digital heart

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PROJECT REPORT

ON

DIGITAL HEART BEAT COUNTER

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Chapter 1

ANATOMY OF HUMAN HEART

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1.1 Anatomy of human heart

The human heart is located in the chest between the lungs, behind the sternum and

above the diaphragm. It weighs between 200 to 425 grams and is a little larger than

the size of a fist [2, 3, 4]. The basis end and the apex end of the heart lie on its main

axis which is oriented from the back-top-right to the front-bottom-left of the torso .

Everyday it beats in average 100000 times pumping about 7600 liters of blood to the

body [5]. Like a sack, a double-layered membrane called the pericardium surrounds

the heart. Its outer layer covers the roots of the heart’s major blood vessels and is

attached by ligaments to the spinal column, diaphragm, and other parts of your

body. The inner layer of the pericardium is connected to the heart muscle. The

layers are separated by a coating of fluid, letting the heart move as it beats and

keeping it attached to the body. The normal periodic contractions and relaxations of

the heart allow the human cells receiving the necessary amount of oxygen and

nutrients and carrying away their end product of the metabolism.

The walls of the heart are composed of cardiac muscle, Myocardium. It is similar to

skeletal muscle, because it has striations. The cardiac muscle consists of four

chambers: the right and left atria and ventricles. The anterior aspect of the heart is

the right ventricle, whereas the posterior aspect is the left atrium giving the heart its

orientation. The endocardium is defined as the thin serous membrane that lines the

interior of the heart, whereas the epicardium touches the inner layer of the

pericardium that is in actual contact with the surface of the heart. The left ventricle

pumps blood to the systemic circulation, where pressure is considerably higher than

for the pulmonary circulation, which arises from right ventricular outflow. The left

ventricular free wall and the septum is much thicker than the right ventricular wall

[6]. The tricuspid valve lays between the right atrium and ventricle, and the mitral

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valve is between the left atrium and ventricle. Between the right ventricle and the

pulmonary artery lies the pulmonary valve, while the aortic valve is in the outflow

tract of the left ventricle controlling blood flow to the aorta. Carried in the inferior

and superior vena cava, the blood returns from the systemic circulation to the right

atrium [7, 8, 9]. First, it has to go through the right ventricle, then it is

ejected through the pulmonary valve and the pulmonary artery to the lungs. Oxygen-

rich blood returns from the lungs to the left atrium and to the left ventricle. Finally

blood is pumped through the aortic valve to the aorta and the systemic circulation.

The left and right coronary arteries branch off the aorta. They are divided afterward

into numerous smaller arteries supplying oxygen and nourishments to all heart

muscles.

Fig 1.1 : The location and the orientation of the human heart in the

chest

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1.2 Heart Structure

Anatomically, the heart consists of cardiac myocytes, pacemakers and conducting

tissues, and extracellular space. Myofibers are connected together by further strands

of collagen.

1.2.1 Cardiac Myocytes

The cell is the basic unit of living tissue. Cells perform different tasks relating to

their anatomy and physiology, and exhibit a voltage difference across their

membranes. Only nerve and muscle cells are excitable. The working myocardium

consists of muscle cells or cardiomyocytes, which have in general a roughly

cylindrical shape and are able to produce mechanical tension. The individual

contractile muscle cells account more than half of the heart’s weight. In atria, they

are quite smaller in length and diameter than in ventricles. Each cardiac myocyte is

bounded by a complex cell membrane, sarcolemma, separating its intracellular

components from the extracellular space.

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1.4 The Heart Valves (illustration)

Four types of valves regulate blood flow through your heart:

• The tricuspid valve regulates blood flow between the right atrium and right

ventricle.

• The pulmonary valve controls blood flow from the right ventricle into the

pulmonary arteries, which carry blood to your lungs to pick up oxygen.

• The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium

into the left ventricle.

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http://www.texasheartinstitute.org/HIC/Anatomy/valves.cfm

http://www.texasheartinstitute.org/HIC/Anatomy/valves.cfm



• The aortic valve opens the way for oxygen-rich blood to pass from the left

ventricle into the aorta, your body’s largest artery, where it is delivered to the rest

of your body.

1.4 The Conduction System

Electrical impulses from your heart muscle (the myocardium) cause your heart to

contract. This electrical signal begins in the sinoatrial (SA) node, located at the top of the

right atrium. The SA node is sometimes called the heart’s “natural pacemaker.” An

electrical impulse from this natural pacemaker travels through the muscle fibers of the

atria and ventricles, causing them to contract. Although the SA node sends electrical

impulses at a certain rate, your heart rate may still change depending on physical

demands, stress, or hormonal factors.

1.4 The Circulatory System

Your heart and circulatory system make up your cardiovascular system. Your heart works

as a pump that pushes blood to the organs, tissues, and cells of your body. Blood delivers

oxygen and nutrients to every cell and removes the carbon dioxide and waste products

made by those cells. Blood is carried from your heart to the rest of your body through a

complex network of arteries, arterioles, and capillaries. Blood is returned to your heart

through venules and veins. If all the vessels of this network in your body were laid end-

to-end, they would extend for about 60,000 miles (more than 96,500 kilometers), which

is far enough to circle the earth more than twice!

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Chapter 2

INTRODUCTION TO DIGITAL HEART-BEAT

COUNTER

The heart-beat rate, also known as the pulse rate, is the number of times a person’s heart beats in a minute. It is one of the four vital signs that are often taken by

doctors to assess the most basic functions of the patient’s body. So counting

of heart-beats sometimes becomes essential for proper treatment.

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Although the pulse rate can be measured manually by ourselves, an electronic digital

heart-beat counter gives the opportunity to measure it automatically and continuously.

Here is a digital heart-beat counter that has the following features.

A piezoelectric accelerometer used as the sensor.

1. A blinking LED for visual indication of heart-beats.

2. Counts are automatic and displayed on a 2-digit, 7-segement display.

3. Continuous monitoring can be done.

4. Counting can be read from a remote place.

5. The processed signal can be fed to a data-acquisition system (DAS) to observe or

save the nature of the pulse.

6. Works off AC mains or batteries.

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Chapter 3

PRINCIPLE

A person’s heart forces hic blood to flow through the arteries. As a result, the arteries

throb in synchronization with the beating of the heart. This throbbing can be felt at the

person’s wrist and other places over the body.

Electronically, this throbbing can be sensed with an accelerometer that generates

electrical signals against the vibration-resulted processing of the signals. The counter the

pulses for 10 seconds and then displays the same for the text five seconds. The process

repeats as long as the accelerometer sensor is tied tightly around the person’s wrist.

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Fig 3.1 : Block Digram of Digital Heart Beat Counter

Chapter 4

ACCELEROMETER

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4.1 What is an accelerometer?

An accelerometer measures the real-time, instantaneous acceleration of the object on

which the accelerometer is mounted. It transduces the acceleration, which results from

some shock or vibration, into a proportional analogue signal. Although there exist

numerous types of accelerometers, the piezoelectric type is the most widely used.

4.2 Piezoelectric accelerometer

The basic construction of a high-impedance, single-axis piezoelectric accelerometer is

shown in Fig. 1. At the heart of the accelerometer is a piezoelectric crystal. Apart from

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the natural quartz, many ceramics are nowadays used as the piezoelectric crystal for

accelerometer construction. The most common ceramics used fro this purpose are lead

metaniobate, leadzirconate and lead titanate. A small mass is affixed over the crystal. The

whole system is housed in an enclosure such that the mass can move along the axis

shown, while the spring opposes its movement.

When the accelerometer is subjected to acceleration, the mass exerts a force on the

crystal along the axis of the accelerometer. The magnitude of the force is dependent upon

two laws: Newton’s second law of motion (P=mf) and Hook’s law fro linear spring

temporary infinitesimal change (dx) in the dimension of the crystal, is directly

proportional to the acceleration (f). Here ‘k’ is the spring constant.

When such an accelerometer is tightly coupled to one’s wrist, throbbing of arteries

supplies this acceleration. Due to temporary deformation of the crystal by the exerted

force, the piezoelectric crystal develops a charge across the across the electrodes attached

to its lower and upper surfaces. The crystal regains its original dimensions as soon as the

acceleration disappears.

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Fig 4.1 : Basic construction of high impedance, single axis

Piezoelectric accelerometer

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Chapter 5

CIRCUIT DESCRIPTION

The circuit of digital heart-beat counter. The total circuit can be divided into various

sections as follows: preamplifier, low-pass filter pulse monitor, and pulse counter with

digital readouts.

5.1 Preamplifier

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As indicated above, at the heart of the circuit is a piezoelectric accelerometer or

vibration sensor. When attached to a person’s wrist tightly, the sensor outputs an

electrical charge, directly proportional to the magnitude of throbbing of the arteries. The

charge gives a voltage of the order of a few millivolts across very high impedance of the

piezoelectric crystal. Hence, a high-input impedance preamplifier is required to amplify

the signal properly from the accelerometer. Although a single ‘FET-Input’ operational

amplifier (op-amp) can be used for it, an instrumentation amplifier is the ideal choice, as

it greatly enhances the CMRR. A high CMRR considerably reduces the ground noise and

other common-mode noises from the surrounding environment.

In the circuit here, three op-amps IC1, IC2 and IC3 (all MOSFET input CA3140)

unitedly act as an instrumentation amplifier. The gain can be altered easily by simply

varying resistor R3.

5.2 Low-pass filter

The output signal from the instrumentation amplifier gets adulterated with some

harmonics of 50HZ AC power frequency, along with some other high-frequency

interfering signal coming from the surrounding. A Sallen key low-pass filter (LPF) is

used to reduce all these interferences.

The amplified output voltage from IC3 of the 3-op-amp intrumentation amplifier is fed

to op-amp IC4 through resistor R10. Op-amp IC4 along with resistor R10 and R12 and

capacitors C4 and C5 forms the unity-gain Sallen key low-pass filter. Although the

presence of R11 and VR3 (offset adjustable) reduces the output voltage slightly, the

upper cut-off frequency of the filter, set by the said registers and capacitors, is 1.5 HZ

(approx.). All frequencies above 10 HZ would be greatly filtered out.

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5.3 Pulse monitor

A part of the filtered output from IC4 is fed through a one-stage RC low-pass filter

comprising R14 and C7,to pin 3 of op-amp IC5 (µA741). The RC filter enhances the

steepness of the previous filter response curve. This additional stage of amplification is

required for driving LED1 and LED2.

The LEDs blink in synchronization with heart-beat pulses coming from the

accelerometer. These are fed though diodes D1 and d2 such that while One LED blinks

during diastoles, the other one blinks during systoles. The stage has a gain of ‘22’

(approx.).

5.5 Pulse counter and digital readouts

CMOS decade counters IC9 and IC10 (each CD4033) connected in tandem form the 2-

digit decimal counter, which counts the heart-beat pulses coming from the Sallen Key

low-pass filter (LPF). If pin 2 (CE input) of IC10 is at logic 0, each pulse from the LPF

advances the counter by ‘1.’ The logic condition of pin 2 is dependent upon the logic

condition of the monoshot configured around IC8 (NE555). The time period of the

monoshot is governed by the combination of resistor R22, preset VR5 and capacitor C12,

and can be set for 10 seconds. Another monoshot, configured around IC7 (NE555), can

be set by varying preset VR6 to give a time period of 15 seconds.

The two monoshots are triggered simultaneously whenever a low-going pulse from the

LPF reaches the common trigger input (pin 2 of each NE555) line. As soon as they are

triggered, their respective output goes low at the same time. While the output of IC8

stays in this logic state for 10 seconds, the output of IC7 is designed to stay low for

additional five seconds.

Transistor T2 inverts the output of IC8 (logic1) to drag CE input of IC10 (pin 2) to

logic 0. As soon as IC8 is triggered, the leading edge of the positive-going output pulses

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resets decade counters IC9 and IC10 via capacitor C13. The two 7-segment display DIS1

and DIS2 now show the counts as ’00.’ The counter is now enabled to count for 10

seconds.

Since the output of monoshot IC7 is triggered at the same time, pin 9 of the OR gate

IC6 goes high. It remains high for the time equal to the time period of IC7, i.e., 15

seconds. During that period, no further heart-beat pulse is allowed to trigger monoshot

IC7 or IC8. This is because the output of OR gate holds the common trigger input high.

However, the beating pulses are allowed to teach counter goes on counting the pulses as

long as the output of IC8 remains high. At the end of 10 seconds, the output of IC8 goes

low. This disables IC10 and no further counting is allowed. The so-far counted result is

now displayed on 7-segment displays – DIS1 and DIS2 –connected to the output of

decade counters IC9 and IC10, respectively.

At the end of 15 seconds, the output of monshot IC7 again goes low, allowing the

incoming pulses to trigger the monoshots to repeat the cycle. The process continues as

long as the accelerometer is tied to one’s wrist.

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Fig 5.1 : Circuit digram of digital heart beat counter

5.6 Power supply

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Fig. shows the power supply circuit. The 230V AC mains is stepped down by

transformer X1 to deliver a secondary output of 9V-0-9V, 500 ma. The transformer

output is rectified by a full-wave bridge rectifier comprising diodes D3 through D6,

filtered by capacitors C14 and C15, and regulated by IC11 and IC12. Regulators 7805

and 79-5 provide +5V regulated supply to the circuit. Capacitors C16I and C17 bypass

any ripple present in the regulated supply.

Fig 5.2 : Power supply circuit

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Chapter 6

CONSTRUCTION OF SENSOR

6.1 Method of construction :

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Instead of a commercial accelerometer, a self-constructed piezoelectric accelerometer is

used in this project. It is constructed by using a ceramic piezobuzzer element. These

elements are widely used in landline telephone sets to produce ring tones. In the market,

they are found in two varieties: with oscillator and without oscillator. The without-

oscillator variety is suitable for our purpose .

The diameters of the brass plate and the silver layer of the piezobuzzer plate used in this

project are around 27 mm and 18 mm, respectively. To start construction, first of all

remove the top cover of the plastic case. Connect one of the 2- core cable to the brass

plate of the element. The shielded part of the cable should be kept open, but it should not

touch the element.

Mount the mass (1cm long piece of solid cylindrical brass rod having 1cm diameter)

centrally over the white silver layer with some adhesive-like Quickfix. Add the adhesive

at the sides of the mass to fix it over the crystal. Allow sufficient time fro drying up.

Generally, the cases have mounting holes at diametrically opposite sides. Attach a

length of Velcro belt (hooks) with the help of a small nut-bolt through one of the

mounting holes. Similarly, attach another length of Velcro belt (loops) at the other

mounting hole of the case. Bridge the two holes with a small piece of Velcro belt

(hooks/loops). The piece should be short enough to put some pressure on the top surface

of the brass rod. Too low or too high a pressure would hamper the sensitivity of the

accelerometer. The hooks-loops combination of the Velcro belts should be long enough

so that the accelerometer can grip a person’s wrist tightly.

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Fig 6.1 : Telephone piezobuzzer

6.2 Adjusting the offsetBefore using the counter, adjust it properly for effective functioning. To do so,

adjust the effective trimpots as follows: disconnect the accelerometer if connected, and

connect a 1-kilo-ohm resistor in between the two input leads of the instrumentation

amplifier (pin 2 of IC1 and IC2). Connect a digital voltmeter (DVM) across the outputs

of IC1 and IC2 (pin 6). Adjust offset trimpot VR1 to get 0.000V reading on the

voltmeter. Then adjust offset trimpot VR2 to get 0.000V reading at pin 6 of difference

amplifier IC3. Similarly, adjust VR3 to get 0.000Vat pin 6 of op-amp IC4. The output of

IC5 can not be set to 0.000V by similar adjustment. Try to keep it at its minimum by

varying trimpot VR4. It may be set to 0.a5V.

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6.3 Testing the amplifier

With a 1-kilo-ohm resistor in between the inputs, connect pin 2 of IC1 to +5 volts

through a 1-mega-ohm resistor and pin 2 of IC2 through another 1-mega-ohm resistor. As

a result, the input of the instrumentation amplifier would be driven by a 4m V DC

differential signal. The differential voltage at the outputs of IC1 and IC2 would be about

0.6V.

Although the Sallen Key filter is configured as unity gain, the presence of the offset-

adjusting resistors reduces the input voltage, and hence the out put at pin 6 of IC4 would

reduce to around 0.4V. With such an input voltage signal, the output at IC5 goes to

saturation and it is towards the +5V supply side. Reserving the polarity of the differential

voltage at the input of IC1 and IC2 would drag it to the –5V supply side. Depending upon

the direction of excursion of the output of IC5, either LED1 or LED2 starts glowing.

Now connect the accelerometer removing the 1-kilo-ohm and the other two 1-mega-ohm

resistors. A slight movement of the accelerometer with hand would trigger the

monoshots. The LEDs would also blink.

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6.4 Using the counter

The heart-beat rate (pulse) of any person can be measured merely by fastening the

accelerometer tightly around his wrist with the help of the two Velcro belts attached to it.

After a few moments, LED1 and LED2 fo the pulse-monitor would start blinking in

synchronization with the person’s hart-beats. The digital counter also starts counting at

the same time. It would count for 10 seconds and after that the 2-digit, 7-segment display

gives steady counts for the next 5 seconds. The cycle repeats as long as the as the

accelerometer is tied to the person’s wrist. The displayed counts should be multiplied by

‘6’ to get the counts/minute.

Monitoring of the heart-beat rate of a person from a remote place is also possible. To

do so, the 2-digit, 7-segment counter may be placed at the remote place and the signal

output from the LPF may be conveyed to the counter via a length of the coaxial cable.

Besides its rate, some other qualities of the pulse reflect the state of the cardiovascular

system. These are its rhythm, fullness and shape fo the pulse wave. The signal output

from the LPF/amplifier IC5 may be fed to a DAS system for monitoring all these

characteristics.

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Chapter 7

PCB DESIGN AND LAYOUT

An actual-size, single-side PCB for digital heart-beat counter is shown in Fig. 6 and its

component layout in Fig. 7. Since CA3140 is MOSFET input op-amp, it possesses a very

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high input impedance. The piezoelectric accelerometer is also a very high-output

impedance. Device. Hence, a glassepoxy PCB is used for the construction job to avoid

any leakage of current through the PCB. It would otherwise reduce the circuit gain and

sensitivity of the accelerometer. The shielded cable connecting the accelerometer to the

PCB may be around 1.5 meters long. The trimpots used for offset adjustments should be

25-turn type.

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Fig 7.1 : Actual size single- side PCB fot the digital heart beatcounter

PCB Layout :

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Fig 7.2 : Component layout for the PCB

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Chapter 8

LIST OF COMPONENTS

Semiconductors:

IC1-IC3…………………………CA 3140 operational amplifierIC4-IC5…………………………CA7410.operational amplifierIC6……………………………..CD4071 OR Gate

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IC7,IC8………….......................NE555 timerIC9,IC10………………………CD4033 counter,sevensegment display driver

IC11…….……………………..+5V 7805 regulator

IC12...........................................-5V 7905 regulatorDIS1,DIS2........................LT543 commen-cathode,7-segmentdisplayD1-D6…………………………..1N4007 DiodeLED1,LED2……………………..5mm LED

T1,T2….........................BC377 npn transistor

Resistors

R1,R2,R14,R16,R20,R25............... 470-kilo-ohm

R,4R5,15R,R24 ........................... 22-kilo ohm

R3............................................ 270 ohm

R6-R13,R22,R23............................ 1-mega ohm

R17.................................................. 560 kilo ohm

R18,R19....................................... 1 kilo ohm

R21................................................. 27-kilo ohm

R26................................................. 100 kilo ohm VR1-VR4....................... 10-kilo ohm, 25-

turn trimpot

VR5,VR6…………………………. 1-mega ohm preset

Capacitors

C1-C3, C6-C8 …………………………0.1microFarad ceramicdisk

C4,C5…………………………….47 nano farad

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C10-C12………………………………….4.7 microFarad,12VelectrolyticC9,C11,C13……………………………0.01 microFarad ceramicdisk

C14,C15 .....………………………1000 microFarad,25VelectrolyticC16,C17 ………………………….100 microFarad,16Velectrolytic

Miscellaneous

230V AC primary to 9V-0-9V,500msecondary transformer.

Piezobuzzer

Velcro belt

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Chapter 9

DESCRIPTION OF COMPONENTS

9.1 RESISTENCE

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.

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Resistance is the opposition of a material to the current. It is measured in Ohms ( ). All

conductors represent a certain amount of resistance, since no conductor is 100% efficient.

To control the electron flow (current) in a predictable manner, we use resistors.

Electronic circuits use calibrated lumped resistance to control the flow of current.

Broadly speaking, resistor can be divided into two groups viz. fixed & adjustable

(variable) resistors. In fixed resistors, the value is fixed & cannot be varied. In variable

resistors, the resistance value can be varied by an adjuster knob. It can be divided into (a)

Carbon composition (b) Wire wound (c) Special type. The most common type of resistors

used in our projects is carbon type. The resistance value is normally indicated by colour

bands. Each resistance has four colours, one of the band on either side will be gold or

silver, this is called fourth band and indicates the tolerance, others three band will give

the value of resistance (see table). For example if a resistor has the following marking on

it say red, violet, gold. Comparing these coloured rings with the colour code, its value is

27000 ohms or 27 kilo ohms and its tolerance is ±5%. Resistor comes in various sizes

(Power rating). The bigger, the size, the more power rating of 1/4 watts. The four colour

rings on its body tells us the value of resistor value as given below.

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

from the stated value.

9.1.1 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.

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one with a stated (called nominal) value of 100 and a tolerance of +-10% could

have any value between 90 and 110

9.1.2 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.

9.1.3 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.

9.1.4 Colour Coding

Black--------------------------------------------0

Brown-------------------------------------------1

Red----------------------------------------------2

Orange------------------------------------------3

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Yellow------------------------------------------4

Green--------------------------------------------5

Blue----------------------------------------------6

Violet--------------------------------------------7

Grey---------------------------------------------8

White--------------------------------------------9

Fig 9.1 : Different type of resistors

The first rings give the first digit. The second ring gives the second digit. The third

ring indicates the number of zeroes to be placed after the digits. The fourth ring gives

tolerance (gold ±5%, silver ± 10%, No colour ± 20%).In variable resistors, we have the

dial type of resistance boxes. There is a knob with a metal pointer. This presses over

brass pieces placed along a circle with some space b/w each of them.

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Resistance coils of different values are connected b/w the gaps. When the knob is

rotated, the pointer also moves over the brass pieces. If a gap is skipped over, its

resistance is included in the circuit. If two gaps are skipped over, the resistances of both

together are included in the circuit and so on.

A dial type of resistance box contains many dials depending upon the range,

which it has to cover. If a resistance box has to read upto 10,000 , it will have three

dials each having ten gaps i.e. ten resistance coils each of resistance 10 . The third dial

will have ten resistances each of 100 .The dial type of resistance boxes is better because

the contact resistance in this case is small & constant.

9.2 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 thedielectric. 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 not critical in many electronic circuits), the tolerance and the stability.There are two additional factors.

The working voltage

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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.

The leakage current

No dielectric is a perfect insulator but the loss of charge through it

as leakage current’ should be small.

9.2.1 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 eachstrip 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 from0.01uF 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 radiofrequency 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.

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(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 are obtained 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

Chapter10

SEMICONDUCTOR COMPONENTS

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10.1 Transistors

The name is transistor derived from ‘transfer resistors’ indicating a solid state

Semiconductor device. In addition to conductor and insulators, there is a third class of material that exhibits proportion of both. Under some conditions, it acts as an insulator,

and under other conditions it’s a conductor. This phenomenon is called Semi-conducting

and allows a variable control over electron flow. So, the transistor is semi conductor

device used in electronics for amplitude. Transistor has three terminals, one is the

collector, one is the base and other is the emitter, (each lead must be connected in the

circuit correctly and only then the transistor will function). Electrons are emitted via one

terminal and collected on another terminal, while the third terminal acts as a control

element. Each transistor has a number marked on its body. Every number has its own

specifications.

There are mainly two types of transistor (i) NPN & (ii) PNP

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10.1.1 NPN Transistors:

When a positive voltage is applied to the base, the transistor begins to conduct by

allowing current to flow through the collector to emitter circuit. The relatively small

current flowing through the base circuit causes a much greater current to pass through the

emitter / collector circuit. The phenomenon is called current gain and it is measure in

beta.

10.1.2 PNP Transistor:

It also does exactly same thing as above except that it has a negative voltage on its

collector and a positive voltage on its emitter.

Fig 10.1 : Symbols & representation of transistors

Transistor is a combination of semi-conductor elements allowing a controlled current

flow. Germanium and Silicon is the two semi-conductor elements used for making it.

There are two types of transistors such as POINT CONTACT and JUNCTION

TRANSISTORS. Point contact construction is defective so is now out of use. Junction

triode transistors are in many respects analogous to triode electron tube.

A junction transistor can function as an amplifier or oscillator as can a triode tube, but

has the additional advantage of long life, small size, ruggedness and absence of cathode

heating power.

Junction transistors are of two types which can be obtained while manufacturing.

42



The two types are: -

(1) PNP TYPE: This is formed by joining a layer of P type of germanium to an N-P Junction

(2) NPN

TYPE: This is formed by joining a layer of N type

germanium to a P-N Junction.

Both types are shown in figure, with their symbols for

representation. The centre section is called the base, one

of the outside sections-the emitter and the other outside

section-the collector. The direction of the arrowhead gives the direction of the

conventional current with the forward bias on the emitter. The conventional flow is

opposite in direction to the electron flow.

10.1.3 Operation of PNP Transistor :

A PNP transistor is made by sand witching two PN germanium or silicon diodes, placed

back to back. The centre of N-type portion is extremely thin in comparison to P region.

The P region of the left is connected to the positive terminal and N-region to the negative

terminal i.e. PN is biased in the forward direction while P region of right is biased

negatively i.e. in the reverse direction as shown in Fig. The P region in the forward

P N P

N P N

43



biased circuit is called the emitter and P region on the right, biased negatively is called

collector. The centre is called base.

Fig 10.2 : Working of PNP transistor

The majority carriers (holes) of P region (known as emitter) move to N region as they are

repelled by the positive terminal of battery while the electrons of N region are attracted

by the positive terminal. The holes overcome the barrier and cross the emitter junction

into N region. As the width of base region is extremely thin, two to five percent of holes

recombine with the free electrons of N-region which result in a small base current while

the remaining holes (95% to 98%) reach the collector junction. The collector is biasednegatively and the negative collector voltage aids in sweeping the hole into collector

region.

As the P region at the right is biased negatively, a very small current should flow but the

following facts are observed:-

1) A substantial current flows through it when the emitter junction is biased in

a forward direction.

2) The current flowing across the collector is slightly less than that of the

emitter and ,

44



3) The collector current is a function of emitter current i.e. with the

decrease or increase in the emitter current a corresponding change in the

collector current is observed.

The facts can be explained as follows:-

1. As already discussed that 2 to 5% of the holes are lost in recombination with the

electron n base region, which result in a small base current and hence the collector

current is slightly less than the emitter current.

2. The collector current increases as the holes reaching the collector junction are

attracted by negative potential applied to the collector.

3. When the emitter current increases, most holes are injected into the base

region, which is attracted by the negative potential of the collector and hence

results in increasing the collector current. In this way emitter is analogous to the

control of plate current by small grid voltage in a vacuum triode.

Hence we can say that when the emitter is forward biased and collector is

negatively biased, a substantial current flows in both the circuits. Since a small emitter voltage of about 0.1 to 0.5 volts permits the flow of an appreciable emitter current the

input power is very small. The collector voltage can be as high as 45 volts.

45



10.2 L.E.D. (Light Emitting Diode)

1

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.

10.2.1 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

46



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.

10.2.2 External resistor.

Unless an LED is of the ‘constant-

current type’ (incorporating an

integrated circuit regulator—see Unit 20.4—for 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

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

10.2.3 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

47



supply. Each segment needs a separate current-limiting resistor and all the cathodes (or

anodes) are joined together to form a common connection

10.3 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 connections 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 for detection. Zener

diodes are used in the circuit to control the voltage.

48



Fig 10.3 : Symbols & representation of diodes

Some common diodes are:-

1. Zener diode.

2. Photo diode.

3. Light Emitting diode.

10.3.1 ZENER DIODE:-

A zener diode is specially designed junction diode, which can operate

continuously without being damaged in the region of reverse break down voltage. One of

the most important applications 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 R of suitable

value.

10.3.2 PHOTO DIODE:-

A photo diode is a junction diode made from photo- sensitive semiconductor or

material. In such a diode, there is a provision to allow the light of suitable frequency to

fall on the p-n junction. It is reverse biased, but the voltage applied is less than the break

down voltage. As the intensity of incident light is increased, current goes on increasing

till it becomes maximum. The maximum current is called saturation current.

10.3.3 LIGHT EMITTING DIODE (LED):-

When a junction diode is forward biased, energy is released at the junction diode

is forward biased, energy is released at the junction due to recombination of electrons and

49



holes. In case of silicon and germanium diodes, the energy released is in infrared region.

In the junction diode made of gallium arsenate or indium phosphide, the energy is

released in visible region. Such a junction diode is called a light emitting diode or LED.

10.4 7-Segment Display

Design LED Products 7-segment display technology is scalable to meet individual

customer requirements. Less than 2mm thick they can be made to any size and include

other illuminated icons, text or backlights to create a fully customized display product.

The following data is based on Design LED Products 7-Segment evaluation (part No. 10-

10003) component as shown below.

Fig 10.4 : Dimensions of a 7- segment display

50



10.4.1 Component specification

Display Format 7 independent display segments

Viewing Area 7 segments each of 16.0(W) × 5.0(H) mm (1mm non illuminated border

between segments)

Dimensions 33.0(W) × 59.0(H) × 1.2 max.(D) mm

Weight 10g max.

Viewing Angle Lambertian Luminance >500 Cd/m2

Colour Red

10.4.2 Environmental factors

Operating Temp min. 0o C max. 50o C

Storage Temp. min. -20o C max. 70o C

Operating Humidity 5% - 95% RH

10.4.3 Electrical Specification

LED Drive requirements and specification See LED specification data sheet 4-10002

51



Current/ Voltage 7 channels 1.9 V (typ) @ 20mA each

Track resistance TBD Ohms/cm Insulation Resistance TBD Ohms

Dielectric Strength TBD Electrical connection 10 way 1mm pitch FFC/FPC

10.4.4 Optical Specifications

Luminance: Note 1 >500 Cd/m2 Colour: Note 2 Red

Homogeneity: Note 3 >70% Viewing Angle: Note 4 Lambertian

Light isolation: Note 5 >100:1

10.4.5 Notes

1. Measured with calibrated luminance meter, can be modified or optimized by

reselection of LED(s).

2. See LED data sheet 4-10002 for colour co-ordinates and binning specification.

3. Homogeneity – this refers to global homogeneity (or luminance variations across the

panel) on

scale ~10mm, and local homoge neity (or bright/dark spots or defects) on scale ~1mm.

Value shows minimum level permitted as percentage of highest measured luminance on

the sample. This level would not be visible to human viewer.

4. Top graphic layer is lambertian diffuser – not measured

52



5. Light isolation – this ratio relates to the ratio of luminance measured between two side-

by-side segments, one simultaneously switched ON the other OFF. This gives a measure

of contrast ratio between segments. Under standardambient lighting conditions, the OFF

segment should appear not illuminated to observer.

10.5 555 Timer IC

The block diagram and pin connections are shown in figure; R1, R2 C1 and C2 are

external components. (Note that the circle is omitted from the transistor symbol in an

IC). Threshold (pin 6) is joined to trigger (pin 2). Initially C1 charges up through R1

and R2 and, when the voltage across it just exceeds 2\3Vcc, the output from the

threshold comparator (with a reference voltage 2\3 Vcc on its other input form the

voltage divider chain formed by the three equal resistor R in series across Vcc) goes

‘high’ and resets the flip-flop, i.e. Q goes ‘high’. This has two results. First, the output

from the IC (pin 3) goes ‘low’ (due to the inverting buffer output stage) and second,

Tr1 switches it and R2.

Fig 10.5 : Astable operation of 555 timer IC

53



10.5.1 555 Timer as an astable device

When the voltage across C1 has fallen to just below 1\3 Vcc, the output from the

trigger comparator (with a reference voltage of 1\3 Vcc at its other input form the

three-resistor chain) goes ‘high’ and sets the flip-flop. Q therefore goes ‘low’ with two

results. First, the output from the IC goes ‘high’ and second, Tr1 turns off (since its base is no longer positive) so letting C1 charge up to 2\3 Vcc again through R1 and

R2, as it did at the start. This cycle is repeated continuously giving an oscillatory

output with a rectangular waveform which is ‘high’ while C1 is charging and ‘low’

while it discharges.

54



10.6 CD4033 IC (CMOS Decade Counter/Divider)

10.6.1 Description

CD4033BMS 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.

55



Fig 10.6 : Pin dig. & functional dig. Of CD 4033

10.6.2 Features

• High Voltage Types (20V Rating)

• Decoded 7 Segment Display Outputs and Ripple

Blanking

• Counter and 7 Segment Decoding in One Package

• Easily Interfaced with 7 Segment Display Types

• Fully Static Counter Operation DC to 6MHz (typ.) at VDD =

10V

• Ideal for Low-Power Displays

• “Ripple Blanking” and Lamp Test

• 100% Tested for Quiescent Current at 20V

56



• Standardized Symmetrical Output Characteristics

• 5V, 10V and 15V Parametric Ratings

• Schmitt-Triggered Clock Inputs

• Meets All Requirements of JEDEC Tentative Standards No. 13B, “Standard

Specifications for Description of “B” Series CMOS Device’s

10.6.3 Applications

• Decade Counting 7 Segment Decimal Display

• Frequency Division 7 Segment Decimal Displays

• Clocks, Watches, Timers (e.g. ÷ 60, ÷ 60, ÷12 Counter/ Display

• Counter/Display Driver For Meter Applications

The CD4033BMS has provisions for automatic blanking of the non-significant zeros in a

multi-digit decimal number which results in an easily readable display consistent with

normal writing practice. For example, the number 0050.0700 in an eight digit display

would be displayed as 50.07. Zero suppression on the integer side is obtained by

connecting the RBI terminal of the CD4033BMS associated with the most significant

digit in the display to a low-level voltage and connecting the RBO terminal of that stage

to the RBI terminal of the CD4033BMS in the next-lower significant position in the

display. This procedure is continued for each succeeding

CD4033BMS on the interger side of the display.

57



On the fraction side of the display the RBI of the CD4033BMS associated with the least

significant bit is connected to a low-level voltage and the RBO of that CD4033BMS is

connected to the RBI terminal of the CD4033BMS in the next more-significant-bit

position. Again, this procedure is continued for all CD4033BMS’s on the fraction side of

the display. In a purely fractional number the zero immediately preceding the decimal

point can be displayed by connecting the RBI of that stage to a high level voltage (instead

of to the RBO of the next more-significant-stage). For example: optional zero → 0.7346.

Likewise, the zero in a number such as 763.0 can

be displayed by connecting the RBI of the CD4033BMS associated with it to a high-level

voltage.Ripple blanking of non-significant zeros provides an appreciable savings in

display power. The CD4033BMS has a LAMP TEST input which, when connected to a

high-level voltage, overrides normal decoder operation and enables a check to be made

on possible display malfunctions by putting the seven outputs in the high state.

10.7 CA3140 Operational amplifier

The CA3140A and CA3140 are integrated circuit operational amplifiers that combine the

advantages of high voltage PMOS transistors with high voltage bipolar transistors on a

single monolithic chip. The CA3140A and CA3140 BiMOS operational amplifiers

feature gate protected MOSFET (PMOS) transistors in the input circuit to provide very

high input impedance, very low input current, and high speed performance. The

CA3140A and CA3140 operate at supply voltage from 4V to 36V (either single or dual

supply). These operational amplifiers are internally phase compensated to achieve stable

operation in unity gain follower operation, and additionally, have access terminal for a

supplementary external capacitor if additional frequency roll-off is desired. Terminals are

also provided for use in applications requiring input offset voltage nulling. The use of

PMOS field effect transistors in the input stage results in common mode input voltage

capability down to 0.5V below the negative supply terminal, an important

attribute for single supply applications. The output stage uses bipolar transistors and

includes built-in protection against damage from load terminal short circuiting to either

supply rail or to ground. The CA3140A and CA3140 are intended for operation at supply

voltages up to 36V (±18V).

58



10.7.1 Features

- MOSFET Input Stage

- Very High Input Impedance (ZIN) -1.5T. (Typ)

- Very Low Input Current (Il) -10pA (Typ) at ±15V

- Wide Common Mode Input Voltage Range (VlCR) – Can be Swung 0.5V Below

Negative Supply Voltage Rail

-Output Swing Complements Input Common Mode

10.7.2 Range

• Directly Replaces Industry Type 741 in Most

• Applications

Applications

• Ground-Referenced Single Supply Amplifiers in

Automobile and Portable Instrumentation

• Sample and Hold Amplifiers

• Long Duration Timers/Multivibrators

(µseconds-Minutes-Hours)

• Photocurrent Instrumentation

• Peak Detectors

• Active Filters

• Comparators

• Interface in 5V TTL Systems and Other Low

Supply Voltage Systems

• All Standard Operational Amplifier Applications

• Function Generators

59



• Tone Controls

• Power Supplies

• Portable Instruments

• Intrusion Alarm Systems

Fig 10.7 : Pin dig. of CA 3140 IC

20

02

60



FN957.7

kkkkkkl;kl;k

DC Supply Voltage (Between V+ and V- Terminals) . . . . . . . . . 36V

Differential Mode Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . 8V

DC Input Voltage . . . . . . . . . . . . . . . . . . . . . (V+ +8V) To (V- -0.5V)

Input Terminal Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1mA

Output Short Circuit Duration. (Note 2) . . . . . . . . . . . . . . Indefinite

Operating Conditions

Temperature Range. . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC

Thermal Resistance (Typical, Note 1) θJA (oC/W) θJC (oC/W)

PDIP Package . . . . . . . . . . . . . . . . . . . 115 N/A

61



SOIC Package . . . . . . . . . . . . . . . . . . . 165 N/A

Maximum Junction Temperature (Plastic Package) . . . . . . . 150oC

Maximum Storage Temperature Range . . . . . . . . . -65oC to 150oC

Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC

10.7.3 Application Information

Circuit Description

As shown in the block diagram, the input terminals may be operated down to 0.5V below

the negative supply rail. Two class A amplifier stages provide the voltage gain, and a

unique class AB amplifier stage provides the current gain necessary to drive low-impedance loads.A biasing circuit provides control of cascoded constant current flow

circuits in the first and second stages. The CA3140 includes an on chip phasecompensating capacitor that is sufficient for the unity gain voltage follower

configuration.

62



10.8 CD4071 (OR Gate IC)

10.8.1 General Description

The CD4071BC and CD4081BC quad gates are monolithic complementary MOS(CMOS) integrated circuits constructed with N- and P-channel enhancement mode

transistors.They have equal source and sink current

capabilities and conform to standard B series output drive. The devices also have buffered outputs which improve transfer characteristics by providing very high gain.All

inputs protected against static discharge with diodes to

VDD and VSS.

10.8.2 Features

Low power TTL compatibility:

Fan out of 2 driving 74L or 1 driving 74LS

5V–10V–15V parametric ratings

Symmetrical output characteristics

Maximum input leakage 1 mA at 15V over full temperature range

Fig 10.8 : Connection dig. of CD 4071

63



Fig 10.9 : Schematic dig. of CD 4071

64



10.9 LM 741 Operational Amplifier

The LM 741 series are general purpose operational amplifiers which feature

improved performance over the industry standards like LM 709

Parametric Table

Gain Bandwidth 1 MHz

Channels 1 Channels

InputOutputType

Not Rail to Rail

Slew Rate 0.5 Volts/usec

Supply Min 10 Volt

Supply Max 36, 44 VoltOffset Voltagemax, 25C

6, 5 mV

Supply CurrentPer Channel

1.7 mA

PowerWiseRating 2

1700 uA/MHz

Gain Bandwidth 1 MHz

Channels 1 Channels

InputOutputType

Not Rail to Rail

Slew Rate 0.5 Volts/usec

Supply Min 10 Volt

Supply Max 36, 44 Volt

Offset Voltagemax, 25C

6, 5 mV

Supply CurrentPer Channel

1.7 mA

PowerWiseRating 2

1700 uA/MHz

Max Input BiasCurrent

800, 1500 nA

Output Current 25 mA

Voltage Noise 30 nV/√Hz

Shut down No

Special Features Vos Adj

Function Op Amp

Temperature Min -55, 0 deg CTemperatureMax

70, 125 deg C

65



Fig 10.10 Pin dig. of LM 741

66



Chapter 11

POWER SUPPLY

11.1 Introduction

In alternating current the electron flow is alternate, i.e. the electron flow increases to

maximum in one direction, decreases back to zero. It then increases in the other direction

67



and then decreases to zero again. Direct current flows in one direction only. Rectifier

converts alternating current to flow in one direction only. When the anode of the diode is

positive with respect to its cathode, it is forward biased, allowing current to flow. But

when its anode is negative with respect to the cathode, it is reverse biased and does not

allow current to flow. This unidirectional property of the diode is useful for rectification.

A single diode arranged back-to-back might allow the electrons to flow during positive

half cycles only and suppress the negative half cycles. Double diodes arranged back-to-

back might act as full wave rectifiers as they may allow the electron flow during both

positive and negative half cycles. Four diodes can be arranged to make a full wave bridge

rectifier. Different types of filter circuits are used to smooth out the pulsations in

amplitude of the output voltage from a rectifier. The property of capacitor to oppose any

change in the voltage applied across them by storing energy in the electric field of the

capacitor and of inductors to oppose any change in the current flowing through them by

storing energy in the magnetic field of coil may be utilized. To remove pulsation of the

direct current obtained from the rectifier, different types of combination of capacitor,

inductors and resistors may be also be used to increase to action of filtering.

11.2 Need of power supplyPerhaps all of you are aware that a ‘power supply’ is a primary requirement for the ‘Test

Bench’ of a home experimenter’s mini lab. A battery eliminator can eliminate or replace

the batteries of solid-state electronic equipment and the equipment thus can be operated

by 230v A.C. mains instead of the batteries or dry cells. Nowadays, the use of

commercial battery eliminator or power supply unit has become increasingly popular as

power source for household appliances like transreceivers, record player, cassette players,

digital clock etc.

11.3 Theory

11.3.1 USE OF DIODES IN RECTIFIERS

68



Electric energy is available in homes and industries in India, in the form of alternating

voltage. The supply has a voltage of 220V (rms) at a frequency of 50 Hz. In the USA, it

is 110V at 60 Hz. For the operation of most of the devices in electronic equipment, a dc

voltage is needed. For instance, a transistor radio requires a dc supply for its operation.

Usually, this supply is provided by dry cells. But sometime we use a battery eliminator in

place of dry cells. The battery eliminator converts the ac voltage into dc voltage and thus

eliminates the need for dry cells. Nowadays, almost all-electronic equipment includes a

circuit that converts ac voltage of mains supply into dc voltage. This part of the

equipment is called Power Supply. In general, at the input of the power supply, there is a

power transformer. It is followed by a diode circuit called Rectifier. The output of the

rectifier goes to a smoothing filter, and then to a voltage regulator circuit. The rectifier circuit is the heart of a power supply.

11.3.2 RECTIFICATION

Rectification is a process of rendering an alternating current or voltage into a

unidirectional one. The component used for rectification is called ‘Rectifier’. A rectifier

permits current to flow only during the positive half cycles of the applied AC voltage by

eliminating the negative half cycles or alternations of the applied AC voltage. Thus

pulsating DC is obtained. To obtain smooth DC power, additional filter circuits are

required.

A diode can be used as rectifier. There are various types of diodes. But, semiconductor

diodes are very popularly used as rectifiers. A semiconductor diode is a solid-state device

consisting of two elements is being an electron emitter or cathode, the other an electron

collector or anode. Since electrons in a semiconductor diode can flow in one direction

only-from emitter to collector- the diode provides the unilateral conduction necessary for

69



rectification. Out of the semiconductor diodes, copper oxide and selenium rectifier are

also commonly used.

It is possible to rectify both alternations of the input voltage by using two diodes in the

circuit arrangement. Assume 6.3 V rms (18 V p-p) is applied to the circuit. Assume

further that two equal-valued series-connected resistors R are placed in parallel with the

ac source. The 18 V p-p appears across the two resistors connected between points AC

and CB, and point C is the electrical midpoint between A and B. Hence 9 V p-p appears

across each resistor. At any moment during a cycle of vin, if point A is positive relative

to C, point B is negative relative to C. When A is negative to C, point B is positive

relative to C. The effective voltage in proper time phase which each diode "sees" is in

Fig. The voltage applied to the anode of each diode is equal but opposite in polarity at

any given instant.

When A is positive relative to C, the anode of D1 is positive with respect to its cathode.

Hence D1 will conduct but D2 will not. During the second alternation, B is positive

relative to C. The anode of D2 is therefore positive with respect to its cathode, and D2

conducts while D1 is cut off.

There is conduction then by either D1 or D2 during the entire input-voltage cycle.

Since the two diodes have a common-cathode load resistor R L, the output voltage across

R L will result from the alternate conduction of D1 and D2. The output waveform vout

across R L, therefore has no gaps as in the case of the half-wave rectifier.

The output of a full-wave rectifier is also pulsating direct current. In the diagram, the two

equal resistors R across the input voltage are necessary to provide a voltage midpoint C

70



for circuit connection and zero reference. Note that the load resistor R L is connected

from the cathodes to this center reference point C.

An interesting fact about the output waveform vout is that its peak amplitude is not 9 V

as in the case of the half-wave rectifier using the same power source, but is less than 4½

V. The reason, of course, is that the peak positive voltage of A relative to C is 4½ V, not

9 V, and part of the 4½ V is lost across R.

Though the full wave rectifier fills in the conduction gaps, it delivers less than half the

peak output voltage that results from half-wave rectification.

11.3.3 Bridge Rectifier

A more widely used full-wave rectifier circuit is the bridge rectifier. It requires four

diodes instead of two, but avoids the need for a centre-tapped transformer. During the

positive half-cycle of the secondary voltage, diodes D2 and D4 are conducting and diodes

D1 and D3 are non-conducting. Therefore, current flows through the secondary winding,

diode D2, load resistor RL and diode D4. During negative half-cycles of the secondary

voltage, diodes D1 and D3 conduct, and the diodes D2 and D4 do not conduct. The

current therefore flows through the secondary winding, diode D1, load resistor RL and

diode D3. In both cases, the current passes through the load resistor in the same direction.

Therefore, a fluctuating, unidirectional voltage is developed across the load.

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Filtration

The rectifier circuits we have discussed above deliver an output voltage that

always has the same polarity: but however, this output is not suitable as DC power supplyfor solid-state circuits. This is due to the pulsation or ripples of the output voltage. This

should be removed out before the output voltage can be supplied to any circuit. Thissmoothing is done by incorporating filter networks. The filter network consists of

inductors and capacitors. The inductors or choke coils are generally connected in series

with the rectifier output and the load. The inductors oppose any change in the magnitudeof a current flowing through them by storing up energy in a magnetic field. An inductor

offers very low resistance for DC whereas; it offers very high resistance to AC. Thus, a

series connected choke coil in a rectifier circuit helps to reduce the pulsations or ripples

to a great extent in the output voltage. The fitter capacitors are usually connected in parallel with the rectifier output and the load. As, AC can pass through a capacitor but

DC cannot, the ripples are thus limited and the output becomes smoothed. When thevoltage across its plates tends to rise, it stores up energy back into voltage and current.Thus, the fluctuations in the output voltage are reduced considerable. Filter network

circuits may be of two types in general:

CHOKE INPUT FILTER

If a choke coil or an inductor is used as the ‘first- components’ in the filter

network, the filter is called ‘choke input filter’. The D.C. along with AC pulsation fromthe rectifier circuit at first passes through the choke (L). It opposes the AC pulsations but

allows the DC to pass through it freely. Thus AC pulsations are largely reduced. The

further ripples are by passed through the parallel capacitor C. But, however, a little nippleremains unaffected, which are considered negligible. This little ripple may be reduced by

incorporating a series a choke input filters.

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CAPACITOR INPUT FILTER

If a capacitor is placed before the inductors of a choke-input filter network, thefilter is called capacitor input filter. The D.C. along with AC ripples from the rectifier

circuit starts charging the capacitor C. to about peak value. The AC ripples are then

diminished slightly. Now the capacitor C, discharges through the inductor or choke coil,which opposes the AC ripples, except the DC. The second capacitor C by passes the

further AC ripples. A small ripple is still present in the output of DC, which may be

reduced by adding additional filter network in series.

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CIRCUIT DIAGRAM

74



TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another

through inductively coupled electrical conductors. A changing current in the first circuit(the primary) creates a changing magnetic field; in turn, this magnetic field induces a

changing voltage in the second circuit (the secondary). By adding a load to the secondary

circuit, one can make current flow in the transformer, thus transferring energy from onecircuit to the other.

The secondary induced voltage VS is scaled from the primary VP by a factor ideally equalto the ratio of the number of turns of wire in their respective windings:

By appropriate selection of the numbers of turns, a transformer thus allows an alternating

voltage to be stepped up — by making NS more than NP — or stepped down, by making it

less.

Transformers are some of the most efficient electrical 'machines',[1] with some large units

able to transfer 99.75% of their input power to their output.[2] Transformers come in arange of sizes from a thumbnail-sized coupling transformer hidden inside a stagemicrophone to huge units weighing hundreds of tons used to interconnect portions of

national power grids. All operate with the same basic principles, though a variety of

designs exist to perform specialized roles throughout home and industry.

75

http://en.wikipedia.org/wiki/Electrical_energy

http://en.wikipedia.org/wiki/Electrical_network

http://en.wikipedia.org/wiki/Inductive_coupling

http://en.wikipedia.org/wiki/Electrical_conductor

http://en.wikipedia.org/wiki/Electric_current

http://en.wikipedia.org/wiki/Electromagnetic_induction

http://en.wikipedia.org/wiki/Electrical_load

http://en.wikipedia.org/wiki/Alternating_current


http://en.wikipedia.org/wiki/Electrical_efficiency

http://en.wikipedia.org/wiki/Transformer#cite_note-flanagan_p2.1-0


http://en.wikipedia.org/wiki/Transformer#cite_note-energie-1


http://en.wikipedia.org/wiki/Microphone

http://en.wikipedia.org/wiki/Power_grid

http://en.wikipedia.org/wiki/Electrical_energy

http://en.wikipedia.org/wiki/Electrical_network

http://en.wikipedia.org/wiki/Inductive_coupling

http://en.wikipedia.org/wiki/Electrical_conductor

http://en.wikipedia.org/wiki/Electric_current

http://en.wikipedia.org/wiki/Electromagnetic_induction

http://en.wikipedia.org/wiki/Electrical_load



http://en.wikipedia.org/wiki/Electrical_efficiency



http://en.wikipedia.org/wiki/Microphone

http://en.wikipedia.org/wiki/Power_grid



TRANSFORMER is a device that transfers electrical energy from one circuit to another

by electromagnetic induction (transformer action). The electrical energy is always

transferred without a change in frequency, but may involve changes in magnitudes of voltage and current. Because a transformer works on the principle of electromagnetic

induction, it must be used with an input source voltage that varies in amplitude. There are

many types of power that fit this description; for ease of explanation and understanding,transformer action will be explained using an ac voltage as the input source.

In a preceding chapter you learned that alternating current has certain advantages over

direct current. One important advantage is that when ac is used, the voltage and current

levels can be increased or decreased by means of a transformer.

As you know, the amount of power used by the load of an electrical circuit is equal to thecurrent in the load times the voltage across the load, or P = EI. If, for example, the load in

an electrical circuit requires an input of 2 amperes at 10 volts (20 watts) and the source is

capable of delivering only 1 ampere at 20 volts, the circuit could not normally be used

with this particular source. However, if a transformer is connected between the sourceand the load, the voltage can be decreased (stepped down) to 10 volts and the current

increased (stepped up) to 2 amperes. Notice in the above case that the power remains thesame. That is, 20 volts times 1 ampere equals the same power as 10 volts times 2

amperes.

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