Major Pjkt Report

8/6/2019 Major Pjkt Report

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CHAPTER-1

1.1 INTRODUCTION :

Security is a matter of prime importance in todays era of terrorism and violence.OurArmy and Security forces are faced with the tedious task of safeguarding our territories

and the citizens of our country.In such a scenario the use of ultra modern electronic

equipments becomes an unavoidable essentiality.The battleground in todays era is in the

form of a sophisticated equipment itself.

Our project utilizes the concept of production of high voltage spark of around 24000

volts,enough to make somebody unconscious but not deemed to cause any potential

harm.Unlike the field implementation where voltages as high as 15 lakh volts are

produced we are supposed to produce a voltage of around 24000 volts with the help of

EHT which is an oscillatory high voltage transformer.This high voltage will be seen in

the form of a blue lightning discharge.The spark will be initiated in the direction of the

coming object with the help of a stepper motor.Following are the features of this project:

It has high speed of operation.

It is highly sensitive.

It is portable .

It is user friendly

1.2 PROJECT DESCRIPTION:

COMPONENTS USED:

1. TRANSMITTER RECEIVER:-

The transmitter receiver pair is used to sense the presence of any signal and sends the

information to microcontroller.

2. OPERATIONAL AMPLIFIER:-

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The signal so received is of very small amplitude so in order to increase its amplitude

OP-AMP Is used.

3. MICROCONTROLLER:-

Microcontroller is used to do all the programming of the circuit.It runs according to the

program. We need not to build very large circuits. By using this we can control the work

of large circuitry through the help of the program which can be easily burnt into it.

4.CURRENT AMPLIFIER:-

ULN2803 is the Darlington array which is a current amplifier which amplifies the current

of the signal coming from the microcontroller.

5. RELAY:-

A relay is an electrical switch that opens and closes under the control of anotherelectrical

circuit. In the original form, the switch is operated by an electromagnet to open or close

one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is

able to control an output circuit of higher power than the input circuit, it can be

considered to be, in a broad sense, a form of an electrical amplifier.

6. PULSE GENERATION:-

The 555 timer is one of the most remarkable integrated circuits ever developed. It comes

in a single or dual package and even low power cmos versions exist - ICM7555.

Common part numbers are LM555, NE555, LM556, NE556. The 555 timer consists of

two voltage comparators, a bi-stable flip flop, a discharge transistor, and a resistor divider

network.

7. STEPPER MOTOR:-

A stepper motor (orstep motor) is a brushless, synchronous electric motor that

can divide a full rotation into a large number of steps. The motor's position can be

controlledprecisely without any feedback mechanism (see Open-loop controller),

as long as the motor is carefully sized to the application. Stepper motors are

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similar to switched reluctance motors (which are very large stepping motors with

a reduced pole count, and generally are closed-loop commutated.)

8. E.H.T.:-

E.H.T stands foe extremely high tension. It is akind of step up transformer used to step

up very low voltage to thousands of kilovolts.

9.POWER SUPPLY:-

Power supply is used to drive the circuit. Inappropriate voltage will damage the entire

circuitry therefore it constitutes a very important part of the circuit.Every electronic

circuit requires power for its operation. Every function simple or complex is controlledby the power supply. Even a little variation in voltage can damage all the circuitry. So

power supply is of prime importance in all the circuits. The power supply which we get is

a.c. operating at 220Volts.But as our electronic circuits work only on d.c. therefore; we

cannot employ direct usage of supply which we get. In order to overcome this, we require

various process namely transformation, rectification, smoothing or filtering and

regulation.

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1.3 BLOCK DIAGRAM AND CIRCUIT DIAGRAM:

FIG 1.1 SECURITY SYSTEM USING HIGH VOLTAGE SPARKS

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FIG 1.2 CIRCUIT DIAGRAM

1.4 LIST OF COMPONENTS:

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CHAPTER-2

DESCRIPTION OF COMPONENTS USED

S.No. Code Name Value Price

1. R1,R4,R7

R3,R6

Resistors 10k

220 ohms

25 paisa

each

2. R2-R5 Potentiometer 10k 5

3. C1,C2

C3

Capacitors 33Pf

10F

1

1

4. IC1A,IC2A

IC3

IC4

IC5

U$2

Q3

T1,T2

D1

LED1,LED2

OK1

OP-AMP

Microcontroller

Current amplifier

Timer

Regulator

Transistor

Phototransistor

Diode

IR LED

Optocoupler

LM324

AT89S51

ULN2803

NE555

LM7805

BC547

LPT80A

1N4007

5mm

4N35

10

50

20

6

10

2

150

1

1

20

5. Q1

U$1

Crystal

Reset switch

Battery

12MHz

1.2A,12V

10

5

400

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2.1 SENSORS:

First of all, two sensors are used in which the IR LED acts as a transmitter and Photo

detector as a receiver. Along with this LED, a resistor (220)

is used in series to limitthe current.

2.1.1 REQUIREMENT IN THE PROJECT:

IR LED emits infrared radiation. This radiation illuminates the surface in front of LED.

Surface reflects the infrared light. Depending on reflectivity of the surface, amount of

light reflected varies. This reflected light is made incident on reverse biased IR sensor.

When photons are incident on reverse biased junction of this diode, electron-hole pairs

are generated, which results in reverse leakage current. Amount of electron-hole pairs

generated depends on intensity of incident IR radiation. More intense radiation results in

more reverse leakage current. This current can be passed through a resistor so as to get

proportional voltage. Thus as intensity of incident rays varies, voltage across resistor will

vary accordingly.

This voltage can then be given to OPAMP based comparator.Output of the comparator

can be read by uC.

FIG 2.1 IR SENSOR AND LED PAIR

2.1.2 CONSTRUCTION AND WORKING:

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The actual sensor on the chip is made from natural or artificial pyroelectric materials,

usually in the form of a thin film, out ofgallium nitride (GaN), caesium nitrate (CsNO3),

polyvinyl fluorides, derivatives ofphenylpyrazine, and The actual sensor on the chip is

made from natural or artificial pyroelectric materials, usually in the form of a thin film,

out ofgallium nitride (GaN), caesium nitrate (CsNO3),polyvinyl fluorides, derivatives of

phenylpyrazine, and cobalt phthalocyanine. Lithium tantalate (LiTaO3) is a crystal

exhibiting bothpiezoelectric and pyroelectric properties.

The sensor is often manufactured as part of an integrated circuit and may be comprised of

one (1), two (2) or four (4) 'pixels' comprised of equal areas of the pyroelectric material.

Pairs of the sensor pixels may be wired as opposite inputs to a differential amplifier.

R1 is to prevent the emitter (clear) LED from melting itself. Choose a R1 value so that

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Comparator is a device which compares two voltages orcurrents and switches its output

to indicate which is larger. More generally, the term is also used to refer to a device that

compares two items ofdata.

LM324N Op amp IC has been used as a comparator. It is a 14 pin IC. It consists of 4 op-amps as shown in the pin diagram below:

FIG 2.3 PIN DIAGRAM OF COMPARATOR


The operational amplifier (LM324) is used as a comparator lying below the sensor. It

checks if the light is being received by the photo detector or not. If the light is received

then it gives the output as 1 otherwise 0.


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A standard op-amp without negative feedback can be used as a comparator, as indicated

in the following diagram.

FIG 2.4 BASIC COMPARATOR CIRCUIT

When the non-inverting input (V+) is at a higher voltage than the inverting input (V-), the

high gain of the op-amp causes it to output the most positive voltage it can.

When the non-inverting input (V+) drops below the inverting input (V-), the op-amp

outputs the most negative voltage it can. Since the output voltage is limited by the supply

voltage, for an op-amp that uses a balanced, split supply, (powered by VS) this action

can be written:

Vout = VS. sgn (V+ V) where sgn (x) is the signum function. Generally, the positive

and negative supplies VS will not match absolute value:

Vout V-) else VS- when (V+ < V-).

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Equality of input values is very difficult to achieve in practice. The speed at which the

change in output results from a change in input (often called the slew rate in operational

amplifiers) is typically in the order of 10ns to 100ns, but can be as slow as a few tens of

s.

2.3 MICROCONTROLLER:

2.3.1 INTRODUCTION:

Microcontroller is a general purpose device meant to read data, to perform limited

calculations on that data and to control its environment based on those calculations. The

prime use of a microcontroller is to control the operation of a machine using a fixed

program that is stored in ROM and that does not change over the lifetime of the system.

Microcontroller is a true computer on a chip. It incorporates all the features found in a

microprocessor like CPU, ALU, PC, SP and registers. It also has additional features

needed to make a complete computer like ROM, RAM, parallel input-output, serial input-

output, counters and a clock circuit.

A microcontroller (often abbreviated MCU) is a single computer chip (integrated circuit)

that executes a user program, normally for the purpose of controlling some device hence

named as microcontroller.

The program is normally contained either in a second chip, called an EPROM, or within

the same chip as the microcontroller itself. A microcontroller is normally found in

devices such as microwave ovens, automobiles, keyboards, CD players, cell phones,

VCRs, security systems, time & attendance clocks, etc.Microcontroller-based systems are generally smaller, more reliable, and cheaper. They

are ideal for the types of applications described above where cost and unit size are very

important considerations. In such applications it is almost always desirable to produce

circuits that require the smallest number of integrated circuits, that require the smallest

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amount of physical space, require the least amount of energy, and cost as little as

possible.

Microcontrollers are hidden inside a surprising number of products these days. If your

microwave oven has an LED orLCD screen and a keypad, it contains a microcontroller.

All modern automobiles contain at least one microcontroller, and can have as many as

six or seven. The engine is controlled by a microcontroller, as are the anti-lock brakes,

the cruise control and so on. Any device that has a remote control almost certainly

contains a microcontroller: TVs, VCRs and high-end stereo systems all fall into this

category. Digital cameras, cell phones, answering machines, laser printers, telephones

(the ones with caller ID, 20-number memory, etc.), pagers, and refrigerators,dishwashers, washers and dryers (the ones with displays and keypads). Basically, any

product or device that interacts with its user has a microcontroller buried inside

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2.3.2 BLOCK DIAGRAM

FIG 2.5 BLOCK DIAGRAM OF MICROCONTROLLER

1 INTERRUPT CONTROL: - The interrupt control basically handles the interrupts

whether they should be handled or not. For the same purpose two registers of 8-

bits are present i.e. IP and IE i.e. interrupt priority and interrupt enable.

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2 ON CHIP FLASH: - Flash memory is present on the chip.

3 ON CHIP RAM: - RAM is also present on the chip.

4 TIMERS: - Timer control registers of 8 bits are also present on the chip. The

counter input is given to the timers.

5 SERIAL PORTS: - the serial ports are also present on chip which allows the

microcontroller to communicate serially.

6 I/O PORTS: - the I/O ports basically provides the input and output ports. These

are present on the chip of microcontroller itself. They are of 8 bits. There is no

requirement for providing the external interface. Basically there are 4 ports i.e.

port 0, port 1, port 2 and port 3. PORT 0 provides both data and addresses along

with I/O pins. PORT 1 provides only I/O pins. PORT 2 provides I/O pins and the

remaining addresses. PORT 3 provides I/O pins and

WR,RD,T0,T1,INT0,INT1,RXD,TXD

7 BUS CONTROL: - The control registers are present i.e. TCON, TMOD, SCON,

PCON, IP, IE.

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8051

MICRO

CONTROLLER

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

40

39

38

37

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

P1.0

P1.1

P1.2

P1.3

P1.4P1.5

P1.6

P1.7

RST

( RXD ) P3.0

(TXD) P3.1

(INT0 ) P3.2

(INT1) P3.3

(T0) P3.4

(T1) P3.5

(WR) P3.6

(RD) P3.7XTAL2

XTAL1

GND

VCC

P0.7 (AD0)

P0.6 (AD1)

P0.5 (AD2)

P0.4 (AD3)P0.3 (AD4)

P0.2 (AD5)

P0.1 (AD6)

P0.0 (AD7)

EA\VPP

ALE

PSEN

P2.7 (A15)

P2.6 (A14)

P2.5 (A13)

P2.4 (A12)

P2.3 (A11)

P2.2 (A10)

P2.1 (A9)

P2.0 (A8)

8 OSCILLATOR: -A particular frequency is provided i.e. 11.0592 MHz by a crystal

oscillator.

2.3.3 PIN DIAGRAM :

FIG 2.6 PIN DIAGRAM OF 8051

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8051 is a 40 pin IC packed in DIP (Dual line packaging). This means that the pin

performs the dual functions. Basically 8051 is a 40 pin IC but it performs 64 functions.

This is due to the reason that 24 pins are multiplexed pins. So these pins perform dual

functions and make it a total of 64 functions.

1.VCC: - PIN (40) - This pin is used to supply voltage to the micro controller. Generally

+5V is provided to microcontroller.

2.GND: - PIN (20) - This pin is used for ground.

3.RST: - (PIN 9) It is a Reset Input. When this pin is given a high for the two continuous

machine cycles while the oscillator is running, the device gets resets.

4.ALE: - (PIN 30): - It is an Address latch enable. With the bit set the ALE is enabled

during the MOVX or MOVC instruction.

5.PSEN: - (PIN 29): - Program Store Enabled is the read strobe to external program

memory. When the AT89C51 is executing code from external memory, This pin is

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activated during each machine cycle, except that two activation are skipped during each

access to external data memory.

6.PORT 0 :-( PINS 32-39 i.e. P0.0-P0.7) Port 0 is an 8 bit bi-directional I/O port. When

1s are written to the pins then port 0 acts as high impedance inputs. Port 0 may also be

configured to be the multiplexed address/data bus (i.e. AD0-AD7) during accesses to

external program and data memory.

7.PORT 1:- Port 1 is an 8 bit bi-directional I/O port with internal pull-ups.When 1s are

written to the 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 currentbecause of internal pull-ups. Port 1 also receives the low order addresses bytes during

Flash programming and verification.

8.PORT 2:- Port 2 is an 8 bit bi-directional I/O port. 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 because of internal pull ups. Port 2 emits the high

order addresses byte during fetches from external program memory and during accesses

to external program memory, data memory that use 16bit addresses. In this application,

this uses strong internal pull-ups when emitting 1s.

9.PORT 3:- (PINS 10-17 i.e. P3.0-P3.7) Port 3 is an 8-bit bi-directional I/O port. So

along with providing the I/O various other operations are also performed.

2.3.4 MEMORY ORGANISATION:

The diagram showing the organization of memory in a microcontroller is as follows:

The8051 microcontroller actually includes a whole family of microcontrollers that have

numbers ranging from 8031 to 8751 and are available in NMOS and CMOS

constructions in a variety of package types. The 8051 has internal RAM and ROM.

Memory for variable data can be altered as the program runs.

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1) INTERNAL RAM

The 128-byte internal RAM is organized into three distinct areas:

Thirty-two bytes from address 00h to 1Fh that make up 32 working registersorganized as four banks of eight registers each.

A bit addressable area of 16 bytes occupies RAM byte addresses 20h to 2Fh

forming a total of 128 addressable bits.

A general purpose RAM area above the bit area, from 30h to 7Fh, addressable as

bytes.

2) INTERNAL ROM

In 8051, data memory and program code memory are two different entities. Internal

ROM occupies code addresses 0000h to 0FFFh. If program address exceeds 0FFFh then

8051 automatically fetches code from external program memory. Code bytes could also

be fetched exclusively from external memory 0000h to FFFFh by connecting the EA pin

to the ground.

2.3.5 FEATURES OF MICROCONTROLLER:

1. Perform a single set of functions.

2. Works in a time constrained environment.

3. Provides high-performance and reliability.

4. Mostly Embedded systems have low cost because they are mass produced in millions.

5. Some Embedded systems have mechanical moving parts like disk drives as they are

less reliable as compared to solid state parts such as Flash memory.

6. High Integration of Functionality.

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7. Microcontrollers sometimes are called single-chip computers because they have on-

chip memory and I/O circuitry and other circuitries that enable them to function as small

standalone computers without other supporting circuitry.

8. Field Programmability, Flexibility.

9. Microcontrollers often use EEPROM or EPROM as their storage device to allow field

programmability so they are flexible to use. Once the program is tested to be correct then

large quantities of microcontrollers can be programmed to be used in embedded systems.

10. Easy to Use: Assembly language is often used in microcontrollers and since they

usually follow RISC architecture, the instruction set is small. The development package

of microcontrollers often includes an assembler, a simulator, a programmer to "burn" the

chip and a demonstration board. Some packages include a high level language compiler

such as a C compiler and more sophisticated libraries.

11. Eight bit CPU with registers A and B.

12. Sixteen bit program counter and data pointer.

13. Eight bit program status word.

14. Eight bit stack pointer.

15. Internal ROM of 4K.

16. Internal RAM of 128 bytes: Four register banks, each containing eight registers.

Sixteen bytes, which may be addressed at bit level. Eighty bytes of general-purpose data

memory.

17. Thirty two input/output pins arranged as four 8-bit ports: P0-P3.

18. Two 16-bit timer/counters: T0 and T1.

19. Full duplex serial data receiver/transmitter: SBUF.

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20. Control register: TCON, TMOD, SCON, PCON, IP.

21. Two external and three internal interrupt sources.

22. Oscillator and clock circuits.

2.3.6 MICROCONTROLLER VERSUS MICROPROCESSOR:

By microprocessor is meant the general- purpose microprocessors such as Intels x86

family. These microprocessors contain no RAM, no ROM, and no I/O ports on the chip

itself. Whereas a microcontroller has a fixed amount of RAM, ROM and I/O ports in the

chip itself.

Thus a system designer using a general- purpose microprocessor such as Pentium must

add RAM, ROM, I/O ports, and timers externally to make them functional.

The addition of these external components makes these systems bulkier and much more

expensive. But they have the advantage of versatility such that the designer can decide on

the amount of RAM, ROM, and I/O ports as per his/her requirement.

In case of a microcontroller the fixed amount of on-chip ROM, RAM, and the number of

I/O ports makes them ideal for many applications in which coat and space are critical.

Thus microcontrollers are the preferred choice for many embedded systems.


Microcontroller is used to do all the programming of the circuit.It runs according to the

program. We need not to build very large circuits. By using this we can control the work

of large circuitry through the help of the program which can be easily burnt into it.

2.3.8 ATMELS AT89C51:

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In our project, we have used the microcontroller AT89C51, a version of popular 8051,

manufactured by ATMEL Corporation. The first two letters in the name is for the

manufacturer.

The AT89C52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K

bytes of in-system programmable Flash memory. The device is manufactured using

Atmels high-density nonvolatile memory technology and is compatible with the

industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the

program memory to be reprogrammed in-system or by a conventional nonvolatile

memory programmer. By combining a versatile 8-bit CPU with in-system programmable

Flash on a monolithic chip, the Atmel AT89C52 is a powerful microcontroller which

provides a highly-flexible and cost-effective solution to many embedded control

applications.

The AT89C52 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 AT89C52 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.

2.3.9 FEATURES:

The various features of AT89C51 are given below:

TABLE 2.1 FEATURES OF AT89C51

Feature Value

ROM 4K Bytes

RAM 128 Bytes

Timers 2

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I/O pins 32

Serial ports 1

Interrupt Sources 6

2.3.10 BLOCK DIAGRAM:

The block diagram of AT89C51 is shown below:

FIG 2.8 BLOCK DIAGRAM OF AT89C51

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2.3.11 PIN DIAGRAM:

FIG 2.9 PIN DIAGRAM OF AT89C51

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2.3.12 PIN DESCRIPTION:

VCC -Supply voltage (all packages except 42-PDIP).

GND -Ground (all packages except 42-PDIP; for 42-PDIP GND connects only the logic

core and the embedded program memory).

VDD -Supply voltage for the 42-PDIP which connects only the logic core and the

embedded program memory.

PWRVDD -Supply voltage for the 42-PDIP which connects only the I/O Pad Drivers.

The application board must connect both VDD and PWRVDD to the board supply

voltage.

PWRGND- Ground for the 42-PDIP which connects only the I/O Pad Drivers.

PWRGND and GND are weakly connected through the common silicon substrate, but not

through any metal link. The application board mustconnect both GND and PWRGND to

the board ground.

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Port 0 -Port 0 is an 8-bit open drain bi-directional 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 bi-directional 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.

Port 1 also receives the low-order address bytes during Flash programming and

verification.




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.

Port 2 also receives the high-order address bits and some control signals during Flash

programming and verification.



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are externally being pulled low will source current (IIL) because of the pull-ups.

Port 3 receives some control signals for Flash programming and verification.

Port 3 also serves the functions of various special features of the AT89S51, as shown in

the following table.

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.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the

bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is

weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in

external execution mode.

PSEN -Program Store Enable (PSEN) is the read strobe to external program memory.

When the AT89S51 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

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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

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FIG 2.10 MICRONTROLLER INTERFACING

2.4 CURRENT AMPLIFIER:

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ULN2803 is the Darlington array which is a current amplifier which amplifies the current

of the signal coming from the microcontroller.

Relay is an electro mechanical switch which converts electrical signal into mechanical

output and provides the isolation between the two connections.

The signal so received is of very small amplitude in order to amplify it current amplifier

is used. The current amplifier used in this project is ULN2803.


The output from the controller is of very small amplitude and is not capable of driving the

motor so to increase its amplitude current amplifier (ULN2803) is used. It provides so

much of the current that is required to drive the motor.

FIG 2.11 PIN DIAGRAM OF ULN2803

Featuring continuous load current ratings to 500 mA for each of the drivers, the Series

ULN28xxA/LW and ULQ28xxA/LW high voltage, high-current Darlington arrays are

ideally suited for interfacing between low-level logic circuitry and multiple peripheral

power loads. Typical power loads totaling over 260 W (350 mA x 8, 95 V) can be

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controlled at an appropriate duty cycle depending on ambient temperature and number of

drivers turned on simultaneously. Typical loads include relays, solenoids, stepping

motors, magnetic print hammers, multiplexed LED and incandescent displays, and

heaters. All devices feature open-collector outputs with integral clamp diodes.

The ULx2803A, ULx2803LW, ULx2823A, and ULN2823LW have series input resistors

selected for operation directly with 5 V TTL or CMOS. These devices will handle

numerous interface needs particularly those beyond the capabilities of standard logic

buffers.

The ULx2804A, ULx2804LW, ULx2824A, and ULN2824LW have series input resistors

for operation directly from 6 V to 15 V CMOS or PMOS logic outputs.

The ULx2803A/LW and ULx2804A/LW are the standard Darlington arrays. The outputs

are capable of sinking 500 mA and will withstand at least 50 V in the off state. Outputs

may be paralleled for higher load current capability. The ULx2823A/LW and

ULx2824A/LW will withstand 95 V in the off state.

These Darlington arrays are furnished in 18-pin dual in-line plastic packages (suffix A)

or 18-lead small-outline plastic packages (suffix LW). All devices are pinned with

outputs opposite inputs to facilitate ease of circuit board layout. Prefix ULN devices are

rated for operation over the temperature range of -20C to +85C; prefix ULQ devices

are rated for operation to -40C.

2.5 VOLTAGE REGULATOR:

FIG 2.12 VOLTAGE REGULATOR 7805

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Voltage regulator is a device which is used to regulate the input voltage to a desired fixed

dc value. The regulation is usually obtained from an IC voltage regulator unit, which

takes a dc voltage and provides a somewhat lower dc voltage, which remains the sameeven if the input dc voltage varies or the output load connected to the dc voltage changes.

Regulator IC units contain the circuitry for reference source, comparator amplifier,

control device, and overload protection all in a single IC.


7805 is an integrated three-terminal positive fixed linear voltage regulator. It supports an

input voltageof 7 volts to 35 volts and output voltage of 5 volts. It typically has a current

rating of 1 amp although both higher and lower current models are available. Its output

voltage is fixed at 5.0V. The 7805 also have a built-incurrent limiteras a safety feature.

The 7805 will automatically reduce output current if it gets too hot. It belongs to a family

of three-terminal positive fixed regulators with similar specifications and differing fixed

voltages from 8 to 15 volts.

2.5.2 IC 7805-

The 78XX series is for positive voltage regulators. 5 at the end indicates the output dcvoltage. This voltage regulator requires a minimum of 6.3 V. Thus if a signal having

variations above 6.3 V is applied at the input of 7805 will produce 5 V fixed dc at the

output.

FIG 2.13 7805 PIN DIAGRAM

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The input voltage is applied at pin 1. Pin 2 is grounded. The output is taken from Pin 3.

For obtaining a stable dc of 5 V it is necessary to have a minimum of 6.3 V at the output

because IC itself also has a voltage drop. This IC generates a lot of heat during its

operation. Therefore a heat sink is also there to prevent this IC from damage.

2.6 POWER SUPPLY :

The term power supply is more commonly abbreviated to PSU, this will be used from

hereon in.

Telecommunications equipment is designed to operate on voltages lower than the

domestic Mains voltage. In order to reduce this voltage a PSU is used.

To provide a useable low voltage the PSU needs to do a number of things:-

Reduce the Mains AC (Alternating current) voltage to a lower level.

Convert this lower voltage from AC to DC (Direct current)

Regulate the DC output to compensate for varying load (current demand)

Provide protection against excessive input/output voltages.

Reduction of AC Mains

This is achieved by using a device known as a Transformer an electromagnetic device

consisting of an ferrous iron core which has a large number of turns of wire wound

around it, known as the Primary Winding

The ends of these turns of wire being connected to the input voltage (in this case Mains

AC).

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2

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A second number of turns of wire are wound around the Primary Winding, this set being

known as the Secondary Winding.

The difference between the number of turns provides us with a way of reducing (in our

case) a high AC voltage to a lower one.

Conversion of AC to DC

To convert our now low AC voltage to DC we use a Rectifier Diode connected to the

Secondary Winding.

This is a silicon diode, which has operation analogous to a bicycle tyre valve (as the

valve only allows air to flow into the tyre, the diode only allows current to flow in one

direction)

As our low AC voltage will be working at a frequency of 50Hz (Mains AC frequency) it

is desirable to reduce the inherent hum on this to a lower level.

This is achieved by a technique known as Smoothing (Ironing out the bumps in the

AC).

A simple way to reduce the hum is to use Full Wave Rectification.

Today this is usually done by four diodes in a bridge configuration known as a Bridge

Rectifier.(This can be four individual diodes or a dedicated self contained package)

Regulation of Output Voltage

The Electrolytic Capacitor is a device capable of storing energy the amount of energy and

the time it remains stored depending on the value.

In a simple PSU the easiest way to provide regulation to compensate for varying load

conditions is to use a pair of relatively high value Electrolytic Capacitors.

Their values in this case being in the region of 470uF to 2000uF depending on the

application and the amount of current required from the output of the unit.

One of these capacitors is connected across the DC output of the rectifier diode(s) or

bridge, this capacitor also providing an extra degree of smoothing the output waveform.

The second capacitor is connected via a low value, medium to high wattage resistor,

which assists in limiting the current demand.

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Protection against excessive voltages

In a simple PSU the easiest way to do this is by providing fuses at the input to the

transformer, generally in the live side of the mains supply, also at the DC outputs.

In the event of an excessive input voltage, or excessive current being drawn from theoutput, one of these fuses should normally blow protecting the PSU and the equipment

connected to it.

The transformer may also be fitted with an internal or external thermal fuse, which will

open if the transformer becomes hot due to the aforementioned conditions.



circuitry therefore it constitutes a very important part of the circuit.

Every electronic circuit requires power for its operation. Every function simple or

complex is controlled by the power supply. Even a little variation in voltage can damage

all the circuitry. So power supply is of prime importance in all the circuits. The power

supply which we get is a.c. operating at 220Volts.But as our electronic circuits work only

on d.c. therefore; we cannot employ direct usage of supply which we get.

FIG 2.14 BLOCK DIAGRAM OF REGULATED POWER SUPPLY

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circuitry therefore it constitutes a very important part of the circuit.

Every electronic circuit requires power for its operation. Every function simple or

complex is controlled by the power supply. Even a little variationin voltage can damage

all the circuitry. So power supply is of prime importance in all the circuits. The power

supply which we get is a.c. operating at 220Volts.But as our electronic circuits work only

on d.c. therefore; we cannot employ direct usage of supply which we get : . In order to

overcome this, we require various process namely transformation, rectification,

smoothing or filtering and regulation. All these process using bridge rectifier are

illustrated below

2.6.2 TRANSFORMATION:-

As already discussed the supply which we get is 220V A.C. supply. In order to decrease

the magnitude of the voltage we make use of step down transformer. This transformer has

more windings in the primary coil than in the secondary coil. So the voltage output at the

secondary is an A.C. supply with magnitude less than 220V.

2.6.3 RECTIFICATION:-

As all the electronic circuits work on DC therefore this low voltage A.C. cannot be

directly fed to our circuit. Thus a process of rectification is required. In this process, A.C.

voltage is converted into D.C. voltage using two semiconductor rectifying diodes .

Now as the two diodes D1 and D2 are connected in the opposite manner. Therefore one

of the diode gets forward biased during the positive half of the a.c input and other gets

forward biased during the negative half of the a.c. input. Thus during the positive half

cycle rectification takes place through diode D1 (diode D2 being reverse biased, cannot

rectify) and during the negative half cycle, the rectification takes place through the diode

D2(diode D1 being reverse biased, cannot rectify). But as at least one of the diode always

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remain in the conducting mode therefore both the halves of the a.c. input gets rectified

and hence the name full wave rectifier.

2.6.4 SMOOTHING/FILTRATION:-

The output of the rectification process is a varying D.C. As the D.C. waveform cannot be

varying so it means that rectification is not 100% efficient due to which there is still some

component of the input A.C. present in the D.C. voltage which is responsible for the

variation. So in order to remove this A.C. component we require filtration or smoothing

of the signal. This can be done using an electrolytic capacitor of 2200uf. As the capacitor

offers infinite impedance to the D.C. signal and Zero impedance to the A.C. signal

therefore, it allows the A.C. component to pass through and blocks the D.C. component.

This means it will filter out the D.C. component from the input signal. Thus the output of

the process will be a pure D.C. supply as shown below:

Now there is still some variation indicating that output D.C. voltage is not having

constant magnitude. This is due to the capacitor used for filtration. Its time of charging

and discharging are not equal due to which the filtration is not up to the mark. For

making the output voltage assume a constant value we need a voltage regulator.

2.6.5 REGULATION:-

Voltage regulator is used for this purpose mainly from the series of 78- - of the transistor.

For getting the constant output of 5 volts we make use of 7805 voltage regulator. This

process takes place as shown below:

This completes all the processes. Now we have a constant D.C. supply with us which can

be fed to any electronic circuit without any problem

2.7 TRANSFORMER:

A "transformer" changes one voltage to another. This attribute is useful in many ways.

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A transformer doesn't change power levels. If you put 100 Watts into a transformer, 100

Watts come out the other end. [Actually, there are minor losses in the transformer

because nothing in the real world is 100% perfect. But transformers come pretty darn

close; perhaps 95% efficient.]

A transformer is made from two coils of wire close to each other (sometimes wrapped

around an iron or ferrite "core"). Power is fed into one coil (the "primary"), which creates

a magnetic field. The magnetic field causes current to flow in the other coil (the

"secondary"). Note that this doesn't work for direct current (DC): the incoming voltage

needs to change over time - alternating current (AC) or pulsed DC.

FIG 2.15 IRON CORE

The number of times the wires are wrapped around the core ("turns") is very important

and determines how the transformer changes the voltage.

If the primary has fewer turns than the secondary, you have a step-up transformer

that increases the voltage.

If the primary has more turns than the secondary, you have a step-down

transformerthat reduces the voltage.

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If the primary has the same number of turns as the secondary, the outgoing

voltage will be the same as what comes in. This is the case for an isolation

transformer.

In certain exceptional cases, one large coil of wire can serve as both primary and

secondary. This is the case with variable auto-transformers and xenon strobe

trigger transformers.

2.7.1 S TEP-UP TRANSFORMERS :-

FIG 2.16 STEP UP TRANSFORMER

A "step-up transformer" allows a device that requires a high voltage power supply to

operate from a lower voltage source. The transformer takes in the low voltage at a high

current and puts out the high voltage at a low current.

Examples:

You are a Swiss visiting the U.S.A., and want to operate your 220VAC shaver off

of the available 110 VAC.

The CRT display tube of your computer monitor requires thousands of volts, but

must run off of 220 VAC from the wall.

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2.7.2 STEP-DOWN TRANSFORMERS:-

FIG 2.17 STEP DOWN TRANSFORMER

A "step-down transformer" allows a device that requires a low voltage power supply to

operate from a higher voltage. The transformer takes in the high voltage at a low current

and puts out a low voltage at a high current. Examples:

Your Mailbu-brand landscape lights run on 12VAC, but you plug them into the

220 VAC line.

Your doorbell doesn't need batteries. It runs on 220 VAC, converted to 12VAC.

2.7.3 VARIABLE AUTO-TRANSFORMERS :

FIG 2.18 VARIABLE AUTO TRANSFORMERS

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A "variable auto-transformer" (variac) can act like a step-up transformer or step-down

transformer. It has a big knob on top that allows you to dial in whatever output voltage

you want.

2.7.4 SIGNAL TRANSFORMERS:

"Signal transformers" also take one thing in and transform it to another thing out. But in

this case, the power levels are low, and the transformed thing carries some type ofinformation signal.

In most cases, these transformers are thought of as impedance matching.

2.8STEPPER MOTOR:

A stepper motor (orstep motor) is abrushless, synchronous electric motorthat

can divide a full rotation into a large number of steps. The motor's position can be

controlledprecisely without any feedback mechanism (see Open-loop controller),

as long as the motor is carefully sized to the application. Stepper motors are

similar to switched reluctance motors (which are very large stepping motors with

a reduced pole count, and generally are closed-loop commutated.)

FIG 2.19 STEPPER MOTOR

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Stepper motors operate differently from DC brush motors, which rotate when voltage is

applied to their terminals. Stepper motors, on the other hand, effectively have multiple"toothed" electromagnets arranged around a central gear-shaped piece of iron. The

electromagnets are energized by an external control circuit, such as a microcontroller. To

make the motor shaft turn, first one electromagnet is given power, which makes the gear's

teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are thus

aligned to the first electromagnet, they are slightly offset from the next electromagnet. So

when the next electromagnet is turned on and the first is turned off, the gear rotates

slightly to align with the next one, and from there the process is repeated. Each of those

slight rotations is called a "step," with an integer number of steps making a full rotation.

In that way, the motor can be turned by a precise angle.

2.9 EHT:

The transformer used in our project is known as Extra High Tension or Flyback

Transformer.It is special transformer which was primarily designed to generate high

current sawtooth signals at a relatively high frequency.It was invented as a means to

control the horizontal movement of the electron beam in a cathode ray tube(CRT).Unlike

conventional transformers a flyback transformer is not fed with a signal of the same

waveshape as the intended output current.A convenient side effect of such a transformer

is the the considerable energy that is available in its magnetic circuit.This can be

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exploited using extra windings that can be used to provide power to operate other parts of

the equipment.

Unlike mains transformer,a flyback transformer is designed not just to transfer energy,but

also to store it for a significant fraction of the switching period.This is achieved by

winding the coils on a ferrite core with an air gap.The air gap increases the reluctance of

the magnetic circuit and therefore its ability to store energy.

The primary winding of the transformer is driven by a switch from a DC supply.When

the switch is switched on,the primary inductance causes the current to build up in a

ramp.When the switch is switched off,the current is forced to return quickly to zero.

2.10 H-BRIDGE:

A very popular circuit for driving DC motors (ordinary or gearhead) is called an H-

bridge. It's called that because it looks like the capital letter 'H' on classic schematics. The

great ability of an H-bridge circuit is that the motor can be driven forward or backward at

any speed, optionally using a completely independent power source.


H-Bridge acts as an interface between microcontroller and motor. It is formed using

relays.

relay is an electrical switch that opens and closes under the control of another electrical

Circuit.

2.10.2 CONSTRUCTION AND WORKING :

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An H-bridge design can be really simple for added protection and isolation. An H-bridge

can be implemented with various kinds of components (common bipolar transistors, FET

transistors, MOSFET transistors, power MOSFETs, or even chips).

Physical motion of some form helps differentiate a robot from a computer. It would be

nice if a motor could be attached directly to a chip that controls the movement. But, most

chips can't pass enough current or voltage to spin a motor. Also, motors tend to be

electrically noisy (spikes) and can slam power back into the control lines when the motor

direction or the speed of the motor changes.

Specialized circuits (motor drivers) have been developed to supply motors with power

and to isolate the other ICs from electrical problems. These circuits can be designed such

that they can be completely separate boards, reusable from project to project.

H-bridge which is sometimes called a "full bridge" is so named because it has four

switching elements at the "corners" of the H and the motor forms the cross bar. The basic

bridge is shown in the figure below:

FIG 2.20 H-BRIDGE

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Of course the letter H doesn't have the top and bottom joined together, but hopefully the

picture is clear.The key fact to note is that there are, in theory, four switching elements

within the bridge. These four elements are often called, high side left, high side right, low

side right, and low side left (when traversing in clockwise order). The switches are turned

on in pairs, either high left and lower right, or lower left and high right, but never both

switches on the same "side" of the bridge.

If both switches on one side of a bridge are turned on, it creates a short circuit between

the battery plus and battery minus terminals. This phenomenon is called shoot through in

the Switch-Mode Power Supply (SMPS) literature.

If the bridge is sufficiently powerful it will absorb that load and the batteries used will

simply drain quickly. Usually however the switches melt. To power the motor, we turn

on two switches that are diagonally opposed.

In the picture shown below,

FIG 2.21 WORKING OF H-BRIDGE

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imagine that the high side left and low side right switches are turned on. The current flow

is shown in green.The current flows and the motor begins to turn in a "positive" direction.

If now high side right and low side left switched are turned on, current flows in the other

direction through the motor and the motor turns in the opposite direction.

If each switch can be controlled independently then such a bridge is called a "four

quadrant device" (4QD).

We have now built a small truth table that tells the state of each switch, which further

tells what the bridge will do. As each switch has one of two states, and there are four

switches, there are 16 possible states.

However, since any state that turns both switches on one side on is "bad". There are in

fact only four useful states (the four quadrants) where the transistors are turned on.

2.11 PRESET AND SWITCHES:

Electric switches:

An electric switch is defined as the device for making, breaking or changing connection

sequence in an electric circuit, switch thus essentially consists of a fixed part and a

moving contact. The two types of switches used in our circuit are:

Toggle Switch: This switch is mainly used for ON\OFF control of a.c.

mains or d.c. power supplies. These switches employ sliding contact system. The

switch enclosure is accomplished by a lever. Commercially available toggle

switches can be locking or non- locking type. Two and three position switches are

available.

FIG 2.21 TOGGLE SWITCH

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Tactile Switch: tactile switch uses a clicking sound for distinctive feel to

make it easy to tell whether the switch is in on or off position. This is also known

as a push to on switch. These switches have tendency to produce bounce when

contact opens or closes. Bouncing duration increases with increase in operation

time.

FIG 2.22 TACTILE SWITCH

Preset:Preset is also a variable

resistance, just like the potentiometer, but different in construction and application. Preset

is a service control, in contrast to potentiometer, which is a user control. Preset, therefore,

is mounted directly on PCB.

FIG 2.23 PRESET


They are designed to be mounted directly onto the circuit board and adjusted only when

the circuit is built. For example to set the frequency of an alarm tone or the sensitivity of

a light-sensitive circuit. A small screwdriver or similar tool is required to adjust presets.

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In construction, preset has a carbon resistance track . The sliding contact is without the

long spindle and the knob mounting facility. The sliding contact has just a provision of

thin slot in middle. The sharp edge of screw driver is put in this slot in order to rotate the

sliding contact over the resistance track.

Preset has two end terminals A and B between which a resistance track is there. A

sliding contact moves over this resistance track. This sliding contact is connected to

terminal C. The sliding contact can be moved over the resistance track by putting the

screw driver in the slot provided for this purpose. When the screw driver is rotated, the

sliding contact moves over the resistance track.

The rating of a preset is written on it by manufacturer. The rating is the maximum value of

the resistance up to which the resistance can be varied. Thus, this rating is the resistance

between end terminals.

2.12 DIODE:

A diode is a component that restricts the direction of flow ofcharge carriers. Essentially,

it allows an electric current to flow in one direction, but blocks it in the opposite

direction. Thus, the diode can be thought of as an electronic version of a check valve.

Circuits that require current flow in only one direction will typically include one or more

diodes in the circuit design

FIG 2.24 DIODE

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Today the most common diodes are made from semiconductormaterials such as silicon

orgermanium.

Most modern diodes are based on semiconductor p-n junctions. In a p-n diode,

conventional current flows from the p-type side (the anode) to the n-type side (the

cathode), but not in the opposite direction. Another type of semiconductor diode, the

Schottky diode, is formed from the contact between a metal and a semiconductor rather

than by a p-n junction.

FIG 2.25 DIODE SCHEMATIC SYMBOL

A semiconductor diode's current-voltage, or I-V, characteristic curve is shown below.

FIG 2.26 VI CHARACTERISTICS OF DIODE

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When a p-n junction is first created, conduction band (mobile) electrons from the N-

doped region diffuse into the P-doped region where there is a large population of holes

(places for electrons in which no electron is present) with which the electrons

"recombine".

When a mobile electron recombines with a hole, the hole vanishes and the electron is no

longer mobile. Thus, two charge carriers have vanished. The region around the p-n

junction becomes depleted ofcharge carriers and thus behaves as an insulator.

However, the depletion width cannot grow without limit. For each electron-hole pair that

recombines, a positively-charged dopant ion is left behind in the N-doped region, and a

negatively charged dopant ion is left behind in the P-doped region. As recombination

proceeds and more ions are created, an increasing electric field develops through the

depletion zone which acts to slow and then finally stop recombination. At this point, there

is a 'built-in' potential across the depletion zone.

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If an external voltage is placed across the diode with the same polarity as the built-in

potential, the depletion zone continues to act as an insulator preventing a significant

electric current. This is the reverse biasphenomenon.

However, if the polarity of the external voltage opposes the built-in potential,

recombination can once again proceed resulting in substantial electric current through the

p-n junction. For silicon diodes, the built-in potential is approximately 0.6 V. Thus, if an

external current is passed through the diode, about 0.6 V will be developed across the

diode such that the P-doped region is positive with respect to the N-doped region and the

diode is said to be 'turned on' as it has a forward bias.

2.12.1 TYPES OF SEMICONDUCTOR DIODE:

Avalanche diodes:

Diodes that conduct in the reverse direction when the reverse bias voltage exceeds the

breakdown voltage. These are electrically very similar to Zener diodes, and are often

mistakenly called Zener diodes, but break down by a different mechanism, the avalanche

effect.

Tunnel diodes:

These have a region of operation showing negative resistance caused by quantum

tunneling, thus allowing amplification of signals and very simple bistable circuits. These

diodes are also the type most resistant to nuclear radiation.

FIG 2.27 SYMBOL OF TUNNEL DIODE

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Gunn diodes:

These are similar to tunnel diodes in that they are made of materials such as GaAs or InP

that exhibit a region of negative differential resistance. With appropriate biasing, dipole

domains form and travel across the diode, allowing high frequency microwave oscillators

to be built

Light-emitting diodes (LEDs):

In a diode formed from a direct band-gap semiconductor, such as gallium arsenide,

carriers that cross the junction emit photons when they recombine with the majority

carrier on the other side. Depending on the material, wavelengths (or colors) from the

infrared to the near ultraviolet may be produced.

Laser diodes:

When an LED-like structure is contained in a resonant cavity formed by polishing the

parallel end faces, a laser can be formed. Laser diodes are commonly used in optical

storage devices and for high speed optical communication.

Photodiodes:

All semiconductors are subject to optical charge carrier generation. This is typically an

undesired effect, so most semiconductors are packaged in light blocking material.

Photodiodes are intended to sense light(photo detector), so they are packaged in materials

that allow light to pass, and are usually PIN (the kind of diode most sensitive to light).

.

FIG 2.28 SYMBOL OF PHOTODIODE

Varactor diodes:

These are used as voltage-controlled capacitors. These are important in PLL (phase-

locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as

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those in television receivers, to lock quickly, replacing older designs that took a long time

to warm up and lock.

FIG 2.29 SYMBOL OF VARACTOR DIODE

Zener diodes:

Diodes that can be made to conduct backwards. This effect, called Zener breakdown,

occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage

reference. In practical voltage reference circuits Zener and switching diodes are

connected in series and opposite directions to balance the temperature coefficient to near

zero.

FIG 2.30 SYMBOL OF ZENER DIODE

2.13 CAPACITOR :

Capacitor is another passive component used in electronic circuits. A capacitor

construction consists of two metallic plates or films separated by a dielectric. The

dielectric used can be paper, polyester, mica, ceramic or electrolyte.

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It is the dielectric used in the capacitors on basis of which the capacitors are categorized.

Therefore, capacitor can be of following types:

Paper Capacitor

Polyester Capacitor

Mica Capacitor

Ceramic Capacitor

Electrolytic Capacitor

The capacity ranges of these capacitors vary from type to type. Ceramic capacitors have

usually very low capacitance with few pico farad rating. The electrolytic capacitors are

high capacity ones, with capacity up to few thousand micro farads.

The capacitors are also rated for maximum value of voltage which they can withstand.

This maximum operating voltage is decided on basis of the breakdown voltage of the

dielectric used between the plates. Breakdown voltage of a capacitor is the voltage at

which the dielectric used ceases to be a dielectric, and starts conducting. This gives rise

to short circuiting of the plates, and hence, the capacitor. The two types of capacitors

used in our circuit are:

Electrolytic Capacitor:

FIG 2.31 ELECTROLYTIC CAPACITORS

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Disc Capacitor:

FIG 2.32 DISC CAPACITORS

2.14 RESISTORS:

A resistor is a passive component. It introduces resistance i.e. opposition to the flow of

current in a circuit. Resistors are used in electronic circuits for setting biases, voltage

division, controlling gain, fixing time constants, matching and loading circuits, heat

generation and related applications.

Resistance is basic property of the conducting material as given

Where R is resistance

L is length of conductor

A is area of cross-section of the conductor

is specific resistivity of the material

Thus, resistance depends upon physical dimensions of the resistor and resistivity of theconducting material used.

Many applications of the resistors require fixed resistance, while sometimes, variable

resistance is required which can be varied according to need. Depending on these, two types

of resistors are available.

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Fixed resistors

Variable resistors

Fixed resistors are those, for which the value of resistance is fixed, i.e., it can not be

varied except the change creeping in due to age or environmental factors. Carbon

composition resistors and wire- wound resistors are examples of fixed resistors.

Variable resistors, on the other hand are those resistors, value of which can be varied by

physically moving some control or supplying external energy. Presets and potentiometers

are the examples of physically variable resistors.

The color coding diagram of resistor is as follows:

FIG 2.33 COLOUR CODING SCHEME OF RESISTORS

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2.15 PULSE GENERATOR:

The 555 timer is one of the most remarkable integrated circuits ever developed. It comes

in a single or dual package and even low power cmos versions exist - ICM7555.

Common part numbers are LM555, NE555, LM556, NE556. The 555 timer consists of

two voltage comparators, a bi-stable flip flop, a discharge transistor, and a resistor divider

network.

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FIG 2.34 CIRCUIT DIAGRAM OF PULSE GENERATOR

2.16 OPTOCOUPLERS:

The Optocoupler is used in electronics, an opto-isolator (or optical isolator, optical

coupling device, Optocoupler, photo coupler, or photoMOS) is a device that uses a short

optical transmission path to transfer an electronic signal between elements of a circuit,

typically a transmitterand a receiver, while keeping them electrically isolatedsince the

electrical signal is converted to a light beam, transferred, then converted back to an

electrical signal, there is no need for electrical connection between the source and

destination circuits.

2.16.1 APPLICATIONS:

Power supply regulators

Digital logic inputs

Microprocessor inputs

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2.17 TRANSISTOR:

In electronics, a transistor is a semiconductor device commonly used to amplify or switch

electronic signals. A transistor is made of a solid piece of a semiconductormaterial, with

at least three terminals for connection to an external circuit. A voltage or current applied

to one pair of the transistor's terminals changes the current flowing through another pair

of terminals. Because the controlled (output) power can be much larger than the

controlling (input) power, the transistor provides amplification of a signal. The transistor

is the fundamental building block of modern electronic devices, and is used in radio,

telephone, computer and other electronic systems. Some transistors are packaged

individually but most are found in integrated circuits.

FIG 2.35 ASSORTED DISCRETE TRANSISTORS

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2.17.1 TYPES:

Transistors are categorized by:

1. Semiconductor material : germanium, silicon, gallium arsenide, silicon carbide, etc.

2. Structure: BJT, JFET, IGFET (MOSFET), IGBT, "other types"

3. Polarity:NPN, PNP (BJTs); N-channel, P-channel (FETs)

4. Maximum power rating: low, medium, high

5.Maximum operating frequency: low, medium, high, radio frequency (RF),

microwave (The maximum effective frequency of a transistor is denoted by the term fT,

an abbreviation for "frequency of transition". The frequency of transition is the frequency

at which the transistor yields unity gain).

FIG 2.36 VARIOUS TYPES OF TRANSISTORS

PNP P-channel

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NPN N-channel

BJT symbol JFET symbol

6. Application: switch, general purpose, audio, high voltage, super-beta, matched pair

7. Physical packaging: through hole metal, through hole plastic, surface mount, ball grid

array, power modules

8. Amplification factor hfe (transistor beta)

2.18 PCB MANUFACTURING :

Printed circuit board popularly known as PCB provides both physical, structure for

mounting and holding electronic component as well as the electrical interconnection

between components. A PCB consist of non non-conducting substrate upon which a

conductive pattern or circuit is formed. Copper is the most prevalent conductor. Although

nickel, silver UN un-lead and gold may also be used as etch resists or top level metal.

When the electronic component is an electronic assembly, also called a printed circuit

assembly (PCA). This assembly is the basic building block for all large electronic system.

From toys to toaster to telecommunications. The various processes involved in

fabrication of the plate

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2.18.1 CLEANING OF PLATE:

To start with, general purpose copper clad is selected of desired size according to the

circuit layout. The plate is then washed with suitable solvent so as to remove any oxide

grease or dirt.

2.18.2 PCB LAYOUT:

A circuit is made considering following factor in mind:-

1. Position of component (properly spaced)

2. Inductive loop should be avoided.

3. The grounding system should be separated into grounds conductors.

4. Undesirable coupling should be avoided.

5. Power supply tracks should be of adequate width to withstand a possible shot

circuit system.

6. Use of jumper should be minimum or avoided as far as possible.

7. It should be easy to connect to board to test equipment.

Considering these factors a layout is made. A mirror image of pattern is prepared and

carbon copied onto the copper clad laminate with the help of sharp pencil or ball pointed

pen and position of holes must be marked carefully. Then with fine brush and enamel

mark trace as copied earlier. Then board is dried for at least four to six hours before

developing.

2.18.3 DEVELOPING OF PCB (ETCHING):

In this all excessive copper is removed from the copper clad laminate, and only pattern is

left behind developing is done in a solution of heated tap water and ferric chloride. To

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100ml tap water around 30 to 40 gms of ferric chloride is added. A few drops of HCL

may be added to speed up the process. The board with the copper side facing upward

should be placed in a flat-bottomed plastic tray and the aqueous solution of ferric chloride

poured. The etching process would take 40 to 60 minutes to complete depending upon the

size of the PCB. Then board is washed under the running water and dried. The printed

pattern should be clearly visible otherwise allow it to stand in the solution for some more

time. The paint should be removed with the help of alcohol or period.

2.18.4 DRILLING:

For drilling the plate one can use high tensile steel bit of diameter 1 mm and following

points should be kept in mind:-

FOR ICS;-

1. Always use IC bases, as direct soldering of IC may damage them.

2. The drilling of holes is in such manner so as to correspond to IC bases exact that

no faces any problem in measuring the pins of the bases.

2.18.5 FOR OTHER COMPONENTS:-

1. The holes are exactly placed so that component fix exactly in the holes without

any bending or stretching of leads of component.

2. For drilling of holes for fixing PCB in chassis always ensure that no copper

line passes near the holes.

2.18.6 MOUNTING OF COMPONENTS:

All the components are according to the component assembly diagram are mounted in the

appropriate holes.

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2.19.1 DESOLDERING & RESOLDERING:

Due to the dissolution of the base metals into the solder, solder should never be reused.

Once the solders capacity to dissolve base metal has been achieved, the solder will not

properly bond with the base metal and a cold solder joint with a hard and brittle

crystalline appearance will usually be the t\result. It is in good practice to remove solder

from a joint prior to resoldering desoldering wicks or vacuum desoldering equipment

can be used. Desoldeing wicks contain plenty of flux that will lift the contamination from

the copper trace and any device leads that are present. This will leave a bright, shiny,

clean joint to be resoldered. The lower melting point of solder means it can be melted

away from the base metal, leaving it mostly intact though the outer layer will be tinned

with solder. Flux will remain which can easily be removed by abrasive or chemical

processes. This tinned layer will allow solder to flow into a new joint, as well as making

the solder flow very quickly and easily.

2.19.2 SOLDERING TOOLS:

Hand-soldering tools include the electric soldering iron, which has a variety of tips

available ranging from blunt to very fine to chisel heads for hot-cutting plastics, andthe soldering gun, which typically provides more power, giving faster heat-up and

allowing larger parts to be soldered. Hot-air guns and pencils allow reworkof component

packages which cannot easily be performed with irons and guns.

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FIG 2.37 SOLDERING IRON

Soldering torches are a type of soldering device that uses a flame rather than a soldering

iron tip to heat solder. Soldering torches are often powered by butane [10] and are available

in sizes ranging from very small butane/oxygen units suitable for very fine but high-

temperature jewelry work, to full-size oxy-fuel torches suitable for much larger work

such as copper piping.

Common multipurpose propane torches, the same kind used for heat-stripping paint and

thawing pipes, can be used for soldering pipes and other fairly large objects (but not

electronics,) either with or without a soldering tip attachment; pipes are generally

soldered with a torch by directly applying the open flame.

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A soldering copper is a tool with a large copper head and a long handle which is heated in

a blacksmith's forge fire and used to apply heat to sheet metal for soldering. Typical

soldering coppers have heads weighing between one and four pounds. The head provides

a thermal mass, which can store enough heat for soldering large areas between re-heating

the copper in the fire.

FIG 2.38 SOLDERING TOOLS

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