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A PROJECT REPORT ON SOLAR POWER PLANT USING PHOTOVOLTAIC CELLS Submitted in partial fulfillment of the requirements For the award of the degree BACHELOR OF ENGINEERING IN ____________________________________ ENGINEERING SUBMITTED BY -------------------- (--------------) --------------------- (---------------) --------------------- (---------------) DEPARTMENT OF _______________________ ENGINEERING __________COLLEGE OF ENGINEERING AFFILIATED TO ___________ UNIVERSITY CERTIFICATE This is to certify that the dissertation work entitled SOLAR POWER PLANT USING PHOTOVOLTAIC CELLS is the work don ________________ ___ ____________________submitted in partial fulfillment for the award of ‘BACHELOR OF TECHNOLOGY IN ENGINEERING (B.TECH)’in __________________________Engineering from______________ College of Engineering affiliated to _________ University, ODISHA . ________________ ____________ (Head of the department, MECH) (Assistant Professor) EXTERNAL EXAMINER  ACKNOWLEDGEMENT The satisfaction and euphoria that accompany the successful completion of any task would be incomplete without the mentioning of the people whose constant guidance and encouragement made it possible. We take pleasure in presenting before you, our project, which is result of studied blend of both research and knowledge. We express our earnest gratitude to our internal guide, Assistant Professor ______________, Department of Mech , our project guide, for his constant support, encouragement and guidance. We are grateful for his cooperation and his valuable suggestions. Finally, we express our gratitude to all other members who are involved either directly or indirectly for the completion of this project. DECLARATION We, the undersigned, declare that the project entitled ‘SOLAR POWER PLANT USING PHOTOVOLTAIC CELLS ’, being submitted in partial fulfillment for the award of Bachelor of Engineering Degree in mechanical Engineering, affiliated to _________ University, is the work carried out by us. __________ _________ _________ __________ _________ _________ CONTENTS PAGE NO. ABSTRACT 9 INTRODUCTION TO EMBEDDED SYSTEMS 10 BLOCK DIAGRAM 16 HARDWARE REQUIREMENTS 17 4.1 VOLTAGE REGULATOR (LM7805) 20 4.2 MICROCONTROLLER (AT89C51/AT89C52) 24 4.3 LED 34 4.4 PWM 36 4.5 MOSFET (IRF630/IRF520) 38 4.6 PUSH BUTTONS 39 4.7 BC547 4.8 1N4007 /1N4148 4.9 RESISTOR 4.10 CAPACITOR 41 4.11 PHOTOVOLTAIC CELLS / SOLAR CELLS 4.12 LM324 4.13 SOLAR PANNEL 5. SOFTWARE REQUIREMENTS 56 5.1 IDE 57 5.2 CONCEPT OF COMPILER 57 5.3 CONCEPT OF CROSS COMPILER 58 5.4 KEIL C CROSS COMPILER 59 5.5 BUILDING AN APPLICATION IN UVISION2 59 5.6 CREATING YOUR OWN APPLICATION IN UVISION2 59 5.7 DEBUGGING AN APPLICATION IN UVISION2 60 5.8 STARTING UVISION2 & CREATING A PROJECT 61 5.9 WINDOWS_ FILES 61 5.10 BUILDING PROJECTS & CREATING HEX FILES 61 5.11 CPU SIMULATION 62 5.12 DATABASE SELECTION 62 5.13 START DEBUGGING 63 5.14 DISASSEMBLY WINDOW 63 5.15 EMBEDDED C 64 6. SCHEMATIC DIAGRAM 66 6.1 DESCRIPTION 67 7. LAYOUT DIAGRAM 71 8. BILL OF MATERIALS 72 9. CODING 75 9.1 COMPILER 76 9.2 SOURCE CODE 84 10. HARDWARE TESTING 88 10.1 CONTINUITY TEST 88 10.2 POWER ON TEST 89 11. RESULTS 69 12. CONCLUSION 93 13. BIBLIOGRAPHY 94 LIST OF FIGURES PAGE NO. 2(a) EMBEDDED DESIGN CALLS 12 2(b) ‘V’ DIAGRAM 12 3 BLOCK DIAGRAM OF THE PROJECT 16 4.1 A TYPICAL TRANSFORMER 19 4.2(a) BLOCK DIAGRAM OF VOLTAGE REGULATOR 21 4.2(b) RATING OF VOLTAGE REGULATOR 22 4.2(c) PERFORMANCE CHARACTERISTICS OF VOLTAGE REGULATOR 22 4.5(a) BLOCK DIAGRAM OF AT89S52 27 4.5(b) PIN DIAGRAM OF AT89S52 28 4.5(c) OSCILLATOR CONNECTIONS 32 4.2(d) EXTERNAL CLOCK DRIVE CONFIG. 33 4.6 IR LEDS 35 4.9(a) PUSH BUTTONS 49 4.9(b) PUSH ON BUTTON 51 4.9(c) TABLE FOR TYPES OF PUSH BUTTONS 53 4.10 BC547 58 6. SCHEMATIC DIAGRAM 66 1. ABSTRACT The Sun is a direct source of energy Using renewable energy technologies, we can convert the solar energy into electricity Solar powered lighting is a relatively simple concept in a basic way the system operates like a bank account withdrawal from the battery to power the light source must be compensated for by commensurate deposits of energy from the solar panels. As long as the system is designed so deposits exceed withdrawals on an average daily basis, the battery remains charged and light source is reliably powered. The sun provides a direct source of energy to the solar Panel. The Battery is recharged during the day by direct –current (DC) electricity produced by the solar panel. Electronic controls are used between the battery, light source and solar panels to protect the battery from over charge and discharge and to control the timing and operation of the light. 2. INTRODUCTION TO EMBEDDED SYSTEMS  What is embedded system? An Embedded System is a combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a specific function. An embedded system is a microcontroller-based, software driven, reliable, real-time control system, autonomous, or human or network interactive, operating on diverse physical variables and in diverse environments and sold into a competitive and cost conscious market. An embedded system is not a computer system that is used primarily for processing, not a software system on PC or UNIX, not a traditional business or scientific application. High-end embedded & lower end embedded systems. High-end embedded system - Generally 32, 64 Bit Controllers used with OS. Examples Personal Digital Assistant and Mobile phones etc .Lower end embedded systems - Generally 8,16 Bit Controllers used with an minimal operating systems and hardware layout designed for the specific purpose. SYSTEM DESIGN CALLS: Figure 3(a): Embedded system design calls EMBEDDED SYSTEM DESIGN CYCLE Figure 3(b) “V Diagram” Characteristics of Embedded System An embedded system is any computer system hidden inside a product other than a computer. They will encounter a number of difficulties when writing embedded system software in addition to those we encounter when we write applications. Throughput – Our system may need to handle a lot of data in a short period of time. Response–Our system may need to react to events quickly. Testability–Setting up equipment to test embedded software can be difficult. Debugability–Without a screen or a keyboard, finding out what the software is doing wrong (other than not working) is a troublesome problem. Reliability – embedded systems must be able to handle any situation without human intervention. Memory space – Memory is limited on embedded systems, and you must make the software and the data fit into whatever memory exists. Program installation – you will need special tools to get your software into embedded systems. Power consumption – Portable systems must run on battery power, and the software in these systems must conserve power. Processor hogs – computing that requires large amounts of CPU time can complicate the response problem. Cost – Reducing the cost of the hardware is a concern in many embedded system projects; software often operates on hardware that is barely adequate for the job. Embedded systems have a microprocessor/ microcontroller and a memory. Some have a serial port or a network connection. They usually do not have keyboards, screens or disk drives. APPLICATIONS Military and aerospace embedded software applications Communication Applications Industrial automation and process control software Mastering the complexity of applications. Reduction of product design time. Real time processing of ever increasing amounts of data. Intelligent, autonomous sensors. CLASSIFICATION Real Time Systems. RTS is one which has to respond to events within a specified deadline. A right answer after the dead line is a wrong answer. RTS CLASSIFICATION Hard Real Time Systems Soft Real Time System HARD REAL TIME SYSTEM "Hard" real-time systems have very narrow response time. Example: Nuclear power system, Cardiac pacemaker. SOFT REAL TIME SYSTEM "Soft" real-time systems have reduced constrains on "lateness" but still must operate very quickly and repeatable. Example: Railway reservation system – takes a few extra seconds the data remains valid. 3. BLOCK DIAGRAM 4. HARDWARE REQUIREMENTS HARDWARE COMPONENTS: VOLTAGE REGULATOR (LM 7805) MICROCONTROLLER (AT89S52/AT89C51) LED PUSH BUTTONS BC547 1N4007/1N4148 RESISTOR CAPACITOR PHOTOVOLTAIC CELLS/SOLAR CELLS LM317 SOLAR PANNEL 4.1 VOLTAGE REGULATOR 7805 Features • Output Current up to 1A. • Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V. • Thermal Overload Protection. • Short Circuit Protection. • Output Transistor Safe Operating Area Protection. Description The LM78XX/LM78XXA series of three-terminal positive regulators are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a Wide range of applications. Each type employs internal current limiting, thermal shutdown and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output Current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents. Internal Block Diagram FIG 4.2(a): BLOCK DIAGRAM OF VOLTAGE REGULATOR Absolute Maximum Ratings TABLE 4.2(b): RATINGS OF THE VOLTAGE REGULATOR 4.2 MICROCONTROLLER AT89S52 The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density non volatile memory technology and is compatible with the industry standard 80C51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non volatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. Features: • Compatible with MCS-51 Products • 8K Bytes of In-System Programmable (ISP) Flash Memory Endurance: 10,000 Write/Erase Cycles • 4.0V to 5.5V Operating Range • Fully Static Operation: 0 Hz to 33 MHz • Three-level Program Memory Lock • 256 x 8-bit Internal RAM • 32 Programmable I/O Lines • Three 16-bit Timer/Counters • Eight Interrupt Sources • Full Duplex UART Serial Channel • Low-power Idle and Power-down Modes • Interrupt Recovery from Power-down Mode • Watchdog Timer • Dual Data Pointer • Power-off Flag • Fast Programming Time • Flexible ISP Programming (Byte and Page Mode) • Green (Pb/Halide-free) Packaging Option Block Diagram of AT89S52: Fig 4.5(a): Block Diagram Of AT89S52 Pin Configurations of AT89S52 FIG 4.5(b): PIN DIAGRAM OF AT89S52 Pin Description: VCC: Supply voltage. GND: Ground Port 0: Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance inputs. Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification. Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX). Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external data memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups. RST: Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. This pin drives high for 98 oscillator periods after the Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is enabled. ALE/PROG: Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory. PSEN: Program Store Enable (PSEN) is the read strobe to external program memory. When the AT89S52 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. EA/VPP: External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming. XTAL1: Input to the inverting oscillator amplifier and input to the internal clock operating circuit. XTAL2: Output from the inverting oscillator amplifier Oscillator Characteristics: XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed. FIG 4.5(c): Oscillator Connections FIG 4.5(d): External Clock Drive Configuration Idle Mode In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset. Power down Mode In the power down mode the oscillator is stopped, and the instruction that invokes power down is the last instruction executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is terminated. The only exit from power down is a hardware reset. Reset redefines the SFRs but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. 4.3 LED Light Emitting Diodes (LED) have recently become available that are white and bright, so bright that they seriously compete with incandescent lamps in lighting applications. They are still pretty expensive as compared to a GOW lamp but draw much less current and project a fairly well focused beam. The diode in the photo came with a neat little reflector that tends to sharpen the beam a little but doesn't seem to add much to the overall intensity. When run within their ratings, they are more reliable than lamps as well. Red LEDs are now being used in automotive and truck tail lights and in red traffic signal lights. You will be able to detect them because they look like an array of point sources and they go on and off instantly as compared to conventional incandescent lamps. LEDs are monochromatic (one color) devices. The color is determined by the band gap of the semiconductor used to make them. Red, green, yellow and blue LEDs are fairly common. White light contains all colors and cannot be directly created by a single LED. The most common form of "white" LED really isn't white. It is a Gallium Nitride blue LED coated with a phosphor that, when excited by the blue LED light, emits a broad range spectrum that in addition to the blue emission, makes a fairly white light. There is a claim that these white LED's have a limited life. After 1000 hours or so of operation, they tend to yellow and dim to some extent. Running the LEDs at more than their rated current will certainly accelerate this process. There are two primary ways of producing high intensity white-light using LED’S. One is to use individual LED’S that emit three primary colours—red, green, and blue—and then mix all the colours to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works. Due to metamerism, it is possible to have quite different spectra that appear white. LEDs are semiconductor devices. Like transistors, and other diodes, LEDs are made out of silicon. What makes an LED give off light are the small amounts of chemical impurities that are added to the silicon, such as gallium, arsenide, indium, and nitride. When current passes through the LED, it emits photons as a byproduct. Normal light bulbs produce light by heating a metal filament until it is white hot. LEDs produce photons directly and not via heat, they are far more efficient than incandescent bulbs. Fig 3.1(a): circuit symbol Not long ago LEDs were only bright enough to be used as indicators on dashboards or electronic equipment. But recent advances have made LEDs bright enough to rival traditional lighting technologies. Modern LEDs can replace incandescent bulbs in almost any application. 4.4 PWM Pulse-width modulation (PWM) is a commonly used technique for controlling power to an electrical device, made practical by modern electronic power switches. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switching’s have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies. The term duty cycle describes the proportion of on time to the regular interval or period of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM works also well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle. PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel. Power delivery PWM can be used to adjust the total amount of power delivered to a load without losses normally incurred when a power transfer is limited by resistive means. The drawbacks are the pulsations defined by the duty cycle, switching frequency and properties of the load. With a sufficiently high switching frequency and, when necessary, using additional passive electronic filters the pulse train can be smoothed and average analog waveform recovered. High frequency PWM power control systems are easily realisable with semiconductor switches. As has been already stated above almost no power is dissipated by the switch in either on or off state. However, during the transitions between on and off states both voltage and current are non-zero and thus considerable power is dissipated in the switches. Luckily, the change of state between fully on and fully off is quite rapid (typically less than 100 nanoseconds) relative to typical on or off times, and so the average power dissipation is quite low compared to the power being delivered even when high switching frequencies are used. Modern semiconductor switches such as MOSFETs or Insulated-gate bipolar transistors (IGBTs) are quite ideal components. Thus high efficiency controllers can be built. Typically frequency converters used to control AC motors have efficiency that is better than 98 %. Switching power supplies have lower efficiency due to low output voltage levels (often even less than 2 V for microprocessors are needed) but still more than 70-80 % efficiency can be achieved. Variable-speed fan controllers for computers usually use PWM, as it is far more efficient when compared to a potentiometer or rheostat. (Neither of the latter is practical to operate electronically; they would require a small drive motor). Light dimmers for home use employ a specific type of PWM control. Home use light dimmers typically include electronic circuitry which suppresses current flow during defined portions of each cycle of the AC line voltage. Adjusting the brightness of light emitted by a light source is then merely a matter of setting at what voltage (or phase) in the AC half cycle the dimmer begins to provide electrical current to the light source (e.g. by using an electronic switch such as a triac). In this case the PWM duty cycle is the ratio of the conduction time to the duration of the half AC cycle defined by the frequency of the AC line voltage (50 Hz or 60 Hz depending on the country). These rather simple types of dimmers can be effectively used with inert (or relatively slow reacting) light sources such as incandescent lamps, for example, for which the additional modulation in supplied electrical energy which is caused by the dimmer causes only negligible additional fluctuations in the emitted light. Some other types of light sources such as light-emitting diodes (LEDs), however, turn on and off extremely rapidly and would perceivably flicker if supplied with low frequency drive voltages. Perceivable flicker effects from such rapid response light sources can be reduced by increasing the PWM frequency. If the light fluctuations are sufficiently rapid, the human visual system can no longer resolve them and the eye perceives the time average intensity without flicker (see flicker fusion threshold). In electric cookers, continuously-variable power is applied to the heating elements such as the hob or the grill using a device known as a Simmer tat. This consists of a thermal oscillator running at approximately two cycles per minute and the mechanism varies the duty cycle according to the knob setting. The thermal time constant of the heating elements is several minutes, so that the temperature fluctuations are too small to matter in practice. Applications Telecommunications Power delivery Voltage regulation Audio effects and amplification. 4.5 MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a device used for amplifying or switching electronic signals. The basic principle of the device was first proposed by Julius Edgar Lilienfeld in 1925. In MOSFET’s, a voltage on the oxide-insulated gate electrode can induce a conducting channel between the two other contacts called source and drain. The channel can be of n-type or p-type and is accordingly called an nMOSFET or a pMOSFET. It is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. Comparison of enhancement-mode and depletion-mode MOSFET symbols, along with JFET symbols (drawn with source and drain ordered such that higher voltages appear higher on the page than lower voltages). An example of using the MOSFET as a switch Fig 4.9: MOSFET as switch In this circuit arrangement an Enhancement-mode N-channel MOSFET is being used to switch a simple lamp "ON" and "OFF" (could also be an LED). The gate input voltage VGS is taken to an appropriate positive voltage level to turn the device and the lamp either fully "ON", (VGS = +ve) or a zero voltage level to turn the device fully "OFF", (VGS = 0). If the resistive load of the lamp was to be replaced by an inductive load such as a coil or solenoid, a "Flywheel" diode would be required in parallel with the load to protect the MOSFET from any back-emf. Above shows a very simple circuit for switching a resistive load such as a lamp or LED. But when using power MOSFET's to switch either inductive or capacitive loads some form of protection is required to prevent the MOSFET device from becoming damaged. Driving an inductive load has the opposite effect from driving a capacitive load. For example, a capacitor without an electrical charge is a short circuit, resulting in a high "inrush" of current and when we remove the voltage from an inductive load we have a large reverse voltage build up as the magnetic field collapses, resulting in an induced back-emf in the windings of the inductor. For the power MOSFET to operate as an analogue switching device, it needs to be switched between its "Cut-off Region" where VGS = 0 and its "Saturation Region" where VGS (on) = +ve. The power dissipated in the MOSFET (PD) depends upon the current flowing through the channel ID at saturation and also the "ON-resistance" of the channel given as RDS (on). 4.6 PUSH BUTTONS Fig.4.8(a): Push Buttons A push-button (also spelled pushbutton) or simply button is a simple switch mechanism for controlling some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. Buttons are most often biased switches, though even many un-biased buttons (due to their physical nature) require a spring to return to their un-pushed state. Different people use different terms for the "pushing" of the button, such as press, depress, mash, and punch. Uses: In industrial and commercial applications push buttons can be linked together by a mechanical linkage so that the act of pushing one button causes the other button to be released. In this way, a stop button can "force" a start button to be released. This method of linkage is used in simple manual operations in which the machine or process have no electrical circuits for control. Pushbuttons are often color-coded to associate them with their function so that the operator will not push the wrong button in error. Commonly used colors are red for stopping the machine or process and green for starting the machine or process. Red pushbuttons can also have large heads (mushroom shaped) for easy operation and to facilitate the stopping of a machine. These pushbuttons are called emergency stop buttons and are mandated by the electrical code in many jurisdictions for increased safety. This large mushroom shape can also be found in buttons for use with operators who need to wear gloves for their work and could not actuate a regular flush-mounted push button. As an aid for operators and users in industrial or commercial applications, a pilot light is commonly added to draw the attention of the user and to provide feedback if the button is pushed. Typically this light is included into the center of the pushbutton and a lens replaces the pushbutton hard center disk. The source of the energy to illuminate the light is not directly tied to the contacts on the back of the pushbutton but to the action the pushbutton controls. In this way a start button when pushed will cause the process or machine operation to be started and a secondary contact designed into the operation or process will close to turn on the pilot light and signify the action of pushing the button caused the resultant process or action to start. In popular culture, the phrase "the button" refers to a (usually fictional) button that a military or government leader could press to launch nuclear weapons. Push to ON button: Fig. 4.8(b): push on button Initially the two contacts of the button are open. When the button is pressed they become connected. This makes the switching operation using the push button. 4.7 BC547 The BC547 transistor is an NPN Epitaxial Silicon Transistor. The BC547 transistor is a general-purpose transistor in small plastic packages. It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors. BC 547 TRANSISTOR PINOUTS The BC547 transistor is an NPN bipolar transistor, in which the letters "N" and "P" refer to the majority charge carriers inside the different regions of the transistor. Most bipolar transistors used today are NPN, because electron mobility is higher than hole mobility in semiconductors, allowing greater currents and faster operation. NPN transistors consist of a layer of P-doped semiconductor (the "base") between two N-doped layers. A small current entering the base in common-emitter mode is amplified in the collector output. In other terms, an NPN transistor is "on" when its base is pulled high relative to the emitter. The arrow in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. One mnemonic device for identifying the symbol for the NPN transistor is "not pointing in." An NPN transistor can be considered as two diodes with a shared anode region. In typical operation, the emitter base junction is forward biased and the base collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the base emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or "diffuse") through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base. An NPN Transistor Configuration We know that the transistor is a "CURRENT" operated device and that a large current (Ic) flows freely through the device between the collector and the emitter terminals. However, this only happens when a small biasing current (Ib) is flowing into the base terminal of the transistor thus allowing the base to act as a sort of current control input. The ratio of these two currents (Ic/Ib) is called the DC Current Gain of the device and is given the symbol of hfe or nowadays Beta, (β). Beta has no units as it is a ratio. Also, the current gain from the emitter to the collector terminal, Ic/Ie, is called Alpha, (α), and is a function of the transistor itself. As the emitter current Ie is the product of a very small base current to a very large collector current the value of this parameter α is very close to unity, and for a typical low-power signal transistor this value ranges from about 0.950 to 0.999. 4.8 1N4007 Diodes are used to convert AC into DC these are used as half wave rectifier or full wave rectifier. Three points must he kept in mind while using any type of diode. Maximum forward current capacity Maximum reverse voltage capacity Maximum forward voltage capacity Fig: 1N4007 diodes The number and voltage capacity of some of the important diodes available in the market are as follows: Diodes of number IN4001, IN4002, IN4003, IN4004, IN4005, IN4006 and IN4007 have maximum reverse bias voltage capacity of 50V and maximum forward current capacity of 1 Amp. Diode of same capacities can be used in place of one another. Besides this diode of more capacity can be used in place of diode of low capacity but diode of low capacity cannot be used in place of diode of high capacity. For example, in place of IN4002; IN4001 or IN4007 can be used but IN4001 or IN4002 cannot be used in place of IN4007.The diode BY125made by company BEL is equivalent of diode from IN4001 to IN4003. BY 126 is equivalent to diodes IN4004 to 4006 and BY 127 is equivalent to diode IN4007. Fig:PN Junction diode PN JUNCTION OPERATION Now that you are familiar with P- and N-type materials, how these materials are joined together to form a diode, and the function of the diode, let us continue our discussion with the operation of the PN junction. But before we can understand how the PN junction works, we must first consider current flow in the materials that make up the junction and what happens initially within the junction when these two materials are joined together. Current Flow in the N-Type Material Conduction in the N-type semiconductor, or crystal, is similar to conduction in a copper wire. That is, with voltage applied across the material, electrons will move through the crystal just as current would flow in a copper wire. This is shown in figure 1-15. The positive potential of the battery will attract the free electrons in the crystal. These electrons will leave the crystal and flow into the positive terminal of the battery. As an electron leaves the crystal, an electron from the negative terminal of the battery will enter the crystal, thus completing the current path. Therefore, the majority current carriers in the N-type material (electrons) are repelled by the negative side of the battery and move through the crystal toward the positive side of the battery. Current Flow in the P-Type Material Current flow through the P-type material is illustrated. Conduction in the P material is by positive holes, instead of negative electrons. A hole moves from the positive terminal of the P material to the negative terminal. Electrons from the external circuit enter the negative terminal of the material and fill holes in the vicinity of this terminal. At the positive terminal, electrons are removed from the covalent bonds, thus creating new holes. This process continues as the steady stream of holes (hole current) moves toward the negative terminal. 1N4148 The 1N4148 is a standard small signal silicon diode used in signal processing. Its name follows the JEDEC nomenclature. The 1N4148 is generally available in a DO-35 glass package and is very useful at high frequencies with a reverse recovery time of no more than 4ns. This permits rectification and detection of radio frequency signals very effectively, as long as their amplitude is above the forward conduction threshold of silicon (around 0.7V) or the diode is biased Fig: 1N4148 diode Specifications: VRRM = 100V (Maximum Repetitive Reverse Voltage) IO = 200mA (Average Rectified Forward Current) IF = 300mA (DC Forward Current) IFSM = 1.0 A (Pulse Width = 1 sec), 4.0 A (Pulse Width = 1 uSec) (Non-Repetitive Peak Forward Surge Current) PD = 500 mW (power Dissipation) TRR < 4ns (reverse recovery time) Applications High-speed switching Features 1) Glass sealed envelope. (GSD) 2) High speed. 3) High Reliability Construction Silicon epitaxial planar 4.9 RESISTORS A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR Resistors are used as part of electrical networks and electronic circuits. They are extremely commonplace in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome). The primary characteristics of resistors are their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance depends upon the materials constituting the resistor as well as its physical dimensions; it's determined by design. Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals) are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power. A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm's law: Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinking. In a high voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor. The series inductance of a practical resistor causes its behaviour to depart from ohms law; this specification can be important in some high-frequency applications for smaller values of resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology. A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them. Units The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also in common usage. The reciprocal of resistance R is called conductance G = 1/R and is measured in Siemens (SI unit), sometimes referred to as a mho. Thus a Siemens is the reciprocal of an ohm: S = Ω − 1. Although the concept of conductance is often used in circuit analysis, practical resistors are always specified in terms of their resistance (ohms) rather than conductance. Variable resistors Adjustable resistors A resistor may have one or more fixed tapping points so that the resistance can be changed by moving the connecting wires to different terminals. Some wire-wound power resistors have a tapping point that can slide along the resistance element, allowing a larger or smaller part of the resistance to be used. Where continuous adjustment of the resistance value during operation of equipment is required, the sliding resistance tap can be connected to a knob accessible to an operator. Such a device is called a rheostat and has two terminals. Potentiometers A common element in electronic devices is a three-terminal resistor with a continuously adjustable tapping point controlled by rotation of a shaft or knob. These variable resistors are known as potentiometers when all three terminals are present, since they act as a continuously adjustable voltage divider. A common example is a volume control for a radio receiver. Accurate, high-resolution panel-mounted potentiometers (or "pots") have resistance elements typically wire wound on a helical mandrel, although some include a conductive-plastic resistance coating over the wire to improve resolution. These typically offer ten turns of their shafts to cover their full range. They are usually set with dials that include a simple turns counter and a graduated dial. Electronic analog computers used them in quantity for setting coefficients, and delayed-sweep oscilloscopes of recent decades included one on their panels. Resistance decade boxes A resistance decade box or resistor substitution box is a unit containing resistors of many values, with one or more mechanical switches which allow any one of various discrete resistances offered by the box to be dialled in. Usually the resistance is accurate to high precision, ranging from laboratory/calibration grade accuracy of 20 parts per million, to field grade at 1%. Inexpensive boxes with lesser accuracy are also available. All types offer a convenient way of selecting and quickly changing a resistance in laboratory, experimental and development work without needing to attach resistors one by one, or even stock each value. The range of resistance provided, the maximum resolution, and the accuracy characterize the box. For example, one box offers resistances from 0 to 24 megohms, maximum resolution 0.1 ohm, accuracy 0.1%. Special devices There are various devices whose resistance changes with various quantities. The resistance of thermistors exhibit a strong negative temperature coefficient, making them useful for measuring temperatures. Since their resistance can be large until they are allowed to heat up due to the passage of current, they are also commonly used to prevent excessive current surges when equipment is powered on. Similarly, the resistance of a humistor varies with humidity. Metal oxide varistors drop to a very low resistance when a high voltage is applied, making them useful for protecting electronic equipment by absorbing dangerous voltage surges. One sort of photodetector, the photoresistor, has a resistance which varies with illumination. The strain gauge, invented by Edward E. Simmons and Arthur C. Ruge in 1938, is a type of resistor that changes value with applied strain. A single resistor may be used, or a pair (half bridge), or four resistors connected in a Wheatstone bridge configuration. The strain resistor is bonded with adhesive to an object that will be subjected to mechanical strain. With the strain gauge and a filter, amplifier, and analog/digital converter, the strain on an object can be measured. A related but more recent invention uses a Quantum Tunnelling Composite to sense mechanical stress. It passes a current whose magnitude can vary by a factor of 1012 in response to changes in applied pressure. 4.10 CAPACITORS A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors. An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage. The properties of capacitors in a circuit may determine the resonant frequency and quality factor of a resonant circuit, power dissipation and operating frequency in a digital logic circuit, energy capacity in a high-power system, and many other important aspects. A capacitor (formerly known as condenser) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes. A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops in the dielectric that stores energy and produces a mechanical force between the conductors. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called "plates", referring to an early means of construction. In practice the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance. Theory of operation Capacitance Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance. A simple demonstration of a parallel-plate capacitor A capacitor consists of two conductors separated by a non-conductive region. The non-conductive region is called the dielectric or sometimes the dielectric medium. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric mediums are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold equal and opposite charges on their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device. The capacitor is a reasonably general model for electric fields within electric circuits. An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V between them: Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case, capacitance is defined in terms of incremental changes: Energy storage Work must be done by an external influence to "move" charge between the conductors in a capacitor. When the external influence is removed the charge separation persists in the electric field and energy is stored to be released when the charge is allowed to return to its equilibrium position. The work done in establishing the electric field, and hence the amount of energy stored, is given by: Current-voltage relation The current i(t) through any component in an electric circuit is defined as the rate of flow of a charge q(t) passing through it, but actual charges, electrons, cannot pass through the dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each one that leaves the positive plate, resulting in an electron depletion and consequent positive charge on one electrode that is equal and opposite to the accumulated negative charge on the other. Thus the charge on the electrodes is equal to the integral of the current as well as proportional to the voltage as discussed above. As with any anti-derivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation, . Taking the derivative of this, and multiplying by C, yields the derivative form, . The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C with the inductance L. DC circuits RC circuit A simple resistor-capacitor circuit demonstrates charging of a capacitor A series circuit containing only a resistor, a capacitor, a switch and a constant DC source of voltage V0 is known as a charging circuit. If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it follows from Kirchhoff's voltage law that Taking the derivative and multiplying by C, gives a first-order differential equation, At t = 0, the voltage across the capacitor is zero and the voltage across the resistor is V0. The initial current is then i (0) =V0 /R. With this assumption, the differential equation yields where τ0 = RC is the time constant of the system. As the capacitor reaches equilibrium with the source voltage, the voltage across the resistor and the current through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero. AC circuits Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies may be found. The reactance and impedance of a capacitor are respectively where j is the imaginary unit and ω is the angular velocity of the sinusoidal signal. The - j phase indicates that the AC voltage V = Z I lags the AC current by 90°: the positive current phase corresponds to increasing voltage as the capacitor charges; zero current corresponds to instantaneous constant voltage, etc. Note that impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude an AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysis—those frequencies have been "filtered out". Capacitors are different from resistors and inductors in that the impedance is inversely proportional to the defining characteristic, i.e. capacitance. Parallel plate model Dielectric is placed between two conducting plates, each of area A and with a separation of d. The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation . The capacitance is therefore greatest in devices made from materials with a high permittivity. Several capacitors in parallel 4.11 OPAMP LM324 Features Internally frequency compensated for unity gain Large DC voltage gain 100 dB Wide bandwidth (unity gain) 1 MHz (temperature compensated) Wide power supply range: Single supply 3V to 32V or dual supplies ±1.5V to ±16V Very low supply current drain (700 μA) essentially independent of supply voltage Low input biasing current 45 nA (temperature compensated) Low input offset voltage 2 mV and offset current: 5 nA Input common-mode voltage range includes ground Differential input voltage range equal to the power supply voltage Large output voltage swing 0V to V+ − 1.5V Unique Characteristics In the linear mode the input common-mode voltage range includes ground and the output voltage can also swing to ground, even though operated from only a single power supply voltage. The unity gain cross frequency is temperature compensated. The input bias current is also temperature compensated. Fig.3.6: Pin Diagram of LM324 The LM124 series consists of four independent, high gain, internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. Application areas include transducer amplifiers, DC gain blocks and all the conventional op amp circuits which now can be more easily implemented in single power supply systems. For example, the LM124 series can be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily provide the required interface electronics without requiring the additional ±15V power supplies. Advantages Eliminates need for dual supplies Four internally compensated op amps in a single package Allows directly sensing near GND and VOUT also goes to GND Compatible with all forms of logic 4.12 PHOTOVOLTAIC CELLS/SOLAR CELLS How Solar Panels Work? Rays of sunlight hit the solar panel (also know as a photovoltaic/ (PV) cells) and are absorbed by semi-conducting materials such as silicone. Electrons are knocked loose from their atoms, which allow them to flow through the material to produce electricity. This process whereby light (photo) is converted into electricity (voltage) is called the photovoltaic (PV) effect. An array of solar panels converts solar energy into DC (direct current) electricity. The DC electricity then enters an inverter. The inverter turns DC electricity into 120-volt AC (alternating current) electricity needed by home appliances. The AC power enters the utility panel in the house. The electricity (load) is then distributed to appliances or lights in the house. When more solar energy is generated that what you're using - it can be stored in a battery as DC electricity. The battery will continue to supply your home with electricity in the event of a power blackout or at nighttime. When the battery is full the excess electricity can be exported back into the utility grid, if your system is connected to it. Utility supplied electricity can also be drawn form the grid when not enough solar energy is produced and no excess energy is stored in the battery, i.e. at night or on cloudy days. The flow of electricity in and out of the utility grid is measured by a utility meter, which spins backwards (when you are producing more energy that you need) and forward (when you require additional electricity from the utility company). The two are offset ensuring that you only pay for the additional energy you use from the utility company. Any surplus energy is sold back to the utility company. This system is referred to as "net-metering". Solar Energy is measured in kilowatt-hour. 1 kilowatt = 1000 watts. 1 kilowatt-hour (kWh) = the amount of electricity required to burn a 100 watt light bulb for 10 hours. According to the US Department of Energy, an average American household used approximately 866-kilowatt hours per month in 1999 costing them $70.68. About 30% of our total energy consumption is used to heat water. THE SUN produces radiant energy by consuming hydrogen in nuclear fusion reactions. Solar energy is transmitted to the earth in portions of energy called photons, which interact with the earth's atmosphere and surface. It takes about 8 minutes and 20 seconds for the sun's energy to reach the earth. THE EARTH receives and collects solar energy in the atmosphere, oceans, and plant life. Interactions between the sun's energy, the oceans, and the atmosphere, for example, create winds, which can produce electricity when directed through aerodynamically designed wind machines. SOLAR PHOTOVOLTAIC CELLS convert solar radiation into electricity (photovoltaic literally means "light energy"; "photo" = light, "voltaic" = energy). Individual cells are packaged into modules, like the one shown at the right; groups of modules are called arrays. Photovoltaic arrays act like a battery when the sun is shining, producing a stream of direct current (DC) electricity and sending it into the building or sharing it with the grid. THE DC DISCONNECT SWITCH allows professional electricians to disconnect the photovoltaic array from the rest of the system. With the switch in the "off" position, workers can safely perform maintenance on other system components. THE INVERTER converts direct current (DC) electricity generated by the array into alternating current (AC) electricity for use in the building. Most electrical loads (energy-consuming devices like lights, motors, computers, and air conditioners) in schools, homes and businesses use AC electricity. THE TRANSFORMER ensures that the voltage of the electricity coming from the inverter is compatible with the voltage of the electricity in the building. THE AC DISCONNECT disconnect switch allows professional electricians to disconnect the building's electrical system from the solar photovoltaic system. With the AC disconnect switch in the "off" position, workers can safely perform maintenance on the solar photovoltaic system's components. THE ELECTRIC METER keeps track of the amount of electrical energy produced by the solar photovoltaic system and sends electronic signals to the data acquisition system where they are recorded. Electrical energy is measured in kilowatt-hours. How much energy is contained in a kilowatt-hour? We're glad you asked. Use our calculator to find out. Photovoltaic Cells: Converting Photons to Electrons Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce. 4.13 SOLAR PANEL A solar panel (photovoltaic module or photovoltaic panel) is a packaged interconnected assembly of solar cells, also known as photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Because a single solar panel can only produce a limited amount of power, many installations contain several panels. A photovoltaic system typically includes an array of solar panels, an inverter, may contain a battery and interconnection wiring How Solar Panels Work Photovoltaic (PV) cells are formed from a wafer of semi-conductor material and although there are now several types in production using different materials, the most common semi-conductor used is silicon. Pure crystalline silicon is a poor electrical conductor but treat it with tiny quantities of an impurity, either phosphorous or arsenic (a process called “doping”) and enough electrons of these materials are freed to enable a current to pass through. Electrons are negatively charged so this type of silicon is called N-Type. Dope silicon with gallium or boron and “holes” are created in the crystalline lattice where a silicon electron has nothing to bond with. These holes can conduct electrical current and the lack of an electron creates a positive charge so this type of silicon is therefore called P-Type. Both types of silicon are modest electrical conductors, hence the name semiconductors. Put a layer of each kind together in a wafer, such as in a PV cell, and the free electrons in the N side migrate towards the free holes on the P side. This causes a disruption to the electrical neutrality where the holes and electrons mix at the junction of the two layers. Eventually a barrier is formed preventing the electrons from crossing to the P side and an electrical field is formed, separating both sides. This electrical field acts as a diode, allowing electrons to pass from the P side to the N side, but not vice versa. Expose the cell to light, and the energy from each photon (light particle) hitting the silicon, will liberate an electron and a corresponding hole. If this happens within range of the electric field’s influence, the electrons will be sent to the N side and the holes to the P one, resulting in yet further disruption of electrical neutrality. Apply an external pathway connecting both sides of the silicon wafer and electrons will flow back to their original P side to unite with the holes sent there by the electric field. This flow of electrons is a current; the electrical field in the cell causes a voltage and the product of these two is power. Several factors affect the efficiency of a solar cell. Some cells, mainly ones made from a single material, are only efficient in certain light wavelengths. Single material cells can at the very most expect to convert about 25% of the light hitting it to electrical power. 6.1 SCHEMATIC DIAGRAM EXPLANATION POWER SUPPLY The circuit uses standard power supply comprising of a step-down transformer from 230v to 12v and 4 diodes forming a Bridge Rectifier that delivers pulsating dc which is then filtered by an electrolytic capacitor of about 470microf to 1000microF. The filtered dc being unregulated IC LM7805 is used to get 5v constant at its pin no 3 irrespective of input dc varying from 9v to 14v. The input dc shall be varying in the event of input ac at 230volts section varies in the ratio of v1/v2=n1/n2. The regulated 5volts dc is further filtered by a small electrolytic capacitor of 10 micro f for any noise so generated by the circuit. One LED is connected of this 5v point in series with a resistor of 330ohms to the ground i.e. negative voltage to indicate 5v power supply availability. The 5v dc is at 12v point is used for other applications as on when required. SOLAR CHARGING CIRCUIT: In this Solar Charging Circuit we are using SOLAR PANEL. Here we are using MOSFET whose gate is connected to emitter of the transistor (BC547) drain is connected to +VE terminal & source is connected to GND is parallel to MOSFET a battery of 12V is connected collector of transistor is connected to +ve terminal with resistor R1 of 18K. Whose base is connected to o/p of 1st op-amp (LM324) through resistor R3 of 100K. Pin 11 is connected to GND Pin 4 is connected to VCC for both op-amps’s known as U1: A & U1:B. 2nd Pin of U1:A is connected to Pin 1 of op-amp through two resistors R4 of 330K R5 of 330k. Pin 3 and Pin 5 all shorted and connected to POT of 5K, 6th Pin is connected to GND through resistor R10 of 120K. And 7th Pin is o/p Pin with resistor R7 of 2K & LED. UI:C is also an op-amp whose 10th Pin is connected to POT of 5K and one of the terminal is also connected to 2nd Pin of U1:A where 9th Pin is connected to GND, 4th & 11th Pin are VCC and GND. Where 8th Pin is o/p Pin which is connected to Gate of MOSFET, Q2 through Diode IN4148 where 9th Pin is also connected to drain of MOSFET whose gate is also connected to POT of RV1 who will get another o/p of U1:D known as Pin 14. Whose 12th Pin is connected to RV5 ,22K. PRESET 13th Pin is connected to 4diodes in series known as D5, D6, D7,D8 source is connected to GND. WORKING The project uses one IC lm324 having 4 op-amps used as comparators that is U1:A,B,C,D. U1:A is used for sensing over charging of the battery to be indicated by action of U1:B o/p fed D1. Diodes D5 to D8 all connected in series are forward biased through R14 and D3 .this provides a fixed reference voltage of 0.65*4= 2.6v at anode point of D8 which is fed to pin 2 U1:A through R11, pin 13 of of U1:D, pin 6 of U1:bB via R9 and pin 10 of U1:C via 5K variable resistor. Solar panel being a current source is used to change battery B1 via D10. While the battery is fully charged the voltage at cathode point of D10 goes up. This results in the set point voltage at pin 3 of U1:A to go up above the reference voltage because the potential divider formed out of R12, 5K variable resistor,R13 goes up. This results in pin no 1 of U1:A to go high to switch ‘ON’ the transistor Q1 that places drive voltage to the Mosfet IRF640 .such that the current from solar panel is bypassed via D11 and the Mosfet drain and source. Simultaneously pin 7 of U1:B also goes high to drive a led D1 indicating battery is being fully charged. While the load is used by the switch operation Q2 usually provides a path to the (-ve) while the (+ve) is connected to the dc (+ve) via the switch in the event over load the reference voltage at pin 10 results in pin 8 of U1:C going low to remove the drive to the gate through the D4 the Mosfet Q2 that disconnects the load. In the event of over load Q2 voltage across drain and source goes up those results in pin no 9 going above pin no 10 via R22. In the event of battery voltage falling below minimum voltage duly sensed by D3,R6,RV5 and R16 combination at pin 12 results in pin no 14 going zero to remove the drive to Q2 gate via R20 and Rv1. The correct operation of the load in normal condition is indicated by D9 while the Mosfet Q2 conducts. This project is meant stepped intensity control of cluster of LED’S. The application area is to replace the conventional street lighting that uses HID(High Intensity Discharge) lamp such as mercury vapor, sodium vapor, metal halide which cannot be subjected to intensity control. LED’S lamp have the advantage of instant switch on as compared to HID lamp. For controlling the intensity LED lamps can be fed with varying duty cycle from a dc source to control the intensity while HID lamps generally operated from ac source cannot be fed with controlled supply as any break would result in failure of the discharge path instantly. So restarting takes few minutes thus making it unsuitable for intensity control by power control. The concept of intensity control helps saving of electrical energy. The LED’S used in combination with suitable driving transistors from the microcontroller duly programmed for a practical application. For example the LED lights used for the purpose of street lights are switched ON at the dusk with full intensity till 11pm with 99% duly cycle. With each hour a advancing from 11pm the duty cycle changes to 10% less progressively so that by the morning the ON time duty cycle reaches to 10% from 90% at 11pm and finally to zero meaning the lights are OFF from morning i.e., from “dawn to dusk”. The operation repeats again from the dusk with full intensity till 11pm from 6pm and at 12 mid night it is 80% duty cycle, 1’o clock 70%, 2’o clock 60%, 3’o clock 50% ,4’o clock 40% and so on till 10% and finally OFF at the dawn. In order to demonstrate the same from a 12v dc source 4 LED’S in series with 8*3=24 strings are connected in series with a MOSFET acting as a switch. The MOSFET could be IRF520 or Z44 as available in the market. Each LED is a white LED and from the data sheet it is seen that it operates at 2.5v. Thus 4 LED’S in series needs 10v. Therefore a resistor is connected with 10ohms, 10 watts rings in series with the LED’S where the balance voltage is dropped from 12v by limiting the current for safe operation of the LED’S. As the MOSFET switch requires a higher dc voltage at its gate another switching transistor BC547 is used that interfaces from the microcontroller to the gate of the MOSFET. While the microcontroller pin21 delivers a high logic, the transistor BC547 switches on to divert the drive voltage of the MOSFET so that the MOSFET switch is OFF. While the controller delivers a low logic to transistor BC547 is switched OFF which enables drive voltage availability to the gate of the MOSFET by the ratio 10:1 as formed by the potential divider 1k and 10k. Thus approximately 10v is available at the gate of the MOSFET while transistor BC547 is OFF. The MOSFET switches ON between its drain and source that completes its path of current flow through the LED’S. Therefore with varying duty cycle from 90% to 10% the current flowing through the LED reduces that result in lesser intensity as described earlier.  7. LAYOUT DIAGRAM 8. BILL OF MATERIALS R1, R3,R4, R12 = 10k R5 = 240 OHMS P1,P2 =10K preset P3 = 10k pot or preset R10 = 470K, R9= 2M2 R11 = 100K R8=10 OHMS 2 WATT T1----T4 = BC547 A1/A2 = 1/2 IC324 ALL ZENER DIODES = 4.7V, 1/2 WATT D1---D3,D6 = 1N4007 D4,D5 = 6AMP DIODESIC2 = IC555 IC1 = LM338 RELAYS = 12V,400 OHMS, SPDT BATTERY = 12V, 26AH SOLAR PANEL = 21V OPEN CIRCUIT, 7AMP @SHORT CIRCUIT. MISCELLANOUS 7805 1 BATTERY 12V 1 BC547 2 SOLAR PANEL 1 ASSEMBLED PCD PLAIN PCB ZEROBOARD CUTTER SOLDERING IRON SCREW DRIVER MULTIMETER SOLDERING LEAD 10. HARDWARE TESTING 10.1 CONTINUITY TEST: In electronics, a continuity test is the checking of an electric circuit to see if current flows (that it is in fact a complete circuit). A continuity test is performed by placing a small voltage (wired in series with an LED or noise-producing component such as a piezoelectric speaker) across the chosen path. If electron flow is inhibited by broken conductors, damaged components, or excessive resistance, the circuit is "open". Devices that can be used to perform continuity tests include multi meters which measure current and specialized continuity testers which are cheaper, more basic devices, generally with a simple light bulb that lights up when current flows. An important application is the continuity test of a bundle of wires so as to find the two ends belonging to a particular one of these wires; there will be a negligible resistance between the "right" ends, and only between the "right" ends. This test is the performed just after the hardware soldering and configuration has been completed. This test aims at finding any electrical open paths in the circuit after the soldering. Many a times, the electrical continuity in the circuit is lost due to improper soldering, wrong and rough handling of the PCB, improper usage of the soldering iron, component failures and presence of bugs in the circuit diagram. We use a multi meter to perform this test. We keep the multi meter in buzzer mode and connect the ground terminal of the multi meter to the ground. We connect both the terminals across the path that needs to be checked. If there is continuation then you will hear the beep sound. 10.2 POWER ON TEST: This test is performed to check whether the voltage at different terminals is according to the requirement or not. We take a multi meter and put it in voltage mode. Remember that this test is performed without microcontroller. Firstly, we check the output of the transformer, whether we get the required 12 v AC voltage. Then we apply this voltage to the power supply circuit. Note that we do this test without microcontroller because if there is any excessive voltage, this may lead to damaging the controller. We check for the input to the voltage regulator i.e., are we getting an input of 12v and an output of 5v. This 5v output is given to the microcontrollers’ 40th pin. Hence we check for the voltage level at 40th pin. Similarly, we check for the other terminals for the required voltage. In this way we can assure that the voltage at all the terminals is as per the requirement. 2