Security Watching All the Time (S.W.A.T.)
A Project Report Submitted
By
Alauddin, Mohammad 08-
10935-2
Faisal, Md. Shahed 08-
10879-2
Sarker, Sanjay Kumar 08-
11560-2
Under the Supervision ofKamrul Hasan
LecturerFaculty of Engineering
American International University-Bangladesh
Department of Electrical and Electronics EngineeringFaculty of Engineering
American International University-Bangladesh
Fall Semester – 2011
DeclarationThis is to certify that this project is our original work. No part of this work has been
submitted elsewhere partially or fully for achieving an award or any other degree or
diploma. Any material reproduced in this project has been properly acknowledged.
Student’s Name & Signature
-------------------------------------Alauddin, MohammadID: 08-10935-2Dept: EEE
-------------------------------------Faisal, Md. ShahedID: 08-10879-2Dept: EEE
-------------------------------------Sarker, Sanjay KumarID: 08-11560-2Dept: EEE
I
ApprovalThe project titled ‘Security Watching All the Time (S.W.A.T.)’ has been submitted to the
following respected members of the Board of Examiners of the Faculty of Engineering in
partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical
and Electronic Engineering on November 2011 by the following students and has been
accepted as satisfactory.
Alauddin, MohammadID: 08-10935-2Dept: EEE
Faisal, Md. ShahedID: 08-10879-2Dept: EEE
--------------------------------Kamrul Hasan
Lecturer & SupervisorFaculty of EngineeringAmerican International University-Bangladesh
--------------------------------Md. Mohiuddin Uzzal
Lecturer & ExternalFaculty of EngineeringAmerican International University-Bangladesh
Sarker, Sanjay KumarID: 08-11560-2Dept: EEE
--------------------------------Dr. Carman Z. Lamagna
Vice ChancellorAmerican International University-Bangladesh
--------------------------------Dr. A B M Siddique Hossain
DeanFaculty of EngineeringAmerican International University-Bangladesh
II
Acknowledgement
We are heartily thankful to our supervisor, Kamrul Hassan, Lecturer, Department of EEE,
American International University-Bangladesh, whose unflinching encouragement,
guidance from the initial to the final level enabled us to develop an understanding of the
subject and make us capable of completing the project. His originality has triggered and
nourished our intellectual maturity without which this would not have been possible.
It is a pleasure to thank Dr. Carmen Z. Lamagna, honorable Vice Chancellor, American
International University-Bangladesh, who exceptionally inspired and enriched our growth
as a student.
We owe our deepest gratitude to Prof. Dr. ABM Siddique Hossain, Dean, Department of EEE,
American International University-Bangladesh; Mr. Md. Mohiuddin Uzzal, Lecturer,
Department of EEE, American International University-Bangladesh, for their unequivocal
support.
Our heartfelt gratitude goes to all of those who had no direct involvement in our project but
had an immense impact on our entire work, especially our parents through inseparable
love and undying support, our friends who helped us realizing our destination and dreams.
We express our apology to those whose names we could not mention, but every single
person of them has been a great help for us.
Last, but by no means least, we express our heartiest gratefulness to the Almighty, without
his divine blessings it would not have been possible for us to complete this project
successfully. For any errors or inadequacies that may remain in this work, of course, the
responsibility is entirely our own.
III
AbstractSecurity problem has been a matter of concern over the years in Bangladesh. Indoor
security is one of them. We aspire to achieve a goal of the high level security for a
home/room/bank with our project. With the invention of new and sophisticated way of
robbery, it has been threatened immensely for people. The objective of this project is to
design a security monitoring system with which the owner do not have to worry about his
indoor goods. The best part of our project is it is made with typical electrical components;
hence, it’s quite simple, yet, very powerful. Moreover, it will be cost effective, so more and
more people will be able to use it for their security needs.
Our target was to make the circuit as simple as possible. So we selected the components
very carefully. We implemented three phase of security in the whole monitoring system.
Whenever an outsider enters the room the owner will be notified by a buzzer. A wireless
close circuit camera will automatically record indoor activities and will show on a display
monitor accessible to the owner. Also a counter will count the number of outsiders entered
the room.
We have tested our monitoring system in a room and verified the operation of this project.
The experimental results showed that our security system can effectively enhance indoor
security.
IV
Overview of the Project ReportThe project report consists of five chapters.
Chapter 1 gives an introduction to the project and a brief description of the different areas
that made up the project.
Chapter 2 will introduce the components that were used in the project. There will be an
articulation of each component as well as their functions.
Chapter 3 will introduce the sensor and principle of the counter used in the system.
Chapter 4 will give an idea about the operation and diagram of each circuit. There will also
be an explicative description on the different modes of operation.
Chapter 5 will reveal the discussions and limitations of the project, and then the future
plans about how this project can be improved further. Lastly a small conclusion of the
whole project work.
V
Table of ContentDECLARATION……………………………………………………………………………………………………...I
APPROVAL…………………………………………………………………………………………………………..II
ACKNOWLEDGEMENT………………………………………………………………………………………..III
ABSTRACT………………………………………………………………………………………………………….IV
OVERVIEW OF THE PROJECT……………………………………………………………………………….V
CHAPTER 1: INTRODUCTION
1.1 Introduction…………………………………………………………………………………………………...1
1.2 Motivation……………………………………………………………………………………………………...1
1.3 Objective………………………………………………………………………………………………………..2
CHAPTER 2: ELECTRICAL AND ELECTRONIC COMPONENTS
2.1 Resistors………………………………………………………………………………………………………...3
2.1.1 Unit…………………………………………………………………………………………………..3
2.1.2 Classification of Resistors…………………………………………………………………..4
2.1.3 Function of Resistors…………………………………………………………………………5
2.1.4 Power Dissipation……………………………………………………………………….…….7
2.2 Capacitor………………………………………………………………………………………………….…….8
2.2.1 Unit…………………………………………………………………………………………….…….9
2.2.2 Types of Capacitor……………………………………………………………………….……9
2.2.3 Capacitor Characteristics…………………………………………………………………11
2.2.4 Theory of Operation………………………………………………………………………...13
2.3 Diode……………………………………………………………………………………………………………14
2.3.1 Function of Diodes…………………………………………………………………………..15
2.3.2 Types of Diodes……………………………………………………………………………….15
2.3.3 Current-voltage Characteristics………………………………………………………..15
2.3.4 Application of Diodes………………………………………………………………………16
2.3.5 Full Wave Rectifier…………………………………………………………………………..16
2.4 Voltage Transformer…………………………………………………………………………………….17
2.4.1 Single Phase Voltage Transformer…………………………………………………...18
2.4.2 Principal of Transformer Action………………………………………………………19
2.5 Light Emitting Diode (LED)…………………………………………………………………………...21
2.5.1 Types of LEDs………………………………………………………………………………….21
2.5.2 Colors of LEDs………………………………………………………………………………....22
2.5.3 Sizes, Shapes and Viewing Angles of LEDs………………………………………...22
2.5.4 Considerations for Use…………………………………………………………………….23
2.5.5 Advantages……………………………………………………………………………………..24
2.6 Voltage Regulator…………………………………………………………………………………………25
2.6.1 Measures of Regulator Quality…………………………………………………………25
2.6.2 DC Voltage Stabilizers……………………………………………………………………...27
2.7 Relay……………………………………………………………………………………………………………27
2.7.1 Electromagnetic Relay Construction………………………………………………...27
2.7.2 Relay Contact Types………………………………………………………………………..29
2.8 MOSFET……………………………………………………………………………………………………….29
2.8.1 Basic Structure………………………………………………………………………………..30
2.8.2 Types of MOSFET…………………………………………………………………………....30
2.8.3 Modes of Operation………………………………………………………………………...33
2.9 Buzzer………………………………………………………………………………………………………….35
2.9.1 Types of Buzzers……………………………………………………………………………..35
2.9.2 Working Principle of Passive Electromagnetic Buzzer………………………36
2.9.3 Application……………………………………………………………………………………...36
2.10 Close Circuit Camera…………………………………………………………………………………...36
2.10.1 Video Cameras………………………………………………………………………………37
2.10.2 Digital Still Cameras………………………………………………………………………38
CHAPTER 3: SENSOR AND COUNTER
3.1 Sensor………………………………………………………………………………………………………….39
3.1.1 Types of Sensors……………………………………………………………………………..39
3.1.2 Passive Infrared (PIR) Sensor…………………………………………………………..40
3.2 Counter………………………………………………………………………………………………………..43
3.2.1 Analog-to-Digital Converter…………………………………………………………….43
3.2.2 Seven-segment Display……………………………………………………………………46
CHAPTER 4: CIRCUIT OPERATION
4.1 Introduction…………………………………………………………………………………………………49
4.2 Component Used…………………………………………………………………………………………..49
4.3 Operation……………………………………………………………………………………………………..50
CHAPTER 5: OVERALL CONCLUSION
5.1 Discussion……………………………………………………………………………………………………52
5.2 Limitation…………………………………………………………………………………………………….52
5.3 Future Plans…………………………………………………………………………………………………52
5.4 Conclusion……………………………………………………………………………………………………53
APPENDICES
Appendix A………………………………………………………………………………………………………...54
Appendix B………………………………………………………………………………………………………...57
REFERENCE…………………………………………………………………………………………………………………60
Chapter 1
Introduction
1.1 Introduction
The theory of electrical circuits represents one of the most important parts of any electrical
engineering education. A theory is a general statement of principle abstracted from
observation. And a model to be useful, it must be realistic and yet very simple enough to
understand and manipulate. These requirements are not easily fulfilled as realistic models
are seldom simple and simple models are seldom realistic. Our project is built up to
overcome this.
A project should not only be something that will grow us as an engineer, it should be
something that will benefit the mankind. The project was undertaken after understanding
this universal truth. We have tried to enable the security of the room of
home/office/shop/bank with a high rate of accuracy. There will be an automatic
monitoring on anyone entering the room and whatever activities he performs inside. So
using this security arrangement the owner does not have to worry about the security of the
room. He will just monitor any signal that is coming in the circuit carried by him. By
monitoring the output an owner can check if someone is trying to breach the security.
1.2 Motivation
Robbery has become very common in Bangladesh. Office lockers are not safe now for
keeping the important documents. This is a dismaying condition. The increasing rate of
robbery has just caught our mind that how this situation can be handled. Firstly we thought
about the available monitoring systems in our country. But we found that there is some
lacking in those systems. Moreover, they are expensive. So things are more problematic for
the normal people. These were the incentives that motivated us to do something with room
security system.
1
1.3 Objective
The main objective of our project is to ensure the room security at a very high level but
with a low cost. We will design the monitoring system with basic electrical components so
that the cost remains low. To differentiate our work with other’s work we will specify the
manual instruction. Considering the different environment different modes will be
arranged so that user does not have to bother.
There’s an important feature in this project – a camera will record all the internal activities
of a room when someone’s inside it. There will be a buzzer which will start making sound
and a signal will also be sent in the circuit holding by the user.
2
Chapter 2
Electrical and Electronic Components
2.1 Resistors
A resistor is an electrical component that limits or regulates the flow of electrical current in
an electronic circuit. Resistors can also be used to provide a specific voltage for an active
device such as a transistor.
When a resistor is introduced to a circuit the flow of current is reduced. The higher the
value of the resistor is the smaller/lower the flow of current. It produces a voltage across
it’s terminals that is proportional to the current passing through it in accordance with
Ohm’s law,
V=IR
The symbol used in schematic and electrical drawings for a resistor can either be a ‘zigzag’
type line (US, Japan) or a rectangular box (Europe).
Figure 2.1: Standard resistor symbols
2.1.1 Unit
Ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm.
Commonly used multiples and submultiples in electrical and electronic usage are the
milliohm (1 mΩ = 10-3 Ω), kilo-ohm (1 kΩ = 103 Ω) and mega-ohm (1 MΩ = 106 Ω).
3
2.1.2 Classification of Resistors
The primary characteristics of a resistor are the resistance, tolerance, maximum working
voltage and power rating. Other characteristics include temperature coefficient, noise,
inductance and capacitance.
Although resistors come in various forms they can be divided into two basic types —
a) Fixed resistors
b) Variable resistors or Potentiometers
Fixed resistors: A fixed resistor is a component with two wires which obeys Ohm’s law.
Electronic engineers and manufacturers have adopted some standards for fixed resistors.
Variable resistors: Variable resistors are usually a stubby cylindrical shape with a rod
poking out one end and with three metal tags.
(a) Fixed resistors (b) Variable resistor
Figure 2.2: Two basic types of resistors
All modern resistors can be classified into four broad groups —
Carbon Composition Resistor: Made of carbon dust or graphite paste, low wattage values.
Film or Cermet Resistor: Made from conductive metal oxide paste, very low wattage
values.
4
Wire-wound Resistor: Metallic bodies for heat sink mounting, very high wattage ratings.
Semiconductor Resistor: High frequency/precision surface mount thin film technology.
(a) Carbon Composite Resistor (b) Film or Cermet Resistor
(c) Wire-wound Resistor (d) Semiconductor Resistor
Figure 2.3: Different types of resistors
2.1.3 Function of Resistors
As we mentioned before the behavior of an ideal resistor is dictated by the relationship
specified in Ohm’s law:
V=IR
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I),
where the constant of proportionality is the resistance (R). Equivalently, Ohm’s law can be
stated as:
I=VR
5
This formulation of Ohm’s law states that, when a voltage (V) is maintained across a
resistance (R), a current (I) will flow through the resistance.
This formation is often used in practice. For example, if V is 12 volts and R is 400 ohms, a
current of 12/400 = 0.03 amperes will flow through the resistance R.
Resistors in a parallel configuration have the same potential difference (voltage). To find
their total equivalent resistance (Req),
Figure 2.5: Parallel Connection of Resistors
The parallel property can be represented in equations by two vertical lines “||” (as in
geometry) to simplify equations. For two resistors,
Req=R1∨¿R2=R1 R2
R1+R2
The current through resistors in series stays the same, but the voltage across each resistor
can be different. The sum of the potential differences is equal to the total voltage. To find
their total resistance (Req),
Figure 2.6: Series connection of Resistors
A resistor network that is a combination of parallel and series can be broken up into
smaller parts that are either one of the other. For instance,
6
Figure 2.7: Combination of series and parallel connection
The practical application to resistors is that a resistance of any non-standard value can be
obtained by connecting standard values in series or in parallel.
2.1.4 Power Dissipation
The power P dissipated by a resistor (or the equivalent resistance of a resistor network) is
calculated as:
P=I 2V=IV=VR
The first form is a restatement of Joule's first law. Using Ohm's law, the two other forms can
be derived.
The total amount of heat energy released over a period of time can be determined from the
integral of the power over that period of time:
W=∫t1
t2
v ( t ) i ( t )dt
If the average power dissipated by a resistor is more than its power rating, damage to the
resistor may occur, permanently altering its resistance; this is distinct from the reversible
change in resistance due to its temperature coefficient when it warms. Excessive power
dissipation may raise the temperature of the resistor to a point where it can burn the
7
circuit board or adjacent components, or even cause a fire. There are flameproof resistors
that fail (open circuit) before they overheat dangerously.
2.2 Capacitor
The capacitor is a passive electronic component that holds a charge in the form of an
electrostatic field. They are often used in combination with transistors in DRAM, acting as
storage cells to hold bits.
Capacitors typically consist of conducting plates separated by thin layers of dielectric
material, such as dry air or mica. The plates on opposite sides of the dielectric material are
oppositely charged and the electrical energy of the charged system is stored in the
polarized dielectric.
When a voltage is applied across the two plates of a capacitor a concentrated field flux is
created between them, allowing a significant difference of free electrons (a charge) to
develop between the two plates.
Figure 2.8: Different types of capacitors
The schematic symbol for a capacitor is two short parallel lines (representing the plates)
separated by a gap (dielectric). At that two parallel lines (plates) are attached two pins for
connection to other components.
8
Figure 2.9: Capacitor symbols
2.2.1 Unit
The unit of capacitor is farad (F). It is named after Michael Faraday, a nineteenth century
English chemist and physicist.
A capacitor has a capacitance of 1 farad if 1 coulomb of charge is deposited on the plates by
a potential difference of 1 volt across the plates. The farad, however, is generally too large a
measure of capacitance for most practical applications. So microfarad (10-6 F) or picofarad
(10-12 F) is more commonly used.
2.2.2 Types of Capacitor
There are a very large variety of different types of capacitor available in the market place
and each one has its own set of characteristics and applications from small delicate
trimming capacitors up to large power metal-can type capacitors used in high voltage
power correction and smoothing circuits. Like resistors, there are also variable types of
capacitors which allow us to vary their capacitance value for use in radio or "frequency
tuning" type circuits. Capacitor types are —
Film Capacitor: Film Capacitors are the most commonly available of all types of capacitors,
consisting of a relatively large family of capacitors with the difference being in their
dielectric properties. These include polyester (Mylar), polystyrene, polypropylene,
polycarbonate, metallized paper, Teflon etc. Film type capacitors are available in
capacitance ranges from as small as 5pF to as large as 100uF depending upon the actual
type of capacitor and its voltage rating.
9
Figure 2.10: Film capacitors (Radial Lead type and Axial Lead type)
Ceramic Capacitors: Ceramic Capacitors are made by coating two sides of a small
porcelain or ceramic disc with silver and are then stacked together to make a capacitor.
Ceramic capacitors have a high dielectric constant (High-K) and are available so that
relatively high capacitances can be obtained in a small physical size. Ceramic capacitors
have values ranging from a few picofarads to one or two microfarads but their voltage
ratings are generally quite low.
Electrolytic Capacitors: Electrolytic capacitors are high voltage capacitors. The majority
of electrolytic types of capacitors are polarized. These are generally used in DC power
supply circuits due to their large capacitances and small size to help reduce the ripple
voltage or for coupling and decoupling applications. One main disadvantage of electrolytic
capacitors is their relatively low voltage rating.
Figure 2.11: Electrolytic capacitor
Dielectric Capacitor: Dielectric Capacitors are usually of the variable type were a
continuous variation of capacitance is required for tuning transmitters, receivers and
10
transistor radios. Variable dielectric capacitors are multi-plate air-spaced types that have a
set of fixed plates (the stator vanes) and a set of movable plates (the rotor vanes) which
move in between the fixed plates. The position of the moving plates with respect to the
fixed plates determines the overall capacitance value. The capacitance is generally at
maximum when the two sets of plates are fully meshed together. High voltage type tuning
capacitors have relatively large spacing or air-gaps between the plates with breakdown
voltages reaching many thousands of volts.
Figure 2.12: Dielectric capacitor
2.2.3 Capacitor Characteristics
There are a bewildering array of capacitor characteristics and specifications associated
with the humble capacitor, so here are just a few of the more important ones —
1. Working Voltage, (WV): The working voltage is the maximum continuous voltage
either DC or AC that can be applied to the capacitor without failure during its working life.
DC and AC voltage values are usually not the same for a capacitor as the AC voltage value
refers to the R.M.S. value. Common working DC voltages are 10V, 16V, 25V, 35V, 50V, 63V,
100V, 160V, 250V, 400V and 1000V and are printed onto the body of the capacitor.
2. Tolerance, (±%): As with resistors, capacitors also have a tolerance rating expressed as
a plus-or-minus value either in picofarads (±pF) for low value capacitors, generally less
than 100pF or as a percentage (±%) for higher value capacitors, generally higher than
100pF. Capacitors are rated according to how near to their actual values they are compared
to the rated nominal capacitance with colored bands or letters used to indicated their
11
actual tolerance. The most common tolerance variation for capacitors is 5% or 10% but
some plastic capacitors are rated as low as ±1%.
3. Leakage Current: The dielectric used inside the capacitor to separate the conductive
plates is not a perfect insulator resulting in a very small current flowing or "leaking"
through the dielectric due to the influence of the powerful electric fields built up by the
charge on the plates when applied to a constant supply voltage. This small DC current flow
in the region of nano-amps (nA) is called the capacitors Leakage Current. It is a result of
electrons physically making their way through the dielectric medium, around its edges or
across its leads and which will over time fully discharging the capacitor if the supply
voltage is removed. The film/foil type capacitor has extremely low leakage currents while
the leakage current of aluminium electrolytics increases with temperature.
4. Working Temperature, (T): Changes in temperature around the capacitor affect the
value of the capacitance because of changes in the dielectric properties. If the air or
surrounding temperature becomes too hot or too cold the capacitance value of the
capacitor may change so much as to affect the correct operation of the circuit. The normal
working range for most capacitors is -30°C to +125°C with nominal voltage ratings given
for a Working Temperature of no more than +70°C. Generally electrolytics cannot be used
below about -10°C, as the electrolyte jelly freezes.
5. Temperature Coefficient, (TC): The Temperature Coefficient of a capacitor is the
maximum change in its capacitance over a specified temperature range. It is generally
expressed linearly as parts per million per degree centigrade (PPM/°C), or as a percent
change over a particular range of temperatures. Some capacitors are nonlinear (Class 2
capacitors) and increase their value as the temperature rises giving them a temperature
coefficient that is expressed as a positive "P". Some capacitors decrease their value as the
temperature rises giving them a temperature coefficient that is expressed as a negative "N".
For example "P100" is +100 ppm/°C or "N200", which is -200 ppm/°C etc. However, some
capacitors do not change their value and remain constant over a certain temperature
range; such capacitors have a zero temperature coefficient or "NPO".
12
6. Polarization: Polarization generally refers to the electrolytic type capacitors but mainly
the aluminium electrolytics, with regards to their electrical connection. The majority are
polarized types, that is the voltage connected to the capacitor terminals must have the
correct polarity, i.e. positive to positive and negative to negative. Incorrect polarization can
cause the oxide layer inside the capacitor to break down resulting in very large currents
flowing through the device resulting in destruction.
7. Equivalent Series Resistance, (ESR): The Equivalent Series Resistance, or ESR, of a
capacitor is the AC impedance of the capacitor when used at high frequencies and includes
the resistance of the dielectric material, the DC resistance of the terminal leads, the DC
resistance of the connections to the dielectric and the capacitor plate resistance all
measured at a particular frequency and temperature. The ESR of electrolytic capacitors
increases over time as their electrolyte dries out. Capacitors with very low ESR ratings are
available and are best suited when using the capacitor as a filter.
2.2.4 Theory of Operation
The capacitor is a reasonably general model for electric fields within electric circuits. An
ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of
charge ±Q on each conductor to the voltage V between them,
C=QV
Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to
vary. In this case, capacitance is defined in terms of incremental changes,
C=dqdv
Work must be done by an external influence to "move" charge between the conductors in a
capacitor. When the external influence is removed the charge separation persists in the
electric field and energy is stored to be released when the charge is allowed to return to its
equilibrium position. The work done in establishing the electric field, and hence the
amount of energy stored, is given by,
13
W=∫q=0
Q
Vdq=∫q=0
QqCdq=1
2Q2
C=1
2CV 2=1
2VQ
The current i(t) through any component in an electric circuit is defined as the rate of flow
of a charge q(t) passing through it, but actual charges, electrons, cannot pass through the
dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each
one that leaves the positive plate, resulting in an electron depletion and consequent
positive charge on one electrode that is equal and opposite to the accumulated negative
charge on the other. Thus the charge on the electrodes is equal to the integral of the current
as well as proportional to the voltage as discussed above. As with any anti-derivative, a
constant of integration is added to represent the initial voltage v(t0). This is the integral
form of the capacitor equation,
v (t )=q( t)C
= 1C∫t 0
t
i (τ )dτ+v ( t0)
Taking the derivative of this, and multiplying by C, yields the derivative form,
i (t )=dq (t)dt
=Cdv (t )dt
2.3 Diode
Diodes are semiconductor devices which might be
described as passing current in one direction only. In
electronics, a diode is a two-terminal electronic
component that conducts electric current in only on
direction.
Diodes can be used as voltage regulators, tuning devices
in rf tuned circuits, frequency multiplying devices in rf
circuits, mixing devices in rf circuits, switching
applications or can be used to make logic decisions in digital circuits.
14
2.3.1 Function of a Diodes
The main function of a diode is to block the current in one direction and allow current to
flow in the other direction. Current flowing through the diode is called forward current.
2.3.2 Types of Diodes
There are several types of diodes. Such as —
Rectifier diodes: These are the most common type of diodes. They are mainly used to
allow flow of current in one direction and by doing that they can convert AC to DC.
Detector diodes: These are more sensitive than normal rectifier diodes. They are used in
radios and televisions to convert radio signals to audio or television signals.
Zenner diodes: These diodes are the opposite of the normal diodes, because they are
designed to conduct current in the backwards direction but only at a very precise voltage.
Capacitance diodes: it act as tunable capacitance and are also used in radios and TVs to
allow electronic automatic tuning.
2.3.3 Current-voltage Characteristics
The graph below shows the electrical characteristics of a typical diode —
Figure 2.14: Diode characteristic graph
15
When a small voltage is applied to the diode in the forward direction, current flows easily.
Because the diode has a certain amount of resistance, the voltage will drop slightly as
current flows through the diode. A typical diode causes a voltage drop of about 0.6 - 1V
(VF) (In the case of silicon diode, almost 0.6V). This voltage drop needs to be taken into
consideration in a circuit which uses many diodes in series. Also, the amount of current
passing through the diodes must be considered. When voltage is applied in the reverse
direction through a diode, the diode will have a great resistance to current flow. Different
diodes have different characteristics when reverse-biased. A given diode should be selected
depending on how it will be used in the circuit. The current that will flow through a diode
biased in the reverse direction will vary from several mA to just µA, which is very small.
2.3.4 Application of Diodes
Some ways in which the diode can be used are listed here.
A diode can be used as a rectifier that converts AC (Alternating Current) to DC
(Direct Current) for a power supply device.
Diodes can be used to separate the signal from radio frequencies.
Diodes can be used as an on/off switch that controls current.
2.3.5 Full Wave Rectifier
In a full wave rectifier circuit two diodes are
used, one for each half of the cycle. A
transformer is used whose secondary
winding is split equally into two halves with
a common center tapped connection, (C).
This configuration results in each diode
conducting in turn when its anode terminal is
positive with respect to the transformer
center point C producing an output during
both half-cycles.
16
Figure 2.15: Full wave rectifier circuit and the resultant output waveform
The full wave rectifier circuit consists of two power diodes connected to a single load
resistance (RL) with each diode taking it in turn to supply current to the load. When point A
of the transformer is positive with respect to point C, diode D1 conducts in the forward
direction as indicated by the arrows. When point B is positive (in the negative half of the
cycle) with respect to point C, diode D2 conducts in the forward direction and the current
flowing through resistor R is in the same direction for both half-cycles. As the output
voltage across the resistor R is the phasor sum of the two waveforms combined, this type of
full wave rectifier circuit is also known as a "bi-phase" circuit.
As the spaces between each half-wave developed by each diode is now being filled in by the
other diode the average DC output voltage across the load resistor is now double that of the
single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage, assuming no
losses.
V d .c .=2V max
π=0.637V max=0.9V RMS
Where: Vmax is the maximum peak value in one half of the secondary winding and VRMS is the
rms value.
The peak voltage of the output waveform is the same as before for the half-wave rectifier
provided each half of the transformer windings have the same rms voltage value. To obtain
a different DC voltage output different transformer ratios can be used.
2.4 Voltage Transformer
A transformer is a device that transfers electrical energy from one circuit to another
through inductively coupled conductors (the transformer's coils). The main purpose of a
voltage transformer is to transfer electrical power between different circuits by converting
one AC voltage source into another AC voltage at the same frequency. Transformers are
basically mechanical devices that consist of one or more coil(s) of wire wrapped around a
common ferromagnetic laminated core. These coils are usually not electrically connected
17
together however, they are connected magnetically through the common magnetic flux Qm
confined to a central core.
Voltage transformers work on Faraday’s principal of
electromagnetic induction. When a current flows through a
coil, a magnetic flux ( ) is produced around the coil. If weΦ
now place a second similar coil next to the first so that this
magnetic flux cuts the second coil of wire, an e.m.f. voltage
will be induced in the second coil. This effect is known as
“mutual induction” and is the basic operation principal of
voltage transformers.
The value of the induced e.m.f in the second coil is proportional to the number of turns and
to the rate of change of magnetic flux. In a voltage transformer these two coils known as the
primary and secondary windings are tightly wrapped around a single core material such as
steel or iron which improves the magnetic coupling between these two coils. Therefore,
each coil has the same number of volts per turn in it producing two different voltages that
are proportional to each other.
2.4.1 Single Phase Voltage Transformer
Figure 2.17: Single phase voltage transformer
18
Figure 2.16: Typical Voltage Transformer
The single-phase voltage transformer has two coils or windings, a primary winding and a
secondary winding that are not in electrical contact with each other. When an electric
current passed through the primary winding, a magnetic field is developed which induces a
voltage into the secondary winding.
Voltage Transformers alter both voltage and current of AC waveforms. The voltage induced
in the secondary winding can be greater or lower than the voltage in primary winding. As
each winding has the same number of volts per turn, the volt-ampere (VI) product in each
winding will also be the same assuming no power losses. Then the power consumed by the
secondary connected load will be equal the power supplied by the primary winding (Pin =
Pout) and is given as:
Primary Power=Secondary Power
V P IP cosϕ=V S I S cosϕ
Where,
Vp is the primary voltage, Ip is the primary current
Vs is the secondary voltage, Is is the secondary current
cos is the power factor of the loadϕ
2.4.2 Principal of Transformer Action
The frequency of the secondary waveform will be “in-phase” with the frequency of the
primary waveform then the cos term cancels out on both sides of the above equation. Weϕ
now know that the output voltage from the secondary winding is directly proportional to
the number of turns of wire in the secondary coil. If we increase or decrease this number of
turns, a larger or smaller voltage will be induced into the secondary winding. Then we can
define the “Turns Ratio” as the number of windings of the primary coil (Np) divided by
number of windings of the secondary coil (Ns). Then the ratio of the primary and secondary
19
voltages is the same as the ratio of the number of turns in each winding. This ratio is known
commonly as the Transformation Ratio and is presented as Np:Ns (no units as it is a ratio).
Then voltage transformers are all about ratios, that is the ratio of windings called the “turns
ratio” to the ratio of the voltage called the “voltage ratio” and this is given as:
Turns ratio=V P
V S
=N P
NS
∴V S=V P .N S
N P
If this turns ratio is equal to one (unity) that is the number of secondary turns equals the
number of primary turns giving a turns ratio of 1:1, the secondary voltage will be of the
same value as the primary voltage producing an isolation transformer. However, if the ratio
is greater than unity and Vs is greater than Vp, this produces a step up transformer.
Likewise, if the ratio is less than unity, and Vs is less than Vp, this produces a step down
transformer.
Transformers do not change power they transfer the same amount of power (assumes ideal
transformer) from the primary side to the secondary side. As electrical power is the
product of volts x amps, if the voltage changes then the current must change to maintain
the same amount of power. That is the current changes opposite to the voltage change and
if one goes up, the other goes down. So if the secondary voltage is greater than the primary
voltage then the secondary current is less than the primary current. If the secondary
voltage is less than the primary voltage then the secondary current is greater than the
primary current. This is called the “current ratio” and is opposite to the previous voltage
and turns ratios.
The ratios of voltage, current and turns for a voltage transformer can be defined as:
Primary TurnsSecondary Turns
= Primary VoltageSecondaryVoltage
= SecondaryCurrentPrimary Current
N P
N S
=V P
V S
=I SIP
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2.5 Light Emitting Diode (LED)
A light-emitting diode or LED is a semiconductor light source. LEDs are used as indicator
lamps in many devices and are increasingly used for other lighting.
When a light-emitting diode is forward biased (switched on), electrons are able to
recombine with electron 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 gap of the semiconductor. LEDs are
often small in area (less than 1 mm2), and integrated optical components may be used to
shape its radiation pattern.
Figure 2.18: Different types of LEDs
2.5.1 Types of LEDs
Miniature LEDs: These are mostly single-die LEDs used as indicators, and they come in
various-sizes from 2 mm to 8 mm, through-hole and surface mount packages. They usually
don't use a separate heat sink. A typical current rating ranges from around 1 mA to above
20 mA. The small size sets a natural upper boundary on power consumption due to heat
caused by the high current density and need for heat sinking.
Mid-range LEDs: Medium power LEDs are often through-hole mounted and used when an
output of a few lumens is needed. They sometimes have the diode mounted to four leads
(two cathode leads, two anode leads) for better heat conduction and carry an integrated
lens. An example of this is the Superflux package, from Philips Lumileds. These LEDs are
21
most commonly used in light panels, emergency lighting and automotive tail-lights. Due to
the larger amount of metal in the LED, they are able to handle higher currents (around 100
mA). The higher current allows for the higher light output required for tail-lights and
emergency lighting.
High power LEDs: High power LEDs (HPLED) can be driven at currents from hundreds of
mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit
over a thousand lumens. Since overheating is destructive, the HPLEDs must be mounted on
a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the
device will fail in seconds. One HPLED can often replace an incandescent bulb in a torch, or
be set in an array to form a powerful LED lamp.
2.5.2 Colors of LEDs
LEDs are available in red, orange, amber, yellow, green, blue and white. The color of an LED
is determined by the semiconductor material, not by the coloring of the package (the
plastic body). LEDs of all colors are available in uncolored packages which may be diffused
(milky) or clear (often described as 'water clear'). The colored packages are also available
as diffused (the standard type) or transparent.
Tri-color LEDs: The most popular type of tri-color LED has a red and a green LED
combined in one package with three leads. They are called tri-color because mixed red and
green light appears to be yellow and this is produced when both the red and green LEDs
are on.
Bi-color LEDs: A bi-color LED has two LEDs wired in 'inverse parallel' (one forwards, one
backwards) combined in one package with two leads. Only one of the LEDs can be lit at one
time and they are less useful than the tri-color LEDs described above.
2.5.3 Sizes, Shapes and Viewing Angles of LEDs
LEDs are available in a wide variety of sizes and shapes. The standard LED has a round
cross-section of 5mm diameter and this is probably the best type for general use, but 3mm
round LEDs are also popular.
22
Round cross-section LEDs are frequently used and they are very easy to install on boxes by
drilling a hole of the LED diameter, adding a spot of glue will help to hold the LED if
necessary. LED clips are also available to secure LEDs in holes. Other cross-section shapes
include square, rectangular and triangular.
As well as a variety of colors, sizes and shapes, LEDs also vary in their viewing angle. This
tells you how much the beam of light spreads out. Standard LEDs have a viewing angle of
60° but others have a narrow beam of 30° or less.
2.5.4 Considerations for Use
Power sources: The current/voltage characteristic of an LED is similar to other diodes, in
that the current is dependent exponentially on the voltage. This means that a small change
in voltage can cause a large change in current. If the maximum voltage rating is exceeded
by a small amount, the current rating may be exceeded by a large amount, potentially
damaging or destroying the LED. The typical solution is to use constant current power
supplies, or driving the LED at a voltage much below the maximum rating. Since most
common power sources (batteries, mains) are not constant current sources, most LED
fixtures must include a power converter. However, the I/V curve of nitride-based LEDs is
quite steep above the knee and gives an If of a few milliamperes at a V f of 3V, making it
possible to power a nitride-based LED from a 3V battery such as a coin cell without the
need for a current limiting resistor.
Electrical polarity: As with all diodes, current flows easily from p-type to n-type material.
However, no current flows and no light is emitted if a small voltage is applied in the reverse
direction. If the reverse voltage grows large enough to exceed the breakdown voltage, a
large current flows and the LED may be damaged. If the reverse current is sufficiently
limited to avoid damage, the reverse-conducting LED is a useful noise diode.
Safety: The vast majority of devices containing LEDs are "safe under all conditions of
normal use", and so are classified as "Class 1 LED product". At present, only a few LEDs—
extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in
23
theory, cause temporary blindness, and so are classified as "Class 2". In general, laser safety
regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs.
2.5.5 Advantages
Efficiency: LEDs emit more light per watt than incandescent light bulbs. Their efficiency is
not affected by shape and size, unlike fluorescent light bulbs or tubes.
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.
Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed
circuit boards.
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.
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.
Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering
the forward current.
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.
Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of
incandescent bulbs.
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 1,000–2,000 hours.
24
Shock resistance: LEDs, being solid state components, are difficult to damage with
external shock, unlike fluorescent and incandescent bulbs which are fragile.
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.
2.6 Voltage Regulator
A voltage regulator is an electrical regulator designed to
automatically maintain a constant voltage level. A voltage
regulator may be a simple "feed-forward" design or may include
negative feedback control loops. It may use an electromechanical
mechanism, or electronic components. Depending on the design,
it may be used to regulate one or more AC or DC voltages.
2.6.1 Measures of Regulator Quality
The output voltage can only be held roughly constant; the regulation is specified by two
measurements:
Load regulation is the change in output voltage for a given change in load current (for
example: "typically 15mV, maximum 100mV for load currents between 5mA and 1.4A, at
some specified temperature and input voltage").
Line regulation or input regulation is the degree to which output voltage changes with
input (supply) voltage changes - as a ratio of output to input change (for example "typically
13mV/V"), or the output voltage change over the entire specified input voltage range (for
example "plus or minus 2% for input voltages between 90V and 260V, 50-60Hz").
Other important parameters are:
25
Figure 2.19: Voltage Regulator
Temperature coefficient of the output voltage is the change in output voltage with
temperature (perhaps averaged over a given temperature range), while...
Initial accuracy of a voltage regulator (or simply "the voltage accuracy") reflects the error
in output voltage for a fixed regulator without taking into account temperature or aging
effects on output accuracy.
Dropout voltage is the minimum difference between input voltage and output voltage for
which the regulator can still supply the specified current. A Low Drop-Out (LDO) regulator
is designed to work well even with an input supply only a volt or so above the output
voltage. The input-output differential at which the voltage regulator will no longer
maintain regulation. Further reduction in input voltage will result in reduced output
voltage. This value is dependent on load current and junction temperature.
Absolute maximum ratings are defined for regulator components, specifying the
continuous and peak output currents that may be used (sometimes internally limited), the
maximum input voltage, maximum power dissipation at a given temperature, etc.
Output noise (thermal white noise) and output dynamic impedance may be specified as
graphs versus frequency, while output ripple noise (mains "hum" or switch-mode "hash"
noise) may be given as peak-to-peak or RMS voltages, or in terms of their spectra.
Quiescent current in a regulator circuit is the current drawn internally, not available to
the load, normally measured as the input current while no load is connected (and hence a
source of inefficiency; some linear regulators are, surprisingly, more efficient at very low
current loads than switch-mode designs because of this).
Transient response is the reaction of a regulator when a (sudden) change of the load
current (called the load transient) or input voltage (called the line transient) occurs. Some
regulators will tend to oscillate or have a slow response time which in some cases might
lead to undesired results. This value is different from the regulation parameters, as that is
the stable situation definition. The transient response shows the behavior of the regulator
on a change. This data is usually provided in the technical documentation of a regulator and
is also dependent on output capacitance.
26
2.6.2 DC voltage Stabilizers
Many simple DC power supplies regulate the voltage using a shunt regulator such as a
zener diode, avalanche breakdown diode, or voltage regulator tube. Each of these devices
begins conducting at a specified voltage and will conduct as much current as required to
hold its terminal voltage to that specified voltage. The power supply is designed to only
supply a maximum amount of current that is within the safe operating capability of the
shunt regulating device (commonly, by using a series resistor).
2.7 Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a
switching mechanism mechanically, but other operating principles are also used. Relays are
used where it is necessary to control a circuit by a low-power signal (with complete
electrical isolation between control and controlled circuits), or where several circuits must
be controlled by one signal. The first relays were used in long distance telegraph circuits,
repeating the signal coming in from one circuit and re-transmitting it to another. Relays
were used extensively in telephone exchanges and early computers to perform logical
operations.
2.7.1 Electromechanical Relay Construction
Relays may be "Normally Open", or "Normally Closed". One pair of contacts is classed as
Normally Open, (NO) or make contacts and another set which are classed as Normally
Closed, (NC) or break contacts. In the normally open position, the contacts are closed only
when the field current is "ON" and the switch contacts are pulled towards the inductive
coil. In the normally closed position, the contacts are permanently closed when the field
current is "OFF" as the switch contacts return to their normal position. These terms
Normally Open, Normally Closed or Make and Break Contacts refer to the state of the
electrical contacts when the relay coil is "de-energized", i.e, no supply voltage connected to
the inductive coil.
27
Figure 2.20: Electromechanical Relay Construction
The relays contacts are electrically conductive pieces of metal which touch together
completing a circuit and allow the circuit current to flow, just like a switch. When the
contacts are open the resistance between the contacts is very high in the Mega-Ohms,
producing an open circuit condition and no circuit current flows. When the contacts are
closed the contact resistance should be zero, a short circuit, but this is not always the case.
All relay contacts have a certain amount of "contact resistance" when they are closed and
this is called the "On-Resistance". With a new relay and contacts this ON-resistance will be
very small, generally less than 0.2 's because the tips are new and clean.Ω
As the contact tips begin to wear, and if they are not properly protected from high
inductive or capacitive loads, they will start to show signs of arcing damage as the circuit
current still wants to flow as the contacts begin to open when the relay coil is de-energized.
This arcing or sparking will cause the contact resistance of the tips to increase further as
the contact tips become damaged. If allowed to continue the contact tips may become so
burnt and damaged to the point where they are physically closed but do not pass any or
very little current. To reduce the effects of contact arcing and high "On-resistances",
modern contact tips are made of, or coated with, a variety of silver based alloys to extend
their life span as given in the following table.
28
2.7.2 Relay Contact Types
As well as the standard descriptions of Normally Open, (NO) and Normally Closed, (NC)
used to describe how the relays contacts are connected, relay contact arrangements can
also be classed by their actions. Electrical relays can be made up of one or more individual
switch contacts with each "contact" being referred to as a "pole". Each one of these contacts
or poles can be connected or "thrown" together by energizing the relays coil and this gives
rise to the description of the contact types as being:
SPST - Single Pole Single Throw
SPDT - Single Pole Double Throw
DPST - Double Pole Single Throw
DPDT - Double Pole Double Throw
with the action of the contacts being described as "Make" (M) or "Break" (B). Then a simple
relay with one set of contacts as shown above can have a contact description of:
Single Pole Double Throw - (Break before Make) ,∨SPDT−(B−M )
Figure 2.21: Relay Contact Configurations
2.8 MOSFET
The Metal Oxide Semiconductor Field Effect Transistor or MOSFET is a transistor used for
amplifying or switching electronic signals. In MOSFETs, a voltage on the oxide-insulated
gate electrode can induce a conducting channel between the two other contacts called
29
source and drain. The channel can be of n-type or p-type, and is accordingly called an
nMOSFET or a pMOSFET (also commonly known as nMOS, pMOS). It is by far the most
common transistor in both digital and analog circuits.
2.8.1 Basic Structure
MOSFETs use an electrical field produced by a gate voltage to alter the flow of charge
carriers, electrons for N-channel or holes for P-channel, through the semiconductive drain-
source channel. The gate electrode is placed on top of a very thin insulating layer and there
are a pair of small N-type regions just under the drain and source electrodes.
it is possible to bias the gate of a MOSFET in either polarity, +ve or -ve. This makes
MOSFETs especially valuable as electronic switches or to make logic gates because with no
bias they are normally non-conducting and this high gate input resistance means that very
little or no control current is needed as MOSFETs are voltage controlled devices.
Figure 2.23: Basic MOSFET structure
2.8.2 Types of MOSFET
Both the P-channel and the N-channel MOSFETs are available in two basic forms, the
Enhancement type and the Depletion type.
30
Depletion type MOSFET: The Depletion-mode MOSFET, which is less common than the
enhancement types is normally switched "ON" without the application of a gate bias
voltage making it a "normally-closed" device. However, a gate to source voltage (VGS) will
switch the device "OFF". For an N-channel MOSFET, a "positive" gate voltage widens the
channel, increasing the flow of the drain current and decreasing the drain current as the
gate voltage goes more negative. In other words, for an N-channel depletion mode
MOSFET: +VGS means more electrons and more current. While a -VGS means less electrons
and less current. The opposite is also true for the P-channel types. Then the depletion mode
MOSFET is equivalent to a "normally-closed" switch.
Figure 2.24: Characteristics graph and symbol of Depletion type MOSFET
Enhancement type MOSFET: The more common Enhancement-mode MOSFET is the
reverse of the depletion-mode type. Here the conducting channel is lightly doped or even
undoped making it non-conductive. This results in the device being normally "OFF" when
31
the gate bias voltage is equal to zero. A drain current will only flow when a gate voltage
(VGS) is applied to the gate terminal greater than the threshold voltage (VTH) level in which
conductance takes place making it a transconductive device. This positive +ve gate voltage
pushes away the holes within the channel attracting electrons towards the oxide layer and
thereby increasing the thickness of the channel allowing current to flow. This is why this
kind of transistor is called an enhancement mode device as the gate voltage enhances the
channel.
Increasing this positive gate voltage will cause the channel resistance to decrease further
causing an increase in the drain current, ID through the channel. In other words, for an N-
channel enhancement mode MOSFET: +VGS turns the transistor "ON", while a zero or -VGS
turns the transistor "OFF". Then, the enhancement-mode MOSFET is equivalent to a
"normally-open" switch.
Figure 2.25: Characteristics graph and symbol of Enhancement type MOSFET
32
Enhancement-mode MOSFETs make excellent electronics switches due to their low "ON"
resistance and extremely high "OFF" resistance as well as their infinitely high gate
resistance.
2.8.3 Modes of Operation
The operation of a MOSFET can be separated into three different modes, depending on the
voltages at the terminals. For an enhancement-mode, n-channel MOSFET, the three
operational modes are:
Cutoff, subthreshold, or weak-inversion mode (WhenV GS<V th): According to the basic
threshold model, the transistor is turned off, and there is no conduction between drain and
source. In reality, the Boltzmann distribution of electron energies allows some of the more
energetic electrons at the source to enter the channel and flow to the drain, resulting in a
subthreshold current that is an exponential function of gate–source voltage. While the
current between drain and source should ideally be zero when the transistor is being used
as a turned-off switch, there is a weak-inversion current, sometimes called subthreshold
leakage. In weak inversion the current varies exponentially with gate-to-source bias VGS as
given approximately by:
ID≈ ID 0eVGS−V th
nV T
Where ID 0 = current atV GS=V th, the thermal voltage V T=kT /q and the slope factor n is
given by,
n=1+CD
COX
With CD = capacitance of the depletion layer and COX = capacitance of the oxide layer.
Triode mode or linear region (When V GS>V th andV Ds<(V GS−V th)): The transistor is
turned on, and a channel has been created which allows current to flow between the drain
and the source. The MOSFET operates like a resistor, controlled by the gate voltage relative
to both the source and drain voltages. The current from drain to source is modeled as:
33
ID=µnCoxWL
((V GS−V th)V DS−V DS
2
2)
Where µn is the charge-carrier effective mobility, W is the gate width, L is the gate length
and Cox is the gate oxide capacitance per unit area. The transition from the exponential
subthreshold region to the triode region is not as sharp as the equations suggest.
Saturation or active mode (When V GS>V th andV Ds>(V GS−V th)): The switch is turned on,
and a channel has been created, which allows current to flow between the drain and
source. Since the drain voltage is higher than the gate voltage, the electrons spread out, and
conduction is not through a narrow channel but through a broader, two- or three-
dimensional current distribution extending away from the interface and deeper in the
substrate. The onset of this region is also known as pinch-off to indicate the lack of channel
region near the drain. The drain current is now weakly dependent upon drain voltage and
controlled primarily by the gate–source voltage, and modeled approximately as:
ID=µnCox
2WL
(V GS−V th )2(1+λ (V DS−V D Ssat))
The additional factor involving , the channel-length modulation parameter, modelsλ
current dependence on drain voltage due to the early effect, or channel length modulation.
According to this equation, a key design parameter, the MOSFET transconductance is:
gm=2 ID
V GS−V th
=2 I DV ov
where the combination V OV=V GS−V th is called the overdrive voltage, and where
V DS sat=V DS−V th accounts for a small discontinuity in ID which would otherwise appear at
the transition between the triode and saturation regions.
Another key design parameter is the MOSFET output resistance rout given by:
rout=1/ λ ID
2.9 Buzzer
34
A buzzer or beeper is an audio signaling device, which may be mechanical,
electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm
devices, timers and confirmation of user input such as a mouse click or keystroke.
A buzzer Symbol
Figure 2.26: An electronic buzzer
2.9.1 Types of Buzzers
Mechanical:
A joy buzzer is an example of a purely mechanical buzzer.
Electromechanical:
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.
Piezoelectric:
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.
2.9.2 Working Principle of Passive Electromagnetic Buzzer
35
Ac signal through the bypass line in the stent in the stent core package produce a column of
alternating magnetic flux, the alternating magnetic flux and magnetic flux for a constant
stack, so that films of molybdenum to a given exchange of signals with the frequency of
vibration and sound resonator. Products of the frequency response and sound pressure
curve and the value gap, molybdenum films inherent vibration frequency (which can be
rough refraction.
For small film thickness of molybdenum), Shell (Tune Helmholtz resonance) frequency of
the magnetometer magnetic wire is directly related to the diameter composed of
electromagnetic buzzer by electromagnetic oscillator, the electromagnetic coil, magnet,
vibration, such as the composition of membrane and shell.
Access to power, the audio signal generated by oscillator current through the
electromagnetic coil to generate magnetic fields of electromagnetic coils. Membrane
vibration in the electromagnetic coil and magnet interaction, the buzzer sound vibration
periodically.
2.9.3 Application
Annunciator panels
Electronic metronomes
Game shows
Microwave ovens and other household appliances
Sporting events such as basketball games
2.10 Close Circuit Camera
Closed-circuit television (CCTV) cameras can produce images or recordings for surveillance
purposes, and can be either video cameras, or digital stills cameras.
36
Figure 2.27: Different types of CC camera
2.10.1 Video Cameras
Video cameras are either analogue or digital, which means that they work on the basis of
sending analogue or digital signals to a storage device such as a video tape recorder or
desktop computer or laptop computer.
Analogue: Can record straight to a video tape recorder which is able to record analogue
signals as pictures. If the analogue signals are recorded to tape, then the tape must run at a
very slow speed in order to operate continuously. This is because in order to allow a 3 hour
tape to run for 24 hours, it must be set to run on a time lapse basis which is usually about 4
frames a second. In one second, the camera scene can change dramatically. A person for
example can have walked a distance of 1 meter, and therefore if the distance is divided into
4 parts i.e. 4 frames or 'snapshots' in time, then each frame invariably looks like a blur,
unless the subject keeps relatively still.
Digital: These cameras do not require a video capture card because they work using a
digital signal which can be saved directly to a computer. The signal is compressed 5:1, but
DVD quality can be achieved with more compression (MPEG-2 is standard for DVD-video,
and has a higher compression ratio than 5:1, with a slightly lower video quality than 5:1 at
37
best, and is adjustable for the amount of space to be taken up versus the quality of picture
needed or desired). The highest picture quality of DVD is only slightly lower than the
quality of basic 5:1-compression DV.
Network: IP cameras or network cameras are analogue or digital video cameras, plus an
embedded video server having an IP address, capable of streaming the video (and
sometimes, even audio). Because network cameras are embedded devices, and do not need
to output an analogue signal, resolutions higher than CCTV analogue cameras are possible.
A typical analogue CCTV camera has a PAL (768×576 pixels) or NTSC (720×480 pixels),
whereas network cameras may have VGA (640×480 pixels), SVGA (800×600 pixels) or
quad-VGA (1280×960 pixels, also referred to as 'megapixel') resolutions.
2.10.2 Digital Still Cameras
These cameras can be purchased in any high street shop and can take excellent pictures in
most situations. The pixel resolution of the current models has easily reached 7 million
pixels (7-mega pixels). Some point and shoot models like those produced by Canon or
Nikon boast resolutions in excess of 10 million pixels. At these resolutions, and with high
shutter speeds like 1/125th of a second, it is possible to take jpg pictures on a continuous
or motion detection basis that will capture not only anyone running past the camera scene,
but even the faces of those driving past. These cameras can be plugged into the USB port of
any computer (most of them now have USB capability) and pictures can be taken of any
camera scene. All that is necessary is for the camera to be mounted on a wall bracket and
pointed in the desired direction.
2.10.3 Wireless Security Cameras
Many consumers are turning to wireless security cameras for home surveillance also.
Wireless cameras do not require a video cable for video/audio transmission, simply a cable
for power. Wireless cameras are also easy and inexpensive to install. Previous generations
of wireless security cameras relied on analog technology; modern wireless cameras use
digital technology which delivers crisper audio, sharper video, and a secure and
interference-free signal.
38
Chapter 3
Sensor and Counter
3.1 Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which
can be read by an observer or by an instrument.
3.1.1 Types of Sensors
Input type transducers or sensors, produce a proportional output voltage or signal in
response to changes in the quantity that they are measuring (the stimulus) and the type or
amount of the output signal depends upon the type of sensor being used. Generally, all
types of sensors can be classed as two kinds, passive and active.
Active: Active sensors require some form of external power to operate, called an excitation
signal which is used by the sensor to produce the output signal. Active sensors are self-
generating devices because their own properties change in response to an external effect
and produce an output voltage, for example, 1 to 10v DC or an output current such as 4 to
20mA DC. For example, a strain gauge is a pressure-sensitive resistor. It does not generate
any electrical signal, but by passing a current through it (excitation signal), its resistance
can be measured by detecting variations in the current and/or voltage across it relating
these changes to the amount of strain or force.
Passive: Unlike the active sensor, a passive sensor does not need any additional energy
source and directly generates an electric signal in response to an external stimulus. For
example, a thermocouple or photodiode. Passive sensors are direct sensors which change
their physical properties, such as resistance, capacitance or inductance etc. As well as
analogue sensors, Digital Sensors produce a discrete output representing a binary number
or digit such as a logic level "0" or a logic level "1".
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3.1.2 Passive Infrared (PIR) Sensor
A Passive Infrared sensor (PIR sensor) is an electronic device that measures infrared (IR)
light radiating from objects in its field of view. PIR sensors are often used in the
construction of PIR-based motion detectors. Apparent motion is detected when an infrared
source with one temperature, such as a human, passes in front of an infrared source with
another temperature, such as a wall. This is not to say that the sensor detects the heat from
the object passing in front of it but that the object breaks the field which the sensor has
determined as the "normal" state. Any object, even one exactly the same temperature as the
surrounding objects will cause the PIR to activate if it moves in the field of the sensors.
All objects above absolute zero emit energy in the form of radiation. Usually infrared
radiation is invisible to the human eye but can be detected by electronic devices designed
for such a purpose. The term passive in this instance means that the PIR device does not
emit an infrared beam but merely passively accepts incoming infrared radiation. “Infra”
meaning below our ability to detect it visually, and “Red” because this color represents the
lowest energy level that our eyes can sense before it becomes invisible. Thus, infrared
means below the energy level of the color red, and applies to many sources of invisible
energy.
Figure 3.1: A PIR Sensor
General description: The PIR (Passive Infra-Red) Sensor is a pyroelectric device that
detects motion by measuring changes in the infrared levels emitted by surrounding objects.
This motion can be detected by checking for a high signal on a single I/O pin.
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In a PIR-based motion detector (usually called a PID, for Passive Infrared Detector), the PIR
sensor is typically mounted on a printed circuit board containing the necessary electronics
required to interpret the signals from the pyroelectric sensor chip. The complete assembly
is contained within a housing mounted in a location where the sensor can view the area to
be monitored. Infrared energy is able to reach the pyroelectric sensor through the window
because the plastic used is transparent to infrared radiation (but only translucent to visible
light). This plastic sheet also prevents the intrusion of dust and/or insects from obscuring
the sensor's field of view, and in the case of insects, from generating false alarms.
A few mechanisms have been used to focus the distant infrared energy onto the sensor
surface. The window may have multiple Fresnel lenses molded into it. Alternatively, some
PIDs are manufactured with internal plastic, segmented parabolic mirrors to focus the
infrared energy. Where mirrors are used, the plastic window cover has no Fresnel lenses
molded into it. This filtering window may be used to limit the wavelengths to 8-14
micrometers which is closest to the infrared radiation emitted by humans (9.4 micrometers
being the strongest).
Feature:
Single bit output
Small size makes it easy to conceal
Compatible with all Parallax microcontrollers
3.3V & 5V operation with <100uA current draw
Theory of Operation:
Pyroelectric devices, such as the PIR sensor, have elements made of a crystalline material
that generates an electric charge when exposed to infrared radiation. The changes in the
amount of infrared striking the element change the voltages generated, which are
measured by an on-board amplifier. The devicecontains a special filter called a Fresnel
lens, which focuses the infrared signals onto the element. As the ambient infrared signals
change rapidly, the on-board amplifier trips the output to indicate motion.
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A person entering a monitored area is detected when the infrared energy emitted from the
intruder's body is focused by a Fresnel lens or a mirror segment and overlaps a section on
the chip that had previously been looking at some much cooler part of the protected area.
That portion of the chip is now much warmer than when the intruder wasn't there. As the
intruder moves, so does the hot spot on the surface of the chip. This moving hot spot causes
the electronics connected to the chip to de-energize the relay, operating its contacts,
thereby activating the detection input on the alarm control panel. Conversely, if an intruder
were to try to defeat a PID, perhaps by holding some sort of thermal shield between himself
and the PID, a corresponding 'cold' spot moving across the face of the chip will also cause
the relay to de-energize — unless the thermal shield has the same temperature as the
objects behind it.
Calibration: The PIR Sensor requires a ‘warm-up’ time in order to function properly. This
is due to the settling time involved in ‘learning’ its environment. This could be anywhere
from 10-60 seconds. During this time there should be as little motion as possible in the
sensors field of view.
Sensitivity: The PIR Sensor has a range of approximately 20 feet. This can vary with
environmental conditions. The sensor is designed to adjust to slowly changing
conditions that would happen normally as the day progresses and the environmental
conditions change, but responds by making its output high when sudden changes
occur, such as when there is motion.
Application: PIDs come in many configurations for a wide variety of applications. The
most common, used in home security systems, have numerous Fresnel lenses or mirror
segments and an effective range of about thirty feet. Some larger PIDs are made with single
segment mirrors and can sense changes in infrared energy over one hundred feet away
from the PID. There are also PIDs designed with reversible orientation mirrors which allow
either broad coverage (110° wide) or very narrow 'curtain' coverage.
PIDs can have more than one internal sensing element so that, with the appropriate
electronics and Fresnel lens, it can detect direction. Left to right, right to left, up or down
and provide an appropriate output signal.
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3.2 Counter
A counter is a device which stores (and sometimes displays) the number of times a
particular event or process has occurred, often in relationship to a clock signal. The counter
we used in this project has two major components —
Analog to Digital Converter, and
Seven-segment Display
3.2.1 Analog to Digital Converter
An Analog to Digital or ADC is an electronic device that converts an input analog voltage or
current to a digital number proportional to the magnitude of the voltage or current.
However, some non-electronic or only partially electronic devices, such as rotary encoders,
can also be considered ADCs.
The digital output may use different coding schemes. Typically the digital output will be a
two's complement binary number that is proportional to the input, but there are other
possibilities. An encoder, for example, might output a Gray code.
Figure3.2: Analog to Digital Converter
43
Resolution:
The resolution of the converter indicates the number of discrete values it can produce over
the range of analog values. The values are usually stored electronically in binary form, so
the resolution is usually expressed in bits. In consequence, the number of discrete values
available, or "levels", is a power of two. For example, an ADC with a resolution of 8 bits can
encode an analog input to one in 256 different levels, since 28 = 256. The values can
represent the ranges from 0 to 255 (i.e. unsigned integer) or from −128 to 127 (i.e. signed
integer), depending on the application.
Response type:
Most ADCs are linear types. The term linear implies that the range of input values has a
linear relationship with the output value.
Accuracy:
An ADC has several sources of errors. Quantization error and (assuming the ADC is
intended to be linear) non-linearity are intrinsic to any analog-to-digital conversion. There
is also a so-called aperture error which is due to a clock jitter and is revealed when
digitizing a time-variant signal (not a constant value). These errors are measured in a unit
called the least significant bit (LSB). In the above example of an eight-bit ADC, an error of
one LSB is 1/256 of the full signal range, or about 0.4%.
Sampling rate:
The analog signal is continuous in time and it is necessary to convert this to a flow of digital
values. It is therefore required to define the rate at which new digital values are sampled
from the analog signal. The rate of new values is called the sampling rate or sampling
frequency of the converter.
A continuously varying bandlimited signal can be sampled (that is, the signal values at
intervals of time T, the sampling time, are measured and stored) and then the original
signal can be exactly reproduced from the discrete-time values by an interpolation formula.
The accuracy is limited by quantization error. However, this faithful reproduction is only
44
possible if the sampling rate is higher than twice the highest frequency of the signal. This is
essentially what is embodied in the Shannon-Nyquist sampling theorem.
Since a practical ADC cannot make an instantaneous conversion, the input value must
necessarily be held constant during the time that the converter performs a conversion
(called the conversion time). An input circuit called a sample and hold performs this task—
in most cases by using a capacitor to store the analog voltage at the input, and using an
electronic switch or gate to disconnect the capacitor from the input. Many ADC integrated
circuits include the sample and hold subsystem internally.
Aliasing:
All ADCs work by sampling their input at discrete intervals of time. Their output is
therefore an incomplete picture of the behavior of the input. There is no way of knowing,
by looking at the output, what the input was doing between one sampling instant and the
next. If the input is known to be changing slowly compared to the sampling rate, then it can
be assumed that the value of the signal between two sample instants was somewhere
between the two sampled values. If, however, the input signal is changing rapidly
compared to the sample rate, then this assumption is not valid.
If the digital values produced by the ADC are, at some later stage in the system, converted
back to analog values by a digital to analog converter or DAC, it is desirable that the output
of the DAC be a faithful representation of the original signal. If the input signal is changing
much faster than the sample rate, then this will not be the case, and spurious signals called
aliases will be produced at the output of the DAC. The frequency of the aliased signal is the
difference between the signal frequency and the sampling rate. For example, a 2 kHz sine
wave being sampled at 1.5 kHz would be reconstructed as a 500 Hz sine wave. This
problem is called aliasing.
Dither:
In A-to-D converters, performance can usually be improved using dither. This is a very
small amount of random noise (white noise), which is added to the input before
conversion. Its effect is to cause the state of the LSB to randomly oscillate between 0 and 1
45
in the presence of very low levels of input, rather than sticking at a fixed value. Rather than
the signal simply getting cut off altogether at this low level (which is only being quantized
to a resolution of 1 bit), it extends the effective range of signals that the A-to-D converter
can convert, at the expense of a slight increase in noise - effectively the quantization error
is diffused across a series of noise values which is far less objectionable than a hard cutoff.
The result is an accurate representation of the signal over time. A suitable filter at the
output of the system can thus recover this small signal variation.
3.2.2 Seven-segment Display
A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display
device for displaying decimal numerals that is an alternative to the more complex dot-
matrix displays. Seven-segment displays are widely used in digital clocks, electronic
meters, and other electronic devices for displaying numerical information.
Figure 3.3: A typical seven-segment LED display
Concept and Visual Structure:
A seven segment display, as its name indicates, is composed of seven elements. Individually
on or off, they can be combined to produce simplified representations of the Arabic
numerals. Often the seven segments are arranged in an oblique (slanted) arrangement,
46
which aids readability. In most applications, the seven segments are of nearly uniform
shape and size (usually elongated hexagons, though trapezoids and rectangles can also be
used), though in the case of adding machines, the vertical segments are longer and more
oddly shaped at the ends in an effort to further enhance readability. Each of the numbers 0,
6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays.
The seven segments are arranged as a rectangle of two vertical segments on each side with
one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment
bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-
segment displays (for full alphanumeric); however, these have mostly been replaced by
dot-matrix displays.
Figure 3.4: Schematic diagram of seven-segment display
Implementation:
In a simple LED package, typically all of the cathodes (negative terminals) or all of the
anodes (positive terminals) of the segment LEDs are connected together and brought out to
a common pin; this is referred to as a "common cathode" or "common anode" device. Hence
a 7 segments plus decimal point package will only require nine pins (though commercial
47
products typically contain more pins, and/or spaces where pins would go, in order to
match industry standard pinouts).
Numbers to 7-segment-code:
A single byte can encode the full state of a 7-segment-display. The most popular bit
encodings are gfedcba and abcdefg - both usually assume 0 is off and 1 is on. The following
table gives the hexadecimal encodings for displaying the digits 0 to F:
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Chapter 4
Circuit Operation
4.1 Introduction
Security monitoring system is used all over the world to ensure the security of our family
and valuables. Still now security assurance is a curse for our country. Available security
systems are not user friendly and affordable enough for every class to maintain. Hence we
designed a security monitoring system based on PIR sensor which is affordable and at the
same time flexible enough to purchase.
4.2 Component Used
AC source
Fuse
Fixed resistor, variable resistor & capacitor
Voltage transformer
Full wave rectifier
Voltage regulator
Breadboard
Relay
PIR sensor
MOSFET
LED
Analog-to-Digital converter
Seven-segment display
Buzzer
Close-circuit camera
Display monitor
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4.3 Operation
An AC voltage source supplies the main power.
A step down transformer takes the source voltage on its primary side and it divides
the voltage into two portions on its secondary side.
Both portion of the AC voltage are taken by two rectifiers and converted into DC
voltage.
One of the DC voltages is passed through a voltage regulator to drive the sensor.
Another DC voltage is used to power up a relay.
The sensor output is connected to an analog-to-digital converter (ADC). The ADC
converts the analog output received from the sensor to a digital pulse and passes it
to a seven-segment display through a driver IC to show the counting.
The sensor output is also connected to the gate of an enhancement type MOSFET
which conducts current from drain to source when it gets a signal from the sensor.
One terminal of the relay is connected to the drain of the MOSFET and when the
MOSFET switches on the relay powers up the buzzer circuit as well as the camera
controller.
The buzzer rings a bell, the LEDs lit on and the camera starts recording surrounding
activities. The output of the camera is shown on a display monitor.
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Figure 4.1: Schematic diagram of the system
51
Chapter 5
Overall Conclusion
5.1 Discussion
It’s not always very easy task to establish a project with an arrant success. Different
environment brings different types there are many obstacles that have to be considered.
Different environment arise different types of problems. Besides, the use of the
components must be precisely valued.
The PIR sensor has a definite rating of power. The power consumed by the sensor is passed
through a voltage regulator. So we had to limit the current flow to an accurate value by
calculating resistor values. We came to understand this fact after damaging a sensor for
over dissipation of power in the circuit.
5.2 Limitation
Almost every project comes out with some limitations or disadvantages. Our project is not
an exception of that. The circuit in our project has some constrains. The perfect execution
of a wireless system depends on both the transmitter and the receiver. The PIR sensor we
used is quite sensitive and detects every possible movement at its range. We had to lessen
the range by controlling its triggering voltage.
5.3 Future Plans
A perfect security system is hard to build. Our monitoring system will do a good job to
provide a medium-level security but when it comes to security there are always scopes for
improvement. We may try to use Global Positioning System (GPS) and microcontroller to
automate the system even more effectively. If we can utilize GPS technology then length
coverage problem will be removed.
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5.4 Conclusion
The main objective of our project was to design and implement an indoor security system
using general electronic components which are easy to use and cost effective. Our system is
very reliable that can be afforded by every class of our society. So if anyone intends to have
a secured system, the one that we designed is one of the most efficient one, with prompt
response without any delay.
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Appendices
Appendix A
Data sheet for Series Voltage Regulator 7812
54
55
56
Appendix B
Data sheet for ADC 0804
57
58
59
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15. http://www.datasheet.org.uk
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