1info4eee | Information For Electrical & Electronics Engineering1. INTRODUCTIONOne of the most promising renewable energy sources characterized by a huge potential of conversion intoelectrical power is the solar energy. The conversion of solar radiation into electrical energy by Photo-Voltaic(PV) effect is a very promising technology, being clean, silent and reliable, with very small maintenancecosts and small ecological impact. The interest in the Photo Voltaic conversion systems is visibly reflectedby the exponential increase of sales in this market segment with a strong growth projection for the nextdecades. According to recent market research reports carried out by European Photovoltaic IndustryAssociation (EPIA), the total installed power of PV conversion equipment increased from about 1 GW in2001up to nearly 23 GW in 2009.The continuous evolution of the technology determined a sustained increase of the conversion efficiency ofPV panels, but nonetheless the most part of the commercial panels have efficiencies no more than 20%. Aconstant research preoccupation of the technical community involved in the solar energy harnessingtechnology refers to various solutions to increase the PV panel‟s conversion efficiency. Among PVefficiency improving solutions we can mention: solar tracking, optimization of solar cells geometry,enhancement of light trapping capability, use of new materials, etc. The output power produced by the PVpanels depends strongly on the incident light radiation.The continuous modification of the sun-earth relative position determines a continuously changing ofincident radiation on a fixed PV panel. The point of maximum received energy is reached when the directionof solar radiation is perpendicular on the panel surface. Thus an increase of the output energy of a given PVpanel can be obtained by mounting the panel on a solar tracking device that follows the sun trajectory.Unlike the classical fixed PV panels, the mobile ones driven by solar trackers are kept under optimuminsolation for all positions of the Sun, boosting thus the PV conversion efficiency of the system. The outputenergy of PV panels equipped with solar trackers may increase with tens of percents, especially during thesummer when the energy harnessed from the sun is more important. Photo-Voltaic or PV cells, knowncommonly as solar cells, convert the energy from sunlight into DC electricity. PVs offer added advantagesover other renewable energy sources in that they give off no noise and require practically no maintenance. Atracking system must be able to follow the sun with a certain degree of accuracy, return the collector to itsoriginal position at the end of the day and also track during periods of cloud over.The major components of this system are as follows.Light dependent resistorMicrocontroller.Output mechanical transducer (stepper motor)
2info4eee | Information For Electrical & Electronics Engineering1.1 BackgroundA Solar Tracker is a device onto which solar panels are fitted which tracks the motion of the sun across thesky ensuring that the maximum amount of sunlight strikes the panels throughout the day. The Solar Trackerwill attempt to navigate to the best angle of exposure of light from the sun. This report aims to let the readerunderstand the project work which I have done. A brief introduction to Solar Panel and Solar Tracker isexplained in the Literature Research section. Basically the Solar Tracker is divided into two main categories,hardware and software. It is further subdivided into six main functionalities: Method of Tracker Mount,Drives, Sensors, RTC, Motors, and Power Supply of the Solar Tracker is also explained and explored. Thereader would then be brief with some analysis and perceptions of the information.By using solar arrays, a series of solar cells electrically connected, a DC voltage is generated which can bephysically used on a load. Solar arrays or panels are being used increasingly as efficiencies reach higherlevels, and are especially popular in remote areas where placement of electricity lines is not economicallyviable. This alternative power source is continuously achieving greater popularity especially since therealisation of fossil fuels shortcomings. Renewable energy in the form of electricity has been in use to somedegree as long as 75 or 100 years ago. Sources such as Solar, Wind, Hydro and Geothermal have all beenutilised with varying levels of success. The most widely used are hydro and wind power, with solar powerbeing moderately used worldwide. This can be attributed to the relatively high cost of solar cells and theirlow conversion efficiency. Solar power is being heavily researched, and solar energy costs have now reachedwithin a few cents per kW/h of other forms of electricity generation, and will drop further with newtechnologies such as titanium oxide cells. With a peak laboratory efficiency of 32% and average efficiencyof 15-20%, it is necessary to recover as much energy as possible from a solar power system. This includesreducing inverter losses, storage losses, and light gathering losses. Light gathering is dependent on the angleof incidence of the light source providing power (i.e. the sun) to the solar cell‟s surface, and the closer toperpendicular, the greater the power. If a flat solar panel is mounted on level ground, it is obvious that overthe course of the day the sunlight will have an angle of incidence close to 90° in the morning and theevening. At such an angle, the light gathering ability of the cell is essentially zero, resulting in no output. Asthe day progresses to midday, the angle of incidence approaches 0°, causing a steady increase in power untilat the point where the light incident on the panel is completely perpendicular, and maximum power isachieved. As the day continues toward dusk, the reverse happens, and the increasing angle causes the powerto decrease again toward minimum again. From this background, we see the need to maintain the maximumpower output from the panel by maintaining an angle of incidence as close to 0° as possible. By tilting thesolar panel to continuously face the sun, this can be achieved. This process of sensing and following theposition of the sun is known as Solar Tracking. It was resolved that real-time tracking would be necessary tofollow the sun effectively, so that no external data would be required in operation.
3info4eee | Information For Electrical & Electronics Engineering2. Literature ResearchThis chapter aims to provide a brief knowledge of Solar Panel, Solar Tracker and the components whichmade up Solar Tracker.2.1 Technology of Solar PanelSolar panels are devices that convert light into electricity. They are called solar after the sun because the sunis the most powerful source of the light available for use. They are sometimes called photovoltaic whichmeans "light-electricity". Solar cells or PV cells rely on the photovoltaic effect to absorb the energy of thesun and cause current to flow between two oppositely charge layers. A solar panel is a collection of solarcells. Although each solar cell provides a relatively small amount of power, many solar cells spread over alarge area can provide enough power to be useful. To get the most power, solar panels have to be pointeddirectly at the Sun. The development of solar cell technology begins with 1839 research of French physicistAntoine-Cesar Becquerel. He observed the photovoltaic effect while experimenting with a solid electrode inan electrolyte solution. After that he saw a voltage developed when light fell upon the electrode.According to Encyclopaedia Britannica the first genuine for solar panel was built around 1883 by CharlesFritts. He used junctions formed by coating selenium (a semiconductor) with an extremely thin layer of gold.Crystalline silicon and gallium arsenide are typical choices of materials for solar panels. Gallium arsenidecrystals are grown especially for photovoltaic use, but silicon crystals are available in less-expensivestandard ingots, which are produced mainly for consumption in the microelectronics industry. Norway‟sRenewable Energy Corporation has confirmed that it will build a solar manufacturing plant in Singapore by2010 - the largest in the world. This plant will be able to produce products that can generate up to 1.5 Gigawatts of energy every year. That is enough to power several million households at any one time. Last yearthe world as a whole produced products that could generate just 2 GW in total.2.2 Evolution of Solar TrackerSince the sun moves across the sky throughout the day, in order to receive the best angle of exposure tosunlight for collection energy. A tracking mechanism is often incorporated into the solar arrays to keep thearray pointed towards the sun. A solar tracker is a device onto which solar panels are fitted which tracks themotion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughoutthe day. When compare to the price of the PV solar panels, the cost of a solar tracker is relatively low. Mostphotovoltaic solar panels are fitted in a fixed location- for example on the sloping roof of a house, or onframework fixed to the ground. Since the sun moves across the sky though the day, this is far from an idealsolution. Solar panels are usually set up to be in full direct sunshine at the middle of the day facing South in
4info4eee | Information For Electrical & Electronics Engineeringthe Northern Hemisphere, or North in the Southern Hemisphere. Therefore morning and evening sunlighthits the panels at an acute angle reducing the total amount of electricity which can be generated each day.Fig 2.1 Sun‟s apparent motionDuring the day the sun appears to move across the sky from left to right and up and down above thehorizon from sunrise to noon to sunset. Figure 2.1 shows the schematic above of the Suns apparentmotion as seen from the Northern Hemisphere. To keep up with other green energies, the solar cellmarket has to be as efficient as possible in order not to lose market shares on the global energymarketplace. The end-user will prefer the tracking solution rather than a fixed ground system to increasetheir earnings because:The efficiency increases by 30-40%.The space requirement for a solar park is reduced, and they keep the same output.The return of the investment timeline is reduced.The tracking system amortizes itself within 4 years.In terms of cost per Watt of the completed solar system, it is usually cheaper to use a solartracker and less solar panels where space and planning permit.A good solar tracker can typically lead to an increase in electricity generation capacity of 30-50%.
5info4eee | Information For Electrical & Electronics Engineering3. Project Description3.1 Block DiagramFig 3.1 Block Diagram of Project3.2 Schematic DiagramFig 3.2 Schematic Diagram of Project
6info4eee | Information For Electrical & Electronics Engineering3.3 PRINTED CIRCUIT BOARDAlmost all circuits encountered on electronic equipment (computers, TV, radio, industrial control equipment,etc.) are mounted on printed circuit boards. Close inspection of a PCB reveals that it contains a series ofcopper tracks printed on one or both sides of a fiber glass board. The copper tracks form the wiring patternrequired to link the circuit devices according to a given circuit diagram. Hence, to construct a circuit thenecessity of connecting insulated wires between components is eliminated, resulting in a cleanerarrangement and providing mechanical support for components. Moreover, the copper tracks are highlyconductive and the whole PCB can be easily reproduced for mass production with increased reliability.1) Types of PCBPCBs can be divided into three main categories:Single-sidedDouble-sidedMulti-layered.Single-sided PCBA single-sided PCB contains copper tracks on one side of the board only, as shown in Figure 3.3. Holes aredrilled at appropriate points on the track-so that each component can be inserted from the non-copper side ofthe board, as shown in Figure 3.4. Each pin is then soldered to the copper track.Fig 3.3 Printed circuit board
7info4eee | Information For Electrical & Electronics EngineeringFig 3.4 Single sided PCBDouble-sided PCBDouble-sided PCBs have copper tracks on both sides of the board. The track layout is designed so as not toallow shorts from one side to another, if it is required to link points between the two sides, electricalconnections are made by small interconnecting holes which are plated with copper during manufacture.Fig 3.5 Double sided PCBMulti-layer PCBIn multi-layer PCBs, each side contains several layers of track patterns which are insulated from oneanother. These layers are laminated under heat and high pressure. A multi-layer PCB is shown in Figure 3.6
8info4eee | Information For Electrical & Electronics EngineeringFig 3.6 Multi layered PCB2) MAKING A PCBPCBs commonly available on the market are not particular circuits, but are available as copper clad boards.In other words, the whole area of one or both sides of the board is coated with copper. The user then drawshis track layout on the copper surface, according to his circuit diagram. Next, the untraced copper arearemoved by a process called etching. Here, the unused copper area is dissolved away by an etching solutionand only the required copper tracks remain. The board is then cleaned and drilled at points where eachdevice is to be inserted. Finally, each component is soldered to the board.The etching process depends on whether board is of plain or photo-resist type. These are treated separatelyin the following section.a) Making a PCB out of a plain copper clad boardEquipment requiredThe following items are required:A single-sided copper clad board.Ferric chloride solution, which is the etching liquid.An etch-resist pen is with its ink resisting to ferric chloride.A PCB eraser.Track layout designThe first step is to draw the track layout on the plain copper clad board, according to the circuit to beimplemented which turns on an LED when the push-button is pressed. The lines joining differentcomponents will form the track layout on the PCB. Each component is inserted from the non-copper side ofthe board and its leads appear on the copper side. For example, when viewing the component side, the baseof the BC109 transistor appears to the right of the collector, while from the track side, it appears at the left ofthe collector.b) Making a PCB out of a photo resist boardEquipment requiredPhoto-resist boardFerric chloride solution as etchantA white board markerTransparent polyester film for use as drafting sheetSodium hydroxide solution as developer
9info4eee | Information For Electrical & Electronics EngineeringUltra-violet exposure unitTrack layout designUsing the same principles outlined in section a track layout is drawn to scale on the transparency using thewhite board marker. It may be useful to insert graph paper below the transparent sheet for accuratedimensioning of the layout.Photo-etchingThe principle behind photo-etching is to place the transparency over the copper clad and to expose it to UVradiation, hence leaving the track regions intact and softening unused areas. First, the protective plastic filmis removed from the board. The traced transparency is then placed over the board, being careful to ensurethat the copper side of the design faces upwards. The combination is next placed in a UV exposure unit, withthe transparency facing the fluorescent tubes inside the unit. At the track regions, UV radiation is preventedfrom reaching the board, and hence the photo sensitive remains hardened in these regions. After an exposureof about 5 minutes the board can be removed. The PCB is then placed in a solution of caustic soda whichdissolves away any unhardened photo-sensitive area. After a few minutes of development time, the tracklayout is apparent. The board is finally removed and rinsed in cold water.Final etchingAfter having allowed the tracks to harden for about half an hour, the unmarked copper area is etched byferric chloride solution.3) The following points should be noted:It is a good idea to draft the track layout on graph paper before drawing the final layout on the copperclad.Use an etch resist pen to draw the track layout on the copper clad (the latter must be cleanedinitially).The following lead spacing can be used as a rule of thumb: allow 10 mm for a 1/4 W resistor, 8 mmfor a signal diode, 4 mm for LEDs and ceramic capacitors. The lead spacing may also be measuredbefore drawing.Terminals for the power supply input leads must also be included on the layout.The arrangement of components must be well planned so as to minimize the amount of cooper cladboard required.Allow the ink to dry before etching.
10info4eee | Information For Electrical & Electronics Engineering4) EtchingThe copper clad is now ready to be etched. If the etchant is available in powder form, it needs to be mixedwith water in anon-corrodible container. A powder to water ratio of 2:5 by mass is about right. Etching timemay vary between 10 to as long as 90 minutes, depending on the concentration and temperature of theetchant. The process can be accelerated by warming the solution and by frequently agitating the etchingbath. The ferric chloride solution gradually dissolves any untraced copper area. When etching is complete,only the track layout remains on the board. The latter is then removed the bath and rinsed with clean water.The etch resist ink is finally rubbed away with a PCB eraser, or with very fine grain sand paper.Making a PCB out of a photo-resist copper clad boardThe photo-resist board consists of a single or double sided copper clad coated with a light-sensitive and thelatter is protected with a plastic which should be removed before use. Its advantage over the plain copperclad board is that the track layout does not need to be drawn directly on the board.The use of etch-resist transfersThe use of pens to design track layouts may not give neat result, even when using a ruler. For instance, itmay be difficult to draw tracks with the same line Width or to draw well aligned terminals for ICs anddiscrete devices, Etch-resist PCB symbols and tracks are available for direct transfer to the copper clad or tothe transparency. Transfer is by rubbing down the relevant symbol with a soft pencil.
11info4eee | Information For Electrical & Electronics Engineering4. Components Description4.1 Solar TrackerSolar Tracker is basically a device onto which solar panels are fitted which tracks the motion of the sunacross the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. Afterfinding the sunlight, the tracker will try to navigate through the path ensuring the best sunlight is detected.The design of the Solar Tracker requires many components. The design and construction of it could bedivided into six main parts that would need to work together harmoniously to achieve a smooth run for theSolar Tracker, each with their main function. They are:Methods of Tracker MountMethods of DrivesSensor and Sensor ControllerMotor and Motor ControllerTracker Solving AlgorithmData Acquisition/Interface Card4.2Methods of Tracker Mount1. Single axis solar trackersSingle axis solar trackers can either have a horizontal or a vertical axle. The horizontal type is used intropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in highlatitudes where the sun does not get very high, but summer days can be very long. The single axis trackingsystem is the simplest solution and the most common one used.2. Double axis solar trackersDouble axis solar trackers have both a horizontal and a vertical axle and so can track the Suns apparentmotion exactly anywhere in the World. This type of system is used to control astronomical telescopes, and sothere is plenty of software available to automatically predict and track the motion of the sun across the sky.By tracking the sun, the efficiency of the solar panels can be increased by 30-40%.The dual axis trackingsystem is also used for concentrating a solar reflector toward the concentrator on heliostat systems.4.3 Methods of Drive1. Active TrackersActive Trackers use motors and gear trains to direct the tracker as commanded by a controllerresponding to the solar direction. Light-sensing trackers typically have two photo sensors, such asphotodiodes, configured differentially so that they output a null when receiving the same light flux.
12info4eee | Information For Electrical & Electronics EngineeringMechanically, they should be omnidirectional and are aimed 90 degrees apart. This will cause the steepestpart of their cosine transfer functions to balance at the steepest part, which translates into maximumsensitivity.2. Passive TrackersPassive Trackers use a low boiling point compressed gas fluid that is driven to one side or the other by solarheat creating gas pressure to cause the tracker to move in response to an imbalance.4.4 SensorsA sensor is a device that measures a physical quantity and converts it into a signal which can be read by anobserver or by an instrument.1. Light Dependent ResistorLight Dependent Resistor is made of a high-resistance semiconductor. It can also be referred to as aphotoconductor. If light falling on the device is of the high enough frequency, photons absorbed by thesemiconductor give bound electrons enough energy to jump into the conduction band. The resulting freeelectron conducts electricity, thereby lowering resistance. Hence, Light Dependent Resistors is very useful inlight sensor circuits. LDR is very high-resistance, sometimes as high as 10MΩ, when they are illuminatedwith light resistance drops dramatically.A Light Dependent Resistor is a resistor that changes in value according to the light falling on it. Acommonly used device, the ORP-12, has a high resistance in the dark, and a low resistance in the light.Connecting the LDR to the microcontroller is very straight forward, but some software „calibrating‟ isrequired. It should be remembered that the LDR response is not linear, and so the readings will not change inexactly the same way as with a potentiometer. In general there is a larger resistance change at brighter lightlevels. This can be compensated for in the software by using a smaller range at darker light levels.Fig 4.1 Light Dependent Resistor
13info4eee | Information For Electrical & Electronics Engineering2. PhotodiodePhotodiode is a light sensor which has a high speed and high sensitive silicon PIN photodiode in aminiature flat plastic package. A photodiode is designed to be responsive to optical input. Due to its waterclear epoxy the device is sensitive to visible and infrared radiation. The large active area combined with aflat case gives a high sensitivity at a wide viewing angle. Photodiodes can be used in either zero bias orreverse bias. In zero bias, light falling on the diode causes a voltage to develop across the device, leading toa current in the forward bias direction. This is called the photovoltaic effect, and is the basis for solar cells -in fact a solar cell is just a large number of big, cheap photodiodes. Diodes usually have extremely highresistance when reverse biased. This resistance is reduced when light of an appropriate frequency shines onthe junction. Hence, a reverse biased diode can be used as a detector by monitoring the current runningthrough it. Circuits based on this effect are more sensitive to light than ones based on the photovoltaic effect.Fig 4.2 different type of photo diodes4.5 MotorMotor is use to drive the Solar Tracker to the best angle of exposure of light. For this section, we are usingstepper motor.Stepper MotorFeaturesLinear speed control of stepper motorControl of acceleration, deceleration, max speed and number of steps to moveDriven by one timer interruptFull - or half-stepping driving modeSupports all AVR devices with 16bit timer
14info4eee | Information For Electrical & Electronics EngineeringIntroductionThis application note describes how to implement an exact linear speed controller for stepper motors. Thestepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation. Manyadvantages are achieved using this kind of motors, such as higher simplicity, since no brushes or contacts arepresent, low cost, high reliability, high torque at low speeds, and high accuracy of motion. Many systemswith stepper motors need to control the acceleration/deceleration when changing the speed. This applicationnote presents a driver with a demo application, capable of controlling acceleration as well as position andspeed.Fig 4.3 Stepper MotorsTheoryStepper motorThis application note covers the theory about linear speed ramp stepper motor control as well as therealization of the controller itself. It is assumed that the reader is familiar with basic stepper motor operation,but a summary of the most relevant topics will be given.Bipolar vs. Unipolar stepper motorsThe two common types of stepper motors are the bipolar motor and the Unipolar motor. The bipolar andunipolar motors are similar, except that the Unipolar has a centre tap on each winding as shown in Figure 4.4
15info4eee | Information For Electrical & Electronics EngineeringFig 4.4 Bipolar and Unipolar stepper MotorUnipolar stepper motorStepper motors are very accurate motors that are commonly used in computer disk drives, printers andclocks. Unlike dc motors, which spin round freely when power is applied, stepper motors require that theirpower supply be continuously pulsed in specific patterns. For each pulse the stepper motor moves aroundone step often 15 degrees giving 24 steps in a full revolution.There are two main types of stepper motors -Unipolar and Bipolar. Unipolar motors usually have four coils which are switched on and off in a particularsequence. Bipolar motors have two coils in which the current flow is reversed in a similar sequence. Each ofthe four coils in a Unipolar stepper motor must be switched on and off in a certain order to make the motorturn. Many microprocessor systems use four output lines to control the stepper motor, each output linecontrolling the power to one of the coils. As the stepper motor operates at 5V, the standard transistor circuitis required to switch each coil. As the coils create a back emf when switched off, a suppression diode oneach coil is also required. The table below show the four different steps required to make the motor turn.Table 4.1 Unipolar stepper motor operationStep Coil 1 Coil 2 Coil 3 Coil 41 1 0 1 02 1 0 0 13 0 1 0 14 0 1 1 01 1 0 1 0Look carefully at the table 4.1 and notice that a pattern is visible. Coil 2 is always the opposite or logicalNOT of coil 1. The same applies for coils 3 and 4. It is therefore possible to cut down the number ofmicrocontroller pins required to just two by the use of two additional NOT gates. Fortunately the Darlington
16info4eee | Information For Electrical & Electronics Engineeringdriver IC ULN2003 can be used to provide both the NOT and Darlington driver circuits. It also contains theback emf suppression diodes so no external diodes are required.Bipolar Stepper motorThe bipolar stepper motor has two coils that must be controlled so that the current flows in differentdirections through the coils in a certain order. The changing magnetic fields that these coils create cause therotor of the motor to move around in steps.The bipolar motor needs current to be driven in both directions through the windings, and a full bridgedriver is needed as shown in Figure 4.5 (a). The centre tap on the Unipolar motor allows a simpler drivingcircuit shown in Figure 4.5 (b), limiting the current flow to one direction. The main drawback with theUnipolar motor is the limited capability to energize all windings at any time, resulting in a lower torquecompared to the bipolar motor. The Unipolar stepper motor can be used as a bipolar motor by disconnectingthe centre tap.(a) (b)Fig 4.5 Bipolar and Unipolar drivers with MOS transistorsImplementationA working implementation written in C is included with this application note. Full documentation of thesource code and compilation information is found by opening the „readme.html‟ file included with thesource code. The demo application demonstrates linear speed control of a stepper motor. The user cancontrol the stepper motor speed profile by issuing different commands using the serial port, and the AVRwill drive the connected stepper motor accordingly. The demo application is divided in three major blocks,
17info4eee | Information For Electrical & Electronics Engineeringas shown in the block diagram in Figure 4.6. There is one file for each block and also a file for UARTroutines used by the main routine.Fig 4.6 Block diagram of demo applicationMain c has a menu and a command interface, giving the user control of the stepper motor by a terminalconnected to the serial line. Speed controller c calculates the needed data and generates step pulses to makethe stepper motor follow the desired speed profile. Smdriver.c counts the steps and outputs the correctsignals to control the stepper motor.Timer interruptThe timer interrupt generates the step pulses calls the function Step Counter ( ) and is only running when thestepper motor is moving. The timer interrupt will operate in four different states according to the speedprofile shown in Figure 4.7 and this behaviour is realized with a state machine in the timer interrupt shownin Figure 4.8.Fig 4.7 Operating states for different speed profile parts
18info4eee | Information For Electrical & Electronics EngineeringFig 4.8 State machine for timer interruptWhen the application starts or when the stepper motor is stopped the state-machine remains in the stateSTOP. When setup calculations are done, a new state is set and the timer interrupt is enabled. When movingmore than one step the state-machine goes to ACCEL. If moving only 1 step, the state is changed to DECEL.When the state is changed to ACCEL, the application accelerates the stepper motor until either the desiredspeed is reached and the state is changed to RUN, or deceleration must start, changing the state to DECEL.When the state is set to RUN, the stepper motor is kept at constant speed until deceleration must start, thenthe state is changed to DECEL.It will stay in DECEL and decelerate until the speed reaches zero desirednumber of steps. The state is then changed to STOP.4.6 MicrocontrollerA microcontroller is a single chip that contains the processor, non-volatile memory for the program, volatilememory for input and output, a clock and an I/O control unit also called a computer on a chip, billions ofmicrocontroller units are embedded each year in a myriad of products from toys to appliances toautomobiles. For example, a single vehicle can use 70 or more microcontrollers. The following picturedescribes a general block diagram of microcontroller.FeaturesHigh-performance, Low-power AVR 8-bit MicrocontrollerAdvanced RISC Architecture131 Powerful Instructions – Most Single-clock Cycle Execution32 x 8 General Purpose Working RegistersFully Static OperationUp to 16 MIPS Throughput at 16 MHzOn-chip 2-cycle MultiplierHigh Endurance Non-volatile Memory segments16K Bytes of In-System Self-programmable Flash program memory512 Bytes EEPROM1K Byte Internal SRAMWrite/Erase Cycles: 10,000 Flash/100,000 EEPROMData retention: 20 years at 85°C/100 years at 25°COptional Boot Code Section with Independent Lock BitsIn-System Programming by On-chip Boot ProgramTrue Read-While-Write OperationProgramming Lock for Software Security
19info4eee | Information For Electrical & Electronics EngineeringJTAG InterfaceBoundary-scan Capabilities According to the JTAG StandardExtensive On-chip Debug SupportProgramming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG InterfacePeripheral FeaturesTwo 8-bit Timer/Counters with Separate Prescalers and Compare ModesOne 16-bit Timer/Counter with Separate Prescalers, Compare Mode, and CaptureModeReal Time Counter with Separate OscillatorFour PWM Channels8-channel, 10-bit ADC8 Single-ended Channels7 Differential Channels in TQFP Package Only2 Differential Channels with Programmable Gain at 1x, 10x, or 200xByte-oriented Two-wire Serial InterfaceProgrammable Serial USARTMaster/Slave SPI Serial InterfaceProgrammable Watchdog Timer with Separate On-chip OscillatorOn-chip Analog ComparatorSpecial Microcontroller FeaturesPower-on Reset and Programmable Brown-out DetectionInternal Calibrated RC OscillatorExternal and Internal Interrupt SourcesSix Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standbyand Extended StandbyI/O and Packages32 Programmable I/O Lines40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLFOperating Voltages2.7 - 5.5V for ATmega16L4.5 - 5.5V for ATmega16Speed Grades0 - 8 MHz for ATmega16L0 - 16 MHz for ATmega16
20info4eee | Information For Electrical & Electronics EngineeringPower Consumption @ 1 MHz, 3V, and 25°C for ATmega16LActive: 1.1 mAIdle Mode: 0.35 mAPower-down Mode: < 1 μAATmega16:The ATmega16 is a low-power, high-performance advance RISC8-bit microcontroller with 32K bytes of in-system programmable Flash memory. The on-chip Flash allows the program memory to be reprogrammedin-system or by a conventional non-volatile memory programmer. By combining a versatile 8-bit CPU within-system programmable Flash on a monolithic chip, the Atmel ATmega16 is a powerful microcontroller,which provides a highly flexible and cost-effective solution to many, embedded control applications. TheATmega16 provides the following standard features:32K bytes of Flash, 1024 byte of EEPROM & 2KBINTERNAL S RAM ,32 I/O lines, Watch dog timer, two data pointers, two 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator,8-channel 10 bit ADC andclock circuitry. In addition, the ATmega16 is designed with static logic for operation down to zero frequencyand supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing theRAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode savesthe RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt.
21info4eee | Information For Electrical & Electronics EngineeringFig 4.9 Pin diagram of ATmega16Overview-The ATmega16 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture.By executing powerful instructions in a single clock cycle, the ATmega16 achieves throughputs approaching1 MIPS per MHz allowing the system designed to optimize power consumption versus processing speed.Pin DescriptionsVCC Digital supply voltageGND GroundPort A (PA7 - PA0) Port A serves as the analog inputs to the A/D Converter. Port A also serves as an 8-bitbi-directional I/O port, if the A/D Converter is not used. Port pin scan provide internal pull-up resistors. ThePort A output buffers have symmetrical drive characteristics with both high sink and source capability.When pins PA0 to PA7are used as inputs and are externally pulled low, they will source current if theinternal pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active,even if the clock is not running.Port B (PB7 - PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port Boutput buffers have symmetrical drive characteristics with both high sink and source capability. As inputs,Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port Bpins are tri-stated when a reset condition becomes active, even if the clock is not running.Port C (PC7 - PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port Coutput buffers have symmetrical drive characteristics with both high sink and source capability. As inputs,Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port Cpins are tri-stated when a reset condition becomes active, even if the clock is not running. If the JTAGinterface is enabled, the pull-up resistors on pins PC5 (TDI), PC3 (TMS) and PC2 (TCK) will be activatedeven if a reset occurs.Port D (PD7 - PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port Doutput buffers have symmetrical drive characteristics with both high sink and source capability. As inputs,Port D pins that are externally pulled low will source current if the pull-up resistors are activated. The Port Dpins are tri-stated when a reset condition becomes active, even if the clock is not running.RESET Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset,even if the clock is not running.
22info4eee | Information For Electrical & Electronics EngineeringXTAL1 Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.XTAL2 Output from the inverting Oscillator amplifier.AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally connectedto VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-passfilter.AREF AREF is the analog reference pin for the A/D Converter.Alternate Functions of Port APort A has an alternate function as analog input for the ADC as shown in Table 4.2. If some Port A pins areconfigured as outputs, it is essential that these do not switch when a conversion is in progress. This mightcorrupt the result of the conversion.Table 4.2 Port A Pins Alternate FunctionsPort Pin Alternate FunctionPA7 ADC7 (ADC input channel 7)PA6 ADC6 (ADC input channel 6)PA5 ADC5 (ADC input channel 5)PA4 ADC4 (ADC input channel 4)PA3 ADC3 (ADC input channel 3)PA2 ADC2 (ADC input channel 2)PA1 ADC1 (ADC input channel 1)PA0 ADC0 (ADC input channel 0)The alternate pin configuration of Port B is as follows:• SCK – Port B, Bit 7SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave, thispin is configured as an input regardless of the setting of DDB7. When the SPI is enabled as a Master, thedata direction of this pin is controlled by DDB7. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB7 bit.• MISO – Port B, Bit 6MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master, thispin is configured as an input regardless of the setting of DDB6. When the SPI is enabled as a Slave, the data
23info4eee | Information For Electrical & Electronics Engineeringdirection of this pin is controlled by DDB6. When the pin is forced by the SPI to be an input, the pull-up canstill be controlled by the PORTB6 bit.• MOSI – Port B, Bit 5MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a Slave, thispin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a Master, thedata direction of this pin is controlled by DDB5. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit.• SS – Port B, Bit 4SS: Slave Select input. When the SPI is enabled as a Slave, this pin is configured as an input regardless ofthe setting of DDB4. As a Slave, the SPI is activated when this pin is driven low. When the SPI is enabled asa Master, the data direction of this pin is controlled by DDB4. When the pin is forced by the SPI to be aninput, the pull-up can still be controlled by the PORTB4 bit.• AIN1/OC0 – Port B, Bit 3AIN1, Analog Comparator Negative Input Configure the port pin as input with the internal pull-up switchedoff to avoid the digital port function from interfering with the function of the analog comparator. OC0,Output Compare Match output: The PB3 pin can serve as an external output for the Timer/Counter 0Compare Match. The PB3 pin has to be configured as an output to serve this function. The OC0 pin is alsothe output pin for the PWM mode timer function.• AIN0/INT2 – Port B, Bit 2AIN0, Analog Comparator Positive input Configure the port pin as input with the internal pull-up switchedoff to avoid the digital port function from interfering with the function of the Analog Comparator. INT2,External Interrupt Source 2: The PB2 pin can serve as an external interrupt source to the MCU.• T1 – Port B, Bit 1T1, Timer/Counter1 Counter Source.• T0/XCK – Port B, Bit 0
24info4eee | Information For Electrical & Electronics EngineeringT0 Timer/Counter 0 Counter Source XCK USART External Clock. The Data Direction Register DDB0controls whether the clock is output DDB0 set or input DDB0 cleared. The XCK pin is active only when theUSART operates in Synchronous mode.The alternate pin configuration of Port C is as follows:• TOSC2 – Port C, Bit 7TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set one to enable asynchronous clocking ofTimer/Counter2, pin PC7 is disconnected from the port, and becomes the inverting output of the Oscillatoramplifier. In this mode, a Crystal Oscillator is connected to this pin, and the pin cannot be used as an I/O pin.• TOSC1 – Port C, Bit 6TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set one to enable asynchronous clocking ofTimer/Counter2, pin PC6 is disconnected from the port, and becomes the input of the inverting Oscillatoramplifier. In this mode, a Crystal Oscillator is connected to this pin, and the pin cannot be used as an I/O pin.• TDI – Port C, Bit 5TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data Register. Whenthe JTAG interface is enabled, this pin cannot be used as an I/O pin.• TDO – Port C, Bit 4TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When the JTAGinterface is enabled, this pin cannot be used as an I/O pin. The TD0 pin is tri-stated unless TAP states thatshifts out data are entered.• TMS – Port C, Bit 3TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller state machine.When the JTAG interface is enabled, this pin cannot be used as an I/O pin.• TCK – Port C, Bit 2TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is enabled, thispin cannot be used as an I/O pin.SDA – Port C, Bit 1SDA, Two-wire Serial Interface Data: When the TWEN bit in TWCR is set one to enable the Two-wireSerial Interface, pin PC1 is disconnected from the port and becomes the Serial Data I/O pin for the Two-wireSerial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the
25info4eee | Information For Electrical & Electronics Engineeringinput signal, and the pin is driven by an open drain driver with slew-rate limitation. When this pin is used bythe Two-wire Serial Interface, the pull-up can still be controlled by the PORTC1 bit.• SCL – Port C, Bit 0SCL, Two-wire Serial Interface Clock: When the TWEN bit in TWCR is set one to enable the Two-wireSerial Interface, pin PC0 is disconnected from the port and becomes the Serial Clock I/O pin for the Two-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns onthe input signal, and the pin is driven by an open drain driver with slew-rate limitation. When this pin is usedby the Two-wire Serial Interface, the pull-up can still be controlled by the PORT C0 bit.4.7 LCD DisplayA Liquid Crystal Display is an electronic device that can be used to show numbers or text. There are twomain types of LCD display, numeric display and alphanumeric text displays. The display is made up of anumber of shaped „crystals‟. In numeric displays these crystals are shaped into „bars‟, and in alphanumericdisplays the crystals are simply arranged into patterns of „dots‟. Each crystal has an individual electricalconnection so that each crystal can be controlled independently. When the crystal is „off‟ i.e. when nocurrent is passed through the crystal, the crystal reflect the same amount of light as the background material,and so the crystals cannot be seen. However when the crystal has an electric current passed through it, itchanges shape and so absorbs more light. This makes the crystal appear darker to the human eye - and so theshape of the dot or bar can be seen against the background. It is important to realise the difference between aLCD display and an LED display. An LED display often used in clock radios is made up of a number ofLEDs which actually give off light and so can be seen in the dark. An LCD display only reflect slight, and socannot be seen in the dark.The dot-matrix liquid crystal display controller and driver LSI displays alphanumeric, characters, andsymbols. It can be configured to drive a dot-matrix liquid crystal display under the control of a 4 or 8-bitmicroprocessor. Since all the functions such as display RAM, character generator, and liquid crystal driver,required for driving a dot-matrix liquid crystal display are internally provided on one chip, a minimal systemcan be interfaced with this controller/driver. A single HD44780U can display up to two 8-character lines 16x 2. A 16 x 2 line LCD module to display user information.Fig 4.10 2 x16 LCD Display
26info4eee | Information For Electrical & Electronics Engineering4.8 TRANSFORMER:A transformer is a device that transfers electrical energy from one circuit to another through inductivelycoupled conductors - the transformers coils or windings. Except for air-core transformers, the conductors arecommonly wound around a single iron-rich core, or around separate but magnetically coupled cores. Avarying current in the first or primary winding creates a varying magnetic field in the core of thetransformer. This varying magnetic field induces a varying electromotive force or voltage in the secondarywinding. This effect is called mutual induction.Fig 4.11 TransformerIf a load is connected to the secondary circuit, electric charge will flow in the secondary winding of thetransformer and transfer energy from the primary circuit to the load connected in the secondary circuit. Thesecondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to theratio of the number of turns of wire in their respective windings:By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to bestepped up - by making NS more than NP or stepped down, by making it.BASIC PARTS OF A TRANSFORMERIn its most basic form a transformer consists of:A primary coil or winding.A secondary coil or winding.A core that supports the coils or windings.Refer to the transformer circuit in figure as you read the following explanation: The primary winding isconnected to a 50-hertz ac voltage source. The magnetic field builds up and collapses about the primary
27info4eee | Information For Electrical & Electronics Engineeringwinding. The expanding and contracting magnetic field around the primary winding cuts the secondarywinding and induces an alternating voltage into the winding. This voltage causes alternating current to flowthrough the load. The voltage may be stepped up or down depending on the design of the primary andsecondary windings.THE COMPONENTS OF A TRANSFORMERTwo coils of wire are wound on some type of core material. In some cases the coils of wire are wound on acylindrical or rectangular cardboard form. In effect, the core material is air and the transformer is called anair-core transformer. Transformers used at low frequencies, such as 50 hertz and 400 hertz, require a core oflow-reluctance magnetic material, usually iron. This type of transformer is called an iron-core transformer.Most power transformers are of the iron-core type. The principle parts of a transformer and their functionsare: The core, which provides a path for the magnetic lines of flux. The Primary winding, this receivesenergy from the ac source. The secondary winding, this receives energy from the primary winding anddelivers it to the load. The enclosure, this protects the above components from dirt, moisture, andmechanical damage.4.9BRIDGE RECTIFIERA bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This isa widely used configuration, both with individual diodes wired as shown and with single component bridgeswhere the diode bridge is wired internally.Basic operationAccording to the conventional model of current flow originally established by Benjamin Franklin and stillfollowed by most engineers today, current is assumed to flow through electrical conductors from the positiveto the negative pole. In actuality, free electrons in a conductor nearly always flow from the negative to thepositive pole. In the vast majority of applications, however, the actual direction of current flow is irrelevant.Therefore, in the discussion below the conventional model is retained. In the diagrams below, when the inputconnected to the left corner of the diamond is positive, and the input connected to the right corner isnegative, current flows from the upper supply terminal to the right along the red(positive) path to the output,and returns to the lower supply terminal via the blue (negative) path.
28info4eee | Information For Electrical & Electronics EngineeringFig 4.12 Bridge rectifierWhen the input connected to the left corner is negative, and the input connected to the right corner ispositive, current flows from the lower supply terminal to the right along the red path to the output, andreturns to the upper supply terminal via the blue path.In each case, the upper right output remains positive and lower right output negative. Since this is truewhether the input is AC or DC, this circuit not only produces a DC output from an AC input, it can alsoprovide what is sometimes called "reverse polarity protection". That is, it permits normal functioning of DC-powered equipment when batteries have been installed backwards, or when the leads from a DC powersource have been reversed, and protects the equipment from potential damage caused by reverse polarity.Prior to availability of integrated electronics, such a bridge rectifier was always constructed from discretecomponents. Since about 1950, a single four terminal component containing the four diodes connected in thebridge configuration became a standard commercial component and is now available with various voltageand current ratings.Output smoothingFor many applications, especially with single phase AC where the full-wave bridge serves to convert an ACinput into a DC output, the addition of a capacitor may be desired because the bridge alone supplies anoutput of fixed polarity but continuously varying or pulsating magnitude.
29info4eee | Information For Electrical & Electronics EngineeringFig 4.13 Bridge rectifier in parallel capacitor at the outputThe function of this capacitor, known as a reservoir capacitor is to lessen the variation in the rectified ACoutput voltage waveform from the bridge. One explanation of smoothing is that the capacitor provides a lowimpedance path to the AC component of the output, reducing the AC voltage across, and AC currentthrough, the resistive load. In less technical terms, any drop in the output voltage and current of the bridgetends to be cancelled by loss of charge in the capacitor. This charge flows out as additional current throughthe load. Thus the change of load current and voltage is reduced relative to what would occur without thecapacitor. Increases of voltage correspondingly store excess charge in the capacitor, thus moderating thechange in output voltage / current. The simplified circuit shown has a well-deserved reputation for beingdangerous, because, in some applications, the capacitor can retain a lethal charge after the AC power sourceis removed. If supplying a dangerous voltage, a practical circuit should include a reliable way to safelydischarge the capacitor. If the normal load cannot be guaranteed to perform this function, perhaps because itcan be disconnected, the circuit should include a bleeder resistor connected as close as practical across thecapacitor. This resistor should consume a current large enough to discharge the capacitor in a reasonabletime, but small enough to minimize unnecessary power waste. Because a bleeder sets a minimum currentdrain, the regulation of the circuit, defined as percentage voltage change from minimum to maximum load, isimproved. However in many cases the improvement is of in significant magnitude. capacitor and the loadresistance have a typical time constant τ = RC where C and R are the capacitance and load resistancerespectively. As long as the load resistor is large enough so that this time constant is much longer than thetime of one ripple cycle, the above configuration will produce a smoothed DC voltage across the load.In some designs, a series resistor at the load side of the capacitor is added. The smoothing can then beimproved by adding additional stages of capacitor–resistor pairs, often done only for sub-supplies to criticalhigh-gain circuits that tend to be sensitive to supply voltage noise. The idealized waveforms shown aboveare seen for both voltage and current when the load on the bridge is resistive. When the load includes asmoothing capacitor, both the voltage and the current waveforms will be greatly changed. While the voltageis smoothed, as described above, current will flow through the bridge only during the time when the input
30info4eee | Information For Electrical & Electronics Engineeringvoltage is greater than the capacitor voltage. For example, if the load draws an average current of n Amps,and the diodes conduct for 10% of the time, the average diode current during conduction must be 10n Amps.This non-sinusoidal current leads to harmonic distortion and a poor power factor in the AC supply. In apractical circuit, when a capacitor is directly connected to the output of abridge, the bridge diodes must besized to withstand the current surge that occurs when the power is turned on at the peak of the AC voltageand the capacitor is fully discharged. Sometimes a small series resistor is included before the capacitor tolimit this current, though in most applications the power supply transformers resistance is already sufficient.Output can also be smoothed using a choke and second capacitor. The choke tends to keep the current ratherthan the voltage more constant. Due to the relatively high cost of an effective choke compared to a resistorand capacitor this is not employed in modern equipment.4.10 REGULATOR ICIt is a three pin IC used as a voltage regulator. It converts unregulated DC current into regulated DC current.First pin is used for input, second for ground and third pin gives the rectified and filtered output. It has aninbuilt filtering circuit which removes the ripples present in the rectified DC obtained from full bridgerectifier circuit.Fig 4.14 MCT7805CT voltage regulatorNormally we get fixed output by connecting the voltage regulator at the output of the filtered DC see inabove diagram. It can also be used in circuits to get a low DC voltage from a high DC voltage for examplewe use 7805 to get 5V from 12V. There are two types of voltage regulators 1. fixed voltage regulators 78xx,
31info4eee | Information For Electrical & Electronics Engineering79xx 2. Variable voltage regulators in fixed voltage regulators there is another classification 1. + ve voltageregulators 2.–vevoltage regulators positive voltage regulators this include 78xx voltage regulators. The mostcommonly used ones are 7805 and 7812. 7805 gives fixed 5V DC voltage if input voltage is in 7.5V, 20V.7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed linear voltage regulatorICs. The voltage source in a circuit may have fluctuations and would not give the fixed voltage output. Thevoltage regulator IC maintains the output voltage at a constant value. The xx in 78xx indicates the fixedoutput voltage it is designed to provide. 7805 provides +5V regulated power supply. Capacitors of suitablevalues can be connected at input and output pins depending upon the respective voltage levels.4.11 The Capacitor FilterThe simple capacitor filter is the most basic type of power supply filter. The application of the simplecapacitor filter is very limited. It is sometimes used on extremely high-voltage, low current power suppliesfor cathode ray and similar electron tubes, which require very little load current from the supply. Thecapacitor filter is also used where the power-supply ripple frequency is not critical; this frequency can berelatively high. The capacitor C1 shown in figure 4.15 is a simple filter connected across the output of therectifier in parallel with the load.Fig 4.15 Full wave rectifier with a capacitor filterWhen this filter is used, the RC charge time of the filter capacitor C1 must be short and the RC dischargetime must be long to eliminate ripple action. In other words, the capacitor must charge up fast, preferablywith no discharge a tall. Better filtering also results when the input frequency is high; therefore, the full-wave rectifier output is easier to filter than that of the half-wave rectifier because of its higher frequency. Foryou to have a better understanding of the effect that filtering has on Eavg, a comparison of a rectifier circuitwith a filter and one without a filter is illustrated in figure 4.16 and figure 4.17. The output waveforms infigure 4.16 represent the unfiltered and figure 4.17 represents filtered outputs of the half-wave rectifiercircuit. Current pulses flow through the load resistance RL each time a diode conducts. The dashed line
32info4eee | Information For Electrical & Electronics Engineeringindicates the average value of output voltage. For the half-wave rectifier, Eavg is less than half of the peakoutput voltage. This value is still much less than that of the applied voltage. With no capacitor connectedacross the output of the rectifier circuit, the waveform in figure 4.16 has a large pulsating componentcompared with the average or dc component. When a capacitor is connected across the output figure 4.17,the average value of output voltage Eavg is increased due to the filtering action of capacitor C1UNFILTEREDFig 4.16 Half-wave rectifier without filteringFILTEREDFig 4.17 Half-wave rectifier with filteringThe value of the capacitor is fairly large, several microfarads, thus it presents a relatively low reactance tothe pulsating current and it stores a substantial charge. The rate of charge for the capacitor is limited only bythe resistance of the conducting diode, which is relatively low. Therefore, the RC charge time of the circuitis relatively short. As a result, when the pulsating voltage is first applied to the circuit, the capacitor chargesrapidly and almost reaches the peak value of the rectified voltage within the first few cycles. The capacitorattempts to charge to the peak value of the rectified voltage anytime a diode is conducting, and tends to
33info4eee | Information For Electrical & Electronics Engineeringretain its charge when the rectifier output falls to zero. The capacitor slowly discharges through the loadresistance RL during the time the rectifier is non-conducting.The rate of discharge of the capacitor is determined by the value of capacitance and the value of the loadresistance. If the capacitance and load resistance values are large, the RC discharge time for the circuit isrelative Long. A comparison of the waveforms shown in figure 4.16 and figure 4.17 illustrates that theaddition of C1 to the circuit results in an increase in the average of the output voltage Eavg and a reduction inthe amplitude of the ripple component Er, which is normally present across the load resistance. Now, letsconsider a complete cycle of operation using a half-wave rectifier, a capacitive filter C1, and a load resistorRL. As shown in figure 4.16, the capacitive filter C1 is assumed to be large enough to ensure a smallreactance to the pulsating rectified current. The resistance of RL is assumed to be much greater than thereactance of C1 at the input frequency. When the circuit is energized, the diode conducts on the positive halfcycle and current flows through the circuit, allowing C1 to charge. C1 will charge to approximately the peakvalue of the input voltage. The charge is less than the peak value because of the voltage drop across thediode D1. In the figure 4.16 the heavy solid line on the waveform indicates the charge on C1. In the figure4.17 the diode cannot conduct on the negative half cycle because the anode of D1 is negative with respect tothe cathode. During this interval C1 discharges through the load resistor RL. The discharge of C1 producesthe downward slope as indicated by the solid line on the wave form in the figure 4.17. In contrast to theabrupt fall of the applied ac voltage from peak value to zero, the voltage across C1 and thus across RL duringthe discharge period gradually decreases until the time of the next half cycle of rectifier operation. Keep inmind that for good filtering, the filter capacitor should charge up as fast as possible and discharge as little aspossible as shown in Figure 4.18 and figure 4.19.POSITIVE HALF-CYCLEFig 4.18 Capacitor filter circuitNEGATIVE HALF-CYCLE
34info4eee | Information For Electrical & Electronics EngineeringFig 4.19 Capacitor filter circuitSince practical values of C1 and RL ensure a more or less gradual decrease of the discharge voltage, asubstantial charge remains on the capacitor at the time of the next half cycle of operation. As a result, nocurrent can flow through the diode until the rising ac input voltage at the anode of the diode exceeds thevoltage on the charge remaining on C1. The charge on C1 is the cathode potential of the diode. When thepotential on the anode exceeds the potential on the cathode the charge on C1, the diode again conducts andC1 begins to charge to approximately the peak value of the applied voltage. After the capacitor has chargedto its peak value, the diode will cut off and the capacitor will start to discharge. Since the fall of the ac inputvoltage on the anode is considerably more rapid than the decrease on the capacitor voltage, the cathodequickly become more positive than the anode and the diode ceases to conduct. Operation of the simplecapacitor filter using a full-wave rectifier is basically the same as that discussed for the half-wave rectifier.Referring to figure, you should notice that because one of the diodes is always conducting on alternation, thefilter capacitor charges and discharges during each half cycle. Note that each diode conducts only for thatportion of time when the peak secondary voltage is greater than the charge across the capacitor.Fig 4.20 Full-wave rectifier with capacitor filterAnother thing to keep in mind is that the ripple component Er of the output voltage is an ac voltage and theaverage output voltage Eavg is the dc component of the output. Since the filter capacitor offers relatively low
35info4eee | Information For Electrical & Electronics Engineeringimpedance to ac, the majority of the ac component flows through the filter capacitor. The ac component istherefore bypassed around the load resistance and the entire dc component Eavg flows through the loadresistance. This statement can be clarified by using the formula for XC in a half wave and full-wave rectifier.First, you must establish some values for the circuit. As you can see from the calculations by doubling thefrequency of the rectifier, you reduce the impedance of the capacitor by one-half. This allows the accomponent to pass through the capacitor more easily. As a result, a full wave rectifier output is much easierto filter than that of a half-wave rectifier. Remember the smaller the XC of the filter capacitor with respect tothe load resistance the better the filtering action.Xc =Since the largest possible capacitor will provide the best filtering. Remember, also, that the load resistance isan important consideration. If load resistance is made small, the load current increases, and the average valueof output voltage Eavg decreases. The RC discharge time constant is a direct function of the value of theload resistance therefore the rate of capacitor voltage discharge is a direct function of the current through theload. The greater load current the more rapid the discharge of the capacitor and the lower the average valueof output voltage. For this reason, the simple capacitive filter is seldom used with rectifier circuits that mustsupply a relatively large load current. Using the simple capacitive filter in conjunction with a full-wave orbridge rectifier provides improved filtering because the increased ripple frequency decreases the capacitivereactance of the filter capacitor.4.12 Light Emitting DiodeAn LED is a very simple electronics component which lights up when electricity flows through it. Since it isa diode, electricity can only flow one way. There is usually a flat section on the side of the LED to mark itspolarity: this side should be connected to ground. This side usually also has a shorter leg. In order to preventtoo much current flowing through an LED and damaging it, it should be connected in series with a resistor.Fig 4.21 Light Emitting Diode4.13 ResistorA resistor is a component of a circuit that resists the flow of electrical current. It has two terminals acrosswhich electricity must pass, and it is designed to drop the voltage of the current as it flows from one terminal
36info4eee | Information For Electrical & Electronics Engineeringto the other. Resistors are primarily used to create and maintain known safe currents within electricalcomponents. Resistance is measured in ohms, after Ohms law. This law states that electrical resistance isequal to the drop in voltage across the terminals of the resistor divided by the current being applied. A highohm rating indicates a high resistance to current. This rating can be written in a number of different ways -for example, 81R represents 81 ohms, while 81K represents 81,000 ohms. Materials in general have acharacteristic behavior of opposing the flow of electric charge. This opposition is due to the collisionsbetween electrons that make up the materials. This physical property, or ability to resist current, is known asresistance and is represented by the symbol R. Resistance is expressed in ohms which is symbolized by thecapital Greek letter omega.The resistance of any material is dictated by four factors:Material property-each material will oppose the flow of current differently.Length-the longer the length, the more is the probability of collisions and, hence, the larger theresistance.Cross-sectional area-the larger the area A, the easier it becomes for electrons to flow and, hence, thelower the resistance.Temperature-typically, for metals, as temperature increases, the resistance increases.The amount of resistance offered by a resistor is determined by its physical construction. A carboncomposition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film resistorconsists of a similar ceramic tube, but has conductive carbon film wrapped around the outside. Metal film ormetal oxide resistors are made much the same way, but with metal instead of carbon. A wire wound resistor,made with metal wire wrapped around clay, plastic, or fibre glass tubing, offers resistance at higher powerlevels. Those used for applications that must withstand high temperatures are typically made of materialssuch as cermets, a ceramic-metal composite, or tantalum, a rare metal, so that they can endure the heat.Resistors are coated with paint or enamel, or covered in moulded plastic to protect them. Because they areoften too small to be written on, a standardized color-coding system is used to identify them. The first threecolors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is toits ohm value. This is important for two reasons: the nature of its construction is imprecise, and if used aboveits maximum current, the value can change or the unit itself can burn up. The circuit element used to modelthe current-resisting behavior of a material is the resistor. For the purpose of constructing circuits, resistorsshown in Figure 4.22 are usually made from metallic alloys and carbon compounds. The resistor is thesimplest passive element.
37info4eee | Information For Electrical & Electronics EngineeringFig 4.22 from top to bottom: W, W, and 1-W resistorsTYPES OF RESISTERDifferent types of resistors have been created to meet different requirements. Some resistors are shown inFigure 4.23. The primary functions of resistors are to limit current, divide voltage and dissipate heat. Aresistor is either fixed or variable. Most resistors are of the fixed type that is their resistance remainsconstant. The two common types of fixed resistors wire wound and composition are shown in Figure 4.24.Wire wound resistors are used when there is a need to dissipate a large amount of heat while the compositionresistors are used when large resistance is needed.Fig 4.23 Different types of resistors
38info4eee | Information For Electrical & Electronics Engineering(a) (b)Fig 4.24 Fixed resistors: (a) wire wound type (b) Carbon film typeRESISTOR COLOUR CODESome resistors are physically large enough to have their values printed on them. Other resistors are too smallto have their values printed on them. For such small resistors color coding provides a way of determining thevalue of resistance. As shown in Figure 4.25 the color coding consists of three, four, or five bands of coloraround the resistor.Fig 4.25 Color codingThe first three bands specify the value of the resistance. Bands A and B represent the first and second digitsof the resistance value and C is usually given as a power of 10 as shown in figure 4.25. If present the fourthband D indicates the tolerance percentage. For example a 5 percent tolerance indicates that the actual valueof the resistance is within ± 5 of the color-coded value. When the fourth band is absent, the tolerance istaken by default to be ± 20 percent. The fifth band E, if present is used to indicate a reliability factor whichis a Statistical indication of the expected number of components that will fail to have the indicated resistanceafter working for 1,000 hours. As shown in Figure 4.25 the statement “Big Boys Race Our Young Girls, ButViolet Generally Wins” can serve as a memory aid in remembering the color code.
39info4eee | Information For Electrical & Electronics Engineering5. CONCLUSIONFrom the design of experimental set up with Micro Controller Based Solar Tracking System Using StepperMotor If we compare Tracking by the use of LDR with Fixed Solar Panel System we found that theefficiency of Micro Controller Based Solar Tracking System is improved by 30-45% and it was found thatall the parts of the experimental setup are giving good results. The required Power is used to run the motorby using Step-Down T/F by using 220V AC. Moreover, this tracking system does track the sun in acontinuous manner. And this system is more efficient and cost effective in long run. From the results it isfound that, by automatic tracking system, there is 30 % gain in increase of efficiency when compared withnon-tracking system. The solar tracker can be still enhanced additional features like rain protection and windprotection which can be done as future work.
40info4eee | Information For Electrical & Electronics Engineering6. REFERENCES Rizk J. and Chaiko Y. “Solar Tracking System: More Efficient Use of Solar Panels”, World Academy ofScience, Engineering and Technology 41 2008. Filfil Ahmed Nasir, Mohussen Deia Halboot, Dr. Zidan Khamis A. “Microcontroller-Based Sun PathTracking System”, Eng. & Tech. Journal, Vol. 29, No.7, 2011. Alimazidi Mohammad, Gillispie J, Mazidi, Rolin D. McKinlay, “The 8051 Microcontroller andEmbedded Systems”, An imprint of Pearson Education. Mehta V K, Mehta Rohit, “Principles of Electronics”, S. Chand & Company Ltd. Balagurusamy E, “Programming in ANSI C”, Tata McGraw-Hill Publishing Company Limited. Damm, J. Issue #17, June/July 1990. An active solar tracking system, Home Brew Magazine. Koyuncu B and Balasubramanian K, “A microprocessor controlled automatic sun tracker,” IEEE Trans.Consumer Electron., vol. 37, no. 4,pp. 913-917, 1991. Konar A and Mandal A K, “Microprocessor based automatic sun tracker,” IEE Proc. Sci., Meas.Technol., vol. 138, no. 4, pp. 237-241,1991.