LASER BASED COMMUNICATION LINKA MAJOR PROJECT REPORT

SUBMITTED TO

RAJIV GANDHI PROUDYOGIKI VISHWAVIDYALAYA, BHOPAL

(M.P.)

SUBMITTED BY

SAURABH KOLHE 0206EC071095VATSAL TRIPATHI 0206EC071113VIPIN PATEL 0206EC071115VIRENDRA PATEL 006EC071117VIVEK BHARDWAJ 0206EC071118VIVEK NANDANWAR 0206EC071120

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

ELECTRONICS & COMMUNICATION ENGINEERING

GYAN GANGA INSTITUTE OF TECHNOLOGY & SCIENCES

UNIVERSITY

RAJIV GANDHI PROUDYOGIKI VISHWAVIDYALAYA

MAY 2011

LASER BASED COMMUNICATION LINKA MAJOR PROJECT REPORT

SUBMITTED BY

SAURABH KOLHE 0206EC071095VATSAL TRIPATHI 0206EC071113VIPIN PATEL 0206EC071115VIRENDRA PATEL 006EC071117VIVEK BHARDWAJ 0206EC071118VIVEK NANDANWAR 0206EC071120

Under the Guidance of

MS. BRAJLATA CHOURASIYA

MS. NAMRATA RAPARTIWAR

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

ELECTRONICS & COMMUNICATION ENGINEERING

GYAN GANGA INSTITUTE OF TECHNOLOGY & SCIENCES

UNIVERSITY

RAJIV GANDHI PROUDYOGIKI VISHWAVIDYALAYA

MAY 2011

GYAN GANGA INSTITUTE OF TECHNOLOGY & SCIENCES

BONAFIDE CERTIFICATE

This is to certify that the major project report LASER BASED

COMMUNICATION LINK Submitted by Saurabh Kolhe, Vatsal Tripathi,

Vipin Patel, Virendra Patel, Vivek Bharadwaj and Vivek Nandanwar has been

carried out under my guidance & supervision. The project report is approved for

submission towards partial fulfillment of the requirement for the award of

degree of BACHELOR OF ENGINEERING in ELECTRONICS

&COMMUNICATION ENGINEERING from RAJIV GANDHI

PROUDYOGIKI VISHWAVIDYALAYA, BHOPAL (M.P.)

Signature of Guide Signature of HOD (EC)Ms Brajlata Chourasiya Prof Vinod Kapse

Ms Namrata Rapartiwar

GYAN GANGA INSTITUTE OF TECHNOLOGY & SCIENCES

CERTIFICATE

This is to certify that the major project report LASER BASED

COMMUNICATION LINK Submitted by Saurabh Kolhe, Vatsal Tripathi,

Vipin Patel, Virendra Patel, Vivek Bharadwaj and Vivek Nandanwar has been

carried out under my guidance & supervision. The project report is approved for

submission towards partial fulfillment of the requirement for the award of

degree of BACHELOR OF ENGINEERING in ELECTRONICS

&COMMUNICATION ENGINEERING from RAJIV GANDHI

PROUDYOGIKI VISHWAVIDYALAYA, BHOPAL (M.P.)

Internal Examiner External Examiner

DECLARATION

We hereby declare that the project entitled “LASER BASED COMMUNICATION LINK ‘’ Which is being submitted in partial fulfillment of the requirement for award of the Degree of bachelor of engineering in ELECTRONICS &COMMUNICATION and end Engineering to “ RAJIV GANDHI PROUDYOGIKI VISHWAVIDYALAYA, BHOPAL (M.P.)’’ is an authentic record of our own work done under the guidance of Ms Brajlata Chourasiya & Ms Namrata Rapartiwar, department of electronics & communication &Engineering , GYAN GANGA INSTITUTE OF TECHNOLOGY &SCIENCES , JABALPUR…….

The matter reported in this project has not been submitted earlier for the award of any other degree.

Dated

PlaceSAURABH KOLHE

VATSAL TRIPATHI

VIPIN PATEL

VIRENDRA PATEL

VIVEK BHARDWAJ

VIVEK NANDANWAR

ACKNOWLEDGEMENT

We sincerely express indebtedness to esteemed and revered guide “Ms Brajlata Chourasiya & Ms Namrata Rapartiwar ‘’, Lecturer in Department name for his invaluable guidance.

We take this opportunity to express deep sense of gratitude to our HOD (EC) “Prof Vinod Kapse‘’, Electronics and communication’’ for his encouragement and kind approval.

We are also thankful to our project Co-ordinator “Mr. S.N. Jarholiya”, for his sincere supervision and encouragement.

We are also thank him in providing the computer lab facility .we would like to express our sincere regards to him for advice and counseling from time to time.

We owe sincere thanks to all the faculties in ‘’ Electronics and communication ‘’ for their advice and counseling time to time.

DATED:

Place:

ABSTRACT

Laser as a communication medium can provide a good substitute for the present day

communication systems as the problem of interference faced in case of electromagnetic

waves is not there and high deal of secrecy is available. Laser communications offers a viable

alternative to RF communications for inter satellite links and other applications where high

performance links are a necessity. High data rate, small antenna size, narrow beam

divergence, and a narrow field of view are characteristics of laser communications that offer

a number of potential advantages for system design.

The purpose of the project is to determine the feasibility of replacing microwave

communications with laser communications to remote locations. This link is unreliable and

can be disrupted in fog or rain. The current system has a slow data rate of 1.54 Mbps,

equivalent to using a dial up modem on any individual computer. When this link goes down,

all communications to and from the stationare lost, leaving the station unable to carry out its

missions. The system proposed to solve this problem utilizes a long cavity laser operating at

1550 nm. The system will also use redundancies as well as spatial diversity of seven lasers to

achieve reliability and high data rates averaging 2.4 Gbps. The transmitter and receiver will

be set up on gimbals connected to a control system that ensures alignment based off a pulse

train on the receiver plate. This pulse train also ensures that the signal is penetrating the

atmosphere over the 8 mile distance. A comparison between the microwave and laser

communications was completed and future work includes implementing a proposed three

phase test plan.

A basic communication system is made up of three main parts being the

transmitter, the medium over which the message is being sent, and the receiver. A good

example of this is two people communicating from one side of a room to the other. If the

person wants to communicate with the other person, he/she speaks words towards the

direction of the other individual who receives the voice information and determines the

message. This example is much like how any general communication system works. First, the

message is determined that needs to be sent to the receiving end. The message is then sent to

the transmitter. The transmitter, much like the person’s mouth, is sending the signal

containing the message from one person to the other. This can be compared to using an

antenna to send out a signal. The signal then must travel through some type of medium to

reach the receiver. For the two people talking, this medium would be air. But, sometimes this

medium is some type of cable or wire. The signal is then collected by the receiver, which is

comparable to the person on the receiving end hearing the sound of the person’s voice.

Sometimes the signal can be immediately understood, but other times the signal must first be

decoded in order to understand the message.

LIST OF TABLE

1 PIN SPECIFICATION OF 555 TIMER 17

2 PIN SPECIFICATION OF LM 3869 IC 20

3 PIN SPECIFICATION OF CD4033 IC 22

4 PIN SPECIFICATION OF NE567 IC 25

5 COLOUR CODING TECHNIQUES FOR RESISTORS 36

6 COMPONENT LIST 63

LIST OF SYMBOLS

1 LDR 19

2 LOW VOLTAGE AUDIO AMPLIFIER

20

3 SCHEMATIC SYMBOL FOR PNP AND NPN TYPE BJTs

45

4 THE SYMBOL OF AN NPN

BIPOLAR

JUNCTIONTRANSISTOR

49

5 THE SYMBOL OF A NPN

BIPOLARTRANSISTOR

50

6 A ZENER DIODE 52

TABLE OF CONTENTS

BONAFIDE CERTIFICATE i

CANDIDATE’S DECLARATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

LIST OF TABLE v

LIST OF SYMBOLS vi

1. INTRODUCTION 1

1.1 BLOCK DIAGRAM

EXPLANATION

2

1.1.1 CONDENSOR MICROPHONE 2

1.1.2 TRANSMITTING SECTION 2

1.1.3 LASER TORCH 2

1.1.4 RECEIVING SECTION 3

1.1.5 LOUDSPEAKER 3

2 LITERATURE RIVIEW 4

2.1 OPTICAL & MICROWAVE

COMMUNICATION SYSTEM

CONCEPTUAL DESIGN FOR A

REALISTIC INTERSTELLAR

EXPLORER

4

2.2 OPTICAL COMMUNICATION

SYSTEMS FOR SMART DUST

5

2.3 TOWARD A WIRELESS OPTICAL

COMMUNICATION LINK

BETWEENTWO SMALL

6

UNMANNED AERIAL VEHICLES

2.4 FREE SPACE OPTICAL

COMMUNICATION LINK

7

3 METHODOLOGY 8

3.1 SYSTEM DESCRIPTION 8

3.2 THE TRANSMITTER CIRCUIT 9

3.3 THE RECIEVER CIRCUIT 11

4 DEVICES & TOOLS 14

4.1 LASER 14

4.2 555 TIMER 16

4.3 MICROPHONE 17

4.4 LIGHT DEPENDENT RESISTOR 18

4.5 LOW VOLTAGE AUDIO

AMPLIFIER IC LM386

19

4.6 DECADE COUNTER IC CD4033 20

4.7 SEVEN SEGMENT DISPLAY 22

4.8 PHASE LOCKED LOOP NE567 24

4.9 MELODY GENERATOR IC UM66 25

4.10 LINEAR REGULATOR 26

4.11 RESISTORS 30

4.12 VARIABLE RESISTORS 38

4.13 CAPACITOR 40

4.14 TRANSISTOR 45

4.15 ZENER DIODE 51

5 DESIGN & IMPLEMENTATION 53

5.1 PCB MANUFACTURING

PROCESS

53

5.2 BOARD TYPES 53

5.3 DESIGN SPECIFICATION 54

5.3.1 STEPS TAKEN WHILE

PREPARING CIRCUIT

54

5.3.1.1 PCB DESIGNING 54

5.3.1.2 LAYOUT DESIGN 54

5.3.1.2.1 ETCHING PROCESS 55

5.3.1.2.2 COMPONENT ASSEMBLY 56

5.3.1.2.3 SOLDERING 57

6 RESULT 58

7 CONCLUSION & FUTURE SCOPE 59

7.1 CONCLUSION 59

7.2 FUTURE SCOPES 59

8 REFERENCES 60

9 APPENDIX 61

9.1 PCB LAYOUT 61

9.2 COMPONENT LAYOUT 62

9.3 COMPONENT LIST 63

9.4 DATASHEETS 65

9.4.1 CD4033BMS 65

9.4.2 LM 7806 68

9.4.3 LM386 70

9.4.4 NE 567 74

9.4.5 NE555 TIMER 77

CHAPTER 1

INTRODUCTION

Laser as a communication medium can provide a good substitute for the present day

communication systems as the problem of interference faced in case of electromagnetic

waves is not there and high deal of secrecy is available. Laser communications offers a viable

alternative to RF communications for inter satellite links and other applications where high-

performance links are a necessity. High data rate, small antenna size, narrow beam

divergence, and a narrow field of view are characteristics of laser communications that offer

a number of potential advantages for system design. The present paper involves the study of

wireless, open channel communication system using laser a carrier for voice signals. Using

this circuit we can communicate with your own neighbors wirelessly. Instead of RF signals,

light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light

up to a distance of about 500 meters. The phototransistor of the receiver must be accurately

oriented towards the laser beam from the torch. If there is any obstruction in the path of laser

beam, no sounds will be heard from the receiver.

1.1BLOCK DIAGRAM EXPLANATION

1.1.1CONDENSER MICROPHONE

It is also called a capacitor or electrostatic microphone. Condenser means capacitor, which

stores energy in the form of an electric field. Condenser microphones require power from a

battery or external source. Condenser also tends to be more sensitive and responsive than

dynamic, making them well suited to capturing subtle nuances in a sound. The diaphragm

vibrates when struck by sound waves, changing the distance between the two plates and

therefore changing the capacitance. Specifically when the plates are closer together

capacitance increases and a charge current occurs and this current will be used to trigger the

transmitting section.

1.1.2 TRANSMITTING SECTION

The transmitter section comprises condenser microphone. In transmitter the frequency is generated

which is used to match the frequency in the phase locked loop used in the receiver section. A switch S

is used to generate a tone which is transmitted by the transmitter to the receiver section so that

receiver can generate a tone so that the user near the receiver can know that any one at the

transmitting end wants to talks to him. The condenser mic used in the transmitter section is used to

convert the acoustic signals to the electrical signals which are modulated and send through a laser

beam used in the transmitter section.

1.1.3 LASER TORCH

Here we use the light rays coming from laser torch as the medium for transmission. Laser had

potential for the transfer of data at extremely high rates, specific advancements were needed in

component performance and systems engineering, particularly for space-qualified hardware. Free

space laser communications systems are wireless connections through the atmosphere. They work

similar to fiber optic cable systems except the beam is transmitted through open space. The laser

systems operate in the near infrared region of the spectrum. The laser light across the link is at a

wavelength of between 780 - 920 nm. Two parallel beams are used, one for transmission and one for

reception.

1.1.4 RECEIVING SECTION

The receiver circuit uses an NPN phototransistor as the light sensor that is followed by a two

stage transistor preamplifier and LM386-based audio power amplifier. The receiver doesn't

need any complicated alignment. Just keep the phototransistor oriented towards the remote

transmitter's laser point and adjust the volume control for a clear sound.

1.1.5 LOUD SPEAKER

A loudspeaker (or "speaker") is an electro acoustic transducer that converts an electrical

signal into sound. The speaker moves in accordance with the variations of an electrical signal

and causes sound waves to propagate through a medium such as air or water.

CHAPTER 2

LITERATURE REVIEW

2.1 Optical and microwave communications system conceptual design for a realistic

interstellar explorer

B.G. Boone, R.S. Bokulic, G.B. Andrews, R.L. McNutt, Jr and N. Dagalakisb

ABSTRACT

The concept of a realistic interstellar explorer has been addressed by the Johns Hopkins

University Applied Physics Laboratory (JHU/APL) with support from the NASA Institute for

Advanced Concepts (NIAC). This paper discusses the requirements, conceptual design and

technology issues associated with the optical and RF communications systems envisioned for

this mission, in which the spacecraft has a projected range of 1000 AU. Well before a range

of 100 AU interactive control of the spacecraft becomes nearly impossible, necessitating a

highly autonomous craft and one-way communications to Earth. An approach is taken in

which the role of the optical downlink is emphasized for data transfer and that of the

microwave uplink emphasized for commands. The communication system is strongly

influenced by the large distances involved, the high velocities (20 AU/year or ~ 95 km/s) as

well as the requirements for low-mass (~ 10 kg), low prime power (~ 15 W), reliability, and

spacecraft autonomy. An optical terminal concept is described that has low mass and prime

power in a highly integrated and novel architecture, but new technologies are needed to meet

the range, mass, and power requirements. These include high-power, “wall-plug” efficient

diode-pumped fiber lasers; compact, lightweight, and low-power micro-electromechanical

(MEM) beam steering elements; and lightweight diffractive quasi-membrane optics. In

addition, a very accurate star tracking mechanism must be fully integrated with the laser

downlink to achieve unprecedented pointing accuracy (~ 400 nrad RMS). The essential

optical, structural, mechanical, and electronic subsystems are described that meet the mission

requirements, and the key features of advanced technologies that need to be developed are

discussed. The conclusion from this preliminary effort is that an optical communications

downlink out to 1000 astronomical units (AU) is within the realm of technical feasibility in

the next 5-10 years if the identified technical risks for the new technologies can be retired.

2.2. Optical Communication Systems for Smart Dust

Yunbin Song

ABSTRACT

In this thesis, the optical communication systems for millimeter-scale sensing and communication

devises known as “Smart Dust” are described and analyzed. A smart dust element is a self-

contained sensing and communication system that can be combined into roughly a cubic-

millimeter mote to perform integrated, massively distributed sensor networks. The suitable

passive optical and fiber-optic communication systems will be selected for the further

performance design and analysis based on the requirements for implementing these systems.

Based on the communication link designs of the free-space passive optical and fiber-optic

communication systems, the simulations for link performance will be performed.

2.3 Toward a Wireless Optical Communication Link between Two Small Unmanned Aerial VehiclesM. Last, B.S. Leibowitz, B. Cagdaser, A. Jog, L. Zhou, B. Boser, K.S.J. Pister

ABSTRACT

A communication system between two autonomous micro air vehicles is proposed. Laser

communication offers advantages in range, power, and bandwidth when line of sight is

available. Beam steering is accomplished using gyro-stabilized MEMS micro mirrors. A

custom CMOS smart-pixel imager implements a 1Mbps receiver, including analog front-end

and variable-gain amplifier at each pixel. Algorithms are presented for initial link

establishment and maintenance.

2.4 Free Space Optical Laser Communication Link

Andrew W. Rebeiro and Rodney Tan

ABSTRACT

A Free Space Optical (FSO) LASER Communication Link is presented. This project deals

with the development of a full-duplex FSO analogue / digital transceiver. In this information

age, the demand for high speed, high bandwidth communications channel, is ever increasing.

FSO is presented as a solution to these demands in that it is free to implement, easy to install

and of very high bandwidth. The reader is introduced to the FSO system of communication

and the development of a small scale communicator using laser as the carrier signal for

information transfer. Experimental results explain the performance of the completed system

and offer methods of maximizing efficiency of such FSO-based communication systems.

CHAPTER 3METHODOLOGY

3.1 SYSTEM DESCRIPTION

Fig shows the block diagram of laser based system for one way speech communication. It

comprises transmitter receiver and a common DC power supply section. The power supply

section at one end of the link provides regulated 6V to the receiver transmitter circuit. For

two way communication, you need to use an identical system with the positions of the

receiver and the transmitter reversed with this system.

In the transmitter the intensity of the laser beam is modulated by the output of an always on

code oscillator (operating at 10-15 kHz).Using a push to on switch the tone

oscillator(operating at 1-2khz) is momomentarily activated to alert the person at the receiver

end before starting a voice communication using the microphone.

The receiver receives the intensity modulated light signals through a light sensor and outputs

the code and 1 kHz tone/voice.

The circuit for detecting the code signals is built around a phase locked loop(PLL-1 ).The

absence of code signal indicates interception of the laser beam and activates an audio visual

warning at the remote receiver. For detecting the 1kHz call/tone signal, another phase locked

loop (PLL-2)is used. The call detection is indicated by a buzzer sound and an LED.

3.2 THE TRANSMITTER CIRCUIT

The transmitter circuit consists of a code oscillator, condenser microphone and an AF mixer

stage.

The code oscillator comprising IC NE555 (IC2) is wired as an astable multivibrator operating

at 10-15 kHz frequency. The actual oscillation frequency is decided by the timing

components including resistors R2 and R3, preset VR1and capacitor C4.We can adjust VR1

to vary the oscillation frequency to match with the centre frequency to match with the center

frequency of PLL-1 at the remote receiver end. The output of IC is fed to the base of the

mixer transistor T1 via diode D1 and level control pot meter VR3 and resistor R6.

Similarly, the tone/call oscillator comprising IC NE555 (IC3) is wired as an astable

multivibrator to provide a 1-2 kHz tone when tactile switch S1 is depressed. We can adjust

VR2 to change the tone frequency to match with the center frequency of PLL-2 at the remote

receiver end. Resistor R10 is used to pull reset pin 4 of IC3low when switch S1 is open.

The output of IC3 is also coupled to the base of the mixer transistor via capacitor C7,

resistor R7, preset VR4 and capacitor C9.Preset VR 4 is connected across the condenser

microphone to adjust the audio signals when someone speaks into the microphone. Preset

VR4 is used to vary the biasing signals.

The outputs of IC2 and IC3 and voice signals are mixed by transistor T1 to drive the laser

pointer LED. The mixer output modulates the intensity of light signals emitted by the laser

diode module in accordance with the level of the code oscillator and tone and audio signals

available at the bade of the mixer transistor.

Laser:

The laser diodes can be constructed using a variety of different materials to produce

distinctive wavelengths. Semiconductor laser diodes produce a much higher output power

and highly directional beams compared to the LEDs. The laser must be operated with a large

drive current to get a high density of ready to combine electrons at the pn junction. The

transmitter circuit shows the output power vs. forward current characteristics of a laser diode.

We can divide it into spontaneous emission A and laser oscillation region B. The current

required for starting oscillations is called threshold current (Ith)while the forward (excitation)

current necessary for maintaining the diodes specified optical output is called its operating

current(Iop)

For the 5mW laser shown in the transmitter circuit the typical values of threshold and

operating currents are 30mA and 45 mA, respectively. Keychain laser pointers available in

the market have a power output of 5mW with forward current limited to 20 to 5mA.Thus a

laser diode module of keychain type visible laser pointer may be used for this transmitter

circuit.

3.3 THE RECIEVER CIRCUIT

The receiver consists of a light sensor, a signal preamplifier, audio amplifier code detector

(with audio/visual alarm) and call/tone detector with buzzer indication. It uses a light

dependent resistor (LDR) as the light sensor. The resistance of LDR varies depending on the

incident light intensity, which in turn is a function of its modulation by the mixed output of

code and tone or audio signals at the transmitter mixer stage. The output of the LDR sensor is

amplified by a two stage transistor preamplifier.

The preamplifier output is coupled via following capacitor into:

1. The audio power amplifier built around IC LM386

2. Phase locked loop (PLL-1) IC5.

3. Phase locked loop (PLL-2) IC6.

The preamplifier output is fed into input pin 3 of audio power amplifier LM386 (IC4)

through volume control potmeter VR7.Capacitor C28 bypasses the noise signal and higher

order frequencies representing the code signal. The audio output (comprising voice and tone

channels) from pin 5 of IC4 is coupled to loudspeaker LS1 through capacitor C30.

A snubber network comprising capacitors and resistors is used for output stability.IC LM386

is a low voltage audio amplifier. Its gain is internally set to 20 to keep external part count

low.

The preamplifier output, as stated earlier, is also connected to phase locked loopIC5 and

IC6.(each NE567) through capacitors C25 and C26,respectively.IC NE567 is a highly stable

phase locked loop with synchronous AM lock detection and power output circuitary.It is

primarily used as a frequency decoder, which drives load whenever a sustained frequency

falling within its its detection band is present with its self biased input. The center frequency

of the band and output delay is independently determined by external components.

LINK CONTINUITY AND DISCONTUINITY INDICATION:

IC5 is used to detect the 10-15 kHzsignal.In the absence of any input signal, the center

frequency of its internal free running, current controlled oscillator is determined by resistor

R19 and capacitor C9.Preset VR5 is used for tuning IC5 to the desired center frequency in the

10-15kHz range, which should match the frequency of the code generator in the transmitter.

The output at pin 8 of IC5 remains low as long as the transmitted code is detected by IC5.As

a result, LED1 lights up to indicate continuity of the optical link/path for communications.

When the laser beam is interrupted due to any reason, the output at pin 8 of IC5 goes high

to drive transistor T4 and its collector voltage falls to trigger monostable circuits built around

IC7 and IC9(each NE555),respectively. As a result, the output at pin 3 of these ICs goes high

for the predetermined time period. The time periods of timers IC7 and IC8 depends on the

values of resistor capacitor combinations R26-31 and R25-C34,respectively.Since output pin

3 of IC7 is connected to pin1 of decade counterCD4033 (IC9),it provides a clock pulse to

counter IC9 to increment its count, indicating interruption of the laser light beam. The current

count is shown on a 7 segment display (D1S1) connected to a 7 segment decoded outputs of

counter IC9.Resistor R30 is used as a current limiting resistor in the common cathode path of

D1S1.

For frequent interruptions of light beam, the output of decade counter IC9 keeps

incrementing the count. After the count reaches 9 the next interruption resets the counter and

it starts a fresh .The counter/display can also be reset manually by momentarily depressing

press to on switch S2.

As stated earlier, IC7 and IC8 are triggered simultaneously. Thus with each interruption of

the light beam, the output of IC8 is pulsed high for a predetermined time to provide around

3V(determined by the output of zener diode ZD1) to melody IC UM66(IC10).Thus IC10

generates a melodious tune whenever the light beam is interrupted. The output of IC10 is

amplified by transistor T5 to drive loudspeaker LS2.

For initiating a call, the person at the transmitter end depresses switch S1 to alert the

remote end person of an impending voice communication. Thus the modulated light output

from the transmitter contains 1-2 kHz tone component in addition to the 10-15 kHz code

oscillator output. After detection and preamplification,1-2khz tone is decoded by PLL-2

circuit build around IC6,whose center frequency is adjusted to match the frequency of

tone/call oscillator in the transmitter.

IC6 is thus used as the call detector.Reisitor R20 and capacitor C22 decide the center

frequency of its inbuilt oscillator in the absence of an input signal. Capacitors C23 and C24

serve as low pass filter and output filters respectively. Preset VR6 is used for tuning the

inbuilt oscillator.

Thus when the 1-2khz tone component is detected by IC6,its output pin 8 goes low to light

up LED3 as also sound piezobuzzer PZ1 to alert the receiver end person. Since the 1-2khz

tone component at the output of the preamplifier also passed through LM386 power

amplifier, the tone is heard from loudspeaker LS-1 as well.

VOICE COMMUNICATION:

For voice communication, the person at the transmitter end speaks into the mic while call

switch S1 is open. The modulated light beam contains the 10-15 kHz code frequency and

voice components. After demodulation at the receiver, the 10-15 kHz code frequency and

voice components. After demodulation at the receiver, the 10-15 kHz code component is

largely bypassed by capacitor C28 at the input of LM386, while the voice component (up to

3400Hz) is attenuated insignificantly. Thus speech is reproduced at the output of LM386 via

loud speaker LS1.The code component (10-15 kHz) is detected by PLL IC5 signifying

uninterrupted light path which is indicated by LED2 as explained earlier.

CHAPTER 4

DEVICES & TOOLS

4.1LASERLASER is also known as Light Amplification by Stimulated Emission of Radiation. A laser is

a device that emits light (electromagnetic radiation) through a process of optical amplification

based on the stimulated emission of photons. Light emitters are a key element in any fiber

optic system. This component converts the electrical signal into a corresponding light signal

that can be injected into the fiber. The light emitter is an important element because it is often

the most costly element in the system, and its characteristics often strongly influence the final

performance limits of a given link. Laser Diodes are complex semiconductors that convert an

electrical current into light. The conversion process is fairly efficient in that it generates little

heat compared to incandescent lights. Five inherent properties make lasers attractive for use

in fiber optics.

Type

Gas lasers

Chemical lasers

Excimer lasers

Solid-state lasers

Fiber lasers

Photonic crystal lasers

Semiconductor lasers

Dye lasers

Free electron lasers

Exotic laser

WORKING OF A LASER:

A LASER works on the principle of spontaneous emission. Spontaneous emission is the

process by which a light source such as an atom, molecule, nanocrystal or nucleus in an

excited state undergoes a transition to a state with a lower energy, e.g., the ground state and

emits a photon. Spontaneous emission of light or luminescence is a fundamental process that

plays an essential role in many phenomena in nature and forms the basis of many

applications, such as fluorescent tubes, older television screens (cathode ray tubes), plasma

display panels, lasers (for startup - normal continuous operation works by stimulated

emission instead) and light emitting diodes

Emission of a photon in a laser

4.2 555 TIMER

The 555 Timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation

and oscillator applications. Depending on the manufacturer, the standard 555 package

includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin

mini dual-in-line package. The 555 has three operating modes.

Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator.

Applications include timers, missing pulse detection, bouncefree switches, touch

switches, frequency divider, capacitance measurement, pulse-width modulation

(PWM) and so on.

Astable - free running mode: the 555 can operate as an oscillator. Uses include LED

and lamp flashers, pulse generation, logic clocks, tone generation, security alarms,

pulse position modulation and so on.

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is

not connected and no capacitor is used. Uses include bounce free latched switches.

555 TIMER

Pin Specification of 555 TimerPin No Signal Name

1 GND

2 Trigger

3 Output

4 Reset

5 Control Voltage

6 Threshold

7 Discharge

8 Vcc

4.3 MICROPHONE

Sound is an amazing thing. All of the different sounds that we hear are caused by minute

pressure differences in the air around us. What's amazing about it is that the air transmits

those pressure changes so well, and so accurately, over relatively long distances. It was a

metal diaphragm attached to a needle, and this needle scratched a pattern onto a piece of

metal foil. The pressure differences in the air that occurred when you spoke toward the

diaphragm moved the diaphragm, which moved the needle, which was recorded on the foil.

When you later ran the needle back over the foil, the vibrations scratched on the foil would

then move the diaphragm and recreate the sound. The fact that this purely mechanical system

works shows how much energy the vibrations in the air can have! All modern microphones

are trying to accomplish the same thing as the original, but do it electronically rather than

mechanically. A microphone wants to take varying pressure waves in the air and convert

them into varying electrical signals. There are five different technologies commonly used to

accomplish this conversion. We use condenser mic in our project.

CONDENSER MICROPHONES

A condenser microphone is essentially a capacitor, with one plate of the capacitor moving in

response to soundwaves. A microphone is an acoustic-to-electric transducer or sensor that

onverts sound into an electrical signal. Microphones are used in many applications such as

tape recorders, karaoke systems, hearing aids, motion picture production, live and recorded

audio engineering, FRS radios, megaphones, in radio and television broadcasting and in

computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such

as ultrasonic checking or knock sensors. Most microphones today use electromagnetic

induction (dynamic microphone), capacitance change (condenser microphone), piezoelectric

generation, or light modulation to produce an electrical voltage signal from mechanical

vibration.

4.4 LDR (LIGHT DEPENDENT RESISTOR):

A photo resistor or light dependent resistor (LDR) is a resistor whose resistance decreases

with increasing incident light intensity. It can also be referred to as a photoconductor.A

photoresistor is made of a high resistance semiconductor. If light falling on the device is of

high enough frequency, photons absorbed by the semiconductor give bound electrons enough

energy to jump into the conduction band. The resulting free electron (and its hole partner)

conduct electricity, thereby lowering resistance.A photoelectric device can be either intrinsic

or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient

semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence

band, and hence the photon must have enough energy to excite the electron across the entire

bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state

energy is closer to the conduction band; since the electrons do not have as far to jump, lower

energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the

device. If a sample of silicon has some of its atoms replaced by phosphorus atoms

(impurities), there will be extra electrons available for conduction. This is an example of an

extrinsic semiconductor.

An LDR

4.5 LOW VOLTAGE AUDIO AMPLIFIER IC LM386:

The LM386 is an integrated circuit consisting of a low voltage audio power amplifier. It is

suitable for battery-powered devices such as radios, guitar amplifiers, and hobbyist projects.

The IC consists of an 8 pin dual in-line package (DIP-8) and can output 0.5 watts power

using a 9-volt power supply.

LM 3869 IC

Pin Specification of LM 3869 IC

Pin No Signal Name

1 Gain

2 -Input

3 +Input

4 GND

5 Vout

6 Vs

7 Bypass

8 Gain

4.6 DECADE COUNTER IC CD4033:

CD4033 consists of a 5 stage Johnson decade counter and an output decoder which converts

the Johnson code to a 7 segment decoded output for driving one stage in a numerical display.

This device is particularly advantageous in display applications

where low power dissipation and/or low package count is important. A high RESET signal

clears the decade counter to its zero count. The counter is advanced one count at the positive

clock signal transition if the CLOCK INHIBIT signal is low. Counter advancement via the

clock line is inhibited when the CLOCK INHIBIT signal is high. The CLOCK INHIBIT

signal can be used as a negative-edge clock if the clock line is held high. Antilock gating is

provided on the JOHNSON counter, thus assuring proper counting sequence. The CARRY-

OUT (Cout) signal completes one cycle every ten CLOCK INPUT cycles and is used to clock

the succeeding decade directly in a multi-decade counting chain. The seven decoded outputs

(a, b, c, d, e, f, g) illuminate the proper segments in a seven segment display device used for

representing the decimal numbers 0 to 9. The 7 segment outputs go high on selection.

CD 4033 Diagram

Pin Specification of CD4033 IC

Pin No Signal Name

1 Clock

2 Clock Inhibit

3 Ripple Blanking In

4 Ripple Blanking Out

5 Carry Out

6 F

7 G

8 Vss

9 D

10 A

11 E

12 B

13 C

14 Lamp Test

15 Reset

16 Vdd

4.7 SEVEN SEGMENT DISPLAY

A seven-segment display, or seven-segment indicator, is a form of electronic display device

for displaying decimal numerals that is an alternative to the more complex dot-matrix

displays. Seven-segment displays are widely used in digital clocks, electronic meters, and

other electronic devices for displaying numerical information. A seven-segment display is a

group of light emitting diodes (LEDs)

A SEVEN SEGMENT DISPLAY

Eight of the LEDs may be arranged in the pattern shown below. This is referred to as a seven-

segment display. There are 7 segments in the pattern. The decimal point is ignored in the

naming of the display.

4.8 PHASE LOCKED LOOP NE567:

A phase-locked loop or phase lock loop (PLL) is a control system that tries to generate an

output signal whose phase is related to the phase of the input "reference" signal. It is an

electronic circuit consisting of a variable frequency oscillator and a phase detector. This

circuit compares the phase of the input signal with the phase of the signal derived from its

output oscillator and adjusts the frequency of its oscillator to keep the phases matched. The

signal from the phase detector is used to control the oscillator in a feedback loop.Frequency is

the derivative of phase. Keeping the input and output phase in lock step implies keeping the

input and output frequencies in lock step. Consequently, a phase-locked loop can track an

input frequency, or it can generate a frequency that is a multiple of the input frequency. The

former property is used for demodulation, and the latter property is used for indirect

frequency synthesis.Phase-locked loops are widely used in radio, telecommunications,

computers and other electronic applications. They may generate stable frequencies, recover a

signal from a noisy communication channel, or distribute clock timing pulses in digital logic

designs such as microprocessors. Since a single integrated circuit can provide a complete

phase-locked-loop building block, the technique is widely used in modern electronic devices,

with output frequencies from a fraction of a hertz up to many gigahertz.

A PLL internal diagram

Pin Specification of NE567 IC:

Pin No Signal Name

1 Output Filter

2 LoopFilter

3 Input

4 V+

5 Timing resistor

6 Timing capacitor

7 GND

8 Output

4.9 MELODY GENERATOR IC UM66:

UM66T is a melody integrated circuit. It is designed for use in bells, telephones, toys etc. It

has an inbuilt tone and a beat generator. The tone generator is a programmed divider which

produces certain frequencies. These frequencies are a factor of the oscillator frequency. The

beat generator is also a programmed divider which contains 15 available beats. Four beats of

these can be selected.  There is an inbuilt oscillator circuit that serves as a time base for beat

and tone generator. It has a 62 notes ROM to play music. A set of 4 bits controls the scale

code while 2 bits control the rhythm code. When power is turned on, the melody generator is

reset and melody begins from the first note. The speaker can be driven by an external npn

transistor connected to the output of UM66.

4.10 LINEAR REGULATOR:

linear regulator is a voltage regulator based on an active device (such as a bipolar junction

transistor, field effect transistor or vacuum tube) operating in its "linear region" (in contrast, a

switching regulator is based on a transistor forced to act as an on/off switch) or passive

devices like zener diodes operated in their breakdown region. The regulating device is made

to act like a variable resistor, continuously adjusting a voltage divider network to maintain a

constant output voltage. It is very inefficient compared to a switched-mode power supply,

since it sheds the difference voltage by dissipating heat.

The transistor (or other device) is used as one half of a potential divider to control the output

voltage, and a feedback circuit compares the output voltage to a reference voltage in order to

adjust the input to the transistor, thus keeping the output voltage reasonably constant. This is

inefficient: since the transistor is acting like a resistor, it will waste electrical energy by

converting it to heat. In fact, the power loss due to heating in the transistor is the current

times the voltage dropped across the transistor. The same function can be performed more

efficiently by a switched-mode power supply (SMPS), but it is more complex and the

switching currents in it tend to produce electromagnetic interference. A SMPS can easily

provide more than 30A of current at voltages as low as 3V, while for the same voltage and

current, a linear regulator would be very bulky and heavy.

Linear regulators exist in two basic forms:

Series regulators

Shunt regulators

o The series regulator works by providing a path from the supply voltage to the load

through a variable resistance (the main transistor is in the "top half" of the voltage

divider). The power dissipated by the regulating device is equal to the power supply

output current times the voltage drops in the regulating device.

o The shunt regulator works by providing a path from the supply voltage to ground

through a variable resistance (the main transistor is in the "bottom half" of the voltage

divider). The current through the shunt regulator is diverted away from the load and

flows uselessly to ground, making this form even less efficient than the series

regulator. It is, however, simpler, sometimes consisting of just a voltage-reference

diode, and is used in very low-powered circuits where the wasted current is too small

to be of concern. This form is very common for voltage reference circuits.

LM7806:

Common solid-state series voltage regulators are the LM78xx (for positive voltages) and

LM79xx (for negative voltages), and common fixed voltages are 6 V (for transistor-transistor

logic circuits) and 12 V (for communications circuits and peripheral devices such as disk

drives). In fixed voltage regulators the reference pin is tied to ground, whereas in variable

regulators the reference pin is connected to the centre point of a fixed or variable voltage

divider fed by the regulator's output. A variable voltage divider (such as a potentiometer)

allows the user to adjust the regulated voltage.

Figure: 1

FIXED REGULATORS:

"Fixed" three-terminal linear regulators are commonly available to generate fixed voltages of

plus 3 V, and plus or minus 5 V, 6V, 9 V, 12 V, or 15 V when the load is less than 1.5

amperes.

The "78xx" series (7805, 7812, etc.) regulate positive voltages while the "79xx" series (7905,

7912, etc.) regulate negative voltages. Often, the last two digits of the device number are the

output voltage; e.g., a 7805 is a +5 V regulator, while a 7915 is a -15 V regulator. There are

variants on the 78xx series ICs, such as 78L and 78S, some of which can supply up to 1.5

Amps.

7805 VOLTAGE REGULATOR:

It looks like a transistor but it is actually an integrated circuit with 3 legs.

It can take a higher, crappy DC voltage and turn it into a nice, smooth 5 volts DC.

You need to feed it at least 8 volts and no more than 30 volts to do this.

It can handle around .5 to .75 amps, but it gets hot. Use a heat sink.

Figure

Fixed voltage Positive and Negative regulator ICs are used in circuits to give precise

regulated voltage. 78 XX series regulator IC can handle maximum 1 ampere current. The

Regulator ICs require minimum 1.5 higher input voltages than their voltage rating. For

example 7805 IC requires minimum 6.5 volts to give 5 volt output.

Here are some circuit designs of IC 7805 to monitor the output voltage.

1. This is the manipulation of the Regulator IC 7805 to give 9 volt regulated output.

Normally the pin2 of the regulator IC is connected to the ground. Here it is connected to a

3.9 volt Zener diode. So the output from the Regulator IC will be 9 volts.

Figure : 32. This circuit can tell whether the IC 7805 is giving output or not. IC 7805 requires

minimum 6.5 volt input to give 5 volt regulated output. When the input voltage is above

6.5 volts, Zener conducts and LED turns on indicating sufficient input voltage. Diffuse

type Red LED requires 1.8 volts and Zener 4.7 volts .So to activate both these, input

voltage should be minimum 6.5 volts. If the input voltage drops below 6.5 volts, Zener

cutoff and LED turns off. This indicates the zero output from the regulator IC.

Figure: 4

3. This is a simple LED monitor to tell the output voltage from 7805. If the input voltage is

above 6.5 volts, LED shows full brightness. When the input voltage reduces below 6.5

volts, brightness of LED decreases.

Figure : 5

4.11 RESISTORS:

A resistor is a two-terminal passive electronic component which implements electrical

resistance as a circuit element. When a voltage V is applied across the terminals of a resistor,

a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of

the constant of proportionality is known as the resistance R, since, with a given voltage V, a

larger value of R further "resists" the flow of current I as given by Ohm's law:

Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in most electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such

as nickel-chrome). Resistors are also implemented within integrated circuits, particularly

analog devices, and can also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than 9 orders of magnitude. When specifying

that resistance in an electronic design, the required precision of the resistance may require

attention to the manufacturing tolerance of the chosen resistor, according to its specific

application. The temperature coefficient of the resistance may also be of concern in some

precision applications. Practical resistors are also specified as having a maximum power

rating which must exceed the anticipated power dissipation of that resistor in a particular

circuit: this is mainly of concern in power electronics applications. Resistors with higher

power ratings are physically larger and may require heat sinking. In a high voltage circuit,

attention must sometimes be paid to the rated maximum working voltage of the resistor.

The series inductance of a practical resistor causes its behavior 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.[1] A family of discrete resistors is also characterized according to its form factor,

that is, the size of the device and position of its leads (or terminals) which is relevant in the

practical manufacturing of circuits using them.

UNITS

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm.

An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured

over a very large range of values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilo Ohm

(1 kΩ = 103 Ω), and mega Ohm (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.

THEORY OF OPREATION:

Ohm's law

The behavior of an ideal resistor is dictated by the relationship specified in Ohm's law:

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I)

passing through it, where the constant of proportionality is the resistance (R).

Equivalently, Ohm's law can be stated:

This formulation of Ohm's law states that, when a voltage (V) is present across a resistance

(R), a current (I) will flow through the resistance. This is directly used in practical

computations. For example, if a 300 ohm resistor is attached across the terminals of a 12 volt

battery, then a current of 12 / 300 = 0.04 amperes (or 40 mill amperes) will flow through that

resistor.

Series and parallel resistors

In a series configuration, the current through all of the resistors is the same, but the voltage

across each resistor will be in proportion to its resistance. The potential difference (voltage)

seen across the network is the sum of those voltages, thus the total resistance can be found as

the sum of those resistances:

As a special case, the resistance of N resistors connected in series, each of the same resistance

R is given by NR.

Resistors in a parallel configuration are each subject to the same potential difference

(voltage), however the currents through them add. The conductance of the resistors then adds

to determine the conductance of the network. Thus the equivalent resistance (Req) of the

network can be computed:

The parallel equivalent resistance can be represented in equations by two vertical lines "||" (as

in geometry) as a simplified notation. For the case of two resistors in parallel, this can be

calculated using:

As a special case, the resistance of N resistors connected in parallel, each of the same

resistance R, is given by R/N.

A resistor network that is a combination of parallel and series connections can be broken up

into smaller parts that are either one or the other. For instance,

However, some complex networks of resistors cannot be resolved in this manner, requiring

more sophisticated circuit analysis. For instance, consider a cube, each edge of which has

been replaced by a resistor. What then is the resistance that would be measured between two

opposite vertices? In the case of 12 equivalent resistors, it can be shown that the corner-to-

corner resistance is 5⁄6 of the individual resistance.

One practical application of these relationships is that a non-standard value of resistance can

generally be synthesized by connecting a number of standard values in series and/or parallel.

This can also be used to obtain a resistance with a higher power rating than that of the

individual resistors used. In the special case of N identical resistors all connected in series or

all connected in parallel, the power rating of the individual resistors is thereby multiplied by

N.

Power Dissipation

The power P dissipated by a resistor (or the equivalent resistance of a resistor network) is

calculated as:

The first form is a restatement of Joule's first law. Using Ohm's

law, the two other forms can be derived.

The total amount of heat energy released over a period of time can be determined from the

integral of the power over that period of time:

Practical resistors are rated according to their maximum power

dissipation. The vast majority of resistors used in electronic circuits absorbs much less than a

watt of electrical power and require no attention to their power rating. Such resistors in their

discrete form, including most of the packages detailed below, are typically rated as 1/10, 1/8,

Resistors required to dissipate substantial amounts of power, particularly used in power

supplies, power conversion circuits, and power amplifiers, are generally referred to as power

resistors; this designation is loosely applied to resistors with power ratings of 1 watt or

greater. Power resistors are physically larger and tend not to use the preferred values, color

codes, and external packages described below.

If the average power dissipated by a resistor is more than its power rating, damage to the

resistor may occur, permanently altering its resistance; this is distinct from the reversible

change in resistance due to its temperature coefficient when it warms. Excessive power

dissipation may raise the temperature of the resistor to a point where it can burn the circuit

board or adjacent components, or even cause a fire. There are flameproof resistors that fail

(open circuit) before they overheat dangerously. Note that the nominal power rating of a

resistor is not the same as the power that it can safely dissipate in practical use. Air

circulation and proximity to a circuit board, ambient temperature, and other factors can

reduce acceptable dissipation significantly. Rated power dissipation may be given for an

ambient temperature of 25 °C in free air. Inside an equipment case at 60 °C, rated dissipation

will be significantly less; a resistor dissipating a bit less than the maximum figure given by

the manufacturer may still be outside the safe operating area and may prematurely fail.

Resistor Marking

Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount

resistors are marked numerically, if they are big enough to permit marking; more-recent small

sizes are impractical to mark. Cases are usually tan, brown, blue, or green, though other

colors are occasionally found such as dark red or dark gray.

Early 20th century resistors, essentially uninsulated, were dipped in paint to cover their entire

body for color coding. A second color of paint was applied to one end of the element, and a

color dot (or band) in the middle provided the third digit. The rule was "body, tip, dot",

providing two significant digits for value and the decimal multiplier, in that sequence.

Default tolerance was ±20%. Closer-tolerance resistors had silver (±10%) or gold-colored

(±5%) paint on the other end.

Four-band resistors

Four-band identification is the most commonly used color-coding scheme on resistors. It

consists of four colored bands that are painted around the body of the resistor. The first two

bands encode the first two significant digits of the resistance value, the third is a power-of-ten

multiplier or number-of-zeroes, and the fourth is the tolerance accuracy, or acceptable error,

of the value. The first three bands are equally spaced along the resistor; the spacing to the

fourth band is wider. Sometimes a fifth band identifies the thermal coefficient, but this must

be distinguished from the true 5-color system, with 3 significant digits.

For example, green-blue-yellow-red is 56×104 Ω = 560 kΩ ± 2%. An easier description can

be as followed: the first band, green, has a value of 5 and the second band, blue, has a value

of 6, and is counted as 56. The third band, yellow, has a value of 104, which adds four 0's to

the end, creating 560,000 Ω at ±2% tolerance accuracy. 560,000 Ω changes to 560 kΩ ±2%

(as a kilo- is 103).

Figures showing colour coding techniques for resistors

Electrical and thermal noise

In amplifying faint signals, it is often necessary to minimize electronic noise, particularly in

the first stage of amplification. As dissipative elements, even an ideal resistor will naturally

produce a randomly fluctuating voltage or "noise" across its terminals. This Johnson–Nyquist

noise is a fundamental noise source which depends only upon the temperature and resistance

of the resistor, and is predicted by the fluctuation–dissipation theorem. Using a larger resistor

produces a larger voltage noise, whereas with a smaller value of resistance there will be more

current noise, assuming a given temperature. The thermal noise of a practical resistor may

also be somewhat larger than the theoretical prediction and that increase is typically

frequency-dependent.

However the "excess noise" of a practical resistor is an additional source of noise observed

only when a current flows through it. This is specified in unit of μV/V/decade - μV of noise

per volt applied across the resistor per decade of frequency. The μV/V/decade value is

frequently given in dB so that a resistor with a noise index of 0 dB will exhibit 1 μV (rms) of

excess noise for each volt across the resistor in each frequency decade. Excess noise is thus

an example of 1/f noise. Thick-film and carbon composition resistors generate more excess

noise than other types at low frequencies; wire-wound and thin-film resistors, though much

more expensive, are often utilized for their better noise characteristics. Carbon composition

resistors can exhibit a noise index of 0 dB while bulk metal foil resistors may have a noise

index of -40 dB, usually making the excess noise of metal foil resistors insignificant. Thin

film surface mount resistors typically have lower noise and better thermal stability than thick

film surface mount resistors. However, the design engineer must read the data sheets for the

family of devices to weigh the various device tradeoffs.

While not an example of "noise" per se, a resistor may act as a thermocouple, producing a

small DC voltage differential across it due to the thermoelectric effect if its ends are at

somewhat different temperatures. This induced DC voltage can degrade the precision of

instrumentation amplifiers in particular. Such voltages appear in the junctions of the resistor

leads with the circuit board and with the resistor body. Common metal film resistors show

such an effect at a magnitude of about 20µV/°C. Some carbon composition resistors can

exhibit thermoelectric offsets as high as 400 µV/°C, whereas specially constructed resistors

can reduce this number to 0.05µV/°C. In applications where the thermoelectric effect may

become important, care has to be taken (for example) to mount the resistors horizontally to

avoid temperature gradients and to mind the air flow over the board.

4.12 VARIABLE RESISTORSVariable Resistors consist of a resistance track with connections at both ends and a wiper

which moves along the track as you turn the spindle. The track may be made from carbon,

cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is

usually rotary but straight track versions, usually called sliders, are also available. Variable

resistors may be used as a rheostat with two connections (the wiper and just one end of the

track) or as a potentiometer with all three connections in use. Miniature versions called

presets are made for setting up circuits which will not require further adjustment. Variable

resistors are often called potentiometers in books and catalogues. They are specified by their

maximum resistance, linear or logarithmic track, and their physical size. The standard spindle

diameter is 6mm.

The resistance and type of track are marked on the body:

    4K7 LIN means 4.7 k linear track.

    1M LOG means 1 M logarithmic track.

Some variable resistors are designed to be mounted directly on the circuit board, but most are

for mounting through a hole drilled in the case containing the circuit with stranded wire

connecting their terminals to the circuit board.

4.13 CAPACITOR:

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.

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 across the dielectric, causing positive charge to collect on one

plate and negative charge on the other plate. Energy is stored in the electrostatic field. 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.

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.

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

Variable resistors

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 OPREATION:

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:

C=Q/V

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to

vary. In this case, capacitance is defined in terms of incremental changes:

Energy storage

Work must be done by an external influence to "move" charge between the conductors in a

capacitor. When the external influence is removed the charge separation persists in the

electric field and energy is stored to be released when the charge is allowed to return to its

equilibrium position. The work done in establishing the electric field, and hence the amount

of energy stored, is given by:

Current-voltage relation

The current i (t) through any component in an electric circuit is defined as the rate of flow of

a charge q (t) passing through it, but actual charges, electrons, cannot pass through the

dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each

one that leaves the positive plate, resulting in an electron depletion and consequent positive

charge on one electrode that is equal and opposite to the accumulated negative charge on the

other. Thus the charge on the electrodes is equal to the integral of the current as well as

proportional to the voltage as discussed above. As with any anti derivative, a constant of

integration is added to represent the initial voltage v (t0). This is the integral form of the

capacitor equation,

Taking the derivative of this, and multiplying by C, yields the derivative form,

The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than

the electric field. Its current-voltage relation is obtained by exchanging current and voltage in

the capacitor equations and replacing C with the inductance L.

DC Circuits:

A simple resistor-capacitor circuit demonstrates charging of a capacitor.

Capacitor markings

Most capacitors have numbers printed on their bodies to indicate their electrical

characteristics. Larger capacitors like electrolytic usually display the actual capacitance

together with the unit (for example, 220 μF). Smaller capacitors like ceramics, however, use

a shorthand consisting of three numbers and a letter, where the numbers show the capacitance

in pF (calculated as XY x 10Z for the numbers XYZ) and the letter indicates the tolerance (J,

K or M for ±5%, ±10% and ±20% respectively).

Additionally, the capacitor may show its working voltage, temperature and other relevant

characteristics.

Example

A capacitor with the text 473K 330V on its body has a capacitance of 47 x 103 pF = 47 nF

(±10%) with a working voltage of 330 V.

Applications

Capacitors have many uses in electronic and electrical systems. They are so common that it is

a rare electrical product that does not include at least one for some purpose.

Energy storage

A capacitor can store electric energy when disconnected from its charging circuit, so it can be

used like a temporary battery. Capacitors are commonly used in electronic devices to

maintain power supply while batteries are being changed. (This prevents loss of information

in volatile memory.)

Conventional capacitors provide less than 360 joules per kilogram of energy density, while

capacitors using developing technologies could provide more than 2.52 kilojoules per

kilogram

In car audio systems, large capacitors store energy for the amplifier to use on demand. Also

for a flash tube a capacitor is used to hold the high voltage.

Pulsed power and weapons

Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor

banks) are used to supply huge pulses of current for many pulsed power applications. These

include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers),

pulse forming networks, radar, fusion research, and particle accelerators.

Large capacitor banks (reservoir) are used as energy sources for the exploding-bridge wire

detonators or slapper detonators in nuclear weapons and other specialty weapons.

Experimental work is under way using banks of capacitors as power sources for

electromagnetic armour and electromagnetic railguns and coilguns.

Power conditioning

A 10,000 microfarad capacitor in a TRM-800 amplifier

Reservoir capacitors are used in power supplies

where they smooth the output of a full or half wave

rectifier. They can also be used in charge pump

circuits as the energy storage element in the generation of higher voltages than the input

voltage.

Capacitors are connected in parallel with the power circuits of most electronic devices and

larger systems (such as factories) to shunt away and conceal current fluctuations from the

primary power source to provide a "clean" power supply for signal or control circuits. Audio

equipment, for example, uses several capacitors in this way, to shunt away power line hum

before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power

source, and bypass AC currents from the power supply. This is used in car audio applications,

when a stiffening capacitor compensates for the inductance and resistance of the leads to the

lead-acid car battery.

Power factor correction

In electric power distribution, capacitors are used for power factor correction. Such capacitors

often come as three capacitors connected as a three phase load. Usually, the values of these

capacitors are given not in farads but rather as a reactive power in volt-amperes reactive

(VAr). The purpose is to counteract inductive loading from devices like electric motors and

transmission lines to make the load appear to be mostly resistive. Individual motor or lamp

loads may have capacitors for power factor correction, or larger sets of capacitors (usually

with automatic switching devices) may be installed at a load center within a building or in a

large utility substation.

Suppression and coupling

Signal coupling

Because capacitors pass AC but block DC signals (when charged up to the applied dc

voltage), they are often used to separate the AC and DC components of a signal. This method

is known as AC coupling or "capacitive coupling". Here, a large value of capacitance, whose

value need not be accurately controlled, but whose reactance is small at the signal frequency,

is employed.

4.14 TRANSISTOR:

A bipolar (junction) transistor (BJT) is a three-terminal electronic device constructed of

doped semiconductor material and may be used in amplifying or switching applications.

Bipolar transistors are so named because their operation involves both electrons and holes.

Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction

between two regions of different charge concentrations. This mode of operation is contrasted

with unipolar transistors, such as field-effect transistors, in which only one carrier type is

involved in charge flow due to drift. By design, most of the BJT collector current is due to the

flow of charges injected from a high-concentration emitter into the base where they are

minority carriers that diffuse toward the collector, and so BJTs are classified as minority-

carrier devices.

Figure: Schematic symbols for PNP- and NPN-type BJTs.

NPN BJT with forward-biased E–B junction and reverse-biased B–C junction. An NPN

transistor can be considered as two diodes with a shared anode. In typical operation, the base-

emitter junction is forward biased and the base–collector junction is reverse biased. In an

NPN transistor, for example, when a positive voltage is applied to the base–emitter junction,

the equilibrium between thermally generated carriers and the repelling electric field of the

depletion region becomes unbalanced, allowing thermally excited electrons to inject into the

base region. These electrons wander (or "diffuse") through the base from the region of high

concentration near the emitter towards the region of low concentration near the collector. The

electrons in the base are called minority carriers because the base is doped p-type which

would make holes the majority carrier in the base.

To minimize the percentage of carriers that recombine before reaching the collector–base

junction, the transistor's base region must be

thin enough that carriers can diffuse across

it in much less time than the

semiconductor's minority carrier lifetime. In

particular, the thickness of the base must be

much less than the diffusion length of the electrons. The collector–base junction is reverse-

biased, and so little electron injection occurs from the collector to the base, but electrons that

diffuse through the base towards the collector are swept into the collector by the electric field

in the depletion region of the collector–base junction. The thin shared base and asymmetric

collector–emitter doping is what differentiates a bipolar transistor from two separate and

oppositely biased diodes connected in series.

Voltage, current, and charge control

The collector–emitter current can be viewed as being controlled by the base–emitter current

(current control), or by the base–emitter voltage (voltage control). These views are related by

the current–voltage relation of the base–emitter junction, which is just the usual exponential

current–voltage curve of a p-n junction (diode).

The physical explanation for collector current is the amount of minority-carrier charge in the

base region. Detailed models of transistor action, such as the Gummel–Poon model, account

for the distribution of this charge explicitly to explain transistor behavior more exactly. The

charge-control view easily handles phototransistors, where minority carriers in the base

region are created by the absorption of photons, and handles the dynamics of turn-off, or

recovery time, which depends on charge in the base region recombining. However, because

base charge is not a signal that is visible at the terminals, the current- and voltage-control

views are generally used in circuit design and analysis.

In analog circuit design, the current-control view is sometimes used because it is

approximately linear. That is, the collector current is approximately βF times the base current.

Some basic circuits can be designed by assuming that the emitter–base voltage is

approximately constant, and that collector current is beta times the base current. However, to

accurately and reliably design production BJT circuits, the voltage-control (for example,

Ebers–Moll) model is required. The voltage-control model requires an exponential function

to be taken into account, but when it is linearized such that the transistor can be modeled as a

transconductance, as in the Ebers–Moll model, design for circuits such as differential

amplifiers again becomes a mostly linear problem, so the voltage-control view is often

preferred. For translinear circuits, in which the exponential I–V curve is key to the operation,

the transistors are usually modeled as voltage controlled with transconductance proportional

to collector current. In general, transistor level circuit design is performed using SPICE or a

comparable analogue circuit simulator, so model complexity is usually not of much concern

to the designer.

Turn-on, turn-off, and storage delay:

The Bipolar transistor exhibits a few delay characteristics when turning on and off. Most

transistors, and especially power transistors, exhibit long base storage time that limits

maximum frequency of operation in switching applications. One method for reducing this

storage time is by using a Baker clamp.

Transistor 'alpha' and ‘beta’:

The proportion of electrons able to cross the base and reach the collector is a measure of the

BJT efficiency. The heavy doping of the emitter region and light doping of the base region

cause many more electrons to be injected from the emitter into the base than holes to be

injected from the base into the emitter. The common-emitter current gain is represented by βF

or hfe; it is approximately the ratio of the DC collector current to the DC base current in

forward-active region. It is typically greater than 100 for small-signal transistors but can be

smaller in transistors designed for high-power applications. Another important parameter is

the common-base current gain, αF. The common-base current gain is approximately the gain

of current from emitter to collector in the forward-active region. This ratio usually has a value

close to unity; between 0.98 and 0.998. Alpha and beta are more precisely related by the

following identities (NPN transistor):

Structure:

Simplified cross section of a planar NPN bipolar junction transistor

Die of a KSY34 high-frequency NPN transistor, base and emitter connected via bonded wires

A BJT consists of three differently doped semiconductor regions, the emitter region, the base

region and the collector region. These regions are, respectively, p type, n type and p type in a

PNP, and n type, p type and n type in a NPN transistor. Each semiconductor region is

connected to a terminal, appropriately labeled: emitter (E), base (B) and collector (C).

The base is physically located between the emitter and the collector and is made from lightly

doped, high resistivity material. The collector surrounds the emitter region, making it almost

impossible for the electrons injected into the base region to escape being collected, thus

making the resulting value of α very close to unity, and so, giving the transistor a large β. A

cross section view of a BJT indicates that the collector–base junction has a much larger area

than the emitter–base junction.

The bipolar junction transistor, unlike other transistors, is usually not a symmetrical device.

This means that interchanging the collector and the emitter makes the transistor leave the

forward active mode and start to operate in reverse mode. Because the transistor's internal

structure is usually optimized for forward-mode operation, interchanging the collector and the

emitter makes the values of α and β in reverse operation much smaller than those in forward

operation; often the α of the reverse mode is lower than 0.5. The lack of symmetry is

primarily due to the doping ratios of the emitter and the collector. The emitter is heavily

doped, while the collector is lightly doped, allowing a large reverse bias voltage to be applied

before the collector–base junction breaks down. The collector–base junction is reverse biased

in normal operation. The reason the emitter is heavily doped is to increase the emitter

injection efficiency: the ratio of carriers injected by the emitter to those injected by the base.

For high current gain, most of the carriers injected into the emitter–base junction must come

from the emitter. The low-performance "lateral" bipolar transistors sometimes used in CMOS

processes are sometimes designed symmetrically, that is, with no difference between forward

and backward operation.

Small changes in the voltage applied across the base–emitter terminals causes the current that

flows between the emitter and the collector to change significantly. This effect can be used to

amplify the input voltage or current. BJTs can be thought of as voltage-controlled current

sources, but are more simply characterized as current-controlled current sources, or current

amplifiers, due to the low impedance at the base.

Early transistors were made from germanium but most modern BJTs are made from silicon.

A significant minority are also now made from gallium arsenide, especially for very high

speed applications

The symbol of an NPN bipolar junction transistor

NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped

semiconductor (the "base") between two N-doped layers. A small current entering the base is

amplified to produce a large collector and emitter current. That is, an NPN transistor is "on"

when its base is pulled high relative to the emitter.

Most of the NPN current is carried by electrons, moving from emitter to collector as minority

carriers in the P-type base region. Most bipolar transistors used today are NPN, because

electron mobility is higher than Hole mobility in semiconductors, allowing greater currents

and faster operation.

The symbol of a PNP Bipolar Junction Transistor

The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor between

two layers of P-doped material. A small current leaving the base is amplified in the collector

output. That is, a PNP transistor is "on" when its base is pulled low relative to the emitter.

The arrows in the NPN and PNP transistor symbols are on the emitter legs and point in the

direction of the conventional current flow when the device is in forward active mode. A

mnemonic device for the NPN / PNP distinction, based on the arrows in their symbols and

the letters in their names, is not pointing in for NPN and pointing in for PNP.

The BC548 is a general purpose silicon NPN BJT transistor found commonly in

European electronic equipment.

If the TO-92 package is held in front of one's face with the

flat side facing toward you and the leads downward, (see

picture) the order of the leads, from left to right is collector,

base, emitter.

Specifications: The exact specs of a given device depend on

the manufacturer. It is important to check the datasheet for the exact device and brand you are

dealing with. Philips and Telefunken are two manufacturers of the BC548.

Vcbo = 30 V

Ic = 100 mA

Ptotal = 50 mW

ft = 300 MHz

The BC548 is a member of a larger group of similarly numbered transistors. Other part

numbers have different characteristics and ratings. Its complement is the BC558.

A family of older "BC" transistors predates the TO-92 BC54x series, the BC107, BC108 and

BC109, (with complements BC177, BC178 and BC179). These are generally housed in the

TO-18 metal package, the same as what the North American 2N2222 uses. These older

transistors have similar characteristics as the TO-92 BC5xx devices and are electrically

interchangeable.

There are many other devices based on the BC54x family, such as the surface-mount versions

of the BC547, 548 and 549; the BC847, BC848 and BC849.

4.15 ZENER DIODE

A Zener diode is a type of diode that permits current not only in the forward direction like a

normal diode, but also in the reverse direction if the voltage is larger than the breakdown

voltage known as "Zener knee voltage" or "Zener voltage". The device was named after

Clarence Zener, who discovered this electrical property. A conventional solid-state diode will

not allow significant current if it is reverse-biased below its reverse breakdown voltage.

When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high

current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will

be permanently damaged due to overheating. In case of large forward bias (current in the

direction of the arrow), the diode exhibits a voltage drop due to its junction built-in voltage

and internal resistance. The amount of the voltage drop depends on the semiconductor

material and the doping concentrations.

A ZENER DIODE

CHARACTERISTIC GRAPH

CHAPTER 5

DESIGN & IMPLEMENTATION

5.1 PCB MANUFACTURING PROCESS

It is an important process in the fabrication of electronic equipment. The design of PCBs

(Printed Circuit Boards) depends on circuit requirements like noise immunity, working

frequency and voltage levels etc. High power PCB s requires a special design strategy.

The fabrication process to the printed circuit board will determine to a large extent the price

and reliability of the equipment. A common target aimed is the fabrication of small series of

highly reliable professional quality PCBs with low investment. The target becomes especially

important for customer tailored equipment’s in the area of industrial electronics.

The layout of a PCB has to incorporate all the information of the board before one can go on

the artwork preparation. This means that a concept which clearly defines all the details of the

circuit and partly defines the final equipment, is prerequisite before the actual lay out can

start. The detailed circuit diagram is very important for the layout designer but he must also

be familiar with the design concept and with the philosophy behind the equipment.

5.2 BOARD TYPES:

The two most popular PCB types are:

1. Single Sided Boards

The single sided PCBs are mostly used in entertainment electronics where manufacturing

costs have to be kept at a minimum. However in industrial electronics cost factors cannot be

neglected and single sided boards should be used wherever a particular circuit can be

accommodated on such boards.

2. Double Sided Boards

Double-sided PCBs can be made with or without plated through holes. The production of

boards with plated through holes is fairly expensive. Therefore plated through hole boards are

only chosen where the circuit complexities and density of components does not leave any

other choice.

5.3 DESIGN SPECIFICATION:

5.3.1 STEPS TAKEN WHILE PREPARING CIRCUIT

5.3.1.1 PCB DESIGNING

The main purpose of printed circuit is in the routing of electric currents and signal

through a thin copper layer that is bounded firmly to an insulating base material

sometimes called the substrate. This base is manufactured with integrally bounded layers

of thin copper foil which has to be partly etched or removed to arrive at a pre-designed

pattern to suit the circuit connections or other applications as required.

The term printed circuit board is derived from the original method where a printed pattern

is used as the mask over wanted areas of copper. The PCB provides an ideal baseboard

upon which to assemble and hold firmly most of the small components.

From the constructor’s point of view, the main attraction of using PCB is its role as the

mechanical support for small components. There is less need for complicated and time

consuming metal work of chassis contraception except perhaps in providing the final

enclosure. Most straight forward circuit designs can be easily converted in to printed

wiring layer the thought required to carry out the inversion cab footed high light an

possible error that would otherwise be missed in conventional point to point wiring .The

finished project is usually neater and truly a work of art.

Actual size PCB layout for the circuit shown is drawn on the copper board. The board is

then immersed in FeCl3 solution for 12 hours. In this process only the exposed copper

portion is etched out by the solution.

Now the petrol washes out the paint and the copper layout on PCB is rubbed with a

smooth sand paper slowly and lightly such that only the oxide layers over the Cu are

removed. Now the holes are drilled at the respective places according to component

layout as shown in figure.

5.3.1.2 LAYOUT DESIGN:

When designing the layout one should observe the minimum size (component body

length and weight). Before starting to design the layout we need all the required

components in hand so that an accurate assessment of space can be made. Other space

considerations might also be included from case to case of mounted components over the

printed circuit board or to access path of present components.

It might be necessary to turn some components around to a different angular position so

that terminals are closer to the connections of the components. The scale can be checked

by positioning the components on the squared paper. If any connection crosses, then one

can reroute to avoid such condition.

All common or earth lines should ideally be connected to a common line routed around

the perimeter of the layout. This will act as the ground plane. If possible try to route the

outer supply line to the ground plane. If possible try to route the other supply lines around

the opposite edge of the layout through the center. The first set is tearing the circuit to

eliminate the crossover without altering the circuit detail in any way.

Plan the layout looking at the topside to this board. First this should be translated

inversely; later for the etching pattern large areas are recommended to maintain good

copper adhesion. It is important to bear in mind always that copper track width must be

according to the recommended minimum dimensions and allowance must be made for

increased width where termination holes are needed. From this aspect, it can become little

tricky to negotiate the route to connect small transistors.

There are basically two ways of copper interconnection patterns under side the board. The

first is the removal of only the amount of copper necessary to isolate the junctions of the

components to one another. The second is to make the interconnection pattern looking

more like conventional point wiring by routing uniform width of copper from component

to component.

5.3.1.2.1 ETCHING PROCESS:

Etching process requires the use of chemicals. Acid resistant dishes and running water

supply. Ferric chloride is mostly used solution but other etching materials such as

ammonium per sulphate can be used. Nitric acid can be used but in general it is not used

due to poisonous fumes.

The pattern prepared is glued to the copper surface of the board using a latex type of

adhesive that can be cubed after use. The pattern is laid firmly on the copper using a very

sharp knife to cut round the pattern carefully to remove the paper corresponding to the

required copper pattern areas. Then apply the resistant solution, which can be a kind of

ink solution for the purpose of maintaining smooth clean outlines as far as possible.

While the board is drying, test all the components.

Before going to next stage, check the whole pattern and cross check with the circuit

diagram. Check for any free metal on the copper. The etching bath should be in a glass or

enamel disc. If using crystal of ferric- chloride these should be thoroughly dissolved in

water to the proportion suggested. There should be 0.5 lt. of water for 125gm of crystal.

To prevent particles of copper hindering further etching, agitate the solutions carefully by

gently twisting or rocking the tray.

The board should not be left in the bath a moment longer than is needed to remove just

the right amount of copper. Inspite of there being a resistive coating there is no protection

against etching away through exposed copper edges. This leads to over etching. Have

running water ready so that etched board can be removed properly and rinsed. This will

halt etching immediately.

Drilling is one of those operations that call for great care. For most purposes a 0.5mm

drill is used. Drill all holes with this size first those that need to be larger can be easily

drilled again with the appropriate larger size.

5.3.1.2.2 COMPONENT ASSEMBLY

From the greatest variety of electronic components available, which runs into thousands

of different types it, is often a perplexing task to know which is right for a given job.

There could be damage such as hairline crack on PCB. If there are, then they can be

repaired by soldering a short link of bare copper wire over the affected part. The most

popular method of holding all the items is to bring the wires far apart after they have been

inserted in the appropriate holes. This will hold the component in position ready for

soldering.

Some components will be considerably larger .So it is best to start mounting the smallest

first and progressing through to the largest. Before starting, be certain that no further

drilling is likely to be necessary because access may be impossible later.

Next will probably be the resistor, small signal diodes or other similar size components.

Some capacitors are also very small but it would be best to fit these afterwards. When

fitting each group of components mark off each one on the circuit as it is fitted so that if

we have to leave the job we know where to recommence.

Although transistors and integrated circuits are small items there are good reasons for

leaving the soldering of these until the last step. The main point is that these components

are very sensitive to heat and if subjected to prolonged application of the soldering iron,

they could be internally damaged.

All the components before mounting are rubbed with sand paper so that oxide layer is

removed from the tips. Now they are mounted according to the component layout.

5.3.1.2.3 SOLDERING

This is the operation of joining the components with PCB after this operation the circuit

will be ready to use to avoid any damage or fault during this operation following care

must be taken.

1. A longer duration contact between soldering iron bit & components lead can exceed the

temperature rating of device & cause partial or total damage of the device. Hence before

soldering we must carefully read the maximum soldering temperature & soldering time

for device.

2. The wattage of soldering iron should be selected as minimum as permissible for that

soldering place.

3. To protect the devices by leakage current of iron its bit should be earthed properly.

4. We should select the soldering wire with proper ratio of Pb & Tn to provide the suitable

melting temperature. Proper amount of good quality flux must be applied on the soldering

point to avoid dry soldering.

CHAPTER 6

RESULT

The result we got is the successful working of the project and a communication is established

between the two transceivers.

CHAPTER 7

CONCLUSION & FUTURE SCOPE

7.1CONCLUSIONAfter the successful working of the project, it can be concluded that this project issuitable for communication. There can be further up gradations in the projectwhich could lead to a much better system for communication. Some of the possibleways are as follows:

o Instead of the short range laser, high range lasers can be used which range a few hundred kilometers.

7.2 FUTURE SCOPE

In future it can be commissioned in satellites for communication. Lasers can also transmit through glass, however the physical

properties of theglass have to be considered and hence can be used for a verylonge distance communication.

It can be used in inaccessible areas.

CHAPTER 8

REFERENCES

1. [Online] // wikipedia. - www.wikipedia.com.2. [Online] // circuitstoday. - www.circuitstoday.com.3. [Online] // electronics schematics. - www.electroschematic.com.4. [Online] // electronics for you. - www.efy.com.5. D.ROY CHOUDHARY SHALIN B. JAIN LINEAR INTEGRATED CIRCUITS[Book]. - DELHI : NEW AGE INTERNATIONL PUBLISHERS, THIRD EDITION2009.6. ELECTRONICS FOR YOU MAGAZINE [Book].7. GUPTA J.B. ELECTRONICS DEVICE & CIRCUITS [Book]. - INDIA: S.K.KATARIA & SONS, FIRST EDITION DEC 2000. - Vol. 1.8. KUMAR N. SURESH ELECTRONICS DEVICE & CIRCUITS [Book]. - 2008.9. MEHTA V.K. PRINCIPLES OF ELECTRONICS [Book].10. NAVAS K.A. ELECTRONICS LAB MANUAL [Book]. - [s.l.] : Rajath publishers,2008. - Vol. 1&2.11. RAI A. VALLAVE ELECTRONICS DEVICE & CIRCUITS [Book]. - 2007.12.EFY Magzine-june 2004 edition

CHAPTER 9

APPENDIX

9.1 PCB LAYOUT

9.2 COMPONENT LAYOUT

9.3 COMPONENT LIST

IC1 7805 5V regulatorIC2, IC3, IC7, IC8 555 TimerIC4 LM386 low power audio amplifierIC5,IC6 NE567 phase locked loopIC9 decade counter

7-segment decoderIC10 UM66 melody generatorBR1 Bridge rectifierD1 1N4001 rectifier diodeZD1 3.3zener diodeLED1-LED3 5mm red LEDD1S1 LTS543 common cathode display

Resistors

R1, R19, R20, R27, R32 1 kilo ohmR2, R5 5.6 kilo ohmR6, R8, R18, R21, R28 8.2 kilo ohmR7, R12 15 kilo ohmR9 22ohmR10 2kilo ohmR11 68ohmR13, R17, R26 2.2 kilo ohmR14 2.7kilo ohmR15 390 ohmsR16 390 kilo ohmR22 33 kilo ohmR23 4.7ohmR15 390ohmR16 390kilo ohmR22 33 kilo ohmR23 4.7 ohmR15 390 ohmR24 36 kilo ohmR25 560 kilo ohmR29 4.7 kilo ohmR31 10 kilo ohmR30 220 ohmVR1 47 kilo ohm presetVR2 100 kilo ohm presetVR5, VR6 10 kilo ohm presetVR3 10 kilo ohm pot meter

VR4 5 kilo ohm presetVR7 10 kilo ohm pot meter

Capacitors

C1 2200µF, 5V electrolyticC2, C12, C13, C40 100µF, 16V electrolyticC3, C5, C6, C9, C19, C22,C32, C35 0.01µF ceramic diskC4 3.3nF ceramicC7, C10, C11, C14, C15, C17,C20, C26, C29 0.1µF ceramic diskC8,C16,C38 470µF,16V electrolyticC16 56µF ceramic diskC18, C27, C33, C39 10µF, 16V electrolyticC21, C24 2.2µF,16 V electrolyticC25 1nF ceramic diskC23, C28 0.22µF ceramic diskC30 47µF, 16V electrolyticC31 1µF, 16V electrolyticC34 6.8µF,16V electrolyticC37 3.3µF, 16 V electrolytic

Miscellaneous

S1,S2 Push to on tactile switchLS1,LS2 8 ohm,1W loudspeakerMic Condenser microphonePZ1 PiezobuzzerX1 230V AC primary 0-9V,

500mA secondary transformerLS laser module

9.4 DATASHEETS

9.4.1 CD4033BMS

9.4.2 LM 7806

9.4.3 LM386

9.4.4 NE 567

9.4.5 NE555 TIMER