A

Project Report

at

CELL PHONE DETECTOR

Submitted by:

Name (Roll no.)

Aadil Amaan (0905330001) Mahesh Kumar Sahu (0905330040) Pranay Ranjan Maurya (0905330056) Puneet Kumar Gupta (0905330060)

AZAD INSTITUTE OF ENGINEERING &TECHNOLOGY, LUCKNOW

(Affiliated to Gautam Buddha Technical University,Lucknow)

Department of Electronics EngineeringSession (2012-2013)

1

ACKNOWLEDGEMENT

Our sincerest appreciation must be extended by our

faculties. We also want to thank faculties of the College.

They have been very kind and helpful to us. We want to thank

all teaching and non‐teaching staff to support us. Especially

we are thankful to Mr. S. K. Mishra (HOD) for providing this

golden opportunity to work on this project, inspiration during

the course of this project and to complete the project within

stipulated time duration and four walls of College Lab. We

would like to express our sincere gratitude to our Guide Ms.

Sonal Mam for their help during the course of the project

right from selection of the project, their constant

encouragement, expert academic and practical guidance.

2

ABSTRACT

This handy, pocket-size mobile transmission detector or

sniffer can sense the presence of an activated mobile cell

phone from a distance of one and-a-half meters. So it can be

used to prevent use of mobile phones in examination halls,

confidential rooms, etc. It is also useful for detecting the

use of mobile phone for Spying and unauthorized video

transmission. The circuit can detect the incoming and outgoing

calls, SMS and video transmission even if the mobile phone is

kept in the silent mode. The moment the Bug detects RF

transmission signal from an activated mobile phone, it starts

sounding a beep alarm and the LED blinks. The alarm continues

until the signal transmission ceases. Assemble the circuit on

a general purpose PCB as compact as possible and enclose in a

small box like junk mobile case. As mentioned earlier,

capacitor C3 should have a lead length of 18 mm with lead

spacing of 8 mm. Carefully solder the capacitor in standing

position with equal spacing of the leads. The response can be

3

optimized by trimming the lead length of C3 for the desired

frequency. You may use a short telescopic type antenna.

Use the miniature 12V battery of a remote control and a

small buzzer to make the gadget pocket-size. The unit will

give the warning indication if someone uses Mobile phone

within a radius of 1.5 meters.

CONTENTS

PAGE NO.

CHAPTER ONE

1.1 Introduction

(5) 4

1.2 Cellular Phone Technology

(7)

1.2.1 Cellular Phone Features (7)

1.2.2 Cellular Phone Communication Standards

(8)

1.3 Overview of Cell Phone Detector

(9)

1.3.1 Mobile Bug (11)

1.4 Circuit Diagram

(12)

1.5 Description of Circuit Diagram

(13)

CHAPTER TWO2.1 Introduction

(14)

2.2 Block Diagram

(18)

2.3 Block Diagram Explanation

(18)

2.3.1 Transmission Lines

(19)

2.4 PCB Layout

(20)

2.5 PCB Fabrication

(20)

2.5.1 The Printed Circuit Board

(21)

5

2.5.2 Copper-clad Laminates

(21)

2.5.3 Board Cleaning Before Pattern Transfer

(22)

2.5.4 Screen Printing

(22)

2.5.5 Etching

(22)

2.5.6 Chemistry

(22)

2.5.7 Drilling

(23)

2.5.8 Component Mounting

(24)

2.5.9 Soldering

(24)

2.5.10 Soldering Steps

(25)

CHAPTER THREE3.1 Introduction

(26)

3.2 List of Components

(30)

3.3 Components Description

(31)

6

3.3.1 Resistor

(31)

3.3.2 Capacitor

(34)

3.3.3 Transistor

(38)

3.3.4 LED

(45)

3.3.5 Piezo Buzzer

(57)

3.4 Pin Diagram of ICs

(62)

3.4.1 IC CA3130

(62)

3.4.2 IC NE555

(63)

3.5 Working, Applications, and Features of IC CA3130

(63)

3.6 Working, Applications, and Features of IC NE555

(66)

CHAPTER FOUR4.1 Introduction

(71)

4.2 Circuit Testing on Breadboard

(72)

4.3 Working of Cell Phone Detector

(73)

7

4.3.1 Purpose of the circuit

(73)

4.3.2 Concept

(73)

4.3.3 How the circuit works?

(73)

4.3.4 Uses of the capacitor

(74)

4.3.5 How the capacitor senses the RF?

(74)

CHAPTER FIVE5.1 Introduction

(75)

5.2 Applications

(76)

5.3 Advantages

(77)

5.3 Limitations

(78)

5.4 Future Scope

(78)

5.5 References

(79)

CHAPTER ONE

1.1 INTRODUCTION:8

In this chapter we will discuss the overview of

Cell Phone Detector and see its demo circuits. We will also

discuss about circuit diagram and description of the circuit

diagram. But before we discuss the above we have to know about

the previous detection techniques which has been introduced

already in the market.

The first signal detection technique, an existing design

utilizing discrete component is difficult to implement. They

are very affordable to construct, but require precision

tuning. This design is analyzed and found to be inaccurate.

The second signal detection technique, a design using a

down converter, voltage controlled oscillator (VCO), and a

bandpass filter was investigated for cellular phone detection.

The performance of this technique through hardware and

computer modeling is discussed and the results are presented.

The new system is accurate and a practical solution for

detecting cellular phone in a secure facility.

A mobile phone (also known as a cellular phone, cell

phone, and a hand phone) is a device that can make and

receive telephone calls over a radio link while moving around

a wide geographic area. It does so by connecting to a cellular

network provided by a mobile phone operator, allowing access

to the public telephone network. By contrast, a cordless

telephone is used only within the short range of a single,

private base station.

9

In addition to telephony, modern mobile phones also

support a wide variety of other services such as text

messaging, MMS, email, Internet access, short-range wireless

communications (infrared, Bluetooth), business applications,

gaming and photography. Mobile phones that offer these and

more general computing capabilities are referred to as smart

phones.

A cellular network or mobile network is a radio network

distributed over land areas called cells, each served by at

least one fixed-location transceiver known as a cell

site or base station. In a cellular network, each cell uses a

different set of frequencies from neighboring cells, to avoid

interference and provide guaranteed bandwidth within each

cell.

When joined together these cells provide radio coverage

over a wide geographic area. This enables a large number of

portable transceivers (e.g., mobile phones, pagers, etc.) to

communicate with each other and with fixed transceivers and

telephones anywhere in the network, via base stations, even if

some of the transceivers are moving through more than one cell

during transmission.

In a cellular radio system, a land area to be supplied

with radio service is divided into regular shaped cells, which

can be hexagonal, square, circular or some other regular

10

shapes, although hexagonal cells are conventional. Each of

these cells is assigned multiple frequencies (f1 – f6) which

have corresponding radio base stations. The group of

frequencies can be reused in other cells, provided that the

same frequencies are not reused in adjacent neighboring cells

as that would cause co-channel interference.

The increased capacity in a cellular network, compared

with a network with a single transmitter, comes from the fact

that the same radio frequency can be reused in a different

area for a completely different transmission. If there is a

single plain transmitter, only one transmission can be used on

any given frequency. Unfortunately, there is inevitably some

level of interference from the signal from the other cells

which use the same frequency. This means that, in a standard

FDMA system, there must be at least a one cell gap between

cells which reuse the same frequency.

In the simple case of the taxi company, each radio had a

manually operated channel selector knob to tune to different

frequencies. As the drivers moved around, they would change

from channel to channel. The drivers knew which frequency

covered approximately what area. When they did not receive a

signal from the transmitter, they would try other channels

until they found one that worked. The taxi drivers would only

speak one at a time, when invited by the base station operator

(this is, in a sense, time division multiple access (TDMA).

11

Practically every cellular system has some kind of

broadcast mechanism. This can be used directly for

distributing information to multiple mobiles, commonly, for

example in mobile telephony systems, the most important use of

broadcast information is to set up channels for one to one

communication between the mobile transceiver and the base

station. This is called paging. The three different paging

procedures generally adopted are sequential, parallel and

selective paging.

The details of the process of paging vary somewhat from

network to network, but normally we know a limited number of

cells where the phone is located (this group of cells is

called a Location Area in the GSM or UMTS system, or Routing

Area if a data packet session is involved; in LTE, cells are

grouped into Tracking Areas). Paging takes place by sending

the broadcast message to all of those cells. Paging messages

can be used for information transfer. This happens in pagers,

in CDMA systems for sending SMS messages, and in

the UMTS system where it allows for low downlink latency in

packet-based connections.

In a cellular system, as the distributed mobile

transceivers move from cell to cell during an ongoing

continuous communication, switching from one cell frequency to

a different cell frequency is done electronically without

interruption and without a base station operator or manual

switching. This is called the handover or handoff. Typically,

12

a new channel is automatically selected for the mobile unit on

the new base station which will serve it. The mobile unit then

automatically switches from the current channel to the new

channel and communication continues.

1.2 CELLULAR PHONE TECHNOLOGY:

Cellular Phone Technology is rapidly changing. Features

like Bluetooth, USB, high resolution cameras, microphones,

Internet, 802.11 wireless, and memory cards added every year.

Also, the communication technology a cellular phone uses such

as CDMA, GSM, 3G and 4G are rapidly changing.

1.2.1 CELLULAR PHONE FEATURES:

Bluetooth is a secure wireless protocol that operates at

2.4GHz. The protocol uses a master slave structure and is very

similar to having a wireless USB port on your cellular phone.

Device like a printer, keyboard, mouse, audio device, and

storage device can be connected wirelessly. This feature is

only use for hands-free devices but can also be used for file

transfer of picture, music, and other data.

Universal Serial Bus (USB) is a way for cellular phone to

connect to a computer for data transfer. This feature is very

similar to Bluetooth for cellular phone with the exception of

using a cable. On today’s cellular phones this feature is

mainly used for charging the battery or programming by the

manufacturer. It can also be used to transfer picture, music,

and other data.

13

Cameras on cellular phones are a very popular feature

that was added in the last 10 years. In recent years, high

resolution cameras have become a standard feature. Most

cellular phones will come with at least a 2 mega pixel camera

and the more expensive phones can be as much as 8 mega pixels.

Microphones have been featured on cellular phone since

they first came out. In the last 10 years the microphones have

become dual purpose; now there are programs on the phone that

record voice to file such a simple voice recorder or as part

of a video.

Some cellular phones come with 802.11 wireless built in

and allows the phone to connect to any nearby wireless

network. This provides an alternate connection method to the

Internet and saves money if you are on a limited data plan.

Also, connecting with 802.11 is most likely going to provide

better throughput than using the cellular phone network.

All these features make cellular phone today very

versatile. They can connect with almost any storage medium or

computer. In the years to come, cellular phones will continue

to gain more and more features.

1.2.2 CELLULAR PHONE COMMUNICATION STANDARDS:

Currently the three main technologies used by cellular

phone providers are 2G, 3G, and 4G. Each generation of

14

technology uses a different transmission protocol. The

transmission protocols dictate how a cellular phone

communicates with the tower. Some examples are: frequency

division multiple access (FDMA), time division multiple access

(TDMA), code division multiple access (CDMA), Global System

for Mobile Communication (GSM), CDMA2000, wide-band code

division multiple access (WCDMA), and time division

synchronous code division multiple access (TD-SCDMA). All of

these protocols typically operates in the 824-894 MHz band in

the United States. Some protocols such as GSM (depending on

the provider) will use the 1800-2000 MHz band.

1.3 OVERVIEW OF CELL PHONE DETECTOR:

Demo Circuit:

IC1 is designed as a differential

amplifier Non inverting input is connected

to the potential divider R1, R2. Capacitor

15

R1 1M

R2 100K

C1 0.22

C2 47 UF

R3 1M

LED

IC 3130

C2 keeps the non inverting input signal

stable for easy swing to + or – R3 is the

feedback resistor

Figure: 1.1

IC1 functions as a current to voltage converter, since it

converts the tiny current released by the 0.22 capacitor as

output voltage.

At power on output go high and LED lights for a short

period. This is because + input gets more voltage than the –

input. After a few seconds, output goes low because the output

current passes to the – input through R2. Meanwhile, capacitor

C1 also charges. So that both the inputs gets almost equal

voltage and the output remains low. 0.22 capacitor (no other

capacitor can be substituted) remains fully charged in the

standby state.

When the high frequency radiation from the mobile phone

is sensed by the circuit, 0.22 cap discharges its stored

current to the + input of IC1 and its output goes high

momentarily. (in the standby state, output of the differential

amplifier is low since both inputs get equal voltage of 0.5

volts or more). Any increase in voltage at + input will change

the output state to high.

16

The circuit can detect both the incoming and outgoing

calls, SMS and video transmission even if the mobile phone is

kept in the silent mode. The moment the bug detects RF

transmission signal from an activated mobile phone, it starts

sounding a beep alarm and the LED blinks. The alarm continues

until the signal transmission ceases. An ordinary RF detector

using tuned LC circuits is not suitable for detecting signals

in the GHz frequency band used in mobile phones. The

transmission frequency of mobile phones ranges from 0.9 to 3

GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting

gigahertz signals required for a mobile bug.

Here the circuit uses a 0.22μF disk capacitor (C3) to

capture the RF signals from the mobile phone. The lead length

of the capacitor is fixed as 18 mm with a spacing of 8 mm

between the leads to get the desired frequency. The disk

capacitor along with the leads acts as a small gigahertz loop

antenna to collect the RF signals from the mobile phone.

Op-amp IC CA3130 (IC1) is used in the circuit as a

current-to-voltage converter with capacitor C3 connected

between its inverting and non-inverting inputs. It is a CMOS

version using gate-protected p-channel MOSFET transistors in

the input to provide very high input impedance, very low input

current and very high speed of performance. The output CMOS

transistor is capable of swinging the output voltage to within

10 mV of either supply voltage terminal.

17

Capacitor C3 in conjunction with the lead inductance acts

as a transmission line that intercepts the signals from the

mobile phone. This capacitor creates a field, stores energy

and transfers the stored energy in the form of minute current

to the inputs of IC1.This will upset the balanced input of IC1

and convert the current into the corresponding output voltage.

Capacitor C4 along with high-value resistor R1 keeps the

non-inverting input stable for easy swing of the output to

high state. Resistor R2 provides the discharge path for

capacitor C4.Feedback resistor R3 makes the inverting input

high when the output becomes high. Capacitor C5 (47pF) is

connected across ‘strobe’ (pin 8) and ‘null’ inputs (pin 1) of

IC1 for phase compensation and gain control to optimise the

frequency response.

When the mobile phone signal is detected by C3, the

output of IC1 becomes high and low alternately according to

the frequency of the signal as indicated by LED1. This

triggers mono stable timer IC2 through capacitor C7. Capacitor

C6 maintains the base bias of transistor T1 for fast switching

action. The low-value timing components R6 and C9 produce very

short time delay to avoid audio nuisance.

Assemble the circuit on PCB and enclose in a small box

like junk mobile case. As mentioned earlier, capacitor C3

should have a lead length of 18 mm with lead spacing of 8 mm.

Carefully solder the capacitor in standing position with equal

18

spacing of the leads. The response can be optimised by

trimming the lead length of C3 for the desired frequency. You

may use a short telescopic type antenna.

1.3.1 Mobile Bug:

Normally IC1 is off. So IC2 will be also off.

When the power is switched on, as stated above, IC1 will give

a high output and T1 conducts to trigger LED and Buzzer .This

can be a good indication for the working of the circuit.

19

1.4 CIRCUIT DIAGRAM:

Figure 1.2: Circuit Diagram of Cell Phone Detector

20

1.5 CIRCUIT DIAGRAM DESCRIPTION:

An ordinary RF detector using tuned LC circuits is not

suitable for detecting signals in the GHz frequency band used

in mobile phones. The transmission frequency of mobile phones

ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So

a circuit detecting gigahertz signals is required for a cell

phone detector. Here the circuit uses a 0.22pF disk capacitor

(C3) to capture the RF signals from the mobile phone. The lead

length of the capacitor is fixed as 18 mm with a spacing of 8

mm between the leads to get the desired frequency. The disk

capacitor along with the leads acts as a small gigahertz loop

antenna to collect the RF signals from the mobile phone.

Op-amp IC CA3130 (IC1) is used in the circuit as a

current-to-voltage converter with capacitor C3 connected

between its inverting and non-inverting inputs. It is a CMOS

version using gate-protected p-channel MOSFET transistors in

the input to provide very high input impedance, very low input

current and very high speed of performance. The output CMOS

transistor is capable of swinging the output voltage to within

10 mV of either supply voltage terminal.

Capacitor C3 in conjunction with the lead inductance acts

as a transmission line that intercepts the signals from the

mobile phone. This capacitor creates a field, stores energy

and transfers the stored energy in the form of minute current

to the inputs of IC1. This will upset the balanced input of

21

IC1 and convert the current into the corresponding output

voltage.

Capacitor C4 along with high-value resistor R1 keeps the

non-inverting input stable for easy swing of the output to

high state. Resistor R2 provides the discharge path for

capacitor C4. Feedback resistor R3 makes the inverting input

high when the output becomes high. Capacitor C5 (47pF) is

connected across ‘strobe’ (pin 0 and ‘null’ inputs (pin 1) of

IC1 for phase compensation and gain control to optimise the

frequency response.

When the mobile phone signal is detected by C3, the

output of IC1 becomes high and low alternately according to

the frequency of the signal as indicated by LED1. This

triggers monostable timer IC2 through capacitor C7. Capacitor

C6 maintains the base bias of transistor T1 for fast switching

action. The low-value timing components R6 and C9 produce very

short time delay to avoid audio nuisance.

CHAPTER TWO

2.1 INTRODUCTION:

In this chapter we will discuss about the block diagram

of the cell phone detector and also the description of it, PCB

layout and PCB fabrication also included in this chapter to

explain the description of cell detector thoroughly in a

suitable manner. But before this we have to see the main

aspects about this which performs an important role.

22

Using a down converter, voltage controlled oscillator

(VCO), and a bandpass filter in the second technique explored

for cellular phone detection. Two signals inputted in the down

converter. The first signal is from the antenna and is between

829-835 MHz depending on the cellular phone (832 MHz for this

experiment). The signal is from the VCO, which is tuned to 800

MHz band. The down converter multiplies the two signals

together producing the sum and the difference. This is then

filtered by a bandpass filter with the passband lower and

upper edges respectively at 28 MHz and 36 MHz band. Filtering

eliminates the sum of the signals and any environmental noise.

Now all the remains is the difference, a 29-35 MHz signal that

indicates an active cellular phone is in the area. This can

easily be converted using analog to digital converters and

output to an alarm or a computer. Let us see the PCB layout

introduction it will help us in this chapter.

Schematic driven layout is the concept in IC

Layout or PCB layout where the EDA software links the

schematic and layout databases. It was one of the first big

steps forward in layout software from the days when editing

tools were simply handling drawn polygons.

Schematic driven layout allows for several features that make

the layout designer's job easier and faster. One of the most

important is that changes to the circuit schematic are easily

translated to the layout. Another is that the connections

23

between components in the schematic are graphically displayed

in the layout ensuring work is correct by construction.

A printed circuit board, or PCB, is used to mechanically

support and electrically connect electronic components using

components pathways. When the board has only copper tracks and

features, and no circuit elements such as capacitors,

resistors or active devices have been manufactured into the

actual substrate of the board, it is more correctly referred

to as printed wiring board (PWB) or etched wiring board. Use

of the term PWB or printed wiring board although more accurate

and distinct from what would be known as a true printed

circuit board, has generally fallen by the wayside for many

people as the distinction between circuit and wiring has

become blurred. Today printed wiring (circuit) boards are used

in virtually all but the simplest commercially produced

electronic devices, and allow fully automated assembly

processes that were not possible or practical in earlier era

tag type circuit assembly processes.

A PCB populated with electronic components is called

a printed circuit assembly (PCA), printed circuit board

assembly or PCB Assembly (PCBA). In informal use the term

"PCB" is used both for bare and assembled boards, the context

clarifying the meaning.

Alternatives to PCBs include wire wrap and point-to-point

construction. PCBs must initially be designed and laid out,

24

but become cheaper, faster to make, and potentially more

reliable for high-volume production since production and

soldering of PCBs can be automated. Much of the electronics

industry's PCB design, assembly, and quality control needs are

set by standards published by the IPC organization.

Excluding exotic products using special materials or

processes, all printed circuit boards manufactured today can

be built using the following four items which are usually

purchased from manufacturers:

(i) Laminates

(ii) Copper-clad Laminates

(iii) Resin impregnated B-stage cloth (pre-preg)

(iv) Copper foil

Laminates are manufactured by curing under pressure and

temperature layers of cloth or paper with thermo set resin to

form an integral final piece of uniform thickness. The size

can be up to 4 by 8 feet (1.2 by 2.4 m) in width and length.

Varying cloth weaves (threads per inch or cm), cloth

thickness, and resin percentage are used to achieve the

desired final thickness and dielectric characteristics.

Each trace consists of a flat, narrow part of

the copper foil that remains after etching. The resistance,

determined by width and thickness, of the traces must be

sufficiently low for the current the conductor will carry.

Power and ground traces may need to be wider than signal

25

traces. In a multi-layer board one entire layer may be mostly

solid copper to act as a ground plane for shielding and power

return. For microwave circuits, transmission lines can be laid

out in the form of striplines and micro strips with carefully

controlled dimensions to assure a consistent impedance.

In radio-frequency and fast switching circuits

the inductance and capacitance of the printed circuit board

conductors become significant circuit elements, usually

undesired; but they can be used as a deliberate part of the

circuit design, obviating the need for additional discrete

components.

"Multi layer" printed circuit boards have trace layers

inside the board. One way to make a 4-layer PCB is to use a

two-sided copper-clad laminate, etch the circuitry on both

sides, then laminate to the top and bottom pre-preg and copper

foil. Lamination is done by placing the stack of materials in

a press and applying pressure and heat for a period of time.

This results in an inseparable one piece product. It is then

drilled, plated, and etched again to get traces on top and

bottom layers.

Finally the PCB is covered with solder mask, marking

legend, and a surface finish may be applied. Multi-layer PCB's

allows for much higher component density.

26

Block Diagam:

27

Above diagram shows how a cellular phone detector works

by using Down Converter, Bandpass Filter, and Voltage

Controlled Oscillator (VCO). Now we will see how our cell

phone detector works without using above devices.

2.2 BLOCK DIAGRAM OF CELL PHONE DETECTOR:

28

2.3 DESCRIPTION OF BLOCK DIAGRAM:

There are five major blocks in the case of cell phone

detector. They are

(i) Antenna

(ii) LC tuner circuit

(iii) Current to voltage converter

(iv) 555 monoshot circuit

(v) Output stage

The first stage is the Antenna stage. The transmission

frequency of mobile phone ranges from 0.9 to 3 GHz with a

wavelength of 3.3 to 10 cm. These frequencies send by an

active mobile phone need to be received. This function is

carried out by the receiving antenna. An ordinary RF detector

using tuned circuit is not suitable for detecting signals in

the GHz frequency band used in mobile phones. So a circuit

detecting GHz signal is required for a mobile detector.

Here the circuit uses 0.22µF disk capacitor to capture RF

signals from the mobile phones. The lead length of the

capacitor is fixed as 18mm with a spacing of 08mm between the

leads to get the desired frequency. The disk capacitor along

with the leads acts as a small gigahertz loop antenna to

collect the RF signals from the mobile phones. This capacitor

along with the lead inductance act as a transmission lines to

intercept the signals from the mobile. The capacitor creates a

29

field, stores energy and transfers the stored energy in the

form of minute current to the input of a current to voltage

converter circuit. This forms the second stage which is LC

Tuner stage.

The current coming to the input of the converter IC,

upset its balanced input and then convert the current into

corresponding output voltage. When the mobile phone signals

are detected by the input capacitor, the output of the

converter IC, becomes high and low as indicated by the LED.

This triggers the monostable circuit also. The low value

timing components R and C produce very short time delay to

avoid audio nuisance. A buzzer is triggered by using the

output of the monoshot timer. The buzzer along with the LEDF

forms the output stage that provide us the indication as sound

and light respectively.

2.3.1 TRANSMISSION LINE:

A transmission line conveys electromagnetic waves. A pair

of parallel wires and coaxial cables is the commonly employed

transmission lines. It is used to connect transmitter and

antenna, receiver and antenna etc. At low frequency the energy

loss in the connecting wires is negligible. But for higher

frequency the loss can be reduced by using two parallel wires,

one for forward connection and the other for return current. A

transmission line is characterized by its lumped parameter as

described below.

30

Series Resistance:

Due to finite conductivity of the conductors, there is a

uniform distributed resistance. There is also power loss due

to radiation from the lines. Thus the finite conductivity and

radiation loss can be modeled as a series resistance per loop

of length.

Series Inductance:

A current carrying conductor has an associated magnetic

field. Both, the grow and decay of the current is opposed, and

hence it possesses inductance. This inductance is distributed

throughout the line. It acts in series.

Series Capacitance:

The two conducting wires is separated by a distance,

situated in a dielectric medium gives rise to a capacitance

that acts parallel with the wires.

Shunt Leakage Conductance:

Since the wires are separated by a dielectric medium that

cannot be perfect in its insulation, current leaks through it

when the lines carry a current. This leakage of current

through the dielectric between the wires is represented by a

shunt conductance per unit length.

2.4 PCB Layout of the Cell Phone Detector Circuit:

31

Figure: 2.3 PCB Layout

2.5 PCB Fabrication:

2.5.1 The Printed Circuit Board:

Printed Circuit Boards (PCBs) are certainly the most

important element in the fabrication of electronic equipment.

It is the design of properly laid-out PCBs that determine many

of the limiting properties with respect to noise immunity, as

well as to fast-pulse, high frequency and low level

characteristics of equipments. High power PCBs in their turn

requires a special design strategy. The first step in the

production of the printed circuit board is to obtain the

layout of the PCB from the circuit diagram. For obtaining the

layout computer-aided design techniques are used. In this

technique the diagrams are drawn directly on a graphics work

32

station. The software then checks for any design and layout

rules error. After correction of errors, if any, the layout is

obtained based on this layout the printed circuit boards are

fabricated from copper-clad laminates.

2.5.2 Copper-Clad Laminates:

A laminate can be simply described as the product

obtained by pressing layers of a filler material impregnated

with resin under heat and pressure. The commonly used fillers

are a variety of papers, or glass in various forms such as

cloths and continuous filament mat. The resigns could be

phenolic, epoxy, polyester, PTFE (Polytetrafluroethylene),

etc. Each of this fillers and resins contributes intrinsically

to the characteristic properties of the finished copper-clad

laminates. It is further possible to manipulate the properties

of copper clad laminates by fine variations in the

manufacturing process. The large range of possible copper clad

laminates has been standardized in the national and

international specifications. Thus, there are exactly laid

down specification for each copper-clad laminate grade, being

defined by the resin/filler system and the minimum/maximum

limits of the properties. A copper-clad laminate must have a

good copper-to-base laminate bond strength. The appearance of

copper side must be smooth and uniform. All these properties

must be retained during the production of PCB and also under

its working conditions. All electrical and mechanical

properties of the laminates are affected by the environmental

conditions such as humidity, temperature corrosive atmosphere

33

etc. Similarly most of the electrical properties vary with

changing in frequency. Thus while choosing the copper-clad

laminates the various environmental conditions likely to be

encountered are to be considered.

2.5.3 Board Cleaning Before Pattern Transfer:

After choosing the copper-clad laminate it should be

cleaned. The cleaning of the copper-clad prior to resist

application is an essential step for any PCB process using

etch or plating resist. Insufficient cleaning is one of the

reasons most often encountered for difficulties in PCB

fabrication although it might not always be immediately

recognized as this. But it is quite often the reason for poor

resist-adhesion, uneven photo resist-film, pinholes, poor

plating-adhesion, etc. The first step in cleaning process is

scrubbing with a pumice/salt solution. This removes inorganic

matters like particulates and oxide and also performs

degreasing up to a certain extent. The pumice used is of a

very fine grade to minimize deep scratches. After scrubbing

with the abrasive, a water rinse is done to remove slurry.

This is followed by a strong acid dip in hydrochloric acid (10

vol %) which will residual alkali and metallic oxides and

prepare the surface for maximum resist adhesion. A final rinse

using de-ionized gives guarantees that no fresh contamination

is brought on to the surface. The time span until the next

processing step which is screen-printing is made as short as

possible to minimize the formation of fresh oxides.

34

2.5.4 Screen Printing:

Screen-printing is the process by which the conductor

pattern which is on the film master is transferred on to the

copper-clad laminates. With the screen-printing process one

can produce PCBs with a conductor width as low as 2.5mm and

registration error of just 0.1mm on an industrial scale with a

high reliability.

In its basis form the screen-printing process is very

simple. A screen fabric with uniform meshes and openings is

stretched and fixed on a solid frame of a metal or wood. The

circuit pattern is photographically transferred on to the

screen, leaving the meshes in pattern area open, while meshes

in the rest of area are closed. In the actual printing step,

ink is forced by the moving squeegee through the open meshes

on to the surface of material to be printed. The ink

deposition in a magnified cross-section shows the shape of

trapezoid. The ideal screen printing ink should have many

features which cannot be combined. It should dry rapidly on

the PCB but dry slowly on the screen. It should be highly

resistant against all the chemicals but easy to be stripped.

2.5.5 Etching:

After drying of the resist of the copper-clad laminate

the next process is etching. The final copper pattern is

formed by selective removal of all unwanted copper, which is

not protected by etch resist. For small scale PCB production

35

ferric chloride is used as enchant because it is very simple

to use.

2.5.6 Chemistry:

Free acid attack the copper is formed by the hydrolysis

reaction

FeCl3 + 3H2O Fe(OH)3 + 3HCl

………….eq(2.1)

The copper is oxidized by ferric ions, forming cuprous

chloride (CuCl) and ferrous chloride (FeCl2)

FeCl3 + Cu FeCl2 + CuCl

…………eq(2.2)

Cuprous chloride (CuCl) oxidizes further in the etching

solution to cupric chloride (CuCl2)

FeCl3 + CuCl FeCl2 + CuCl2

…………..eq(2.3)

The built up cupric chloride (CuCl2) itself reacts also with

copper and forms cuprous chloride (CuCl)

CuCl2 + Cl 2CuCl

…………….eq(2.4)

36

After etching is over the ferric chloride, contaminated

surface should be cleaned. After a simple spray water rinse, a

dip in a 5% (volume) oxalic acid solution is done to remove

the copper and iron salt. A vigorous final water rinse has to

flow.

2.5.7 Drilling:

After the etching operation the next step is drilling of

component mounting holes in the PCBs. Holes are made by

drilling whenever a superior holes finish or plated-through

holes process is required and where the tool costs for a

punching tool cannot be justified. Therefore drilling is

applied by all the professional grade PCB manufacturer and

generally and in all the smaller PCB production plan and in

laboratories. The importance of holes drilling into PCBs has

further gone up with electronic component miniaturization and

is need for smaller diameters (diameter less than half the

board thickness) and higher package density where hole

punching is practically ruled out. This is done using drilling

machines with suitable size drill bits. To compensate for

laminate resilience the drill bit diameter is chosen 0.05mm

bigger than the holes diameter expected. The usual size of

hole is 0.8 mm and for bigger components like preset and power

devices the size is 1.2 mm. The production of holes with

diameter and tolerances as specified above should not need any

special attention: a suitable drilling machine with a

correctly sharpened drill bit will provide these results.

After drilling the required number of holes of specified

37

dimensions the next step is mounting the components on the

PCB.

2.5.8 Component Mounting:

Component mounting on the PCB in such a way to minimize

the cracking of solder joints due to mechanical stress on the

joint. This can be ensured by bending of the axial component

lead in a manner to guarantee and optimum retention of the

component on the PCB while a minimum stress is introduced on

the solder joint. Bending is done with care taken not to

damage the component or its leads. The lead bending radius is

chosen to be approximately two times the lead diameter. The

bent leads should fit into the holes perpendicular to the

board so that any stress on the component lead junction is

minimized. The component lead bending is done using a bending

tool for easy but perfect component preparation.

2.5.9 Soldering:

Soldering is the process of joining metals by using lower

melting point metal or alloy with joining surface.

Solder:

Soldering is the process of joining materials. Soldered

joints in electronics switches will establish strong

electrical connection between components leads. The popularly

used solders are alloys of tin and lead melt below the melting

point of the tin.

38

Flux:

In order to make the surface accept to make the solder

readily, the component terminals should be free from oxide and

other obstructing films. The leads should be cleaned

chemically or by abrasion using blades or knives.

A small amount of lead coating can be done on cleaned

portion of the lead using soldered iron. This process is

called thinning. Zink Chloride or Ammonium Chloride separately

or in combination is mostly used as fluxes. These are

available in petroleum jelly as paste flux. The residue which

remains after soldering may be washed out with more water

accompanied by brushing.

Soldering Iron:

It is tool used to melt solder and apply at the joint in

the circuit. It operates at 230v supply. The iron bit at the

tip of it gets heated within few minutes. 50W or 25W soldering

irons are commonly used for soldering purpose.

2.5.10 Soldering Steps:

For proper soldering on PCBs the soldering steps are:

(i) Make the layout of component in the circuit. Plug in the

cord of the soldering iron into the mains to get heated.

(ii) Straighten and remove the coating of components leads

using a blade or knife. Apply a little flux on the leads. Take

39

a little solder on soldering iron and apply the molten solder

on the leads. Care must be taken to avoid the components to

getting heated up.

(iii) Mount the components on PCB by bending the leads of

components using noise pliers.

(iv) Apply flux on the joints and solder the joints. Soldering

must be done in minimum to avoid the dry soldering and heating

up of components.

(v) Wash the residue using water and brush.

CHAPTER THREE

3.1 Introduction:

40

In this chapter we will see the components used in the

cell phone detector and also discuss about the main aspects of

their working and features. But before the discussing of above

let us see about some quality of the semiconductor devices.

Semiconductor devices are electronic components that

exploit the electronic properties of semiconductor materials,

principally silicon, germanium, and gallium arsenide, as well

as organic semiconductors. Semiconductor devices have

replaced thermionic devices (vacuum tubes) in most

applications. They use electronic conduction in the solid

state as opposed to the gaseous state or thermionic

emission in a high vacuum.

Semiconductor devices are manufactured both as single

discrete devices and as integrated circuits(ICs), which

consist of a number—from a few (as low as two) to billions—of

devices manufactured and interconnected on a single

semiconductor substrate, or wafer.

Semiconductor materials are so useful because their behavior

can be easily manipulated by the addition of impurities, known

as doping. Semiconductor conductivity can be controlled by

introduction of an electric or magnetic field, by exposure

to light or heat, or by mechanical deformation of a doped mono

crystalline grid; thus, semiconductors can make excellent

sensors.

41

Current conduction in a semiconductor occurs via mobile

or "free" electrons and holes, collectively known as charge

carriers. Doping a semiconductor such as silicon with a small

amount of impurity atoms, such as phosphorus or boron, greatly

increases the number of free electrons or holes within the

semiconductor. When a doped semiconductor contains excess

holes it is called "p-type", and when it contains excess free

electrons it is known as “n-type”, where p (positive

for holes) or n (negative for electrons) is the sign of the

charge of the majority mobile charge carriers. The

semiconductor material used in devices is doped under highly

controlled conditions in a fabrication facility.

By far, silicon (Si) is the most widely used material in

semiconductor devices. Its combination of low raw material

cost, relatively simple processing, and a useful temperature

range make it currently the best compromise among the various

competing materials. Silicon used in semiconductor device

manufacturing is currently fabricated into bowls that are

large enough in diameter to allow the production of 300 mm (12

in.) wafers.

Germanium (Ge) was a widely used early semiconductor

material but its thermal sensitivity makes it less useful than

silicon. Today, germanium is often alloyed with silicon for

use in very-high-speed SiGe devices.

42

Gallium arsenide (GaAs) is also widely used in high-speed

devices but so far, it has been difficult to form large-

diameter bowls of this material, limiting the wafer diameter

to sizes significantly smaller than silicon wafers thus making

mass production of GaAs devices significantly more expensive

than silicon. Other less common materials are also in use or

under investigation.

Silicon carbide (SiC) has found some application as the

raw material for blue light-emitting diodes (LEDs) and is

being investigated for use in semiconductor devices that could

withstand very high operating temperatures and environments

with the presence of significant levels of ionizing radiation.

Various indium compounds (indium arsenide,

indium antimonde, and indium phosphide) are also being used in

LEDs and solid state laser diodes. Selenium sulfide is being

studied in the manufacture of photovoltaic solar cells. The

most common use for organic semiconductors is Organic light-

emitting diodes.

Semiconductors are the foundation of modern electronics,

including radio, computers, and telephones. Semiconductor-

based electronic components include transistors, solar cells,

many kinds of diodes including the light-emitting diode (LED),

the silicon controlled rectifier, photo-diodes, and digital

and analog integrated circuits. Increasing understanding of

semiconductor materials and fabrication processes has made

43

possible continuing increases in the complexity and speed of

semiconductor devices, an effect known as Moore's law.

Semiconductors are defined by their unique electric

conductive behavior. Metals are good conductors because at

their Fermi level, there is a large density of energetically

available states that each electron can occupy. Electrons can

move quite freely between energy levels without a high energy

cost. Metal conductivity decreases with temperature increase

because thermal vibrations of crystal lattice disrupt the free

motion of electrons. Insulators, by contrast, are very poor

conductors of electricity because there is a large difference

in energies (called a band gap) between electron-occupied

energy levels and empty energy levels that allow for electron

motion.

In the classic crystalline semiconductors, electrons can

have energies only within certain bands (ranges). The range of

energy runs from the ground state, in which electrons are

tightly bound to the atom, up to a level where the electron

can escape entirely from the material. Each energy band

corresponds to a large number of discrete quantum states of

the electrons. Most of the states with low energy (closer to

the nucleus) are occupied, up to the valence band.

Semiconductors and insulators are distinguished

from metals by the population of electrons in each band. The

valence band in any given metal is nearly filled with

44

electrons under usual conditions, and metals have many free

electrons with energies in the conduction band. In

semiconductors, only a few electrons exist in the conduction

band just above the valence band, and an insulator has almost

no free electrons.

The ease with which electrons in the semiconductor can be

excited from the valence band to the conduction band depends

on the band gap. The size of this energy gap (band gap)

determines whether a material is semiconductor or

an insulator (nominally this dividing line is roughly 4 eV).

In a crystal, many atoms are adjacent and many energy

levels are possible for electrons. Since there are so many (on

the order of 1022) atoms in a macroscopic crystal, the

resulting energy states available for electrons are very

closely spaced. Since the Heisenberg principle limits the

precision of any measurement of the combination of an

electron's momentum (related to energy) and its position, in a

crystal effectively the available energy levels form a

continuous band of allowed energy levels.

The concept of holes can also be applied to metals, where

the Fermi level lies within the conduction band. With most

metals the Hall effect indicates electrons are the charge

carriers. However, some metals have a mostly filled conduction

band. In these, the Hall effect reveals positive charge

carriers, which are not the ion-cores, but holes. In the case

45

of a metal, only a small amount of energy is needed for the

electrons to find other unoccupied states to move into, and

hence for current to flow. Sometimes even in this case it may

be said that a hole was left behind, to explain why the

electron does not fall back to lower energies: It cannot find

a hole. In the end in both materials electron-

phonon scattering and defects are the dominant causes

for resistance.

The conductivity of semiconductors may easily be modified

by introducing impurities into their crystal lattice. The

process of adding controlled impurities to a semiconductor is

known as doping. The amount of impurity, or dopant, added to

an intrinsic (pure) semiconductor varies its level of

conductivity. Doped semiconductors are referred to

as extrinsic. By adding impurity to pure semiconductors, the

electrical conductivity may be varied by factors of thousands

or millions.

A 1 cm3 specimen of a metal or semiconductor has of the

order of 1022 atoms. In a metal, every atom donates at least

one free electron for conduction, thus 1 cm3 of metal contains

on the order of 1022 free electrons. Whereas a 1 cm3 of sample

pure germanium at 20 °C, contains about 4.2×1022 atoms but only

2.5×1013 free electrons and 2.5×1013 holes. The addition of

0.001% of arsenic (an impurity) donates an extra 1017 free

electrons in the same volume and the electrical conductivity

is increased by a factor of 10,000.

46

ICs were made possible by experimental discoveries

showing that semiconductor devices could perform the functions

of vacuum tubes and by mid-20th-century technology

advancements in semiconductor device fabrication. The

integration of large numbers of tiny transistors into a small

chip was an enormous improvement over the manual assembly of

circuits using discrete electronic components. The integrated

circuits, mass production capability, reliability, and

building-block approach to circuit design ensured the rapid

adoption of standardized Integrated Circuits in place of

designs using discrete transistors.

There are two main advantages of ICs over discrete

circuits: cost and performance. Cost is low because the chips,

with all their components, are printed as a unit

by photolithography rather than being constructed one

transistor at a time. Furthermore, much less material is used

to construct a packaged IC die than to construct a discrete

circuit. Performance is high because the components switch

quickly and consume little power (compared to their discrete

counterparts) as a result of the small size and close

proximity of the components. As of 2012, typical chip areas

range from a few square millimeters to around 450 mm2, with up

to 9 million transistors per mm2. The electrical resistance of

an electrical conductor is the opposition to the passage of

an electric current through that conductor; the inverse

quantity is electrical conductance, the ease at which an

47

electric current passes. Electrical resistance shares some

conceptual parallels with the mechanical notion of friction.

The SI unit of electrical resistance is the ohm (Ω), while

electrical conductance is measured in siemens (S).

An object of uniform cross section has a resistance

proportional to its resistivity and length and inversely

proportional to its cross-sectional area. All materials show

some resistance, except for superconductors, which have a

resistance of zero.

Objects such as wires that are designed to have low

resistance so that they transfer current with the least loss

of electrical energy are called conductors. Objects that are

designed to have a specific resistance so that they can

dissipate electrical energy or otherwise modify how a circuit

behaves are called resistors. Conductors are made of high-

conductivity materials such as metals, in particular copper

and aluminium. Resistors, on the other hand, are made of a

wide variety of materials depending on factors such as the

desired resistance, amount of energy that it needs to

dissipate, precision, and costs.

3.2 List of Components:

RESISTORS1. R1 ________2.2M2. R2 ________100K3. R3 ________2.2M4. R4 ________1K

48

5. R5________12K6. R6________15K

CAPACITORS7. C1 ________22P8. C2 ________22P9. C3 ________0.22 µF10. C4 ________100 µF11. C5_________47P12. C6 _________0.1 µF13. C7_________ 0.1 µF14. C8_________ 0.01 µF15. C9__________4.7 µF

16. IC CA3130

17. IC NE555

18. T1 BC548

19. LED

20. ANTENNA

21. PIEZO BUZZER

22. 5 INCH LONG ANTENNA

23. ON/OFF SWITCH

24. POWER SUPPLY

49

3.3 Components Description:

3.3.1 Resistors:

Figure 3.1: Resistors

A resistor is a two-terminal electronic component that

produces a voltage across its terminals that is proportional

to the electric current through it in accordance with Ohm's

law:

V = IR

Resistors are elements of electrical networks and

electronic circuits and are ubiquitous in most electronic

equipment. Practical resistors can be made of various

50

compounds and films, as well as resistance wire (wire made of

a high-resistivity alloy, such as nickel/chrome).The primary

characteristics of a resistor are the resistance, the

tolerance, maximum working voltage and the power rating. Other

characteristics include temperature coefficient, noise, and

inductance. Less well-known is critical resistance, the value

below which power dissipation limits the maximum permitted

current flow, and above which the limit is applied voltage.

Critical resistance depends upon the materials constituting

the resistor as well as its physical dimensions; it's

determined by design. Resistors can be integrated into hybrid

and printed circuits, as well as integrated circuits. Size,

and position of leads (or terminals) are relevant to equipment

designers; resistors must be physically large enough not to

overheat when dissipating their power.

Significance:

Resistors are found in nearly every circuit because their

ability to limit current allows them to protect electronics

from circuit overload or destruction. Diodes, for example, are

current sensitive and so are almost always coupled with a

resistor when they are placed inside of a circuit. Resistors

are also combined with other electrical components to form

important fundamental circuits. They can be paired with

capacitors to perform as filters or voltage dividers. Another

role is that of the formation of oscillatory AC circuits when

they are coupled with capacitors and inductors.

51

Construction:

Resistors are typically formed from carbon encased in

lacquer but may be made from conductors or semiconductors.

Wire-wound ones are made from coils of metal wire and are

extremely accurate and heat resistant. Carbon film resistors

are made from carbon on a ceramic cylinder and photo

resistors, also called photocells, are made from materials

such as cadmium-sulfide.

Function:

Because resistors convert electrical energy into heat

they form heating elements in irons, toasters, heaters,

electric stoves, hair dryers and similar devices. Their

resistive properties cause them to generate light and are used

to create filaments in light bulbs.

As voltage dividers, resistors are placed in series with

each other. Their function is to produce a particular voltage

from an input that is fixed or variable. The output voltage is

proportional to that of the input and is usually smaller.

Voltage dividers are useful for components that need to

operate at a lesser voltage than that supplied by the input.

Resistors also help filter signals and are used in

oscillatory circuits in televisions and radios.

52

Resistors are used with transducers to make sensor

subsystems. Transducers are electronic components which

convert energy from one form into another, where one of the

forms of energy is electrical. A light dependent resistor,

or LDR, is an example of an input transducer. Changes in the

brightness of the light shining onto the surface of the LDR

result in changes in its resistance. As will be explained

later, an input transducer is most often connected along with

a resistor to make a circuit called a potential divider. In

this case, the output of the potential divider will be a

voltage signal which reflects changes in illumination.

Microphones and switches are input transducers. Output

transducers include loudspeakers, filament lamps and LEDs. Can

you think of other examples of transducers of each type?

In other circuits, resistors are used to direct current

flow to particular parts of the circuit, or may be used to

determine the voltage gain of an amplifier. Resistors are used

with capacitors to introduce time delays.

Most electronic circuits require resistors to make them

work properly and it is obviously important to find out

something about the different types of resistor available, and

to be able to choose the correct resistor value, in ,  , or

M , for a particular application.

53

3.3.2 Capacitors:

Figure 3.2: Capacitors

A capacitor or condenser is a passive electronic

component consisting of a pair of conductors separated by a

dielectric. When a voltage potential difference exists between

the conductors, an electric field is present in the

dielectric. This field stores energy and produces a mechanical

force between the plates. The effect is greatest between wide,

flat, parallel, narrowly separated conductors.

Capacitance (symbol C) is a measure of a capacitor's

ability to store charge. A large capacitance means that more

charge can be stored. Capacitance is measured in farads,

symbol F. However 1F is very large, so prefixes (multipliers)

are used to show the smaller values:

µ (micro) means 10-6 (millionth), so 1000000µF = 1F54

n (nano) means 10-9 (thousand-millionth), so 1000nF = 1µF

p (pico) means 10-12 (million-millionth), so 1000pF = 1nF

Uses of Capacitors:

Capacitors are used for several purposes:

Timing - For example with a 555 timer IC controlling

the charging and discharging.

Smoothing - For example in a power supply.

Coupling - For example between stages of

an audio system and to connect a loudspeaker.

Filtering - For example in the tone control of

an audio system.

Tuning - For example in a radio system.

Storing energy - For example in a camera flash circuit.

Energy storage:

A capacitor can store electric energy when disconnected

from its charging circuit, so it can be used like a

temporary battery. Capacitors are commonly used in electronic

devices to maintain power supply while batteries are being

changed. (This prevents loss of information in volatile

memory.)

55

Conventional electrostatic capacitors provide less than

360 joules per kilogram of energy density, while capacitors

using developing technology can provide more than

2.52 kilojoules per kilogram. In car audio systems, large

capacitors store energy for the amplifier to use on demand.

Power conditioning:

Reservoir capacitors are used in power supplies where

they smooth the output of a full or half wave rectifier. They

can also be used in charge pump circuits as the energy storage

element in the generation of higher voltages than the input

voltage.

Capacitors are connected in parallel with the power

circuits of most electronic devices and larger systems (such

as factories) to shunt away and conceal current fluctuations

from the primary power source to provide a "clean" power

supply for signal or control circuits. Audio equipment, for

example, uses several capacitors in this way, to shunt away

power line hum before it gets into the signal circuitry. The

capacitors act as a local reserve for the DC power source, and

bypass AC currents from the power supply. This is used in car

audio applications, when a stiffening capacitor compensates

for the inductance and resistance of the leads to the lead-

acid car battery.

Power factor correction:

56

In electric power distribution, capacitors are used

for power factor correction. Such capacitors often come as

three capacitors connected as a three phase load. Usually, the

values of these capacitors are given not in farads but rather

as a reactive power in volt-amperes reactive (VAr). The

purpose is to counteract inductive loading from devices

like electric motors and transmission lines to make the load

appear to be mostly resistive. Individual motor or lamp loads

may have capacitors for power factor correction, or larger

sets of capacitors (usually with automatic switching devices)

may be installed at a load center within a building or in a

large utility substation.

Noise filters and snubbers:

When an inductive circuit is opened, the current through

the inductance collapses quickly, creating a large voltage

across the open circuit of the switch or relay. If the

inductance is large enough, the energy will generate

an electric spark, causing the contact points to oxidize,

deteriorate, or sometimes weld together, or destroying a

solid-state switch. A snubber capacitor across the newly

opened circuit creates a path for this impulse to bypass the

contact points, thereby preserving their life; these were

commonly found in contact breaker ignition systems, for

instance. Similarly, in smaller scale circuits, the spark may

not be enough to damage the switch but will

still radiate undesirable radio frequency interference (RFI),

which a filter capacitor absorbs. Snubber capacitors are

57

usually employed with a low-value resistor in series, to

dissipate energy and minimize RFI. Such resistor-capacitor

combinations are available in a single package.

Capacitors are also used in parallel to interrupt units

of a high-voltage circuit breaker in order to equally

distribute the voltage between these units. In this case they

are called grading capacitors.

In schematic diagrams, a capacitor used primarily for DC

charge storage is often drawn vertically in circuit diagrams

with the lower, more negative, plate drawn as an arc. The

straight plate indicates the positive terminal of the device,

if it is polarized.

An ideal capacitor is characterized by a single constant

value, capacitance, which is measured in farads. This is the

ratio of the electric charge on each conductor to the

potential difference between them. In practice, the dielectric

between the plates passes a small amount of leakage current.

The conductors and leads introduce an equivalent series

resistance and the dielectric has an electric field strength

limit resulting in a breakdown voltage.

Capacitors are widely used in electronic circuits to

block the flow of direct current while allowing alternating

current to pass, to filter out interference, to smooth the

output of power supplies, and for many other purposes. They

are used in resonant circuits in radio frequency equipment to

58

select particular frequencies from a signal with many

frequencies.

(1) Ceramic capacitor:

In electronics ceramic capacitor is a capacitorconstructed of alternating layers of metal and ceramic, withthe ceramic material acting as the dielectric. The temperaturecoefficient depends on whether the dielectric is Class 1 orClass 2. A ceramic capacitor (especially the class 2) oftenhas high dissipation factor, high frequency coefficient ofdissipation.

Figure 3.3: ceramic capacitors

A ceramic capacitor is a two-terminal, non-polar device.The classical ceramic capacitor is the "disc capacitor". Thisdevice pre-dates the transistor and was used extensively invacuum-tube equipment (e.g., radio receivers) from about 1930through the 1950s, and in discrete transistor equipment fromthe 1950s through the 1980s. As of 2007, ceramic disccapacitors are in widespread use in electronic equipment,providing high capacity & small size at low price compared toother low value capacitor types.

Ceramic capacitors come in various shapes and styles,including:

(i) disc, resin coated, with through-hole leads

(ii) multi-layer rectangular block, surface mount

(iii) bare leadless disc, sits in a slot in the PCB and issoldered in place, used for UHF applications

(iv) tube shape, not popular now

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(2) Electrolytic capacitor:

Figure 3.4: electrolytic capacitor

An electrolytic capacitor is a type of capacitor that

uses an ionic conducting liquid as one of its plates with a

larger capacitance per unit volume than other types. They are

valuable in relatively high-current and low-frequency

electrical circuits. This is especially the case in power-

supply filters, where they store charge needed to moderate

output voltage and current fluctuations in rectifier output.

They are also widely used as coupling capacitors in circuits

where AC should be conducted but DC should not.

Electrolytic capacitors can have a very high capacitance,

allowing filters made with them to have very low corner

frequencies.

3.3.3 Transistor:

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Figure 3.5: Transistors

A transistor is a semiconductor device commonly used to

amplify or switch electronic signals. A transistor is made of

a solid piece of a semiconductor material, with at least three

terminals for connection to an external circuit. A voltage or

current applied to one pair of the transistor's terminals

changes the current flowing through another pair of terminals.

Because the controlled (output) power can be much more than

the controlling (input) power, the transistor provides

amplification of a signal. Some transistors are packaged

individually but most are found in integrated circuits.

The transistor is the fundamental building block of

modern electronic devices, and its presence is ubiquitous in

modern electronic systems.

The first BJTs were made

from germanium (Ge). Silicon (Si) types currently predominate

but certain advanced microwave and high performance versions

now employ the compound semiconductor material gallium

arsenide (GaAs) and the semiconductor alloy silicon

germanium(SiGe). Single element semiconductor material (Ge and

Si) is described as elemental.

Rough parameters for the most common semiconductor materials

used to make transistors are given in the table to the right;

these parameters will vary with increase in temperature,

electric field, impurity level, strain, and sundry other

factors.

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The junction forward voltage is the voltage applied to

the emitter-base junction of a BJT in order to make the base

conduct a specified current. The current increases

exponentially, as the junction forward voltage is increased.

The values given in the table are typical for a current of 1

mA (the same values apply to semiconductor diodes). The lower

the junction forward voltage the better, as this means that

less power is required to "drive" the transistor. The junction

forward voltage for a given current decreases with increase in

temperature. For a typical silicon junction the change is −2.1

mV/°C. In some circuits special compensating elements

(sensistors) must be used to compensate for such changes.

The density of mobile carriers in the channel of a MOSFET

is a function of the electric field forming the channel and of

various other phenomena such as the impurity level in the

channel. Some impurities, called dopants, are introduced

deliberately in making a MOSFET, to control the MOSFET

electrical behavior.

The electron mobility and hole mobility columns show the

average speed that electrons and holes diffuse through the

semiconductor material with an electric field of 1 volt per

meter applied across the material. In general, the higher the

electron mobility the faster the transistor can operate. The

table indicates that Ge is a better material than Si in this

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respect. However, Ge has four major shortcomings compared to

silicon and gallium arsenide:

Its maximum temperature is limited; it has relatively

high leakage current; it cannot withstand high voltages; it is

less suitable for fabricating integrated circuits.

Because the electron mobility is higher than the hole

mobility for all semiconductor materials, a given bipolar NPN

transistor tends to be swifter than an equivalent PNP

transistor type. GaAs has the highest electron mobility of the

three semiconductors. It is for this reason that GaAs is used

in high frequency applications. A relatively recent FET

development, the high electron mobility transistor (HEMT), has

a hetero structure (junction between different semiconductor

materials) of aluminium gallium arsenide (AlGaAs)-gallium

arsenide (GaAs) which has twice the electron mobility of a

GaAs-metal barrier junction. Because of their high speed and

low noise, HEMTs are used in satellite receivers working at

frequencies around 12 GHz.

Maximum junction temperature values represent a cross

section taken from various manufacturers' data sheets. This

temperature should not be exceeded or the transistor may be

damaged.

Al–Si junction refers to the high-speed (aluminum–

silicon) metal–semiconductor barrier diode, commonly known as

a Schottky diode. This is included in the table because some

silicon power IGFETs have a parasitic reverse Schottky diode

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formed between the source and drain as part of the fabrication

process. This diode can be a nuisance, but sometimes it is

used in the circuit.

Transistor works in such a manner that a current is

applied at one end consisting of one pair of terminals; it

brings changes in the current flowing through another pair of

terminals at other end. Since, the controlled power can be

much more than the controlling power, there takes place the

amplification of a signal. Info to know about transistor is

that there are some transistors which are packaged

individually however; normally the transistors are embedded in

integrated circuits.

One gets an idea about the importance of transistor from

the fact that nowadays, the use of transistor is almost there

in every electronic device. It won’t be inappropriate to say

about transistor that it has become the fundamental building

block of modern electronic devices, and its presence is

everywhere in modern electronic systems.

The transistor considered as the main component in almost

all walks of modern electronics, and is termed as one of the

greatest inventions of modern times.

The importance of transistor in today's life resides on

its capability to be mass produced using a highly automated

process which is possible due to semiconductor device

64

fabrication. It has resulted in making lower cost transistors.

Moreover it can perform multiple functions as transistor can

act as an amplifier by controlling its output in proportion to

the input signal. Or, it can also be used as a switch in high

power applications as well as low power application like logic

gates.

Usage:

The bipolar junction transistor, or BJT, was the most

commonly used transistor in the 1960s and 70s. Even after

MOSFETs became widely available, the BJT remained the

transistor of choice for many analog circuits such as simple

amplifiers because of their greater linearity and ease of

manufacture. Desirable properties of MOSFETs, such as their

utility in low-power devices, usually in the CMOS

configuration, allowed them to capture nearly all market share

for digital circuits; more recently MOSFETs have captured most

analog and power applications as well, including modern

clocked analog circuits, voltage regulators, amplifiers, power

transmitters, motor drivers, etc.

Transistors are commonly used as electronic switches,

both for high-power applications such as switched-mode power

supplies and for low-power applications such as logic gates.

In a grounded-emitter transistor circuit, such as the

light-switch circuit shown, as the base voltage rises, the

emitter and collector current rises exponentially. The

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collector voltage drops because of reduced resistance from

collector to emitter. If the voltage difference between the

collector and emitter were zero (or near zero), the collector

current would be limited only by the load resistance (light

bulb) and the supply voltage. This is

called saturation because current is flowing from collector to

emitter freely. When saturated the switch is said to be on.

Providing sufficient base drive current is a key problem

in the use of bipolar transistors as switches. The transistor

provides current gain, allowing a relatively large current in

the collector to be switched by a much smaller current into

the base terminal. The ratio of these currents varies

depending on the type of transistor, and even for a particular

type, varies depending on the collector current. In the

example light-switch circuit shown, the resistor is chosen to

provide enough base current to ensure the transistor will be

saturated.

In any switching circuit, values of input voltage would

be chosen such that the output is either completely off, or

completely on. The transistor is acting as a switch, and this

type of operation is common in digital circuits where only

"on" and "off" values are relevant.

The common-emitter amplifier is designed so that a small

change in voltage (Vin) changes the small current through the

base of the transistor; the transistor's current amplification

66

combined with the properties of the circuit mean that small

swings in Vin produce large changes in Vout.

Various configurations of single transistor amplifier are

possible, with some providing current gain, some voltage gain,

and some both.

From mobile phones to televisions, vast numbers of

products include amplifiers for sound reproduction, radio

transmission, and signal processing. The first discrete

transistor audio amplifiers barely supplied a few hundred

milliwatts, but power and audio fidelity gradually increased

as better transistors became available and amplifier

architecture evolved. Modern transistor audio amplifiers of up

to a few hundred watts are common and relatively inexpensive.

Advantages:

The key advantages that have allowed transistors to replace

their vacuum tube predecessors in most applications are:

(i) Small size and minimal weight, allowing the development ofminiaturized electronic devices.

(ii) Highly automated manufacturing processes, resulting inlow per-unit cost.

(iii) Lower possible operating voltages, making transistorssuitable for small, battery-powered applications.

(iv) No warm-up period for cathode heaters required afterpower application.

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(v) Lower power dissipation and generally greater energyefficiency.

(vi) Higher reliability and greater physical ruggedness.

(vii) Extremely long life. Some transistorized devices havebeen in service for more than 30 years.

(viii) Complementary devices available, facilitating thedesign of complementary-symmetry circuits, something notpossible with vacuum tubes.

(ix) Insensitivity to mechanical shock and vibration, thusavoiding the problem of microphonics in audio applications.

Limitations:

(i) Silicon transistors do not operate at voltages higher thanabout 1,000 volts (SiC devices can be operated as high as3,000 volts). In contrast, electron tubes have been developedthat can be operated at tens of thousands of volts.

(ii) High power, high frequency operation, such as used inover-the-air television broadcasting, is better achieved inelectron tubes due to improved electron mobility in a vacuum.

(iii) On average, a higher degree of amplification linearitycan be achieved in electron tubes as compared to equivalentsolid state devices, a characteristic that may be important inhigh fidelity audio reproduction.

(iv) Silicon transistors are much more sensitive than electrontubes to an electromagnetic pulse, such as generated by anatmospheric nuclear explosion.

Bipolar junction transistor:The bipolar junction transistor (BJT) was the first type

of transistor to be mass-produced. Bipolar transistors are so

named because they conduct by using both majority and minority

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carriers. The three terminals of the BJT are named emitter,

base, and collector. The BJT consists of two p-n junctions:

the base–emitter junction and the base–collector junction,

separated by a thin region of semiconductor known as the base

region (two junction diodes wired together without sharing anintervening semiconducting region will not make a transistor).

"The [BJT] is useful in amplifiers because the currents at the

emitter and collector are controllable by the relatively small

base current.

In an NPN transistor operating in the active region, the

emitter-base junction is forward biased (electrons and holes

recombine at the junction), and electrons are injected into

the base region. Because the base is narrow, most of these

electrons will diffuse into the reverse-biased (electrons and

holes are formed at, and move away from the junction) base-

collector junction and be swept into the collector; perhaps

one-hundredth of the electrons will recombine in the base,

which is the dominant mechanism in the base current.

By controlling the number of electrons that can leave the

base, the number of electrons entering the collector can be

controlled.[14] Collector current is approximately β (common-

emitter current gain) times the base current. It is typically

greater than 100 for small-signal transistors but can be

smaller in transistors designed for high-power applications.

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3.3.4 LED:

A light-emittingdiode (LED) is anelectronic lightsource. LEDs areused as indicatorlamps in manykinds ofelectronics andincreasingly forlighting. LEDswork by theeffect of

electroluminescence, discovered by accident in 1907. TheLEDwas introduced as a practical electronic component in 1962.All early devices emitted low-intensity red light, but modernLEDs are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.

LEDs are based on the semiconductor diode. When the diode isforward biased (switched on), electrons are able to recombinewith holes and energy is released in the form of light. Thiseffect is called electroluminescence and the color of thelight is determined by the energy gap of the semiconductor.The LED is usually small in area (less than 1 mm2) with

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Electronic symbol

Figure 3.6: LED

integrated optical components to shape its radiation patternand assist in reflection.

LEDs present many advantages over traditional lightsources including lower energy consumption, longer lifetime,improved robustness, smaller size and faster switching.However, they are relatively expensive and require moreprecise current and heat management than traditional lightsources.

Applications of LEDs are diverse. They are used as low-energy indicators but also for replacements for traditionallight sources in general lighting, automotive lighting andtraffic signals. The compact size of LEDs has allowed new textand video displays and sensors to be developed, while theirhigh switching rates are useful in communications technology.

Figure 3.7: Various types LEDs

A light-emitting diode (LED) is a semiconductor light

source. LEDs are used as indicator lamps in many devices and

are increasingly used for other lighting. Appearing as

practical electronic components in 1962, early LEDs emitted

low-intensity red light, but modern versions are available

across the visible, ultraviolet, and infrared wavelengths,

with very high brightness.71

When a light-emitting diode is switched on, electrons are

able to recombine with holes within the device, releasing

energy in the form of photons. This effect is

called electroluminescence and the color of the light

(corresponding to the energy of the photon) is determined by

the energy band gap of the semiconductor. An LED is often

small in area (less than 1 mm2), and integrated optical

components may be used to shape its radiation pattern. LEDs

present many advantages over incandescent light sources

including lower energy consumption, longer lifetime, improved

physical robustness, smaller size, and faster switching.

However, LEDs powerful enough for room lighting are relatively

expensive and require more precise current and heat management

than compact fluorescent lamp sources of comparable output.

Light-emitting diodes are used in applications as diverse

as aviation lighting, automotive lighting, advertising,

general lighting, and traffic signals. LEDs have allowed new

text, video displays, and sensors to be developed, while their

high switching rates are also useful in advanced

communications technology. Infrared LEDs are also used in the

remote control units of many commercial products including

televisions, DVD players and other domestic appliances. LEDs

are also used in seven-segment display.

The LED consists of a chip of semiconducting

material doped with impurities to create a p-n junction. As in

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other diodes, current flows easily from the p-side, or anode,

to the n-side, or cathode, but not in the reverse direction.

Charge-carriers electrons and holes flow into the junction

from electrodes with different voltages. When an electron

meets a hole, it falls into a lower energy level, and

releases energy in the form of a photon.

The wavelength of the light emitted, and thus its color

depends on the band gap energy of the materials forming the p-

n junction. In silicon or germanium diodes, the electrons and

holes recombine by a non-radiative transition, which produces

no optical emission, because these are indirect band

gap materials. The materials used for the LED have a direct

band gap with energies corresponding to near-infrared,

visible, or near-ultraviolet light.

LED development began with infrared and red devices made

with gallium arsenide. Advances in materials science have

enabled making devices with ever-shorter wavelengths, emitting

light in a variety of colors.

LEDs are usually built on an n-type substrate, with an

electrode attached to the p-type layer deposited on its

surface. P-type substrates, while less common, occur as well.

Many commercial LEDs, especially GaN/InGaN, also

use sapphire substrate.

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Most materials used for LED production have very

high refractive indices. This means that much light will be

reflected back into the material at the material/air surface

interface. Thus, light extraction in LEDs is an important

aspect of LED production, subject to much research and

development.

Typical indicator LEDs are designed to operate with no

more than 30–60 milliwatts (mW) of electrical power. Around

1999, Philips Lumileds introduced power LEDs capable of

continuous use at one watt. These LEDs used much larger

semiconductor die sizes to handle the large power inputs.

Also, the semiconductor dies were mounted onto metal slugs to

allow for heat removal from the LED die. LED power densities

up to 300W/cm2 have been achieved.

One of the key advantages of LED-based lighting sources

is high luminous efficiency. White LEDs quickly matched and

overtook the efficacy of standard incandescent lighting

systems. In 2002, Lumileds made five-watt LEDs available with

a luminous efficacy of 18–22 lumens per watt (lm/W). For

comparison, a conventional incandescent light bulb of 60–100

watts emits around 15 lm/W, and standard fluorescent

lights emit up to 100 lm/W. A recurring problem is that

efficacy falls sharply with rising current. This effect is

known as droop and effectively limits the light output of a

given LED, raising heating more than light output for higher

current.

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As of 2012, the Lumiled catalog gives the following as

the best efficacy for each color:

This method involves coating LEDs of one color (mostly

blue LEDs made of InGaN) with phosphors of different colors to

form white light; the resultant LEDs are called phosphor-based

white LEDs.  A fraction of the blue light undergoes the Stokes

shift being transformed from shorter wavelengths to longer.

Depending on the color of the original LED, phosphors of

different colors can be employed. If several phosphor layers

of distinct colors are applied, the emitted spectrum is

broadened, effectively raising the color rendering index (CRI)

value of a given LED.

Phosphor-based LED efficiency losses are due to the heat

loss from the Stokes shift and also other phosphor-related

degradation issues. Their efficiencies compared to normal LEDs

depend on the spectral distribution of the resultant light

output and the original wavelength of the LED itself. For

example, the efficiency of a typical YAG yellow phosphor based

white LED ranges from 3 to 5 times the efficiency of the

original blue LED because of the greater luminous efficacy of

yellow compared to blue light. Due to the simplicity of

manufacturing the phosphor method is still the most popular

method for making high-intensity white LEDs. The design and

production of a light source or light fixture using a

monochrome emitter with phosphor conversion is simpler and

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cheaper than a complex RGB system, and the majority of high-

intensity white LEDs presently on the market are manufactured

using phosphor light conversion.

Among the challenges being faced to improve the

efficiency of LED-based white light sources is the development

of more efficient phosphors. Today the most efficient yellow

phosphor is still the YAG phosphor, with less than 10% Stoke

shift loss. Losses attributable to internal optical losses due

to re-absorption in the LED chip and in the LED packaging

itself account typically for another 10% to 30% of efficiency

loss. Currently, in the area of phosphor LED development, much

effort is being spent on optimizing these devices to higher

light output and higher operation temperatures. For instance,

the efficiency can be raised by adapting better package design

or by using a more suitable type of phosphor. Conformal

coating process is frequently used to address the issue of

varying phosphor thickness.

White LEDs can also be made by coating near-

ultraviolet (NUV) LEDs with a mixture of high-

efficiency europium-based phosphors that emit red and blue,

plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that

emits green. This is a method analogous to the way fluorescent

lamps work. This method is less efficient than blue LEDs with

YAG:Ce phosphor, as the Stokes shift is larger, so more energy

is converted to heat, but yields light with better spectral

characteristics, which render color better. Due to the higher

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radiative output of the ultraviolet LEDs than of the blue

ones, both methods offer comparable brightness. A concern is

that UV light may leak from a malfunctioning light source and

cause harm to human eyes or skin.

LEDs are used increasingly in aquarium lights. In

particular for reef aquariums, LED lights provide an efficient

light source with less heat output to help maintain optimal

aquarium temperatures. LED-based aquarium fixtures also have

the advantage of being manually adjustable to emit a specific

color-spectrum for ideal coloration of corals, fish, and

invertebrates while optimizing photosynthetically active

radiation (PAR), which raises growth and sustainability of

photosynthetic life such as corals, anemones, clams, and

macroalgae. These fixtures can be electronically programmed to

simulate various lighting conditions throughout the day,

reflecting phases of the sun and moon for a dynamic reef

experience. LED fixtures typically cost up to five times as

much as similarly rated fluorescent or high-intensity

discharge lighting designed for reef aquariums and are not as

high output to date.

The lack of IR or heat radiation makes LEDs ideal

for stage lights using banks of RGB LEDs that can easily

change color and decrease heating from traditional stage

lighting, as well as medical lighting where IR-radiation can

be harmful. In energy conservation, the lower heat output of

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LEDs also means air conditioning (cooling) systems have less

heat to dispose of, reducing carbon dioxide emissions.

LEDs are small, durable and need little power, so they

are used in hand held devices such as flashlights. LED strobe

lights or camera flashes operate at a safe, low voltage,

instead of the 250+ volts commonly found in xenon flashlamp-

based lighting. This is especially useful in cameras on mobile

phones, where space is at a premium and bulky voltage-raising

circuitry is undesirable.

LEDs are used for infrared illumination in night

vision uses including security cameras. A ring of LEDs around

a video camera, aimed forward into a retro

reflective background, allows chroma keying in video

productions.

LEDs are now used commonly in all market areas from commercial

to home use: standard lighting, AV, stage, theatrical,

architectural, and public installations, and wherever

artificial light is used.

LEDs are increasingly finding uses in medical and

educational applications, for example as mood enhancement, and

new technologies such as AmBX, exploiting LED versatility.

NASA has even sponsored research for the use of LEDs to

promote health for astronauts.

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Applications:

(i) Flashing LEDs are used as attention seeking indicators

without requiring external electronics. Flashing LEDs resemble

standard LEDs but they contain an

integrated multivibrator circuit that causes the LED to flash

with a typical period of one second. In diffused lens LEDs

this is visible as a small black dot. Most flashing LEDs emit

light of one color, but more sophisticated devices can flash

between multiple colors and even fade through a color sequence

using RGB color mixing.

(ii) Bi-color LEDs are two different LED emitters in one case.

There are two types of these. One type consists of two dies

connected to the same two leads anti parallel to each other.

Current flow in one direction emits one color, and current in

the opposite direction emits the other color. The other type

consists of two dies with separate leads for both dies and

another lead for common anode or cathode, so that they can be

controlled independently.

(iii) Tri-color LEDs are three different LED emitters in one

case. Each emitter is connected to a separate lead so they can

be controlled independently. A four-lead arrangement is

typical with one common lead (anode or cathode) and an

additional lead for each color.

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(iv) RGB LEDs are Tri-color LEDs with red, green, and blue

emitters, in general using a four-wire connection with one

common lead (anode or cathode). These LEDs can have either

common positive or common negative leads. Others however, have

only two leads (positive and negative) and have a built in

tiny electronic control unit.

(v) Alphanumeric LED displays are available in seven-

segment and starburst format. Seven-segment displays handle

all numbers and a limited set of letters. Starburst displays

can display all letters. Seven-segment LED displays were in

widespread use in the 1970s and 1980s, but rising use

of liquid crystal displays, with their lower power needs and

greater display flexibility, has reduced the popularity of

numeric and alphanumeric LED displays.

Other applications:The light from LEDs can be modulated very quickly so they

are used extensively in optical fiber and free space

optics communications. This includes remote controls, such as

for TVs, VCRs, and LED Computers, where infrared LEDs are

often used. Opto-isolators use an LED combined with

a photodiode or phototransistor to provide a signal path with

electrical isolation between two circuits. This is especially

useful in medical equipment where the signals from a low-

voltage sensor circuit (usually battery-powered) in contact

with a living organism must be electrically isolated from any

possible electrical failure in a recording or monitoring

device operating at potentially dangerous voltages. An opto80

isolator also allows information to be transferred between

circuits not sharing a common ground potential.

Many sensor systems rely on light as the signal source.

LEDs are often ideal as a light source due to the requirements

of the sensors. LEDs are used as movement sensors, for example

in optical computer mice. The Nintendo Wii’s sensor bar uses

infrared LEDs. Pulse oxi-meters use them for measuring oxygen

saturation. Some flatbed scanners use arrays of RGB LEDs

rather than the typical cold-cathode fluorescent lamp as the

light source. Having independent control of three illuminated

colors allows the scanner to calibrate itself for more

accurate color balance, and there is no need for warm-up.

Further, its sensors only need be monochromatic, since at any

one time the page being scanned is only lit by one color of

light. 

(i) Touch sensing:

Since LEDs can also be used as photodiodes, they can be

used for both photo emission and detection. This could be

used, for example, in a touch-sensing screen that registers

reflected light from a finger orstylus.

Many materials and biological systems are sensitive to or

dependent on light. Grow lights use LEDs to

increase photosynthesis in plants and bacteria and viruses can

be removed from water and other substances using UV LEDs

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for sterilization. Other uses are as UV curing devices for

some ink and coating methods, and in LED printers.

Plant growers are interested in LEDs because they are

more energy-efficient, emit less heat (can damage plants close

to hot lamps), and can provide the optimum light frequency for

plant growth and bloom periods compared to currently used grow

lights: HPS (high-pressure sodium), metal-halide (MH)

or CFL/low-energy. However, LEDs have not replaced these grow

lights due to higher price. As mass production and LED kits

develop, the LED products will become cheaper.

LEDs have also been used as a medium-quality voltage

reference in electronic circuits. The forward voltage drop

(e.g., about 1.7 V for a normal red LED) can be used instead

of a Zener diode in low-voltage regulators. Red LEDs have the

flattest I/V curve above the knee. Nitride-based LEDs have a

fairly steep I/V curve and are useless for this purpose.

Although LED forward voltage is far more current-dependent

than a good Zener, Zener diodes are not widely available below

voltages of about 3 V.

(ii) Light sources for machine vision systems:Machine vision systems often require bright and

homogeneous illumination, so features of interest are easier

to process. LEDs are often used for this purpose, and this is

likely to remain one of their major uses until price drops low

enough to make signaling and illumination uses more

widespread. Barcode scanners are the most common example of

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machine vision, and many low cost ones use red LEDs instead of

lasers. Optical computer mice are also another example of LEDs

in machine vision, as it is used to provide an even light

source on the surface for the miniature camera within the

mouse. LEDs constitute a nearly ideal light source for machine

vision systems for several reasons:

The size of the illuminated field is usually

comparatively small and machine vision systems are often quite

expensive, so the cost of the light source is usually a minor

concern. However, it might not be easy to replace a broken

light source placed within complex machinery, and here the

long service life of LEDs is a benefit.

LED elements tend to be small and can be placed with high

density over flat or even-shaped substrates (PCBs etc.) so

that bright and homogeneous sources that direct light from

tightly controlled directions on inspected parts can be

designed. This can often be obtained with small, low-cost

lenses and diffusers, helping to achieve high light densities

with control over lighting levels and homogeneity. LED sources

can be shaped in several configurations (spot lights for

reflective illumination; ring lights for coaxial illumination;

back lights for contour illumination; linear assemblies; flat,

large format panels; dome sources for diffused, omni

directional illumination).

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LEDs can be easily strobed (in the microsecond range and

below) and synchronized with imaging. High-power LEDs are

available allowing well-lit images even with very short light

pulses. This is often used to obtain crisp and sharp “still”

images of quickly moving parts.

LEDs come in several different colors and wavelengths,

allowing easy use of the best color for each need, where

different color may provide better visibility of features of

interest. Having a precisely known spectrum allows tightly

matched filters to be used to separate informative bandwidth

or to reduce disturbing effects of ambient light. LEDs usually

operate at comparatively low working temperatures, simplifying

heat management and dissipation. This allows using plastic

lenses, filters, and diffusers. Waterproof units can also

easily be designed, allowing use in harsh or wet environments

(food, beverage, oil industries).

Advantages:

(i) Efficiency: LEDs emit more light per watt

than incandescent light bulbs. The efficiency of LED lighting

fixtures is not affected by shape and size, unlike fluorescent

light bulbs or tubes.

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(ii) Color: LEDs can emit light of an intended color without

using any color filters as traditional lighting methods need.

This is more efficient and can lower initial costs.

(iii) Size: LEDs can be very small (smaller than 2 mm) and are

easily attached to printed circuit boards.

(iv) On/Off time: LEDs light up very quickly. A typical red

indicator LED will achieve full brightness in under

a microsecond. LEDs used in communications devices can have

even faster response times.

(v) Cycling: LEDs are ideal for uses subject to frequent on-

off cycling, unlike fluorescent lamps that fail faster when

cycled often, or HID lamps that require a long time before

restarting.

(vi) Dimming: LEDs can very easily be dimmed either by pulse-

width modulation or lowering the forward current.

(vii) Cool light: In contrast to most light sources, LEDs

radiate very little heat in the form of IR that can cause

damage to sensitive objects or fabrics. Wasted energy is

dispersed as heat through the base of the LED.

(viii) Slow failure: LEDs mostly fail by dimming over time,

rather than the abrupt failure of incandescent bulbs.

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(ix) Lifetime: LEDs can have a relatively long useful life.

One report estimates 35,000 to 50,000 hours of useful life,

though time to complete failure may be longer. Fluorescent

tubes typically are rated at about 10,000 to 15,000 hours,

depending partly on the conditions of use, and incandescent

light bulbs at 1,000 to 2,000 hours. Several DOE

demonstrations have shown that reduced maintenance costs from

this extended lifetime, rather than energy savings, is the

primary factor in determining the payback period for an LED

product.

(x) Shock resistance: LEDs, being solid-state components, are

difficult to damage with external shock, unlike fluorescent

and incandescent bulbs, which are fragile.

(xi) Focus: The solid package of the LED can be designed

to focus its light. Incandescent and fluorescent sources often

require an external reflector to collect light and direct it

in a usable manner. For larger LED packages total internal

reflection (TIR) lenses are often used to the same effect.

However, when large quantities of light is needed many light

sources are usually deployed, which are difficult to focus

or collimate towards the same target.

Disadvantages:

(i) High initial price:

  LEDs are currently more expensive, price per lumen, on an

initial capital cost basis, than most conventional lighting

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technologies. As of 2010, the cost per thousand lumens (kilo

lumen) was about $18. The price is expected to reach $2/kilo

lumen by 2015. The additional expense partially stems from the

relatively low lumen output and the drive circuitry and power

supplies needed.

(ii) Temperature dependence: 

LED performance largely depends on the ambient

temperature of the operating environment – or "thermal

management" properties. Over-driving an LED in high ambient

temperatures may result in overheating the LED package,

eventually leading to device failure. An adequate heat sink is

needed to maintain long life. This is especially important in

automotive, medical, and military uses where devices must

operate over a wide range of temperatures, which require low

failure rates.

(iii) Voltage sensitivity: 

LEDs must be supplied with the voltage above the

threshold and a current below the rating. This can involve

series resistors or current-regulated power supplies.

(iv) Light quality: Most cool-white LEDs have spectra that

differ significantly from a black body radiator like the sun

or an incandescent light. The spike at 460 nm and dip at

500 nm can cause the color of objects to be perceived

differently under cool-white LED illumination than sunlight or

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incandescent sources, due to metamerism, red surfaces being

rendered particularly badly by typical phosphor-based cool-

white LEDs. However, the color rendering properties of common

fluorescent lamps are often inferior to what is now available

in state-of-art white LEDs.

(v) Area light source: 

Single LEDs do not approximate a point source of light

giving a spherical light distribution, but rather

a lambertian distribution. So LEDs are difficult to apply to

uses needing a spherical light field, however different fields

of light can be manipulated by the application of different

optics or "lenses". LEDs cannot provide divergence below a few

degrees. In contrast, lasers can emit beams with divergences

of 0.2 degrees or less.

(vi) Electrical polarity: 

Unlike incandescent light bulbs, which illuminate

regardless of the electrical polarity, LEDs will only light

with correct electrical polarity. To automatically match

source polarity to LED devices, rectifiers can be used.

(vii) Blue hazard: 

There is a concern that blue LEDs and cool-white LEDs are

now capable of exceeding safe limits of the so-called blue-

light hazard as defined in eye safety specifications such as

ANSI/IESNA RP-27.1–05: Recommended Practice for Photo

biological Safety for Lamp and Lamp Systems.

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(viii) Blue pollution:

 Because cool-white LEDs with high color temperature emit

proportionally more blue light than conventional outdoor light

sources such as high-pressure sodium vapor lamps, the strong

wavelength dependence of Rayleigh scattering means that cool-

white LEDs can cause more light pollution than other light

sources. The International Dark-Sky Association discourages

using white light sources with correlated color temperature

above 3,000 K.

(ix) Droop:

The efficiency of conventional InGaN based LEDs decreases

as one increases current above a given level.

3.3.5 Piezo Buzzer:

Figure 3.8: Piezo Buzzer

Piezoelectricity is the ability of some materials

(notably crystals and certain ceramics, including bone) to

generate an electric field or electric potential[1] in response

to applied mechanical stress. The effect is closely related to

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a change of polarization density within the material's volume.

If the material is not short-circuited, the applied stress

induces a voltage across the material. The word is derived

from the Greek piezo or piezein, which means to squeeze or

press.

A buzzer or beeper is a signaling device, usually

electronic, typically used in automobiles, household

appliances such as microwave ovens, or game shows.

It most commonly consists of a number of switches or sensors

connected to a control unit that determines if and which

button was pushed or a preset time has lapsed, and usually

illuminates a light on the appropriate button or control

panel, and sounds a warning in the form of a continuous or

intermittent buzzing or beeping sound.

Initially this device was based on an electromechanical

system which was identical to an electric bell without the

metal gong (which makes the ringing noise). Often these units

were anchored to a wall or ceiling and used the ceiling or

wall as a sounding board. Another implementation with some AC-

connected devices was to implement a circuit to make the AC

current into a noise loud enough to drive a loudspeaker and

hook this circuit up to an 8-ohm speaker. Nowadays, it is more

popular to use a ceramic-based piezoelectric sounder which

makes a high-pitched tone. Usually these were hooked up to

"driver" circuits which varied the pitch of the sound or

pulsed the sound on and off.

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In game shows it is also known as a "lockout system"

because when one person signals ("buzzes in"), all others are

locked out from signaling. Several game shows have large

buzzer buttons which are identified as "plungers". The buzzer

is also used to signal wrong answers and when time expires on

many game shows, such as Wheel of Fortune, Family Feud and The

Price is Right.

The word "buzzer" comes from the rasping noise that

buzzers made when they were electromechanical devices,

operated from stepped-down AC line voltage at 50 or 60 cycles.

Other sounds commonly used to indicate that a button has been

pressed are a ring or a beep.

Early devices were based on an electromechanical system

identical to an electric bell without the metal gong.

Similarly, a relay may be connected to interrupt its own

actuating current, causing the contacts to buzz. Often these

units were anchored to a wall or ceiling to use it as a

sounding board. The word "buzzer" comes from the rasping noise

that electromechanical buzzers made.

A piezoelectric element may be driven by

an oscillating electronic circuit or other audio

signal source, driven with a piezoelectric audio amplifier.

Sounds commonly used to indicate that a button has been

pressed are a click, a ring or a beep.

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(i) What is piezoelectric effect?

  Every day use of this phenomenon is used in load cells.

Load cells are used on large weigh scales for trucks and large

bin scales where materials need to be weighed. The signals

from the cells are calibrated to compensate for the weight of

the scale so that the scale can be zeroed out. The cell

signal, because it is very small, is sent to an amplifier head

where is can be read by the operator in units of weight. The

head unit can be set to read in metric or imperial weights.

(ii) Advantages:

  As explained in your above question on weigh scales the

load cells do away with all the mechanical linkages that the

old systems had to use. These linkages were always prone to

mechanical damage where as the load cells are self contained

sealed units. There are four units per scale, one under each

corner.

A Piezo buzzer is made from two conductors that are

separated by Piezo crystals. When a voltage is applied to

these crystals, they push on one conductor and pull on the

other. The result of this push and pull is a sound wave. These

buzzers can be used for many things, like signaling when a

period of time is up or making a sound when a particular

button has been pushed. The process can also be reversed to

use as a guitar pickup. When a sound wave is passed, they

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create an electric signal that is passed on to an audio

amplifier.

(iii) Uses:

(i) Annunciator panels

(ii) Electronic metronomes

(iii) Game shows

(iv) Microwave ovens and other household appliances

(v) Sporting events such as basketball games

(vi) Electrical alarms

(iv) Piezoelectric Sound Generators (Transducers and Buzzers):

The heart of all piezoelectric sound generators is a

simple piezoceramic disc, consisting of a metal plate, glued

together with a ceramic layer. If the disc is driven by an

external oscillating circuit, the piezo sound generator is

called piezoelectric transducer. If the disc is driven by a

built-in oscillating circuit it‘s called piezoelectric

buzzer. The advantages of these simple structured, acoustic

components are their robustness and cost-efficient sound

solution. Piezo sound generators are the ideal choice for

applications, which need a simple sound signal within a small

frequency range, e. g. warning and control sound signals of

kitchen devices, medical and health care products.

The dimension range of piezo sound generators starts from

the miniaturized size of 11 mm × 9 mm × 1.7 mm up to ø 45 mm

and covers sound pressures between low soft sound and

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aggressive noisy sound. The design of almost all piezoelectric

sound generators is adjusted to meet the most popular

frequencies in the range between 2000 Hz and 5000 Hz.

Operation temperature range is available from -40°C to +120°C.

Standard voltage range is between 3 V and 12 V, in special

cases higher, according to customer’s demand. Piezoelectric

sound generators are available with pins, wires or SMD pads.

(v) Applications of Piezoelectric Ceramics:

A piezoelectric system can be constructed for virtually

any application for which any other type of electromechanical

transducer can be used. For any particular application,

however, limiting factors include the size, weight, and cost

of the piezoelectric system. Piezo ceramic devices fit into

four general categories: piezo generators, sensors, piezo

actuators, and transducers.

(i) Piezoelectric Generators:

Piezoelectric ceramics can generate voltages sufficient

to spark across an electrode gap, and thus can be used as

ignitors in fuel lighters, gas stoves, welding equipment, and

other such apparatus. Piezoelectric ignition systems are small

and simple -- distinct advantages relative to alternative

systems that include permanent magnets or high voltage

transformers and capacitors.

Alternatively, the electrical energy generated by a

piezoelectric element can be stored. Techniques used to make

multilayer capacitors have been used to construct multilayer

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piezoelectric generators. Such piezo generators are excellent

solid state batteries for electronic circuits.

(ii) Piezoelectric Sensors:

A piezoelectric sensor converts a physical parameter,

such as acceleration or pressure, into an electrical signal.

In some sensors the physical parameter acts directly on the

piezoelectric element; in other devices an acoustical signal

establishes vibrations in the element and the vibrations are,

in turn, converted into an electrical signal. Often, the

system provides a visual, audible, or physical response to the

input from the piezo sensor -- automobile seatbelts lock in

response to a rapid deceleration, for example.

 

(iii) Piezo Actuators: Multilayer, Stack, Bending, Stripe:

A piezo actuator converts an electrical signal into a

precisely controlled physical displacement, to finely adjust

precision machining tools, lenses, or mirrors. Piezoelectric

actuators also are used to control hydraulic valves, act as

small-volume pumps or special-purpose motors, and in other

applications. Piezoelectric motors are unaffected by energy

efficiency losses that limit the miniaturization of

electromagnetic motors, and have been constructed to sizes of

less than 1 cm3. A potentially important additional advantage

to piezoelectric motors is the absence of electromagnetic

noise.

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There are two different types of piezo actuators / piezo

multi layers. The first is a stack actuator. A stack

actuator is constructed in one of two ways: discrete stacking

or co-firing depending on the user’s requirements.

The other type of piezo actuator is a stripe actuator or

bending actuator, in which thin layers of piezoelectric

ceramics are bonded together; the thin layers allow the

actuator to bend with a greater deflection but a lower

blocking force than a stack actuator. Alternatively, if

physical displacement is prevented, a piezo actuator will

develop a usable force.

(iv) Piezoelectric Transducer:

Piezoelectric transducers convert electrical energy into

vibrational mechanical energy, often sound or ultra sound,

that is used to perform a task.

Piezoelectric transducers that generate audible sounds afford

significant advantages, relative to alternative

electromagnetic devices -- they are compact, simple, and

highly reliable, and minimal energy can produce a high level

of sound. These characteristics are ideally matched to the

needs of battery-powered equipment.

Because the piezoelectric effect is reversible, a

transducer can both generate an ultrasound signal from

electrical energy and convert incoming sound into an

electrical signal. Some devices designed for measuring

distances, flow rates, or fluid levels incorporate a single96

piezoelectric transducer in the signal sending and receiving

roles, other designs incorporate two transducers and separate

these roles.

Piezoelectric transducers also are used to generate

ultrasonic vibrations for cleaning, atomizing liquids,

drilling or milling ceramics or other difficult materials,

welding plastics, medical diagnostics, or for other purposes.

3.4 Pin Configuration of ICs:

3.4.1 IC CA3130:

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Figure 3.9: IC CA31303.4.2 IC NE555:

Figure 3.10: IC NE555

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3.5 Working, Applications, and Features of IC CA3130:

General Description:

CA3130 are op amps that combine the advantage of both

CMOS and bipolar transistors.

 Gate-protected P-Channel MOSFET (PMOS) transistors are used

in the input circuit to provide very-high-input impedance,

very-low-input current, and exceptional speed performance. The

use of PMOS transistors in the input stage results in common-

mode input-voltage capability down to 0.5V below the negative-

supply terminal, an important attribute in single-supply

applications.

 

A CMOS transistor-pair, capable of swinging the output

voltage to within 10mV of either supply-voltage terminal (at

very high values of load impedance), is employed as the output

circuit.

 

CA3130A and CA3130 are op amps that combine the advantage

of both CMOS and bipolar transistors. Gate protected P-Channel

MOSFET (PMOS) transistors are used in the input circuit to

provide very-high-input impedance, very-low-input current, and

exceptional speed performance. The use of PMOS transistors in

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the input stage results in common-mode input-voltage

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

important attribute in single-supply applications.

A CMOS transistor-pair, capable of swinging the output

voltage to within 10mV of either supply-voltage terminal (at

very high values of load impedance), is employed as the output

circuit. The CA3130 Series circuits operate at supply voltages

ranging from 5V to 16V, (}2.5V to }8V). They can be phase

compensated with a single external capacitor, and have

terminals for adjustment of offset voltage for applications

requiring offset-null capability. Terminal provisions are also

made to permit striding of the output stage. The CA3130A

offers superior input characteristics over those of the

CA3130.

The CA3130 op amp has the following pinouts:

1. Offset null

2. Inv. input

3. Non-inv. input

4. V- and case

5. Offset null

6. Output

7. V+

8. Strobe

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(i) Role of IC CA3130:

This IC is a 15 MHz BiMOS Operational amplifier with

MOSFET inputs and Bipolar output. The inputs contain MOSFET

transistors to provide very high input impedance and very low

input current as low as 10pA. It has high speed of performance

and suitable for low input current applications.

CA3130A and CA3130 are op amps that combine the advantage

of both CMOS and bipolar transistors. Gate-protected P-Channel

MOSFET (PMOS) transistors are used in the input circuit to

provide very-high-input impedance, very-low-input current,

and exceptional speed performance. The use of PMOS transistors

in the input stage results in common-mode input-voltage

capability down to0.5V below the negative-supply terminal, an

important attribute in single-supply applications.

A CMOS transistor-pair, capable of swinging the output

voltage to within 10mV of either supply-voltage terminal (at

very high values of load impedance), is employed as the output

circuit.

The CA3130 Series circuits operate at supply voltages

ranging from 5V to 16V, (2.5V to 8V). They can be phase

compensated with a single external capacitor, and have

terminals for adjustment of offset voltage for applications

requiring offset-null capability. Terminal provisions are

also made to permit striding of the output stage. The

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CA3130A offers superior input characteristics over those of

the CA3130.

(ii) Features:

(i) MOSFET Input Stage Provides:

Very High ZI = 1.5 T

Very Low current . . . . . . =5pA at 15V Operation

(ii) Ideal for Single-Supply Applications

(iii) Common-Mode Input-Voltage Range Includes Negative Supply

Rail; Input Terminals can be Swung 0.5VBelow Negative

Supply Rail

(iv) CMOS Output Stage Permits Signal Swing to Either (or

both) Supply Rails.

(iii) Applications:

(i) Ground-Referenced Single Supply Amplifiers

(ii) Fast Sample-Hold Amplifiers

(iii) Long-Duration Timers/ Mono stables

(iv) High-Input-Impedance Comparators (Ideal Interface with

Digital CMOS)

(v) High-Input-Impedance Wideband Amplifiers

(vi)Voltage Followers (e.g. Follower for Single-Supply D/A

Converter )

(vii) Voltage Regulators (Permits Control of Output Voltage

Down to 0V)

(viii) Peak Detectors

(ix) Single-Supply Full-Wave Precision Rectifiers

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(x) Photo-Diode Sensor Amplifiers.

3.6 Working, Applications and Features of IC NE555:

The NE555 IC is a highly stable controller capable of

producing accurate timing pulses. With a monostable operation,

the time delay is controlled by one external resistor and one

capacitor. With an astable operation, the frequency and duty

cycle are accurately controlled by two external resistors and

one capacitor.

(i) Details of Pin:Ground, is the input pin of the source of the negative DC

voltage trigger, negative input from the lower comparators

(comparator B) that maintain oscillation capacitor voltage in

the lowest 1 / 3 Vcc and set RS flip-flop output, the output

pin of the IC 555.

Reset, the pin that serves to reset the latch inside the IC

to be influential to reset the IC work. This pin is connected

to a PNP-type transistor gate, so the transistor will be

active if given a logic low. Normally this pin is connected

directly to Vcc to prevent reset control voltage, this pin

serves to regulate the stability of the reference voltage

negative input (comparator A). This pin can be left hanging,

but to ensure the stability of the reference comparator A,

usually associated with a capacitor of about 10nF to berorde

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pin ground threshold, this pin is connected to the positive

input (comparator A) which will reset the RS flip-flop when

the voltage on the capacitor from exceeding 2 / 3 V discharge,

this pin is connected to an open collector transistor Q1 is

connected to ground emitter. Switching transistor serves to

clamp the corresponding node to ground on the timing of

certain vcc, pin it to receive a DC voltage supply. Usually it

will work optimally if given a 5-15V. the current supply can

be seen in the datasheet, which is about 10-15mA.

One of the most versatile linear ICs is the 555 timer which

was first introduced in early 1970 by Signetic Corporation

giving the name as SE/NE 555 timer. This IC is a monolithic

timing circuit that can produce accurate and highly stable

time delays or oscillation. Like other commonly used op-amps,

this IC is also very much reliable, easy to use and cheaper in

cost. It has a variety of applications

including monostable and astable multivibrators, dc-dc

converters, digital logic probes, waveform generators, analog

frequency meters and tachometers, temperature measurement and

control devices, voltage regulators etc. The timer basically

operates in one of the two modes either as a monostable (one-

shot) multivibrator or as an astable (free-running)

multivibrator. The SE 555 is designed for the operating

temperature range from – 55°C to 125° while the NE

555 operates over a temperature range of 0° to 70°C.

(ii) The important features of the 555 timer are :

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(i) It operates from a wide range of power supplies ranging

from + 5 Volts to + 18 Volts supply voltage.

(ii) Sinking or sourcing 200 mA of load current.

(iii) The external components should be selected properly so

that the timing intervals can be made into several minutes

Proper selection of only a few external components allows

timing intervals of several minutes along with the frequencies

exceeding several hundred kilo hertz.

(iv) It has a high current output; the output can drive TTL.

(v) It has a temperature stability of 50 parts per million

(ppm) per degree Celsius change in temperature, or

equivalently 0.005 %/ °C.

(vi) The duty cycle of the timer is adjustable with the

maximum power dissipation per package is 600 mW and its

trigger and reset inputs are logic compatible.

Pin Configuration:

Pin 1: Grounded Terminal:  All the voltages are measured with

respect to this terminal.

Pin 2: Trigger Terminal:  This pin is an inverting input to a

comparator that is responsible for transition of flip-

flop   from set to reset. The output of the timer depends on the

amplitude of the external trigger pulse applied to this pin.

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Pin 3: Output Terminal: Output of the timer is available at

this pin. There are two ways in which a load can be connected

to the output terminal either between pin 3 and ground pin

(pin 1) or between pin 3 and supply pin (pin 8). The load

connected between pin 3 and ground supply pin is called

the normally on load and that connected between pin 3 and

ground pin is called the normally off load.

Pin 4: Reset Terminal: To disable or reset the timer a

negative pulse is applied to this pin due to which it is

referred to as reset terminal. When this pin is not to be used

for reset purpose, it should be connected to + VCC to avoid any

possibility of false triggering.

Pin 5: Control Voltage Terminal: The function of this terminal

is to control the threshold and trigger levels. Thus either

the external voltage or a pot connected to this pin determines

the pulse width of the output waveform. The external voltage

applied to this pin can also be used to modulate the output

waveform. When this pin is not used, it should be connected to

ground through a 0.01 micro Farad to avoid any noise problem.

Pin 6: Threshold Terminal: This is the non-inverting input

terminal of comparator 1, which compares the voltage applied

to the terminal with a reference voltage of 2/3 VCC. The

amplitude of voltage applied to this terminal is responsible

for the set state of flip-flop.

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Pin 7: Discharge Terminal: This pin is connected internally to

the collector of transistor and mostly a capacitor is

connected between this terminal and ground. It is called

discharge terminal because when transistor saturates,

capacitor discharges through the transistor. When the

transistor is in cut-off region, the capacitor charges at a

rate determined by the external resistor and capacitor.

Pin 8: Supply Terminal:  A supply voltage of + 5 V to + 18 V

is applied to this terminal with respect to ground (pin 1).

Figure illustrate some basic ideas that will prove useful

in coming blog posts of the 555 timer. Assuming output Q high,

the transistor is saturated and the capacitor voltage is

clamped at ground i.e. the capacitor C is shorted and cannot

charge.

The non-inverting input voltage of the comparator is

referred to as the threshold voltage while the inverting input

voltage is referred to as the control voltage. With R-S flip

flop set, the saturated transistor holds the threshold voltage

at zero. The control voltage, however, is fixed at 2/3

VCC (i.e. at 10 V) because of the voltage divider.

Suppose that a high voltage is applied to the R input.

This resets the flip-flop R-Output Q goes low and the

transistor is cut-off. Capacitor C is now free to charge. As

this capacitor C charges, the threshold voltage rises.

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Eventually, the threshold voltage becomes slightly greater

than (+ 10 V). The output of the comparator then goes

high, forcing the R S flip-flop to set. The high Q output

saturates the transistor, and this quickly discharges the

capacitor. The two waveforms are depicted in figure. An

exponential rise is across the capacitor C, and a positive

going pulse appears at the output Q. Thus capacitor voltage

VC is exponential while the output is rectangular.

(iii) Working Principle:Comparator 1 has a threshold input (pin 6) and a control

input (pin 5). In most applications, the control input is not

used, so that the control voltage equals +2/3 VCC. Output of

this comparator is applied to set (S) input of the flip-flop.

Whenever the threshold voltage exceeds the control voltage,

comparator 1 will set the flip-flop and its output is high.

A high output from the flip-flop saturates the discharge

transistor and discharge the capacitor connected externally to

pin 7. The complementary signal out of the flip-flop goes to

pin 3, the output. The output available at pin 3 is low. These

conditions will prevail until comparator 2 triggers the flip-

flop. Even if the voltage at the threshold input falls below

2/3 VCC, that is comparator 1 cannot cause the flip-flop to

change again. It means that the comparator 1 can only force

the flip-flop’s output high.

To change the output of flip-flop to low, the voltage at

the trigger input must fall below + 1/3 Vcc. When this occurs,

comparator 2 triggers the flip-flop, forcing its output108

low. The low output from the flip-flop turns the discharge

transistor off and forces the power amplifier to output a high.

These conditions will continue independent of the voltage on

the trigger input. Comparator 2 can only cause the flip-flop

to output low.

From the above discussion it is concluded that for the

having low output from the timer 555, the voltage on the

threshold input must exceed the control voltage or + 2/3 VCC.

They also turn the discharge transistor on. To force the

output from the timer high, the voltage on the trigger input

must drop below +1/3 VCC. This also turns the discharge

transistor off.

A voltage may be applied to the control input to change

the levels at which the switching occurs. When not in use, a

0.01 nano Farad capacitor should be connected between pin 5

and ground to prevent noise coupled onto this pin from causing

false triggering.

Connecting the reset (pin 4) to a logic low will place a

high on the output of flip-flop. The discharge transistor will

go on and the power amplifier will output a low. This

condition will continue until reset is taken high. This allows

synchronization or resetting of the circuit’s operation. When

not in use, reset should be tied to +VCC.

(iv) Features:

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(i) High Current Drive Capability (200mA)

(ii) Adjustable Duty Cycle

(iii) Temperature Stability of 0.005%C

(iv) Timing From Sec to Hours

(v) Turn off Time Less Than 2mSec

(v) Applications:

(i) Precision Timing

(ii) Pulse Generation

(iii) Time Delay Generation

(iv) Sequential Timing

CHAPTER FOUR

4.1 Introduction:

In this chapter we will see mainly the circuit testing on

bread-board and working of cell phone detector in brief. The

first test with this cellular phone detector was to just have

an active cellular phone in the room. So the cellular phone

was turned on and a phone call was placed with the detector

nearby. Absolutely nothing came out of the connected

headphones. To troubleshoot this problem, the circuit was

tested with a spectrum analyzer and signal generator. The

antenna was connected to the signal generator at 900 MHz with

10dB of amplitude and the spectrum analyzer was connected to

the headphone jack using the available probes (only 500 MHz

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was available). Injecting the 900 MHz signal into the antennas

resulted in a lower amplitude signal on the output.

To test whether the circuit was resonating at 900MHz, a

bandpass test was performed by stepping the frequency at 100

MHz intervals from 600 MHz to 1.2GHz. The amplitude changed at

each interval, but was actually lower at 900 MHz than anywhere

else and didn't have a bandpass response. The wire wrapped

connections may have changed the impedance of the circuit.

While testing this cellular phone detector it was

discovered that the spectrum analyzer was able to detect the

cellular phone only using a 500 MHz probe. When talking on the

cellular phone, the spectrum analyzer spiked at 832 MHz. This

frequency range to design around for this cellular phone and

is in the range of a GSM phones.

4.2 Circuit Testing on Bread-Board:

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Figure 4.1: Circuit testing

Before the assembling of circuit on PCB we tested it onthe bread-board using the components, connecting wires, and a9V battery.

112

4.3 Working of Cell Phone Detector:

4.3.1 Purpose of the circuit:This circuit is intended to detect unauthorized use of

mobile phones in examination halls, confidential rooms etc. Italso helps to detect unauthorized video and audio recordings.It detects the signal from mobile phones even if it is kept inthe silent mode. It also detects SMS.

4.3.2 Concept:Mobile phone uses RF with a wavelength of 30cm at 872 to

2170 MHz. That is the signal is high frequency with hugeenergy. When the mobile phone is active, it transmits thesignal in the form of sine wave which passes through thespace. The encoded audio/video signal contains electromagneticradiation which is picked up by the receiver in the basestation. Mobile phone system is referred to as “CellularTelephone system” because the coverage area is divided into“cells” each of which has a base station. The transmitterpower of the modern 2G antenna in the base station is 20-100watts.

When a GSM (Global System of Mobile communication)digital phone is transmitting, the signal is time shared with7 other users. That is at any one second, each of the 8 userson the same frequency is allotted 1/8 of the time and thesignal is reconstituted by the receiver to form the speech.Peak power output of a mobile phone corresponds to 2 wattswith an average of 250 milli watts of continuous power. Eachhandset with in a ‘cell’ is allotted a particular frequencyfor its use. The mobile phone transmits short signals atregular intervals to register its availability to the nearestbase station. The network data base stores the informationtransmitted by the mobile phone. If the mobile phone movesfrom one cell to another, it will keep the connection with thebase station having strongest transmission. Mobile phonealways tries to make connection with the available basestation. That is why, the back light of the phone turns on

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intermittently while traveling. This will cause severe batterydrain. So in long journeys, battery will flat with in a fewhours.

AM Radio uses frequencies between 180 kHz and 1.6 MHz. FMradio uses 88 to 180 MHz. TV uses 470 to 854 MHz. Waves athigher frequencies but within the RF region is called Microwaves. Mobile phone uses high frequency RF wave in the microwave region carrying huge amount of electromagnetic energy.That is why burning sensation develops in the ear if themobile is used for a long period. Just like a micro wave oven,mobile phone is ‘cooking’ the tissues in the ear. RF radiationfrom the phone causes oscillation of polar molecules likewater in the tissues. This generates heat through frictionjust like the principle of microwave oven. The strongestradiation from the mobile phone is about 2 watts which canmake connection with a base station located 2 to 3 km away.

4.3.3 How the circuit works?Ordinary LC (Coil-Capacitor) circuits are used to detect

low frequency radiation in the AM and FM bands. The tuned tankcircuit having a coil and a variable capacitor retrieve thesignal from the carrier wave. But such LC circuits cannotdetect high frequency waves near the microwave region. Hencein the circuit, a capacitor is used to detect RF from mobilephone considering that, a capacitor can store energy even froman outside source and oscillate like LC circuit.

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R1 3.9 M

R2 100K R3 1 M

LEDRed

9 V Battery

+

C1

0.22 UF

C2100

25VUF

IC1

IC1

CA 3130

2

3

4

76

0.1

R4 100 R

R5 100R BUZZER

C

Figure 4.2 Circuitry operation

4.3.4 Use of capacitor:A capacitor has two electrodes separated by a

‘dielectric’ like paper, mica etc. The non polarized disccapacitor is used to pass AC and not DC. Capacitor can storeenergy and pass AC signals during discharge. 0.22pF capacitoris selected because it is a low value one and has largesurface area to accept energy from the mobile radiation. Todetect the signal, the sensor part should be like an aerial.So the capacitor is arranged as a mini loop aerial (similar tothe dipole antenna used in TV).In short with this arrangement,the capacitor works like an air core coil with ability tooscillate and discharge current.

4.3.5 How the capacitor senses RF?One lead of the capacitor gets DC from the positive rail

and the other lead goes to the negative input of IC1. So thecapacitor gets energy for storage. This energy is applied tothe inputs of IC1 so that the inputs of IC are almost balancedwith 1.4 volts. In this state output is zero. But at any timeIC can give a high output if a small current is induced to itsinputs. There a natural electromagnetic field around thecapacitor caused by the 50Hz from electrical wiring. When the

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mobile phone radiates high energy pulsations, capacitoroscillates and release energy in the inputs of IC. Thisoscillation is indicated by the flashing of the LED andbeeping of Buzzer. In short, capacitor carries energy and isin an electromagnetic field. So a slight change in fieldcaused by the RF from phone will disturb the field and forcesthe capacitor to release energy.

CHAPTER FIVE

5.1 Introduction:

In this chapter we will see applications, advantages, limitation, future scope, and the conclusions of cell phone detector. Basically this circuit can be used anywhere for detecting the cell phones. Since today is the generation of advanced communication devices and cell phone is the very first need of this. But somehow reasons there is a misuse of these devices. So we have to stop this for our safety. And by using cell phone detectors we can do this very simply. We can use cell phone detector even at our working place, confidential halls, prisons, court room and at many other places where cell phone is not allowed.

But there is a limitation of this device that it can detect only in the range of 1.5-2 meters. So we have to place a number of detectors in a large room. But beyond of this we can simply detect the cells in a range which can covered by the detector.

In future we will increase the range of the detector so that we can detect the cells over a hundreds of meter. So thisis the first step to avoid the unwanted activities using the cell phones.

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5.1 Applications:

(i) Colleges and Universities:During tests and exams the use of mobile phones is

prohibited, for the students could use it to send answers among each other.

By using a GSM-detector this kind of fraud is prohibited.The presence of a GSM-detector can work in a preventing way, because when a GSM-detector is present, the use of mobile phones does not stay unnoticed.

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(ii) Cinemas:In a cinema the use of a mobile phone is undesired. Being

called by someone during a movie is of course very bothering for other people.

With a GSM-detector the use of mobile phones is detected,so the visitor can be informed that this is not allowed.

(iii) Theatres:Just like with a cinema, in theatres the use of mobile

phones is not allowed. The gsm-detector can be used to preventuse.

(iv) Restaurants / Hotels:In hotels and restaurants it is often undesired that a

mobile phone is used at the table or in other areas. A GSM-detector can be installed in these areas to notify guests.

(v) Petrol stations:When tanking at a petrol station, the use of mobile

phones is prohibited, because the mobile signals can interferewith the tanking equipment and because a small spark within the mobile phone could set fire to possible gasoline vapour. With the GSM-detector this prohibition is pointed out to the tanking customer.

(vi) Airplanes:In airplanes the use of mobile phones is prohibited, for

it could interfere with the equipment in the airplane. All thewhile phones are still used illegally, especially in restrooms. By installing a GSM-detector there, this can be prevented.

(vii) Conference rooms:It is often distracting to be called during a meeting.

Also, confidential conversation could be overheard by using

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cell phones, especially by those with a spy function (when someone calls that phone it automatically is picked up withoutringing, so that the person on the other end of the line can hear conversations in the room where the spy phone is placed).By using a GSM-detector you can be assured that this is not the case.

(viii) Hospitals:The signals emitted by mobile phones can interfere with

some electronic equipment inside the hospital. This could havefatal consequences.

The GSM-detector can be placed in any area where the useof mobile phones could interfere with sensitive devices. Theaudio alarm will sound when a phone is used and this way, theperson should immediately switch off his/her phone

(ix) Prisons:In prisons the use of mobile phones is not allowed. It

could occur anyway. By using the gsm-detector the staff can benotified when a mobile phone is used inside the facility.

(x) Power plants:Power plants contain -just like hospitals- a lot of

electronic devices that are sensitive for interference bymobile phones. Therefore, it is prohibited to use mobilephones there. Use a GSM-detector to inspect this.

5.2 Advantages:

Our mission is to be the leading provider of cellular

phone detection capabilities to both business and government

institutions around the world. We are striving to bring a

national debate to the growing proliferation of cell phone use

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in our society today. Using our state of the art products we

are hoping to provide individuals and businesses the tools to

detect and prevent the use of cell phone in sensitive areas.

This product was created in reaction to the growing use

of cell phones around the world, and how that use was

beginning to interfere with our daily lives. When businesses

tried to find solutions to problems involving cell phones,

they found a huge shortcoming in products and services.

Hence, our solution was created to supply this need. To

date we have sold thousands of products to a very wide

audience of businesses and government institutions.  Many of

these include prisons, casinos, embassies, classrooms and

testing facilities, oil rigs, conferences, golf clubhouses,

computer-rooms, data centers, hospitals, and restaurants, to

name just a small few of the vast capabilities of our product.

.

5.3 Limitation:

Range of the circuit:The prototype version has only limited range of 2 meters.

But if a preamplifier stage using JFET or MOSFET transistor isused as an interface between the capacitor and IC, range canbe increased.

5.4 Future scope:

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Trying to increase the detecting range of mobile bug to fewmore meters for observing wide ranges of area. In the futuretime this detector will be improved in all ways.

In future we could be able to detect any range offrequency over a meters of range and this will be very usefulto detect the cell phones where the cell phones areprohibited.

5.5 Conclusion:

This pocket-size mobile transmission detector or sniffer

can sense the presence of an activated mobile cellphone from a

distance of one and-a-half meters. So it can be used to

prevent use of mobile phones in examination halls,

confidential rooms, etc. It is also useful for detecting the

use of mobile phone for spying and unauthorised video

transmission.

In this project we made an attempt to design a mobile

detector which can detect both the incoming and outgoing calls

as well as video transmission even if the mobile is kept at

the silent mode. Our circuit has detected the presence of an

active mobile phone even at a distance of about one and half a

meter. It gave the indication of an active mobile phone by

glowing the LED, according to the receiving frequency and by

buzzing the sound of the buzzer. The alarm continues until the

signal is ceases.

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5.6 References:

(i) www.google.com

(ii) www.wikipedia.org

(iii) www.pdfmachine.com

(iv) www.ecproject.com

(v) www.datasheets4u.com

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