin as input
MSDelay(2);// give some delay
While (1)// start infinite loop
{
While (P2_0==0)// stay here until comparator output is high
{
P1=0;// stop motor
}
While (steps<92)// rotate motor in CCW direction
{
While (P2_0==1)// stay here until comparator output is high
{
P1=0;// stop motor
}
Start_motor(0);// start motor CCW
Steps =steps+4;// increment variable steps by 4
}
While (steps>0)// rotate motor in CW
{
While (P2_0=1)
{
P1=0;
}
Start_motor(1);// start motor CW
Steps=steps_4;// decrement steps by 4
}
}
}
Void MSDelay( unsigned int itime)
{
Unsigned int I,j; For (i=0;i<itime;i++) For(j=0;j<900;j++)
}
Void start_motor (bit dir)
{
If(dir)
{
P1=0x02;
MSDelay (9);
P1=0x04;
MSDelay (9);
P1=0x08;
MSDelay (9);
}
Else
{
P1=0x08;
MSDelay (9);
P1=0x04;
MSDelay (9);
P1=0x02;
MSDelay (9);
P1=0x01;
MSDelay(9);

}

}

CHAPTER-6
6.1 Result and Conclusion

Energy has always been a prerequisite for man in all his endeavors. But the conventional sources of energy are fast dying out. The need therefore, arrives for using non-conventional sources of energy efficiently. The solution lies in the fusion technology. That is using modern technology to tap the vast energy that the sun possesses.
The automated sun tracker aims to solve all the energy problems of the present and the future using solar panel which rotates according to the sun’s position, thereby absorbing maximum amount of sun’s energy and extracting the energy for useful purposes like electrical energy that can be used at home or streetlights and barricade lights can use this mechanism for continuous power generation.
All these devices work best when facing direct sunlight, which is a difficulty due to the rotation of the earth. So a device needs to rotate these equipments in the direction of direct sunlight. A solar tracker is a device which rotates in the direction where maximum sunlight falls. It is more efficient in terms of energy conversion providing an efficiency of about 35% to 40% when used on a large commercial scale.
Thus, the automated sun tracker is the full proof method, which will provide an answer to all the energy problems of man. Hence it aims to utilize the sun’s energy to its full potential in an efficient, easy to use and cost effective manner.

6.2 Suggestions for Future Work

The steps of hardware and software improvements that can be suggested as are:
1. Slip Rings – Mounting the slip rings will enable the zenith axis to have a full rotational degree of freedom and will increase system lifetime.
2. Create PCB for the system and install into the base assembly
3. Rearrange the rabbit ports so that interrupts, motor control and server interactions do not interfere – The first step that should be done is to rearrange the ports so, that to control both motors through the same port. The interrupts and the server interaction need to be synchronized, since both work through the same port on the controller.
4. Mount Solar cell device onto zenith axis
5. Create an array of light sensors for active tracking and write the tracking logic for the system
6. Check algorithm analysis toolbox for errors and repeat the algorithm analysis toolbox
7. Analyze the rest of the algorithms written
8. Increase the time period of analysis
9. Add algorithms to the server
10. Create a Web User Interface

------------------------------------------------- REFERENCES

[1] Bolylested Robert L. and Nashelsky, “Electronic Devices and Circuit Theory”, Eight

Edition, PHI

[2] Sawhney A.K. “A Course in Electrical and Electronics Measurements and Instrumenation”, Nineteenth Edition, Dhanpat Rai & Co. (P) LTD.
[3] D.C. motor control by PWM showing the animation of full and half step sequence of stepper motor, http://engknowledge.com/dc_motor_control_interfacing.aspx
[4] Petrov L A: 2010/2011 –University of Dundee: solar tracking strategies.
[5] www.Expercore.com : connecting stepper motor to microcontroller tutorial.
[6] www.multyremote.com : stepper motor control program.
[7] Documentation of “LM7805 Voltage Regulator” referred from www.fairchildsemi.com
[8] Device Data Sheets on AT89LS52 Microcontroller referred from www.ATMEL.com
[9] M.R. I. Sarker, M. R.A Beg, M.Z. Hossain, M. T. Islamand M. R. Zaman. 2005. Design of a Software ControlledTwo axis Automatic Solar tracking system. Mechanical Engineering Research Journal. Vol. 5