Laser Final

8/8/2019 Laser Final

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PROJECT REPORT

on

IR-Based Voice And Data

Communication


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CERTIFICATE

DEPARTMENT OF ELECTRONICS & COMMUNICATION

This is to certify that Neelam Kothari (0631352807) , a student of Indira Gandhi Institute

of Technology has done her full-semester project under my supervision.

The project work entitled IR-based voice and data communication embodies the

original work done by her during her full semester project training period.

Mrs.Shobha Sharma

Dept. ECE

IGIT,GGSIPU


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ACKNOWLEDGEMENT

It is my duty to record my sincere thanks

and deep sense of gratitude to my respected teacher

Mrs. SHOBHA SHARMA

for her valuable guidance, interest

and constant encouragement for the

fulfillment of the project.

I am also highly obliged to all the respected teachers of IGIT

who provided me the required guidance.


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CONTENTS

1. INTRODUCTION

2. SCIENTIFIC PRINCIPLE3. BLOCK DIAGRAM4. CONSTRUCTION AND WORKING

5. CIRCUIT DESCRIPTION OF TRANSMITTER AND RECIEVERCIRCUIT

6. COMPONENTS USED7. TRANSMITTER CIRCUIT8. RECIEVER CUIRCUIT9. COMPONENTS DESCRIPTION

a) RESISTORSb) CAPACITORSc) TRANSISTORSd) LEDe) DIODEf) OPEN-AMPLIFIERg) CIRCUIT PARAMETERS

10. ADVANTAGES11. DISADVANTAGES

12. APPLICATIONS


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I.R.BASED

COMMUNICATION SYSTEM

INTRODUCTION

For years, laser light has been merely a system for piping light around corners and into the

inaccessible places to allow the hidden to be lighted. But now, laser light has evolved into a system of

significantly greater importance and use. Throughout the world, it is now being used to transmit voice,

television and data signals as light waves. Its advantages as compared with conventional coaxial cable or

twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave

communication systems into operation.

Interest in fibre as a medium began in 1966 when C. Kao and G.A. Hockham at Standard

Telecommunications Laboratory predicated that by removing the impurities in the glass, 20 dB/km

attenuations would be achievable.

One of the most interesting developments in recent years in the field of telecommunication is the

use of laser light to carry information over large distances. It has been proved in the past decade that

lightwave transmission through I.R.BASED is superior than that achieved through wires and microwave

links. TypicallyI.R.BASED has a much lower transmission loss per unit length (0.15-5db/km) and is not

suspectible to electromagnetic interference. Economically also, it serves our purpose. The ever

increasing cost and the lack of space available in the congested metropolitan cities asks for advent of a

less costly system.

The conventional telephonic systems use copper wires, which easily get oxidized and as such

require high maintenance cost. The I.R being made of glass are non-reactive and hence economical.

Also, the noise pick up by the copper wire or in electrical signals is quite substantial whereas in laser

light, the noise pick up is negligible.


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The conventional telephonic systems use copper wires, which easily get oxidized and as such

require high maintenance cost. The I.R.BASED being made of glass are non-reactive and hence

economical. Also, the noise pick up by the copper wire or in electrical signals is quite substantial

whereas in I.R.BASED, the noise pick up is negligible.

BLOCK DIAGRAM

IC8870

SCIENTIFIC PRINCIPLE

The basic principle involved in the exhibit is that any form of energy can be converted into any

other form of energy. So, any kind of physical signal can be converted into electrical signals and these

signals, in turn, can be converted into any other kind of energy by using transducers (Transducer is a

device which converts one kind of energy into another kind of energy).


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In the present model, sound signals are first converted into electrical signals using a mike and

subsequently these electrical signals are converted into optical signals using a L.E.D. (Light Emitting

Diode). Afterwards, these signals are transferred using an optical fibre at the other end. These signals are

converted into electrical signals using a phototransistor. Now these electrical signals are converted into

sound signals using a speaker.

So the sound signals at the mike are regenerated at the receiver end in the speaker. In the above

system, mike, L.E.D., photo-transistor and speaker are all transducers. laser light works on the principle

of total internal reflection of light.adaBB

used BBBLOCK distance of aircraft played an important role in missile control, transport control, army

weather forecast, spacecraf

,. BLOCK DIAGRAM

t co


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CONSTRUCTION AND WORKING

MIKE: Sound signals made at the mike.

AMPLIFIER (A): Signals from mike are amplified so that it can drive and LED.

OPTICAL FIBRE: It carries signals.

PHOTO TRANSISTOR: The electrical signals are regained from the optical signals.

AMPLIFIER (B): Energy of signals is amplified to drive the speaker.

SPEAKER: Electrical signals which are amplified are reconverted into sound signals at the

speaker.

DTMF CODER: It is generates the DTMF signal corresponding to the number entered from the

keyboard.

DTMF RECEIVER/DECODER : It is fed to DTMF decoder which gives the binary output

corresponding to the signal received from the transmitter.

DECODER DRIVER : To drive the 7 segment display.


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THE CIRCUIT

The main part of Circuit is an amplifier. This sound signals (even at a distance of 2 meters from the

mic) are picked up by the condenser microphone and converted into electrical variation, which are

amplified by the op-amp(Operational amplifier)

IC- 741 is use in the inverting mode with a single supply using divider network of resistor the gain of

IC can be set be varying the feed back through R5/6 resistance (can place a 1M variable) .

the output of IC is further amplified buy the push-pull amplifier using transistor BC.548/558 pair, in

this circuit are R2 is feed back resistance with R1/8 and C1/3 to connected IC-741.

The ICs pin 2 is connect VR1 (variable resistance) through connect to O/P of T1 (transistor) also use

6volt DC. The microphone should be placed near the circuit with the shield wire to suppress tune. The

output of the amplifier is taken from emitter of two transistors, with a filter C5 from speaker.

IC 4017 work as a flip- flop. IC-3 is counter work as a switching. Its pin no-2 output, pin no-14 input

and pin-no 15 is reset.

Same process continues in the second amplifier.


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CIRCUIT DESCRIPTION OF SWITCH SECTION

This project was based on photo diodes and phototransistor. Photo diodes had been used as a

transmitter and phototransistor as a receiver. This project had been divided in two part, First part

transmitter section and second part receiver section. Slide switch selected to voice communication and

switching.

TRANSMISSIONSECTION

When switch key is pressed, circuit is energised. The output of the transmit IR beams modulated at

same frequency 1KHz. The receiver uses infrared module. The IR- signal form the transmitter is sensed

by the receiver sensor.

RECEIVER SECTION

This section is worked as a Flip-flop (Bistable). IC-3 is decade counter; its Pin No.14 is input and Pin

No. 2 output. The output of frequency detector stage is used, via a flip-flop, to switch ON or switch

OFF a LED alternately. The receiver uses infrared modules IR-signal from the transmitter is sensed by

the sensor through and its output PIN 1 goes low and switched LED. IC-3 is worked on clock pulse,

which receives to infrared modules at Pin No. 14. Its output at Pin No 2 troughs high.The output of IC-2 is also used for lighting LED-1 indicating presence of signal. When no signal is

available output of sensor module goes high and transistor LED is switched OFF. When another signal

arrives, LED is switched ON and through clock pulse at Pin No. 14 of IC-3. This makes the LED to

switch ON the appliance at first pulse and OFF the appliance at its Second pulse arrived at its sensor.

Transmitter circuits works satisfactorily with 6-9V DC. Battery but receiver circuits needs 6V regulated

supply. The CAMD CM8870/70C provides full DTMF receiver capability by integrating both the band-

split filter and digital decoder functions into a single 18-pin DIP, SOIC,or 20-pin PLCC package. The

CM8870/70C is manufactured using state-of-the-art CMOS process technology for low power

consumption (35mW, MAX) and precise data handling. The filter section uses a switched capacitor

technique for both high and low group filters and dial tone rejection. The CM8870/70C decoder uses

digital counting techniques for the detection and decoding of all 16 DTMF tone pairs into a 4-bit code.

This DTMF receiver minimizes external component count by providing an on-chip differential input


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amplifier, clock generator, and a latched three-state interface bus. The on-chip clock generator requires

only a low cost TV crystal or ceramic resonator as an external component.

Notes:

1. dBm = decibels above or below a reference power

of 1mW into a 600. load.

2. Digit sequence consists of all 16 DTMF tones.

3. Tone duration = 40ms. Tone pause = 40ms.

4. Nominal DTMF frequencies are used.

5. Both tones in the composite signal have

an equal amplitude.

6. Bandwidth limited (0 to 3KHz) Gaussian Noise.

7. The precise dial tone frequencies are

(350Hz and 440Hz) 2%.

8. For an error rate of better than 1 in 10,000

9. Referenced to lowest level frequency component

in DTMF signal.

10. Minimum signal acceptance level is measured with

specified maximum frequency deviation.

11. Input pins defined as IN+, IN, and TOE.

12. External voltage source used to bias VREF.13. This parameter also applies to a third tone injected onto

the power supply.

14. Referenced to Figure 1. Input DTMF tone level

at 28dBm.


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COMPONENTS USED

ICs

IC1, IC-6 741 (OP AMP)IC-2 CM8870 (DTMF DECODER)IC-3 74LS47 (DECODER)IC-4 4514 Demultipluer IC-5 4013 D-type flip-flopIC-7 UM91215B (DTMF CODER)RESISTANCE:

R1, 150

R2,R11,R12 100k

R3, R7 10K

R4, R8 4.7k

R5,R6,R9,R10 15K

R13 220

R14 1

R15-R22 1 5 0 VR-1,VR-2 1M Variable Resistance

CAPACITOR:

C1,C2,C4,C5 0.1 mfd (104 pf)C3 220 mfdMIKE Condenser Microphone

SEMICONDUCTOR:

T1,T3 NPN BC548Q3,Q4 NPN BC548T2,T4 PNP BC558LED Light Emitting DiodeFND 542 Common Anode


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Pt. Photo Transistor 7805 5V Voltage Regulator Diodes All 4001 Rectifier diodes

MISCLLANEOUS:

IC Base As requiredSpeaker 8 ohmsPCB General purposeBattery 6 volt DCX1 9-0-9 Step Down transformer Mains cord General purposeRelay 6V 5amp. (2 Nos.)


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TRANSMITTER CIRCUIT


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RECEIVER CIRCUIT


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RESISTORS

The jobs done by resistors include directing and controlling current, making changing current

produce changing voltage (as in a voltage amplifier) and obtaining variable voltages from fixed ones

(as in a potential divider). There are two main types of resistor-those with fixed values and those that

are variable.

When choosing a resistor there are three factors which have to be considered, apart from the

stated value.

(i) THE TOLERANCE. Exact values cannot be guaranteed by mass-production methods

but this is snot a great disadvantage because in most electronic circuits the values of resistors are not

critical. The tolerance tells us the minimum and maximum values a resistor might have, e.g. one with

a stated (called nominal) value of 100 and a tolerance of +-10% could have any value between

90 and 110

(ii) THE POWER RATING. If the rate which a resistor changes electrical energy into

heat exceeds its power rating, it will overheat and be damaged or destroyed. For most electronic

circuit 0.25 Watt or 0.5 Watt power ratings are adequate. The greater the physical size of a resistor

the greater is its rating.

(iii) THE STABILITY. This is the ability of a component to keep the same value as it

ages despite changes of temperature and other physical conditions. In some circuits this is an

important factor.


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RESISTOR MARKINGS

The value and tolerance of a fixed resistor is marked on it using codes. The resistor has four

coloured bands painted on it towards one end. The first three from the end give the value and the

fourth the tolerance. Sometimes it is not clear which is the first band but deciding where to start

should not be difficult if you remember that the fourth band (which is not always present) will be

either gold or silver, these being colours not used for the first band.

The first band gives the first number, the second band gives the second number and the third

band tells how many noughts (0) come after the first two numbers.

VALUES

NUMBER COLOUR

0 Black

1 Brown

2 Red

3 Orange

4 Yellow

5 Green

6 Blue

7 Violet

8 Gray

9 White


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TOLERANCE CODE

PERCENTAGE COLOUR

+-5% Gold

+-10% Silver

+-20% no 4th

band

VARIABLE RESISTORS

Description. Variable resistors used as volume and other controls in radio and TV set are

usually called bots (short for potential divider- see below). They consist of an incomplete circular

track of either a fixed carbon resistor fore high values and low power (up to 2W ) or of a fixed wire-

wound resistor for high powers. Connections to each end of the track are bought out to two terminal

tags. A wiper makes contact with the track and is connected to a third terminal tag, between the other

two. Rotation of the spindle moves the wiper over the track and changes the resistance between the

center tag and the ones. Slide type variable resistors have a straight track.

In a linear track equal changes of resistance occur when the spindle is rotated through equal

angles. In a log track, the change of resistance at one end of the track is less than at the other for

equal angular rotations.

Maximum values range from a few ohms to several megohms, common values are 10k Ohm,

50k Ohm., 100k Ohm., 500k ohm. and 1M Ohm.


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Some circuits use small preset types, the symbol and form of which are shown in figs. These

are adjusted with a screwdriver when necessary and have tracks of carbon or cermet (ceramic and

metal oxide).


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CAPACITORS

A capacitor stores electric charge. It does not allow direct current to flow through it and it

behaves as if alternating current does flow through. In its simplest form it consists of two parallel

metal plates separated by an insulator called the dielectric. The symbols for fixed and variable

capacitors are given in fig. Polarized types must be connected so that conventional current enters

their positive terminal. Non-polarized types can be connected either way round.

The capacitance (C) of a capacitor measures its ability to store charge and is stated in farads

(f). The farad is sub-divided into smaller, more convenient units.

1 microfarad (1uF) = 1 millionth of a farad = 10-6

F

1 nanofarad (1 nF) = 1 thousand- millionth of a farad = 10-9

F

1 picofarad ( 1pF ) = 1 million-millionth of a farad = 10-12

F

In practice, capacitances range from 1 pF to about 150 000 uF: they depend on the area A of

the plates (large A gives large C), the separation d of the plates (small d gives large C) and the

material of the dielectric (e.g. certain plastics give large C).

When selecting a particular job, the factors to be considered are the value (again this is notcritical in many electronic circuits), the tolerance and the stability. There are two additional factors.

(i) The working voltage. The is the largest voltage (d.c.or pead a.c.) which can be applied

across the capacitor and is often marked on it, e.g. 30V wkg. It is exceeded, the dielectric breaks

down and permanent damage may result.

(ii) The leakage current. No dielectric is a perfect insulator but the loss of charge through

it as leakage current should be small.


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FIXED CAPACITORS

Fixed capacitors can be classified according to the dielectric used; their properties depend on

this. The types described below in (i), (ii) and (iii) are non-polarized, those in (iv) are polarized.

(i) Polyester. Two strips of polyester film (the plastic dielectric) are wound between two

strips of aluminum foil (the plates). Two connections, one to each strip of foil, form the capacitor

leads. In the metallized version, films of metal are deposited on the plastic and act as the plates. Their

good all-round properties and small size make them suitable for many applications in electronics.

Values range from 0.01uF to 10uF or so and are usually marked (in pF) using the resistor colour

code. Polycarbonate capacitors are similar to the polyester type; they have smaller leakage currents

and better stability but cost more.

(ii) Mica. Mica is naturally occurring mineral, which splits into very thin sheets of uniform

thickness. Plates are formed by depositing a silver film on the mica or by using interleaving sheets of

aluminum foil. Their tolerance is low ( + 1% ), stability and working voltage high, leakage current

low but they are used in radio frequency tuned circuits where low loss is important and are pictured

in figs. Polystyrene capacitors have similar though not quite so good properties as mica types but are

cheaper.

(iii) Ceramic. There are several types depending on the ceramic used. One type has similar

properties to mica and is used in radio frequency circuits. In another type, high capacitance values areobtained with small size, but stability and tolerance are poor; they are useful where exact values are

not too important. They may be disc, rod- or plate-shaped. A disc-shaped capacitor is shown in fig.

Values range form 10pF to 1uF.

(iv) Electrolytic. In the aluminum type the dielectric is an extremely thin layer of aluminum

oxide which is formed electrolytically. Their advantages are high values (up to 150 000uF) in a small

volume and cheapness. Their disadvantages are wide tolerance (-20 to + 100% of the value printed on

them), high leakage current and poor stability but they are used where these factors do not matter and

high values are required, e.g. in power supplies. Examples are shown in Fig.

Electrolytics are polarized. Usually their positive terminal is marked with a + or by

a groove; often the aluminum can is the negative terminal. The d.c. leakage current maintains the

oxide layer, otherwise reversed polarity (or disuse) will cause the layer to deteriorate.


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Tantalum electrolytic capacitors can be used instead of aluminum in low voltage circuits where values

do not exceed about 100 uF. They have lower leakage currents.


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TRANSISTORS

Transistors are the most important devices in electronics today. Not only are they made as

discrete (separate) components but integrated circuits (Ics) may contain several thousands on a tiny

slice of silicon. They are three-terminal devices, used as amplifiers and as switches. Non-amplifying

components such as resistors, capacitors, inductors and diodes are said to be passive; transistors are

active capacitors, inductors and diodes are said to be passive; transistors are active components.

The two basic types of transistor are:

(a) the bipolar or junction transistor (usually called the transistor) ; its operation depends on

the flow of both majority and minority carriers;

(b) the unipolar or field effect transistor (called the FET) in which the current is due to

majority carriers only (either electrons or holes).

JUNCTION TRANSISTOR

(i) CONSTRUCTION. The bipolar or junction transistor consists of two p-n junctions in the

same crystal. A very thin slice of lightly doped p-or n-type semiconductor (the base B) is sandwiched

between two thicker, heavily doped materials of the opposite type (the collector C and emitter E).

The two possible arrangements are shown diagrammatically in fig with their symbols. The

arrow gives the direction in which conventional (positive) current flows; in the n-p-n type it points

from B to E and in the p-n-p type it points from B to E and in the p-n-p type from E to B.


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As with diodes, silicon transistors are in general preferred to germanium ones because they

withstand higher temperatures( up to about 1750

C compared with 750

C) and higher voltages, have

lower leakage currents and are better suited to high frequency circuits. silicon n-p-n types, are more

easily mass-produced than p-n-p type, the opposite is true of germanium.

A simplified section of an n-p-n silicon transistor made by the planarplanarprocess in which

the transistor is in effect created on one face (plane) of a piece of semiconducting material; fig.

Shows a transistor complete with case (called the encapsulation) and three wire leads.

(ii) ACTION. An n-p-n silicon transistor is represented and is connected in a common

emitter circuit ; the emitter is joined (via batteries B1 and B2 ) to both the base and the collector . For

transistor action to occur the base emitter junction must be forward biased, i.e. positive terminal of

B1 to p- type base, and the collector base junction reverse biased , i.e. positive terminal of B2 to n-

type collector .

When the base emitter bias is about +0.6 V, electrons ( the majority carriers in the heavilydoped n type emitter ) cross the junction ( as they would in any junction diode) into the base . Their

loss is made good by electrons entering the emitter from the external circuit to form the emitter

current . At the same time holes from the base to the emitter but , since the p- type base is lightly

doped , this is small compared with the electron flow in the opposite direction , i.e. electrons are the

majority carriers in an n-p-n transistor .


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In the base , only a small proportion ( about 1% ) of the electrons from the emitter combine

with the holes in the base because the base is very thin ( less than millionth of a meter ) and is lightly

doped . Most of the electrons are swept through the base , because they are attracted by the positive

voltage on the collector , and the cross base collector junction to become the collector current in

the circuit .

The small amount of electron hole recombination which occurs in the base gives it a

momentary negative charge which is immediately compensated by battery B1 supplying it with

(positive ) holes . The flow of holes to the base from the external circuit creates a small base current .

This keeps the base emitter junction forward biased and so maintains the larger collector current .

Transistor action is turning on ( and controlling ) of a large current through the high resistance

( reverse biased ) collector base junction by a small current through the low resistance ( forward

biased ) base emitter junction . the term transistor refers to this

effect and comes from the two words transfer resistor . Physically the collector is larger than the

emitter and if one is used in place of the other the action is inefficient .

The behavior of a p-n-p transistor is similar to that of the n-p-n type but it is holes that

are the majority carriers which flow from the emitter to the collector and electrons are injected into

the base to compensate for recombination . To obtain correct biasing the polarities of both batteries

must be reversed .


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DIODE

The simplest semiconductor device is made up of a sandwich of P-type semiconducting

material, with contacts provided to connect the P-and n-type layers to an external circuit, this is a

junction Diode. If the positive terminal of the battery is connected to the p-type material (cathode)

and the negative terminal to the N-type material (Anode), a large current will flow. This is called

forward current or forward biased.

If the connection are reversed, a very little current will flow. This is because under this

condition, the p-type material will accept the electrons from the negative terminal of the battery and

the N-type material will give up its free electrons to the battery, resulting in the state of electrical

equilibrium since the N-type material has no more electrons. Thus there will be a small current to

flow and the diode is called Reverse biased.

Thus the Diode allows direct current to pass only in one direction while blocking it in the

other direction. Power diodes are used in concerting AC into DC. In this, current will flow freely

during the first half cycle (forward biased) and practically not at all during the other half cycle

(reverse biased). This makes the diode an effective rectifier, which convert ac into pulsating dc.

Signal diodes are used in radio circuits fro detection, Zener diodes are used in the circuit to control

the voltage.

A diode allows current to flow easily in one direction but not in the other, i.e. its resistance is

low in the conducting or forward direction but very high in the opposing or reverse direction.

Most semiconductor diodes are made from silicon or germanium.

A diode has two leads, the anode and the cathode: its symbol is given in fig (a). The cathode is often

marked by a band at one end fig.(b); it is the lead by which conventional current leaves the diode whenforward biased as the arrow on the symbol shown. In some cases the arrow is marked on the diode

fig.(c) or the shape is different (d), (e)


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There are several kinds of diode, each with features that suit it for a particular job. Three of

the main types are:

(a) The junction diode,

(b) The point-contact diode and

(c) The zener diode

Two identification codes are used for diodes. In the American system the code always starts

with 1N and is followed by a serial number, e.g. IN 4001. in the continental system the first letter

gives the semiconductor material (A=germanium, B= silicon) and the second letter gives the use.

(A=signal diode, Y=rectifier diode, Z=Zener diode.). for example, AA119 is a germanium signaldiode,. To complicate the situation some manufacturers have their own codes.

ZENER DIODE

Zener diodes are very important because they are the key to voltage regulation. The chapter

also includes optoelectronic diodes, Schottky diodes, varactors, and other diodes.

A Zener diode is specially designed junction diode which can operate continuously without

being damaged in the region of reverse breakdown voltage. One of the most important application of

zener diode is the design of constant voltage power supply. The zener diode is joined in reverse bias

to D.C. through a resistance of suitable value.

Small-signal and rectifier diodes are never intentionally operated in the breakdown region

because this may damage them. A zener diode is different; it is a silicon diode hat the manufacturer

has optimized for operation in the breakdown region, zener diodes work best in the breakdown


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region. Sometimes called a breakdown diode, the zener diode is the backbone of voltage regulators,

circuits that hold the load voltage almost constant despite large changes in line voltage and load

resistance.

Figure shows the schematic symbol of a zener diode; another figure is an alternate symbol. In

the either symbol, the lines resemble a z, which stands for zener. By varying the doping level of

silicon diodes, a manufacturer can produce zener diodes with breakdown voltage from about 2 to

200V. These diodes can operate in any of three regions: forward, leakage, or breakdown.

Figure shows the I-V graph of a zener diode. In the forward region, it starts conduction

around 0.7V, just like a ordinary silicon diode, In the leakage region (between zero and breakdown),

it has only a small leakage or reverse current. In a zener diode, the breakdown has a very sharp knee,

followed by an almost vertical Vz over most of breakdown region. Data sheets usually specify the

value of Vz at a particular test current IzT.


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L.E.D.

(LIGHT EMITTING DIODE)

Light emitting diode (LED ) is basically a P-N junction semiconductor diode particularly

designed to emit visible light. There are infra-red emitting LEDs which emit invisible light. The

LEDs are now available in many colour red, green and yellow,. A normal LED emit at 2.4V and

consumes MA of current. The LEDs are made in the form of flat tiny P-N junction enclosed enclosed

in a semi-spherical dome made up of clear colured epoxy resin. The dome of a LED acts as a lens and

diffuser of light. The diameter of the base is less than a quarter of an inch. The actual diameter varies

somewhat with different makes. The common circuit symbols for the LED are shown in fig. 1. It is

similar to the conventional rectifier diode symbol with two arrows pointing out. There are two leads-

one for anode and the other for cathode.

LEDs often have leads of dissimilar length and the shorter one is the cathode. This is not

strictly adhered to by all manufacturers. Sometimes the cathode side has a flat base. If there is doubt,

the polarity of the diode should be identified. A simple bench method is to use the ohmmeter

incorporating 3-volt cells for ohmmeter function. When connected with the ohmmeter: one way there

will be no deflection and when connected the other way round there will be a large deflection of a

pointer. When this occurs the anode lead is connected to the negative of test lead and cathode to the

positive test lead of the ohmmeter.

(ii) External resistor. Unless an LED is of the constant-current type (incorporating an

integrated circuit regulatorsee Unit 20.4for use on a 2 to 18 V d.c. or a. c. supply), it must have

an external resistor R connected in series to limit the forward current which, typically, may be 10 mA(0.01 A). Taking the voltage drop (Vf) across a conducting LED to be about 107 V, R can be

calculated approximately from:

(supply voltage 1.7) V

R =

0.01A


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For example, on a 5 V supply, R = 3.3/0.01 = 330 Ohm.

(i) Action. An LED consists of a junction diode made form the semiconducting compound

gallium arsenide phosphide. It emits light when forward biased, the colour depending on the

composition and impurity content of the compound. At present red, yellow and green LEDs are

available. When a p-n junction diode is forward biased, electrons move across the junction from the

n-type side to the p-type side where they recombine with holes near the junction. The same occurs

with holes going across the junction from the p-type side. Every recombination results in the release

of a certain amount of energy, causing, in most semiconductors, a temperature rise. In gallium

arsenide phosphide some of the energy is emitted as light which gets out of the LED because the

junction is formed very close to the surface of the material. An LED does not light when reverse

biased and if the bias is 5 V or more it may be damaged.

(ii) External resistor. Unless an LED is of the constant-current type (incorporating an

integrated circuit regulatorsee Unit 20.4for use on a 2 to 18 V d.c. or a. c. supply), it must have

an external resistor R connected in series to limit the forward current which, typically, may be 10 mA

(0.01 A). Taking the voltage drop (Vf) across a conducting LED to be about 107 V, R can be

calculated approximately from:

(supply voltage 1.7) V

R =

0.01A


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For example, on a 5 V supply, R = 3.3/0.01 = 330 Ohm.

(iii) Decimal display. Many electronic calculators, clocks, cash registers and measuring

instruments have seven-segment red or green LED displays as numerical indicators (Fig. 9.18(a)).

Each segment is an LED and depending on which segments are energized, the display lights up the

numbers 0 to 9 as in Fig. 9.18(b). Such displays are usually designed to work on a 5 V supply. Each

segment needs a separate current-limiting resistor and all the cathodes (or anodes) are joined together

to form a common connection.

The advantages of LEDs are small size, reliability, long life, small current requirement and

high operating speed.


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SEVEN SEGMENT DISPLAY


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OPEN AMPLIFIER

741-pin functions: (Refer to the internal 741 schematic of Fig. 3)

Pin 1 (Offset Null): Offset nulling, see Fig. 11. Since the op-amp is the differential type, input offset

voltage must

be controlled so as to minimize offset. Offset voltage is nulled by application of a voltage of opposite

polarity to the

ofset. An offset null-adjustment potentiometer may be used to compensate for offset voltage. The null-

offset potentiometer also compensates for irregularities in the operational amplifiermanufacturing process which may cause an offset. Consequently, the null potentiometer is

recommended for critical applications. See Offset Null Adjustment for method.

Pin 2 (Inverted Input): All input signals at this pin will be inverted at output pin 6. Pins 2 and 3 are

very important (obviously) to get the correct input signals or the op amp can not do its work.

Pin 3 (Non-Inverted Input): All input signals at this pin will be processed normally without invertion.

The rest is the same as pin 2.

Pin 4 (-V): The V- pin (also referred to as Vss) is the negative sup-

ply voltage terminal. Supply-voltage operating range for the 741 is -4.5 volts (minimum) to -18 volts

(max), and it is specified for


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operation between -5 and -15 Vdc. The device will operate essentially the same over this range of

voltages without change in timing period. Sensitivity of time interval to supply voltage change is low,

typically 0.1% per volt. (Note: Do not confuse the -V with ground).

Pin 5 (Offset Null): See pin 1, and Fig. 11.

Pin 6 (Output): Output signals polarity will be the oposite of the inputs when this signal is applied to

the op-amps inverting input. For example, a sine-wave at the inverting input will output a

square-wave in the case of an inverting comparator circuit.

Pin 7 (posV): The V+ pin (also referred to as Vcc) is the positive supply voltage terminal of the 741 Op-

Amp IC. Supply-voltage operating range for the 741 is +4.5 volts (minimum) to +18 volts

(maximum), and it is specified for operation between +5 and +15 Vdc. The device will operate

essentially the same over this range of voltages without change in timing period. Actually, the most

significant operational difference is the output drive capability, which increases for both current and

voltage range as the supply voltage is increased. Sensitivity of time interval to supply voltage

change is low, typically 0.1% per volt.

Pin 8 (N/C): The N/C stands for Not Connected. There is no other explanation. There is nothing

connected to this pin, it is just there to make it a standard 8-pin package.

Output Parameters:

1. Output Resistance (Zoi)

The resistance seen looking into the op-amps output.

2. Output Short-Circuit Current (Iosc)

This is the maximum output current that the op-amp can deliver to a load.

3. Output Voltage Swing (Vo max)

Depending on what the load resistance is, this is the maximum peak output voltage that the op-amp can

supply without saturation or clipping.

Dynamic Parameters:

1. Open-Loop Voltage Gain (Aol)

The output to input voltage ratio of the op-amp without external feedback.


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2. Large-Signal Voltage Gain

This is the ratio of the maximum voltage swing to the charge in the input voltage required to drive the

ouput from zero to a specified voltage (e.g. 10 volts).

3. Slew Rate (SR)

The time rate of change of the ouput voltage with the op-amp circuit having a voltage gain of unity

(1.0).

Other Parameters:

1. Supply Current

This is the current that the op-amp will draw from the power supply.

2. Common-Mode Rejection Ratio (CMRR)

A measure of the ability of the op-amp to reject signals that are simultaneously present at both inputs. It

is the ratio of the common-mode input voltage to the generated output voltage, usually

expressed in decibels (dB).

.


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ADVANTAGES:

1. Low power requirements: therefore ideal for laptops, telephones, personal digital assistants

2. Low circuitry costs: $2-$5 for the entire coding/decoding circuitry

3. Simple circuitry: no special or proprietary hardware is required, can be incorporated into the

integrated circuit of a product

4. Higher security: directionality of the beam helps ensure that data isn't leaked or spilled to nearby

devices as it's transmitted

5. Portable

6. Few international regulatory constraints: IrDA (Infrared Data Association) functional devices

will ideally be usable by international travelers, no matter where they may be

7. High noise immunity: not as likely to have interference from signals from other devices

DISADVANTAGES:

1. Line of sight: transmitters and receivers must be almost directly aligned (i.e. able to see each

other) to communicate

2. Blocked by common materials: people, walls, plants, etc. can block transmission

3. Short range: performance drops off with longer distances

4. Light, weather sensitive: direct sunlight, rain, fog, dust, pollution can affect transmission5. Speed: data rate transmission is lower than typical wired transmission

6. The matching of infrared pair is difficult.


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APPLICATIONS:-

1. Augmentative communication devices

2. Computers

a. Mouseb. Keyboards

c. Floppy disk drives

d. Printers

3. Car locking systems

4. Emergency response systems

5. Environmental control systems

a. Windows

b. Doors

c. Lights

d. Curtains

e. Beds

f. Radios

6. Headphones

7. Home security systems

8. Navigation systems

9. Signage

10. Telephones

11. TVs, VCRs, CD players, stereos

12. Toys

13. Infrared technology offers several important advantages as a form of wireless communication.

Laser Final

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