In our daily life, the need of energy increases each and every day. The source of electricity is commonly from motor generators that is generate from the source of coal or other element of fuel. Another new way in this era is by using solar energy. The solar energy convert solar irradiation to power that can be used in common electric appliances. Since solar is a new type of source, the usage of the solar is still small compare to the old conventional ways. The solar energy is converted when the solar cells on the solar panel detects light irradiation. However, the angle of the sun is proportional to the energy converted. If the sun is 90° vertical to the solar panel, the energy received is maximum compare to other angles. In this case, a project is developed to track the solar during the movement of the sun from morning till night. Solar Tracker System is developed by moving the solar panel during anytime of the day that the sun is available and the motor will move the panel to a 90° vertical angle directly to the sun. The system is controlled by microcontroller which will process data from the photodiode and convert it to output for the motor movement. As the result, a prototype of Solar Tracker System is operated and able to achieve the objective of this project.
CHAPTER 1: INTRODUCTION
Sun is the primary source of Energy for the world. The earth receives 16 x 1018 units of energy from the sun yearly, which is around 20,000 times the requirement of mankind on the Earth. Some of it is utilized in photosynthesis which is essential for sustenance of the life on earth. Without sun, it is impossible for a human or living creature to live in this world. Humans nowadays feel uncomforted about the global warming situation. Even this kind of situation bring a lot of negative perception, they should have to think it through the positive way. One of the way to reduce the global warming is to reduce the utilizing of electrical voltage and change to a natural voltage source like wind, rain, tides, sunlight and geothermal heats. Man has tried from time immemorial to harness this infinite source of energy for the sun. But they have been able to tap only a negligibly fraction of this energy till today.
The broad categories of possible large scale applications of solar power are the heating and cooling of residential as well as commercial buildings.
The chemical and Biological conversion of organic material to liquid solid and gaseous fuels.
Conversion of solar energy to Electricity.
In solar tracking project, solar energy for the generation of electrical energy, by using solar cells is used.
The solar cell receives solar energy and it operates on the principle of photovoltaic effect, by using solar cells. Basically the cells are placed in an open and fixed manner.[1]
SOLAR ENERGY OPTIONS
Solar energy has the greatest potential of all the sources of renewable energy and it will be one of the most essential sources of energy especially when other sources in the world have depleted. Solar energy could supply all of the present and future energy needs of the world on a connecting basis. This makes it one of the most promising of the nonconventional energy sources.
Solar Energy can be a main source of power. Its potential is 178 billion MW which is about 20,000 times the world's demand. The energy radiated by the sun on a bright day is approximately 1kw/m2. The problem that is associated with the use of solar energy is that its availability varies widely with time. The variations in availability occur daily, because of the day-night cycle and also seasonally because of Earth's orbit around the sun. In addition, variations occur at a specific location because of local weather conditions. Thus the energy collected with the sun is shining must be stored for use during periods when it is not available.
A lot of attempts have been made to make use of this energy in raising steam which may be used in driving the prime movers for the purpose of generation of electrical energy. However due to large space requirement and uncertainty of availability in constant rate this method becomes ineffective.
Photovoltaic cell is an alternate device used for power generation which converts suns radiation directly into electrical power. Thus power generated can be stored and utilized. [1]
BACKGROUND OF THE PROJECT
With the range of applications for solar energy increases, so as does the need for improved materials and methods used to harness this power source. There are several factors that affect the efficiency of the collection process of solar energy. Major influences on efficiency consist of solar cell efficiency, the amount of source radiation as well as storage techniques. This makes it particularly difficult to make considerable improvements in the performance of the cell, and hence restricts the efficiency of the overall collection process. Therefore, the most attainable method of improving the performance of solar power collection is to increase the mean intensity of radiation received from the source. Tracking systems are designed to orient solar panels toward the sun. This project is very practical and feasible as there are many types solar tracker designs in industry today. In addition, a similar senior project was done in 1994 on the "Sun Luis solar racer 101" electric car by physics major, David Babbitt.[2] However, the 1994 project dealt with manual panel adjustments given sensor data.
OBJECTIVE
Essentially, there are three main objectives that are accomplished by doing this project:
To design and construct a dual axis solar tracking system.
To build a microcontroller solar array that actively tracks the sun to maximum solar panel output.
To build a sensors to locate the sun's position at any instance, and aligning the array using the microprocessor so that all incident rays are normal to the array surface.
SCOPE OF PROJECT
The system consists of a mechanical design and circuit development. The tracker system will follow sun movement from east to west. The movement controlled by the dc motor that using 12volt supply. Therefore, the project scope is as follow.
An automated tracking system which detects the sun during daylight.
Use programmable interface controller to move the motor clockwise or counterclockwise.
MAIN COMPONENTS
1. Solar Panel:
The solar panel is an important component for this project because it uses the solar energy to produce the electricity.
2. Solar Charge Controller:
The voltage produce from solar panel connect to Solar Charge Controller to charge the battery.
3. Day time controller:
The tracker is only active during the day with sunny condition. If the sky is cloudy or at night, the tracker will be turn off.
4. Power Inverter:
To step down the voltage from high voltage to low voltage
5. Servo Motor
To moving the solar panel and its move follow the program at programmable circuit.
6. Light Sensor
Light sensor is a resistor whose resistance decreases with increasing incident light intensity. So that the microcontroller will control the servo motor to move to the higher light incident light intensity area.
PROBLEM STATEMENT
This study aims to seek the following research:
The sun is moving 180° from east to west so the light irradiation is varied due to the rotation cycle of the earth.
Sensor and motor unit controlled by comparing light intensities on either side.
Saves power by turning off the main tracking circuit or the rear sensor when not needed.
A solar panel which is static for instant 45° (east/west) will only take the light irradiation w/m² at the first 90° or the end 180° therefore the maximum power for the solar panel does not occur.
CHAPTER 2: LITERATURE REVEW
Solar tracking methods are used repeatedly to orient photovoltaic panels in path of the sun. Solar tracking methods also might to help maximize investment in photovoltaic system. Solar tracking are advantageous because the sun's location will change gradually over the course of the day. The advantages of utilizing a tracking system can depend primarily on its placement in determining how good it will increase the effectiveness of the solar panels. The solar tracking system can be used most successfully in those areas with low horizons and locations which are free from shade of dawn to dusk each day. Throughout these 12 months the monitoring array will be able to utilize the big open access to understand every accessible electron from the sun. From this, power production is at an optimum and vitality output is increased for the whole year. Those with limited space which means only smaller array needs to be installed, a big benefit for those smaller sites with solely a lesser area to place the equipment; they will be capable to harvest most energy output but they only have to utilize one of the smaller solar tracking home systems. [3]
Previous Study
The movement of earth with respect to sun and vice-versa must be clear before starting with the concept of tracking sun. As per the general theory of relativity given by Albert Einstein, nobody is at absolute rest. Everybody in this universe is moving with respect to each other due gravitational forces being applied by one and another. As a result if we consider earth to be at rest with respect to sun, we can presume sun to be moving with respect to earth. Sun's motion is break into two angles namely Azimuthal angle and the Zenith angle.
Figure:Azimuth and Altitude for Northen Latitudes
1PW= 1015 W
Figure: Solar energy received by earth [4]
Microcontroller Based Automatic Sun Tracker Combine with a New Solar Energy Conversion Unit by F. Huang, D. Tien and James Or.
In 2004 F. Huang, D. Tien and James Or had complete the paper about microcontroller based automatic sun tracker combined with a new solar energy conversion unit. This sun tracker had developed in order to increase the efficiency of the solar panel. The control system that developed base on automatic sun tracker that used was implemented with a dc motor and a dc motor controller. The energy conversion unit in this tracker system that created had an range of solar panel, a single-phase inverter, a step- up chopper, an A.C main power source as well as a microcontroller control unit. This tracker was not uses any sensor to detect the location or the angle of the sun. In this tracker, Maximum Power Point (MPP) detector was use. In simple, the array of solar was set up as sensor. It was operated to find the angle that can provide the highest solar energy and assume that was the most direct angle with the sun. The operation was started by search MPP location. The position and value of MPP will set as reference for find new angle [5].
Single and Dual Axis Solar Tracker:
Single axis solar tracker can be passive or active type. It has manual elevation adjustment on a second axis which is turning throughout the year. In this only azimuthal angle is controlled automatically. But dual axis solar tracker is of active type only. In this both azimuthal and zenith angles are automatically controlled.
(a) (b)
Figure: (a) One Axis Tracking, (b) Two-axis Tracking [6]
Advantage
Disadvantage
One Axis Tracking
More stable system
More Simple mechanical system
Rotation angle can be easily adjusted
Energy needed for the mechanical movements is lesser
More economical due to lesser materials
Cannot rotate to all directions
Receives slightly less energy than maximum
Two-Axis Tracking
More robust system
Receives maximum daytime energy.
Can rotate to all directions
Complex system requiring rotation to be more complicated
The adjustment of the panel involves complex mathematical algorithm
Higher material cost
Higher maintenance requirement
Life span of the system is reduced due to complex mechanical movements
Extra material is needed [6]
Open loop and closed loop controlled type tracker
In B.C. Nakra paper about automatic control, open loop and closed loop type trackers are classified as:
1) OPEN LOOP TYPE TRACKER: It does not require any feedback element.
With the help of solar tracker software all the sun positioning data is calculated and updated regularly in a day with help of microcontroller [7].
2) CLOSED LOOP TYPE TRACKER: There is feedback element in the system.
When sensor senses maximum intensity of light then the output from photo sensor fed to microcontroller. The microcontroller controls the rotation of motor shaft [7].
Types of solar collectors:
Figure: Cylindrical parabolic collector: Geometric Concentration Ratio (CR) range 10 to 40 [7]
Figure: Fresenal collector: Geometric Concentration Ratio (CR) range 10 TO 80 [7]
Figure: Paraboloid Dish Collector: Geometric Concentration Ratio (CR) range 100 TO1000 [7]
Active and passive tracking:
In Alexandru, C.and Pozna, C paper about different tracking strategies for optimizing the energetic efficiency of a photovoltaic system,there are two types of further classification under close type of tracking, namely active tracking and passive tracking. Passive tracking involves photosensitive materials which change their orientation as per the incident radiation. They align themselves so as to achieve radiations normally. Advantage of using these materials is that we can avoid using electronic components such as amplifiers, transistors, microcontrollers, relays, etc. disadvantage of using these materials is the procurement cost, as they are expensive and difficult to procure [8]. Such prevailing smart materials are:
1) Freon based liquid [8]
2) Shape memory alloys [such as NiTi, CuZnAl, CuAlNi [8]
Active tracking on the other hand involves gears, sensors, microcontrollers, logic gates, relays,
Etc. Trackers based on the active tracking track the sun by sensing its rays by the help of sensors
Open Loop Tracking
Active Tracking
Passive Tracking
Advantages
No changes in path due to external disturbances such as clouds
cheaper
Can last long
Easy to produce
Dual axis tracking can be achieved easily
High reliability
Working cost low
Disadvantages
Structure needs to be constructed to be very durable
Need to check the trackers frequently
Clouds as an external disturbance can cause major problem in the path
High initial cost
Just for single tracking
Table: Advantages and Disadvantages of Open Loop Tracking, Active Tracking and Passive Tracking. [8]
CHAPTER 3: SOLAR CELL THEORY
The term "photovoltaic" comes from the Greek φῶς (phÅs) meaning "light", while "voltaic", meaning electric, after the name of Italian famous physicist called Allesandro Volta, after whom a unit of electrical potential by the named volt. Besides this, since since 1849, the term "photo-voltaic" has been use in English. A solar cell or in other words photovoltaic cell is a device that converts light energy directly into electricity by photovoltaic effect. A nuclear fusion reaction that is on the sun's surface resource earth with solar energy. Mainly, this energy is released in the form of electromagnetic radiation in ultraviolet, infrared as well as radio spectral regions. At present, the greatest efficient means of harnessing this power source is the solar cell, which converts solar radiation straight into electricity. Solar cells is a combination various semiconducting materials using numerous device configurations and selecting single-crystal, polycrystalline, as well as amorphous thin-film structures. Materials which become electrically conductive when supplied with light otherwise heat but operate as insulators at low temperature are semiconductor [9].
Over 95% of all the solar cells created globally are made of the semiconductor material Silicon (Si). For the second most easily available element in earth`s crust, silicon has the advantage, of being obtainable in adequate quantities, and the environment is not burden with the processing of silicon. To produce a solar cell, the semiconductor is contaminated or "doped". The semiconductor is contaminated or else "doped' for the production of solar cell. Doping purposely introduces impurities into a tremendously pure (intrinsic) semiconductor for the aim of modulation its electrical properties which one can gain a surplus of positive charge carriers or negative charge carriers from the semiconductor material. If there are two inversely contaminated semiconductor layers are combined, then a p-n-junction are on the edge of the layers [9].
Figure: model of a crystalline solar cell [9]
The solar cell has a single energy band gap. As such, while the cell is wide-open towards the solar spectrum, a photon with energy smaller than Eg does not influence the cell output. A photon that has the energy larger than Eg gives an energy Eg to the cell output, as well as the left over energy will be wasted as heat. Figure 21 shows the ideal equivalent circuit of the cell where as a constant-current source is in parallel with the junction. Besides this, the source IL outcomes from the excitation of additional carriers by solar radiation are the diode saturation current as well as RL is the load resistance.
Figure: Energy-band diagram of a silicon p-n junction solar cell [10]
Figure21: Ideal equivalent circuit of a solar cell [10]
Figure: Schematic representation of a silicon p-n junction solar cell [10]
High efficiency solar cells mean a solar cell that can produce greater electricity per incident solar power unit (watt/watt). Many industries are dedicated to the most cost effective technologies in terms of price per generated power. The two key tactics to reduce the price of photovoltaic electricity are increasing its efficiency (as many of the prices scale with the space occupied per unit of generated power), as well as reducing the price of the solar cells per generated unit of power. Sadly, the latter method might come at the expense of lowering the efficiency, so the total price of the photovoltaic electricity does not certainly reduce by reducing the cost of the solar cells. To increase the photovoltaic efficiency as a challenge thus generated great interest in both academic as well as economic points of view. Researcher introduce many methods like the anti-reflection coating as well as texturization front contacts and emitter, substracte and surface passivation to increase te efficiency of the solar cells.
To reduce reflection, anti-reflection coating and texturization are a kind of optical coating applied to the surface of the lenses and some other optical devices. This increases the efficiency of the system since a smaller amount light is lost. This technique tackles the problem of absorbing sunlight consistently and equally from every angles. Figure show an example of textured surface that is an array of "inverted pyramids" etched into the surface to capture the incoming light [11].
Figure: Textured surface that is an array of "inverted pyramids" etched into the surface to capture the incoming light [12]
3.1 P-Type Semiconductor
When a tiny amount of pentavalent impurities (e.g. Gallium, Indium, Aluminum, and Boron) are added to intrinsic semiconductor, it is called P type semiconductor.
For P type semiconductor, when an electric potential is applied on the exterior, the holes are directed towards the negative electrode. Thus current is produced.
3.2 N- Type Semiconductors
When a tiny amount of pentavalent impurities (e.g. Antimony, Arsenic, Bismuth, and Phosphorus) are added to intrinsic semiconductors, it is called N type semiconductor.
For N type semiconductor, when an exterior electrical field is applied the free electrons are directed towards positive electrode. Thus current is produced.
3.3 PN Junction Silicon Solar Cell
A PN junction is formed from a piece of semiconductor by diffusing P type materials to one half side and N type materials to other half side.
It consists of both types of semiconductor materials. The N type layer is situated towards the sunlight. As N type layer is thin, light can penetrate through it.
The energy of the sunlight will create free electron in the N type material and holes in the p type material. This condition built up the voltage with in the crystal. Because the holes will travel to the +ve region and the holes will travel to the -ve region. This conduction ability is one of the main technical goals in fabricating solar cells.
MAJOR ADVANTAGES OF SOLAR CELLS
Solar cells directly convert the solar radiation into electricity using photovoltaic effect without going through a thermal process.
Solar cells are reliable, modular, durable and generally maintenance free and therefore, suitable even in isolated and remote areas.
Solar cells are quiet, benign, and compatible with almost all environments, respond instantaneously with solar radiation and have an expected life time of 20 or more years.
Solar cells can be located at the place of use and hence no distribution network is required.
MAJOR DISADVANTAGES OF SOLAR CELLS
The conversion efficiency of solar cells is limited to 10 percent. Large areas of solar cell modular are required to generate sufficient useful power.
The present costs of solar cells are comparatively high, making them economically uncompetitive with other conventional power generation methods for terrestrial applications, particularly where the demand of power is very large.
Solar energy is intermittent and solar cells produce electricity when sun shines and in proportion to solar intensity. Hence, some kind of electric storage is required making the whole system more costly. However, in large installations, the electricity generated by solar cells can be fed directly into the electric grid system.
CHAPTER 4: HARDWARE
SOLAR PANEL
Solar panel is also called as photovoltaic panel or photovoltaic module. Solar Panel is a packed interconnected assembly of solar cells. It is a device that converts light energy into to generate electricity from photovoltaic effect. Solar panel makes use of inexhaustible energy that is from the sun and it is a unpolluted as well as environmental friendly means of collecting solar energy. Solar cells rely on the photovoltaic effect to captivate the light energy of the sun as well as cause current to flow between two oppositely charge layers.
There are a few basic types of solar panel but mostly there are three that are commonly used. The three solar panels that are commonly used are monocrystalline solar panel, polycrystalline solar panel, as well as amorphous solar panel. The monocrystalline solar panel is the best is efficiency and the price is very expensive as the solar panels are made with monocrystalline cells. Monocrystalline solar cells use silicon with high purity as well as including a complex crystal growth process. The lengthy silicon rode are formed and processed into single cells that are linked together in the solar panel. For polycrystalline solar panels are also being called as multi-crystalline. Polycrystalline is cheaper compare to monocrystalline and slightly less efficient that monocrystalline cells. This is because the cells are not grown in individual crystals but in a big block of crystal. Apart from monocrystalline and polycrystalline, amorphous solar panel is not actually produced by crystal but a thin layer of silicon deposited on a base material like metal or glass to produce the panel. It is less costly and it is also less efficient [13].
(b) (c)
Figure: (a) Monocrystalline Solar Panel [14], (b) Multicrystalline Solar Panel [15] and (c) Amorphous solar panel [16]
MAXIMIZE POWER GAINED FROM SOLAR CELLS
Through experiments that were conducted during research by Elliot Larard in1998, it was concluded that the current gained from solar cells is influenced by the angle at which incident rays strike the cell surface. With the help of a stationary light source and adjusting the angle at which the light rays strike the solar cell, a plot of current delivered vs. angle of incidence can be created. This property of solar cells is confirmed by the data contained in Table, and illustrated by Figure.
Figure: Incidence Angle of the Sun [17]
Table: Current delivered for various angles of incidence [17]
Figure: Current Delivered vs. Angle of Incidence Graph [17]
After considering the experimental data that was obtained, it can be defined that, the angle of incidence must be held at zero degrees to preserve maximum power output from a solar array. Therefore the array must constantly face the sun. This requires a sun
SERVO MOTOR
Figure: Servo Motor [18]
A servo is a tiny device that has an output shaft. This shaft can be placed to specific angular positions by directing the servo with a coded signal. Provided that the coded signal occurs on the input line, the servo motor will preserve the angular location of the shaft. Beside this, the angular position of the shaft changes as the coded signal changes in time. Servos are mainly used in radio controlled airplanes to position control surfaces like the elevators as well as rudders. They are also used in radio controlled cars where it provides actuation for various mechanical systems such as the steering of a car, puppets, as well as robots.
A servo motor include of a few main parts which is the motor as well as a gearbox, a position sensor, an error amplifier and motor driver and a circuit to interpret the requested position. The radio control receiver system creates a pulse of different length about every 20 milliseconds. Normally, the pulse is about 1 to 2 milliseconds long. The length of the pulse can determined the position of the servo motor.
Figure: Servo Motor Block Diagram [19]
The restrictions for this pulse are that it has a least pulse, a maximum pulse, as well as a repetition rate. With the turning limitations of the servo motor is given, neutral is being defined as a position where the servo has the same volume of potential rotation in the clockwise path as the servo does in the counter clockwise path. It is vital to know that different servos will have dissimilar constraints on servo rotation but all servos have a neutral position and the position is normally around 1.5 milliseconds (ms).
The angle is determined by the length of a pulse which is sent to a control wire is being called as Pulse width Modulation. The servo expects a pulse to be receive every 20 ms. The distance that the motor turns is determine by the length of the pulse that is receive. When these servos are being commanded to move, they will move to the position and hold on that position. If an external force is put on the servo while the servo is holding a position, the servo will resist itself from leaving that position. The highest value of force that the servo can put forth is the torque rating of the servo motor. Position pulse should be sent continuously to instruct the servo to stay in its current position or the servo motor will not hold the position forever.
When a pulse is directed to a servo that is less than 1.5 ms the servo rotates to a certain position. The servo will hold its output shaft some degrees counterclockwise from the neutral position. If the position pulse is larger than 1.5 ms the servo will turn to clockwise direction. The minimal width as well as the largest width of pulse that will determine the servo to turn to a certain position is functions of every servo motor. Dissimilar brands and dissimilar servos of the similar brand will have different maximum as well as minimums. Normally, the minimum pulse will be about 1 ms wide and the maximum pulse will be 2 ms wide [20].
Figure: Pulse Width Modulation of Servo motor [20]
Figure: Position of Servo Motor [20]
Another parameter that varies from servo to other servo is its speed of turning. This is the duration it takes from the servo to go from one position to another position. The worst case turning duration is when the servo at the minimum rotation while it is being directed to turn to the maximum rotation. This can take up to a few seconds on a very great torque servo [20].
DC MOTOR
Figure: D.C. motor
D.C. motors are motors that run using Direct Current from a battery or else D.C. power supply as the source of its energy. Direct Current is being used to describe electricity at constant voltage. While A.C. motors run on Alternating Current, Alternating Current is the current oscillates with a fixed cycle between a positive as well as a negative value. Normally, electrical outlets provide A.C. power to its consumers. When a battery or D.C. power supply is connected between a D.C. motor's electrical leads, the motor converts electrical energy to mechanical work as the output shaft of the D.C. motor turns. An amount of momentary power burst of the rated torque up to five times can be provide by the D.C motor. Without any power interruption, the speed of the D.C motor can be brought down immediately raised in the reverse direction.
Two poles with electromagnet that serve as a rotating armature are in D.C motor. Acommutator or rotary switch is being used to change the current to the opposite direction two times in each cycle. Push and pull against the external permanent magnets are caused by the poles of electromagnet. The commutator changes the polarity of the armature to the opposite direction when the poles of the armature pass through the poles of the permanent magnet. The inertia will preserve the current direction at the occasion when polarity is being switched [20].
Figure: The D.C motor operation [21]
There are 5 major types of DC motor:
Brushless DC motor
Limited-angle torque motor
PM DC motor
Coreless DC motor
Liner DC motor
D.C. motor is used to move the solar panel. The D.C. motor is connecting with string as well as attach to the panel. When the motor rotate, it will move the solar panel and that movement will relocate the angle of the LDR sensor. The LDR sensor will send back the signal of sun location and the motor stopped when the right angle was founded. It all depends from the input provided by sensor.
Normally, D.C. motor type use 12 volt input and available to produce maximum 1.1 watt power as mention in data sheet. A D.C. motor required at least one electromagnet. This electromagnet switches the current flow as the motor turns, changing its polarity to keep the motor running. The motor rotate from positive terminal to negative terminal [21].
For each and every motor, there will be a unique Torque/Speed curve and also the Power curve. The graph shown below displays torque/speed curve of a normal D.C. motor. The torque of the motor is inversely proportional to the speed of the output shaft. Motor characteristics are normally given as two points on the graph:
The stall torque, [Ts], signifies the point on the graph at when the torque at maximum but the shaft of the motor is not rotating.
The no load speed, [Wn], signifies the highest output speed of the motor (when no torque is applied to the output shaft) [22].
Figure: Torque vs. Rotational Speed Plot [22]
Servo Motor
Stepper Motor
DC Motor
Advantages
More reliable
Available in wide range of frame side
Easy to control
Most effective
Fast response
Precision positioning
High holding torque
Long lifespan
Low maintenance
High efficiency
Disadvantages
Need to be control using self-defined PWM
High initial cost
Requires a controller
High initial cost
Requires a controller
Heavy
Servo Motor is choose as it can be controlled using self-defined PWM and the price of a servo is cheaper and the voltage require is lower compare to stepper motor and DC motor.
Programmable Interface CONTROLLER (PIC)
For this project, the controller for the movement is PIC microcontroller. We will describe about the PIC microcontroller and at the same time, it will give more understanding for me to employ this controller. Almost all type of PIC microcontroller is included in a class of 8-bit microcontrollers of RISC architecture. Basically, the PIC architecture is minimized to be a simpler item but it still operates at the same function.
The Harvard architecture is a newer concept than von-Neumann. It was designed as a response for the need to speed up the work of a microcontroller. In Harvard architecture, data bus and address bus are separate. Thus, the data will flow directly through the central processing unit and the address bus is neglected. This greater flow of data will impact for a greater speed of work. Besides that, the architecture will involve for a small number of a fixed length instruction. It means the instruction is not to have to be 8-bit words but it can uses 14 bits for instructions which allows for all instruction to be one word instructions. Microcontrollers with Harvard architecture are called "RISC microcontrollers". RISC is a short form for Reduced Instruction Set Computer. Microcontrollers with von-Neumann's architecture are called 'CISC microcontrollers'. CISC is a short form for Complex Instruction Set Computer. Same as discussion before, RISC microcontroller has a reduced set of instructions, maybe 35 instructions for one cycle. If we compared it with Intel's and Motorola's microcontroller, it has over hundred instructions.
As a simplified point, we can say that the features of PIC microcontroller are:
Separate code as well as data spaces (Harvard architecture).
Small number of fixed length instructions.
Most instructions are in single cycle execution (4 clock cycles), with single delay cycles upon branches as well as skips.
All of the RAM locations function as registers as both the source and/or destination of math as well as other functions.
A hardware stack for the use of storing return addresses.
A small amount of addressable data space (around 256 bytes), extended through banking.
Data space mapped CPU, port as well as peripheral registers.
The program counter is mapped into the data space as well as writable.
Figure: PIC16F877A BLOCK DIAGRAM
Light Sensor
A light sensor is the most common electronic component which can be easily found. The simplest optical sensor is a photo resistor or photocell which is a light sensitive resistor these are made of two types, cadmium sulfide (CdS) and gallium arsenide (GaAs) [4]. The sun tracker system designed here uses the cadmium sulfide (CdS) photocell for sensing the light. This photocell is a passive component whose resistance is inversely proportional to the amount of light intensity directed towards it. It is connected in series with capacitor. The photocell to be used for the tracker is based on its dark resistance and light saturation resistance. The term light saturation means that further increasing the light intensity to the CdS cells will not decrease its resistance any further.
