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

1

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

2

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.

3

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.

__________ _________ _________

__________ _________ _________

4

CONTENTS PAGE NO.

1. ABSTRACT 9

2. INTRODUCTION TO EMBEDDED SYSTEMS 10

3. BLOCK DIAGRAM 16

4. 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

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

6

11. RESULTS 69

12. CONCLUSION 93

13. BIBLIOGRAPHY 94

7

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

8

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.

9

2. INTRODUCTION TO EMBEDDED SYSTEMS

10

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

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EmbeddedSystemsComputerArchitectureSoftwareEngineering

Data CommunicationControlEngineeringElectric motorsand actuators

Sensors andmeasurements

AnalogElectronic design

DigitalElectronic design Integrated circuitdesign

Embedded system design calls on many disciplines

Operating Systems

BuildDownload

DebugTools

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.

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System

Testing

System

Definition

Targeting

Rapid Prototyp

ing

Hardware-in-

the-Loop Testin

g

– 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.

APPLICATIONS1) Military and aerospace embedded software applications

2) Communicat ion Appl icat ions

3) Indust r ia l automat ion and process control sof tware

4) Mastering the complexity of applications.

5) Reduction of product design time.

6) Real time processing of ever increasing amounts of data.

7) 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

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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.

14

3. BLOCK DIAGRAM

15

4. HARDWARE REQUIREMENTS

16

HARDWARE COMPONENTS:

1. VOLTAGE REGULATOR (LM 7805)

2. MICROCONTROLLER (AT89S52/AT89C51)

3. LED

4. PUSH BUTTONS

5. BC547

6. 1N4007/1N4148

7. RESISTOR

8. CAPACITOR

9. PHOTOVOLTAIC CELLS/SOLAR CELLS

10. LM317

11. SOLAR PANNEL

17

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.

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Internal Block Diagram

FIG 4.2(a): BLOCK DIAGRAM OF VOLTAGE REGULATOR

Absolute Maximum Ratings

TABLE 4.2(b): RATINGS OF THE VOLTAGE REGULATOR

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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 Modes20

• 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

21

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

22

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:

23

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

24

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.

25

4.3 LEDLight 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.

26

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

27

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

28

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.

29

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.

30

Applications1) Telecommunications

2) Power delivery

3) Voltage regulation

4) 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).

31

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

32

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:

33

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

34

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

35

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.

36

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.

1. Maximum forward current capacity

2. Maximum reverse voltage capacity

3. Maximum forward voltage capacity

Fig: 1N4007 diodesThe 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

37

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

38

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

39

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

40

4.9 RESISTORSA 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:41

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

42

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 43

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

44

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.

45

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.

46

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

47

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

48

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

49

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

50

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:

o Single supply 3V to 32V

o 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

51

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.

Advantages52

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?

1. Rays of sunlight hit the solar panel (also know as a photovoltaic/ (PV) cells) and are

absorbed by semi-conducting materials such as silicone.

2. 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.

3. An array of solar panels converts solar energy into DC (direct current) electricity.

4. The DC electricity then enters an inverter.

5. The inverter turns DC electricity into 120-volt AC (alternating current) electricity needed

by home appliances.

6. The AC power enters the utility panel in the house.

7. The electricity (load) is then distributed to appliances or lights in the house.

8. 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.

9. When the battery is full the excess electricity can be exported back into the utility grid, if

your system is connected to it.

10. 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.

11. 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 53

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

54

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

55

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

56

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 57

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.

58

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 7 th Pin

is o/p Pin with resistor R7 of 2K & LED. UI:C is also an op-amp whose 10 th 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 14.59

Whose 12th Pin is connected to RV5 ,22K. PRESET 13 th 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.

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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

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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.

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7. LAYOUT DIAGRAM

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8. BILL OF MATERIALSR1, R3,R4,

R12 = 10k

R5 = 240 OHMSP1,P2 =10K presetP3 = 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

64

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 65

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’ 40 th 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.

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