complet finalised

BORDER SECURITY USING WIRELESS INTEGRATED NETWORK (WINS) 2012
BORDER SECURITY USING WIRELESS
INTEGRATED NETWORK (WINS)
A Project Report Submitted
in Partial Fulfillment of the Requirements
for the Degree of
BACHELOR OF TECHNOLOGY
in
ELECTRONICS & COMMUNICATION ENGINEERING
by
Prashant Singh Harish Kumar Vishal Pathak
(2008UEC079) (2007UEC187) (2007UEC056)
Subham Chauhan Abhishek Jain
(2007UEC165) (2007UEC061)
Under the Supervision of
Mrs. (Er.) Avantika Sharma
DEPARTMENT OF ELECTRONICS & COMMUNICATION
ENGINEERING
INSTITUTE OF ENGINEERING & TECHNOLOGY
MANGALAYATAN UNIVERSITY ALIGARH
April, 2012
Mangalayatan University 1

CERTIFICATE
Certified that Prashant Singh (2008UEC079), Harish Kumar (2007UEC187), Vishal
Pathak (2007UEC056), Subham Chauhan (2007UEC165), Abhishek Jain
(2007UEC061) has carried out the research work presented in this report entitled “Border
Security Using Wireless Integrated Network (WINS)” for the award of Bachelor of
Technology in Electronics & Communication Engineering from Mangalayatan
University, Aligarh under my supervision. The report embodies results of original work,
and studies are carried out by the student himself and the contents of the thesis do not form
the basis for the award of any other degree to the candidate or to anybody else from this or
any other University/Institution.
(Mrs. (Er.) Avantika Sharma)
Lecturer & Project Supervisor
Date:
(Dr. Sudhir Kumar Sharma)
Associate Professor & Head
Department of Electronics & Communication Engineering
Mangalayatan University, Aligarh-202125
Date:

DECLARATION
We hereby declare that this submission is our own work and that, to the best of our
knowledge and belief, it contains no material previously published or written by
another person nor material which to a substantial extent has been accepted for the
award of any other degree or diploma of the university or other institute of higher
learning, except where due acknowledgment has been made in the text.
Prashant Singh (2008UEC079)
Harish Kumar (2007UEC187)
Vishal Pathak (2007UEC056)
Subham Chauhan (2007UEC165)
Abhishek Jain (2007UEC061)
Date :

ACKNOWLEDGEMENT
It gives us a great sense of pleasure to present the report of the B. Tech Project undertaken
during B. Tech. Final Year. We owe special debt of gratitude to Mrs. (Er.) Avantika Sharma,
Department of Electronics & Communication Engineering, Institute of Engineering &
Technology, Mangalayatan University, Aligarh for her constant support and guidance
throughout the course of our work. Her sincerity, thoroughness and perseverance have been a
constant source of inspiration for us. It is only her cognizant efforts that our endeavors have
seen light of the day.
We also take the opportunity to acknowledge the contribution of Ass. Professor Sudhir
Sharma, Head, Department of Electronics & Communication Engineering, Institute of
Engineering & Technology, Mangalayatn University, Aligarh for his full support and
assistance during the development of the project.
We also do not like to miss the opportunity to acknowledge the contribution of all faculty
members of the department for their kind assistance and cooperation during the development
of our project. Last but not the least, we acknowledge our friends for their contribution in the
completion of the project.
Prashant Singh (2008UEC079)
Harish Kumar (2007UEC187)
Vishal Pathak (2007UEC056)
Subham Chauhan (2007UEC165)
Abhishek Jain (2007UEC061)

TABLE OF CONTENTS
Topic Page
CERTIFICATE ....................................................................................................... i
DECLARATION .....................................................................................................ii
ACKNOWLEDGEMENTS ....................................................................................iii
CHAPTER 1.INTRODUCTION
The Basic Concept ..............................................................................1
CHAPTER 2. Circuit Description………………………………………………….4
CHAPTER 3.Component Description…………………………………………7
CHAPTER 4. Basic Requirements
Basic Requirments……………………………………………………..10
4.1 Pyro sensor…………………………………………………………….11
4.2 Camera………………………………………………………………...15
4.3 Gun……………………………………………………………………16
4.4 Relay…………………………………………………………………..17
4.5 Television……………………………………………………………...20
4.6 Transformer……………………………………………………………21
4.7 Buzzer…………………………………………………………………30
4.8 Stepper Motor…………………………………………………………32
4.9 Microcontroller………………………………………………………...35
4.10 Regulator……………………………………………………………...60
4.11 Switch………………………………………………………………….65
4.12 Crystals………………………………………………………………...75
4.13 Diode…………………………………………………………………..75
4.14 Reset Circuitry…………………………………………………………82
CHAPTER 5. Problem Description…………………………………………...85
CHAPTER 6. Conclusion……………………………………………………..87
CHAPTER 7. Future Advancement…………………………………………..89
CHAPTER 8. References……………………………………………………..91

CHAPTER- 1
INTRODUCTION

INTRODUCTION
Our project, BORDER SECURITY SYSTEMS, is based on the concept of WIRELESS
INTEGRATED NETWORK SENSORS (WINS).
WINS provides a new monitoring and control capability for the border of the country. It
requires a microwatt of power and produces a less amount of delay to detect the target. Hence
it is reasonably faster.
The border security is the applicable scope for the effort of security check of the border. This
provides with the programmatic outcomes required by the framework for establishing a
perfect security.
The effective border security gives us the power to see the potential threats on the extreme
lines. Thus, emerging as a helping hand for the nation’s security.
The project uses Motion Detector which is the constructional feature of the PIR Sensor. This
is an electronic device that measures IR light radiating from objects in its field of view and is
invisible to the human eye.
The project also uses the stepper motor to control the rotatory motion of the gun. As soon as
the detecting sensor activates, the camera, TV and motor gets activated automatically.
Shooting from the gun is governed according to the requirement that suits to the security
person. This all is operated by the microcontroller commands.
A Relay, operated by an electromagnet is used to switch ON the gun functioning. The Relay
is used to isolate one circuit from the other. The programmatic outcomes required by the
framework for establishing a perfect security.
The effective border security gives us the power to see the potential threats on the extreme
lines. Thus, emerging as a helping hand for the Nation’s security.

The project uses Motion Detector which is the constructional feature of the PIR Sensor. This
is an electronic device that measures IR light radiating from objects in its field of view and is
invisible to the human eye.
The project also uses the stepper motor to control the rotatory motion of the gun. As soon as
the detecting sensor activates, the camera, TV and motor gets activated automatically.
Shooting from the gun is governed according to the requirement that suits to the security
person. This all is operated by the microcontroller commands.
A Relay, operated by an electromagnet is used to switch ON the gun functioning. The Relay
is used to isolate one circuit from the other.
A Step down Transformer is also used that lowers down the voltage from 220 volts AC to 12
volts. This is done as the stepper motor needs the 12 volts voltage for its functioning.
A Microcontroller from the family of 8051 is used which is interfaced with the stepper
motor. Thus the functioning of all the equipments is controlled by the microcontroller. As this
is a computer-on-a-chip.
The microcontroller and its support circuits are often built into or embedded in the devices
they control.

CHAPTER-2
CIRCUIT DESCRIPTION

Circuit Description
It is the schematic of our first test circuit. The PIC's output lines are first buffered by a
4050 hex buffer chip, and are then connected to an NPN transistor. The transistor
used, TIP120, is actually a NPN Darlington (it is shown as a standard NPN). The
TIP120’s act like switches, activating one stepper motor coil at a time.

Due to a inductive surge created when a coil is toggled, a standard 1N4001 diode is
usually placed across each transistor as shown in the figure, providing a safe way of
dispersing the reverse current without damaging the transistor. Sometimes called a
snubbing diode. The TIP120 transistors do not need an external snubbing diode
because they have a built in diode.
So the diodes shown in the drawing are the internal diodes in the TIP120 transistors.
The simplest way to operate a stepper motor with a PIC is with the full step pattern
shown in Table 1. Each part of the sequence turns on only one transistor at a time, one
after the other. After the sequence is completed, it repeats infinitely until power is
removed.
Q1 Q2 Q3 Q4
+ - - -
- + - -
- - + -
- - - +

CHAPTER: 3
COMPONENT LIST

COMPONENT LIST
1. Capacitance
• 1000µf : 3
• 10µf : 1
• 27þf : 3
2. Diode
• IN4007 : 12
3. LED : 8
4. Resistance
• 470Ω : 8
• 10KΩ : 1
• 1KΩ : 5
5. Stepper Motor Coil : 4
6. Switch : 4
7. Transistor :
• NPN : 5
• PNP : 7

CHAPTER: 4
BASIC REQUIREMENTS

BASIC REQUIREMENTS
1. Pyro sensor
2. Camera
3. Gun
4. Relay
5. Television
6. Step Down Transformer
7. Buzzer
8. Stepper Motor
9. Micro Controller
10. Regulator
11. Switch
12. Crystal Used
13. Diode
14. Reset Circuitry

4.1 Pyro sensors
A PIR sensor, or Passive Infrared sensor, is a type of detector that is capable of detecting
infrared light emitting from objects within its field of view. PIR sensors differ from other
infrared sensors because they are only able to receive infrared waves rather than being able to
emit and receive them. Because all objects emit infrared (electromagnetic waves that travel
with heat), PIR sensors are able to detect objects that are in front of them. In fact, PIR sensors
can see many things that humans cannot.
PIR sensors are made of pyroelectric (or thermoelectric) materials and usually contain lenses
or mirrors in order to focus the infrared light for maximum reception. As infrared light comes
in contact with the pyroelectric material, which is usually a thin sheet, it creates an electrical
current that can be measured to determine the intensity of the infrared light (depth perception)
and the direction that it came from.
PIR sensors are made of pyroelectric (or thermoelectric) materials and usually contain lenses
or mirrors in order to focus the infrared light for maximum reception. As infrared light comes
in contact with the pyroelectric material, which is usually a thin sheet, it creates an electrical
current that can be measured to determine the intensity of the infrared light (depth perception)
and the direction that it came from.

Fig1:pyro sensors
Working:
A passive infrared detection and conversion circuit, comprising:
a. a pyrosensor
b. a current amplifier coupled with said pyrosensor
c. a capacitor coupled with said amplifier
d. a signal processor circuit coupled with said capacitor and being operable to charge
said capacitor to a first voltage level and to measure a capacitor discharge time, said
capacitor discharge time being the time required for said capacitor to discharge from
said first voltage level to a second voltage level, and being further operable to
generate an electrical control signal responsive to a variation in said capacitor
discharge time which corresponds to a significant motion event.
The passive infrared detection and conversion circuit wherein, when said pyrosensor is
exposed to infrared motion, it generates a transient current and wherein said capacitor
discharge time corresponds to said transient current.

The passive infrared detection and conversion circuit wherein said signal processor circuit
includes logic operable to compare said capacitor discharge time with a long term average
capacitor discharge time, and wherein said signal processor circuit generates said electrical
control signal only when said capacitor discharge time deviates from said long-term average
capacitor discharge time by a predetermined threshold amount.
The passive infrared detection and conversion circuit wherein said logic of said signal
processor circuit is further operable to calculate and update said long term average capacitor
discharge time based on said capacitor discharge time such that said logic filters out
unwanted background signals.
The passive infrared detection and conversion circuit wherein said logic calculates and
updates said long term average capacitor discharge time by adding a value corresponding to
the difference between said long term average capacitor discharge time and said capacitor
discharge time to said long term average capacitor discharge time.
The passive infrared detection and conversion circuit wherein said current amplifier is a
transistor.
A method for selectively generating a control signal corresponding to motion of an infrared
emitting body, comprising the steps of:
a. Charging a capacitor to a first voltage level;
b. Generating a current corresponding to said infrared motion by means of a pyrosensor;
c. Transmitting said current through a current amplifier;
d. Discharging said capacitor;
e. Measuring a capacitor discharge time, said capacitor discharge time being the time
required for said capacitor to discharge from said first voltage level to a second voltage
level;
f. sensing a significant motion event by a pyrosensor and generating a transient current
responsive thereto;

g. Delivering said current to said capacitor causing a variation in said discharge time; and
h. Generating an electrical control signal responsive to said variation in said capacitor
discharge time.
The method for selectively generating a control signal of further including the step of filtering
out background signals.
The method for selectively generating a control signal further including the steps of
calculating and updating a long term average capacitor discharge time corresponding to said
capacitor discharge time and wherein the step of filtering includes comparing said capacitor
discharge time to said long term average capacitor discharge time.
The method for selectively generating a control signal of wherein the steps of calculating and
updating include updating said long term average capacitor discharge time by adding a value
corresponding to the difference between said long term average capacitor discharge time and
said capacitor discharge time to said long term average capacitor discharge time.
The method for selectively generating a control signal of wherein the step of filtering further
includes the step of comparing said capacitor discharge time with said long term average
capacitor discharge time and generating said control signal if the difference between said
capacitor discharge time and said long term average capacitor discharge time exceeds a
predetermined threshold value.
A method for selectively generating a control signal, comprising the steps of:
a. charging a capacitor to a known first voltage level and allowing said capacitor to
discharge to a second known voltage level at a known discharge rate;
b. modifying the discharge rate of said capacitor in proportion to the current output from
an infrared motion detector;
c. measuring said modified discharge rate of said capacitor; and
d. generating a signal corresponding to said modified discharge rate of said capacitor.

The method for selectively generating a control signal of further including the step of
adjusting a signal threshold in accordance with said discharge rate of said capacitor to
compensate for background signals.
How is this time then calculated?
The speed with which a microcontroller executes instructions is determined by what is known
as the crystal speed. A crystal is a component connected externally to the microcontroller.
The crystal has different values, and some of the used values are 6MHZ, 10MHZ, and 11.059
MHz etc. Thus, a 10MHZ crystal would pulse at the rate of 10,000,000 times per second.
The time is calculated using the formula
No of cycles per second = Crystal frequency in HZ / 12. For a 10MHZ crystal the number of
cycles would be, 10,000,000/12=833333.33333 cycles.
This means that in one second, the microcontroller would execute 833333.33333 cycles.
Hardware Design
A system capable of detecting motion using a dual element PIR sensor using the
MSP430F2013 microcontroller. The MSP430F2013 provides all the required elements for
interfacing to the PIR sensor in a small footprint, using the integrated 16-bit Sigma-Delta
analog-to digital converter (ADC) and built-in front-end PGA (SD16_A). A simplified circuit
that is used to process the PIR sensor output signal is shown. The external components
consist of the bias resistor, RB, required for the sensor and two RC filters formed by R1/C1
and R2/C2. The R1/C1 filter serves as an anti-aliasing filter on the AX+ input.R2/C2 serves
to create a DC bias for the AX- input. With a small peak-to-peak sensor output of the PIR, , a
higher gain setting is required eliminating the possibility that AX- can be tied directly to
VSS. The sensor output signal after the ant aliasing filter is connected to AX+. Simple DC
bias is established for maintaining the input range requirements of the SD16_A By heavily
low pass filtering the sensor output before connecting to AX-.
Software Design:
Analog sampling and data processing is kept to a minimum required to reliably detect
motion. If no motion was detected in the last measurement the SD16_A internal reference is

enabled and a new conversion is started. After the conversion is complete, the SD16_A ISR
is entered and the internal reference is disabled.
4.2 CAMERA
A camera is a device that records/stores images. These images may be still photographs or
moving images such as videos or movies. The term camera comes from the camera
obscura (Latin for "dark chamber"), an early mechanism for projecting images. The modern
camera evolved from the camera obscura.
Cameras may work with the light of the visible spectrum or with other portions of
the electromagnetic spectrum. A camera generally consists of an enclosed hollow with an
opening (aperture) at one end for light to enter, and a recording or viewing surface for
capturing the light at the other end. A majority of cameras have a lens positioned in front of
the camera's opening to gather the incoming light and focus all or part of the image on the
recording surface. Most 20th century cameras used photographic film as a recording surface,
while modern ones use an electronic camera sensor. The diameter of the aperture is often
controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.
4.3 GUN
Gun is a muzzle or breech-loaded projectile firing weapon. In modern parlance, gun is a
projectile weapon using hollow, tubular barrel with a closed end-the breech-as the means of
directing the projectile. Most guns are described by the types of the barrel used, the means of
firing, the purpose of the weapon used, the caliber or the commonly accepted name for a
particular variation.
In Military use, the term “GUN” refers primarily to direct fire weapons that capitalize on
their velocity for penetration and range. These weapons are breeched-loaded and built
primarily for long range fire with a low or almost flat ballistic area.
WORKING OPERATION:

As the semi-conductor technology is experiencing rapid growth, human life gets complicated
without “embedded system”. Nowadays these new technologies are introduced in the
equipments engaged in the battlefield to improve the safety of soldiers and also to ensure
combat effectiveness. Our scope is to develop a mechanism to automatically control the
movement of the air defense gun mounted on the tank. Air defense gun is mounted on the
loader’s hatch in the turret of the tank and is controlled by the loader .It is primarily used to
attack low flying armored vehicles. Presently the gunner has to expose himself to track the
enemy and attack the target and so he becomes vulnerable to external foes, added to it he has
to manually adjust the desired elevation and depression of the air defense gun.
BASIC REQUIREMENTS
The system should enable sighting of the target through a sight, aiming the target in hatch
closed condition by slewing and elevating/ depressing anti-aircraft gun The system should
enable the rotation of loader’s hatch in azimuth plane both in anti-clockwise and clockwise
direction through 360 degree. The movement of air defense gun in the vertical plane is from
-10 degree to +70 degree. The system also requires automatic stopping of gun movement if it
attains the extreme positions in the vertical plane.
TRIGGER
A trigger is a mechanism that actuates the firing sequence of firearms, or a power tool.
Triggers almost universally consist of levers or buttons actuated by the index finger. Rare
variations use the thumb to actuate the trigger.
Firearms use triggers to initiate the firing of a cartridge in the firing chamber of the weapon.
This is accomplished by actuating a striking device through a combination of spring and
kinetic energy operating through a firing pin to strike and ignite the primer.

4.4 RELAY
A relay is an electrically operated switch. It is used to isolate one electrical circuit from
another. It allows a low current control circuits to make or break the electrically isolated high
current circuit path.
Fig 2: Development of magnetic field in a relay as a switch
Many relays use the 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.
Relays are extremely useful when we have a need to control a large amount of current and/or
voltage with a small electrical signal. The relay coil which produces the magnetic field may
only consume fraction of watt of power, while the contact is closed or opened by that
magnetic field may be able to conduct hundreds of times that amount of power to a load.
The basic relay consists of a coil and a set of contacts. The most common relay coil is a
length of magnet wire wrapped around a metal core. When voltage is applied to the coil, the

current passes through the wire and creates a magnetic field. This magnetic field pulls the
contacts together and holds them until the current flow in the coil has stopped.
Fig3: Relay Functioning
The coil voltage and the current carrying capability of the contacts are the major
specifications needed to be considered while selecting a relay.
The current rating on the relay contacts tells how much current can be passed through the
contacts without damage to the contacts.
BASIC DESIGN AND OPERATION:
A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron
yoke which provides a low reluctance path for magnetic flux, a movable iron armature and
one or more sets of contacts. The armature is hinged to the yoke and mechanically linked to
one or more sets of contacts. It is held in place by a spring so that when the relay is de-
energizes there is an air gap in the magnetic circuit. The connection of the armature and the
yoke ensures continuity of the circuit between the moving contacts on the armature.

When an electric current is passed through the coil it generates the magnetic field that attracts
the armature, and the consequent movement of the contact(s) either makes or breaks the
connection with the fixed contact. If the set of contacts was closed when the relay was de-
energized, then the movement opens the contacts and breaks the connection and vice versa if
the contacts were open. When the current to the coil is switched off, the armature is returned
by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually
this force is provided by a spring, but gravity is also used in industrial motor starters.
When the coil is energized by the direct current, a diode is often placed across the coil to
dissipate the energy from the collapsing magnetic field at deactivation which would rather
generate a voltage splice dangerous to semiconductor circuit components.
Fig 4 : An Electro-Mechanical Relay
4.5 Television
Television (TV) is a telecommunication medium for transmitting and receiving moving
images that can be monochromatic (shades of grey) or multi colored. Images are usually
accompanied by sound. "Television" may also refer specifically to a television set, television
programming, and television transmission.
Television has become a major medium of communication and source for home
entertainment. Television is put to varied use in industry, e.g., for surveillance in places
inaccessible to or dangerous for human beings; in science.

Television, transmission and reception of still or moving images by means of electrical
signals, especially by means of electromagnetic radiation energy radiated in the form of a
wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic
field, and if the motion is changing (accelerated), then the magnetic field varies .
A standard television set comprises multiple internal electronic circuits, including those for
receiving and decoding broadcast signals. A visual display device which lacks a tuner is
properly called a monitor, rather than a television. A television system may use different
technical standards such as digital television (DTV) and high-definition television (HDTV).
Television systems are also used for surveillance, industrial process control, and guiding of
weapons, in places where direct observation is difficult or dangerous.
Fig5: Wavelengths existing in a television
4.6 Transformer
A transformer is a static device that transfers electrical energy from one circuit to another
through inductively coupled conductors, the transformer's coils. A varying current in the first
or primary winding creates a varying magnetic flux in the transformer's core and thus a
varying magnetic field through the secondary winding. This varying magnetic field induces a
varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is
called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding
and electrical energy will be transferred from the primary circuit through the transformer to
the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in

proportion to the primary voltage (Vp), and is given by the ratio of the number of turns in the
secondary (Ns) to the number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current
(AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making
Ns less than Np.
In the vast majority of transformers, the windings are coils wound around a ferromagnetic
core, air-core transformers being a notable exception.
Discovery
Fig6: Discovery of principle of mutual induction
Faraday's experiment with induction between coils of wire
The phenomenon of electromagnetic induction was discovered independently by Michael
Faraday and Joseph Henry in 1831. However, Faraday was the first to publish the results of
his experiments and thus receive credit for the discovery.[2]
The relationship between
electromotive force (EMF) or "voltage" and magnetic flux was formalized in an equation
now referred to as "Faraday's law of induction":

.
where the magnitude of the EMF in volts and ΦB is is the magnetic flux through the
circuit (in webers).
Faraday performed the first experiments on induction between coils of wire, including
winding a pair of coils around an iron ring, thus creating the first to roidal closed-core
transformer.
Basic principle:
The transformer is based on two principles:
First, that an electric current can produce a magnetic field (electromagnetism),
And, second that a changing magnetic field within a coil of wire induces a voltage across the
ends of the coil (electromagnetic induction). Changing the current in the primary coil changes
the magnetic flux that is developed. The changing magnetic flux induces a voltage in the
secondary coil.
Fig7: An ideal transformer

An ideal transformer is shown in the adjacent figure. Current passing through the primary
coil creates a magnetic field. The primary and secondary coils are wrapped around a core of
very high magnetic permeability, such as iron, so that most of the magnetic flux passes
through both the primary and secondary coils.
Induction law
The voltage induced across the secondary coil may be calculated from Faraday's law of
induction, which states that:
where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and Φ is
the magnetic flux through one turn of the coil. If the turns of the coil are oriented
perpendicular to the magnetic field lines, the flux is the product of the magnetic flux density
B and the area A through which it cuts. The area is constant, being equal to the cross-sectional
area of the transformer core, whereas the magnetic field varies with time according to the
excitation of the primary. Since the same magnetic flux passes through both the primary and
secondary coils in an ideal transformer, the instantaneous voltage across the primary winding
equals
Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up or
stepping down the voltage
Np/Ns is known as the turns ratio, and is the primary functional characteristic of any
transformer. In the case of step-up transformers, this may sometimes be stated as the
reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for
example, a transformer with primary and secondary windings of, respectively, 100 and 150
turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150.

Ideal power equation
Fig 8: Ideal transformer as a circuit element
If the secondary coil is attached to a load that allows current to flow, electrical power is
transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is
perfectly efficient; all the incoming energy is transformed from the primary circuit to the
magnetic field and into the secondary circuit. If this condition is met, the incoming electric
power must equal the outgoing power:
giving the ideal transformer equation
Transformers normally have high efficiency, so this formula is a reasonable approximation.
If the voltage is increased, then the current is decreased by the same factor. The impedance in
one circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is
attached across the terminals of the secondary coil, it appears to the primary circuit to have an
impedance of (Np/Ns)2
Zs. This relationship is reciprocal, so that the impedance Zp of the
primary circuit appears to the secondary to be (Ns/Np)2
Zp.
Detailed Operation

The simplified description above neglects several practical factors, in particular the primary
current required to establish a magnetic field in the core, and the contribution to the field due
to current in the secondary circuit.
Models of an ideal transformer typically assume a core of negligible reluctance with two
windings of zero resistance.[31]
When a voltage is applied to the primary winding, a small
current flows, driving flux around the magnetic circuit of the core. The current required to
create the flux is termed the magnetizing current; since the ideal core has been assumed to
have near-zero reluctance, the magnetizing current is negligible, although still required to
create the magnetic field.
The changing magnetic field induces an electromotive force (EMF) across each winding.
Since the ideal windings have no impedance, they have no associated voltage drop, and so the
voltages VP and VS measured at the terminals of the transformer, are equal to the
corresponding EMFs. The primary EMF, acting as it does in opposition to the primary
voltage, is sometimes termed the "back EMF". This is due to Lenz's law which states that the
induction of EMF would always be such that it will oppose development of any such change
in magnetic field.
Energy Loss
An ideal transformer would have no energy losses, and would be 100% efficient. In practical
transformers energy is dissipated in the windings, core, and surrounding structures. Larger
transformers are generally more efficient, and those rated for electricity distribution usually
perform better than 98%.
Transformer losses are divided into losses in the windings, termed copper loss, and those in
the magnetic circuit, termed iron loss. Losses in the transformer arise from:
Winding resistance

Current flowing through the windings causes resistive heating of the conductors. At higher
frequencies, skin effect and proximity effect create additional winding resistance and losses.
Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis
within the core. For a given core material, the loss is proportional to the frequency, and is a
function of the peak flux density to which it is subjected.
Eddy currents
Ferromagnetic materials are also good conductors, and a core made from such a material also
constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore
circulate within the core in a plane normal to the flux, and are responsible for resistive
heating of the core material. The eddy current loss is a complex function of the square of
supply frequency and inverse square of the material thickness. Eddy current losses can be
reduced by making the core of a stack of plates electrically insulated from each other, rather
than a solid block; all transformers operating at low frequencies use laminated or similar
cores.

Magnetostriction
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand
and contract slightly with each cycle of the magnetic field, an effect known as
magnetostriction. This produces the buzzing sound commonly associated with transformers,
and can cause losses due to frictional heating.
Mechanical losses
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces
between the primary and secondary windings. These incite vibrations within nearby
metalwork, adding to the buzzing noise, and consuming a small amount of power.
Stray losses
Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is
returned to the supply with the next half-cycle. However, any leakage flux that intercepts
nearby conductive materials such as the transformer's support structure will give rise to eddy
currents and be converted to heat. There are also radiative losses due to the oscillating
magnetic field, but these are usually small.
Equivalent Circuit
The physical limitations of the practical transformer may be brought together as an equivalent
circuit model (shown below) built around an ideal lossless transformer. Power loss in the
windings is current-dependent and is represented as in-series resistances Rp and Rs. Flux
leakage results in a fraction of the applied voltage dropped without contributing to the mutual
coupling, and thus can be modeled as reactances of each leakage inductance Xp and Xs in
series with the perfectly coupled region.
Iron losses are caused mostly by hysteresis and eddy current effects in the core, and are
proportional to the square of the core flux for operation at a given frequency. Since the core
flux is proportional to the applied voltage, the iron loss can be represented by a resistance RC
in parallel with the ideal transformer.

A core with finite permeability requires a magnetizing current Im to maintain the mutual flux
in the core. The magnetizing current is in phase with the flux; saturation effects cause the
relationship between the two to be non-linear, but for simplicity this effect tends to be
ignored in most circuit equivalents. With a sinusoidal supply, the core flux lags the induced
EMF by 90° and this effect can be modeled as a magnetizing reactance (reactance of an
effective inductance) Xm in parallel with the core loss component. Rc and Xm are sometimes
together termed the magnetizing branch of the model. If the secondary winding is made open-
circuit, the current I0 taken by the magnetizing branch represents the transformer's no-load
current. The secondary impedance Rs and Xs is frequently moved (or "referred") to the
primary side after multiplying the components by the impedance scaling factor (Np/Ns)2
.
Fig 9: Transformer equivalent circuit, with secondary impedances referred to the primary side
The resulting model is sometimes termed the "exact equivalent circuit", though it retains a
number of approximations, such as an assumption of linearity. Analysis may be simplified by
moving the magnetizing branch to the left of the primary impedance, an implicit assumption
that the magnetizing current is low, and then summing primary and referred secondary
impedances, resulting in so-called equivalent impedance.
The parameters of equivalent circuit of a transformer can be calculated from the results of
two transformer tests: open-circuit test and short-circuit test.
Application
A major application of transformers is to increase voltage before transmitting electrical
energy over long distances through wires. Wires have resistance and so dissipate electrical
energy at a rate proportional to the square of the current through the wire. By transforming

electrical power to a high-voltage (and therefore low-current) form for transmission and back
again afterward, transformers enable economical transmission of power over long distances.
Consequently, transformers have shaped the electricity supply industry, permitting generation
to be located remotely from points of demand. All but a tiny fraction of the world's electrical
power has passed through a series of transformers by the time it reaches the consumer.
Transformers are also used extensively in electronic products to step down the supply voltage
to a level suitable for the low voltage circuits they contain. The transformer also electrically
isolates the end user from contact with the supply voltage.
Signal and audio transformers are used to couple stages of amplifiers and to match devices
such as microphones and record players to the input of amplifiers. Audio transformers
allowed telephone circuits to carry on a two-way conversation over a single pair of wires. A
balun transformer converts a signal that is referenced to ground to a signal that has balanced
voltages to ground, such as between external cables and internal circuits.
The principle of open-circuit (unloaded) transformer is widely used for characterisation of
soft magnetic materials, for example in the internationally standardised Epstein frame
method.
4.7 Buzzer
A buzzer or beeper is an audio signaling device, which may be mechanical,
electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarms,
timers and confirmation of user input such as a mouse click or keystroke.

Fig10: A buzzer
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.
Uses
• Annunciator panels
• Electronic metronomes
• Game shows
• Microwave ovens and other household appliances

• Sporting events such as basketball games
4.8 STEPPER MOTOR
Motion control, in electronic terms, means to accurately control the movement of an object
based on either speed, distance, load, inertia, rotation angle, synchronism or a combination of
all these factors. There are numerous types of motion control systems, including; Stepper
motor, Linear step motor, DC Brush, Brushless, Servo and more.
The stepper motor is an electromagnetic device that converts digital pulses into mechanical
shaft rotation.
Fig 11: A Stepper Motor
BASICS OF STEPPER MOTOR:
A stepper motor is a brushless, synchronous electric
motor that can divide a full rotation into a
large number of steps. The motor position can be controlled precisely without any feedback
mechanism as long as the motor is carefully sized to the application. These are similar to
switch reluctance motors (very large stepping motors with a reduced pole count).
MOTOR CONSTRUCTION:
The motor consists of multiple electrical windings wrapped in pairs around the outer
stationary portion of the motor. The inner portion consists of iron or magnetic disks mounted
on shaft and suspended on the bearings. The rotor has the projecting teeth which align with

the magnetic fields of the windings. When the coils are energized in sequence by direct
current, the teeth follow the sequence and rotate a discrete distance necessary to re-align with
the magnetic field.
The number of coil combinations and the number of teeth determine the steps (resolution) of
the motor.
A stepper motor is a multi-pole brushless DC motor. These multiple coil pairs can be
connected either positive or negative resulting in four unique full steps. When the coils are
sequenced correctly, the motor rotates forward. When the sequence is reversed, the motor
rotates in reverse. When the sequence is held, the rotor locks (brakes) in place.
The amount of torque required to force the rotor from position is the holding or static torque.
If the rotor slips (step loss), it will align with the next available coil combination, either four
steps forward or four steps backward.

Fig 12: Electrical model of a Stepper Motor
INTERFACING:
Stepper motor is one of the commonly used motor for precise angular movement of all
motors, stepper motor is easiest to control. Its handling simplicity is hard to deny. All there to

do is to bring the sequence of rectangular pulses to one input of step controller and direction
information to another input.
The stepping motor consists of three basic elements, often combined with some type of user
interface (host computer, PLC or Dumb Terminal):
Fig 13: Basic Elements
The Indexer (or controller) is a microprocessor capable of generating step pulses and
direction signals for the driver. In addition, the indexer is typically required to perform many
other sophisticated command functions.
The Driver (or amplifier) converts the indexer command signals into the power necessary to
energize the motor windings. There are numerous types of drivers, with different
current/ampere ratings and construction technology. Not all drivers are suitable to run all
motors, so when designing a Motion Control System the driver selection process is critical.
4.9 MICROCONTROLLER
A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single
integrated circuit containing a processor core, memory, and programmable input/output
peripherals. Program memory in the form of NOR flash or OTP ROM is also often included
on chip, as well as a typically small amount of RAM. Microcontrollers are designed for
embedded applications, in contrast to the microprocessors used in personal computers or
other general purpose applications.
Microcontrollers are used in automatically controlled products and devices, such as
automobile engine control systems, implantable medical devices, remote controls, office
machines, appliances, power tools, and toys. By reducing the size and cost compared to a

design that uses a separate microprocessor, memory, and input/output devices,
microcontrollers make it economical to digitally control even more devices and processes.
Mixed signal microcontrollers are common, integrating analog components needed to control
non-digital electronic systems.
Some microcontrollers may use Four-bit words and operate at clock rate frequencies as low
as 4 kHz, for low power consumption (mill watts or microwatts). They will generally have
the ability to retain functionality while waiting for an event such as a button press or other
interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be
just nano watts, making many of them well suited for long lasting battery applications. Other
microcontrollers may serve performance-critical roles, where they may need to act more like
a digital signal processor (DSP), with higher clock speeds and power consumption.
A microcontroller can be considered a self-contained system with a processor, memory and
peripherals and can be used as an embedded system. The majority of microcontrollers in use
today are embedded in other machinery, such as automobiles, telephones, appliances, and
peripherals for computer systems. These are called embedded systems.
Types of microcontrollers
• Parallax Propeller
• Free scale 68HC11 (8-bit)
Intel 8051
• Silicon Laboratories Pipelined 8051 Microcontrollers
• ARM processors (from many vendors) using ARM7 or Cortex-M3 cores are generally
microcontrollers
• STMicroelectronics STM8 (8-bit), ST10 (16-bit) and STM32 (32-bit)
• Atmel AVR (8-bit), AVR32 (32-bit), and AT91SAM (32-bit)
• Freescale ColdFire (32-bit) and S08 (8-bit)
• Hitachi H8, Hitachi SuperH (32-bit)

• Hyperstone E1/E2 (32-bit, First full integration of RISC and DSP on one processor
core [1996] [1])
• Infineon Microcontroller: 8, 16, 32 Bit microcontrollers for automotive and industrial
applications[6]
• MIPS (32-bit PIC32)
• NEC V850 (32-bit)
• NXP Semiconductors [2] LPC1000, LPC2000, LPC3000, LPC4000 (32-bit), LPC900,
LPC700 (8-bit)
• PIC (8-bit PIC16, PIC18, 16-bit dsPIC33 / PIC24)
• PowerPC ISE
• PSoC (Programmable System-on-Chip)
• Rabbit 2000 (8-bit)
• Texas Instruments Microcontrollers MSP430 (16-bit), C2000 (32-bit), and Stellaris
(32-bit)
• Toshiba TLCS-870 (8-bit/16-bit)
• XMOS XCore XS1 (32-bit)
• Zilog eZ8 (16-bit), eZ80 (8-bit)
MICROCONTROLLER 8051
The Intel 8051 microcontroller is one of the most popular general purpose microcontrollers in
use today. The success of the Intel 8051 spawned a number of clones which are collectively
referred to as the MCS-51 family of microcontrollers, which includes chips from vendors
such as Atmel, Philips, Infineon, and Texas Instruments.

About the 8051
The Intel 8051 is an 8-bit microcontroller which means that most available operations are
limited to 8 bits. There are 3 basic "sizes" of the 8051: Short, Standard, and Extended. The
Short and Standard chips are often available in DIP (dual in-line package) form, but the
Extended 8051 models often have a different form factor, and are not "drop-in compatible".
All these things are called 8051 because they can all be programmed using 8051 assembly
language, and they all share certain features (although the different models all have their own
special features).
Some of the features that have made the 8051 popular are:
• 64 KB on chip program memory.
• 128 bytes on chip data memory (RAM).
• 4 register banks.
• 128 user defined software flags.
• 8-bit data bus
• 16-bit address bus
• 32 general purpose registers each of 8 bits
• 16 bit timers (usually 2, but may have more, or less).
• 3 internal and 2 external interrupts.
• Bit as well as byte addressable RAM area of 16 bytes.
• Four 8-bit ports, (short models have two 8-bit ports).
• 16-bit program counter and data pointer.
• 1 Microsecond instruction cycle with 12 MHz Crystal.
8051 models may also have a number of special, model-specific features, such as UARTs,
ADC, OpAmps, etc...

Fig 14: 8051 PIN DIAGRAM

PIN DESCRIPTION OF 8051
Ports:
There are 4 8-bit ports: P0, P1, P2 and P3.
PORT P0 (pins 32 to 39) PORT P0 can be used as a general purpose 8 bit port when no
external memory is present, but if external memory access is required then PORT P0 acts as a
multiplexed address and data bus that can be used to access external memory in conjunction
with PORT P2. P0 acts as AD0-AD7
PORT P1 (Pins 1 to 8): The port P1 is a general purpose input/output port which can be used
for a variety of interfacing tasks. The other ports P0, P2 and P3 have dual roles or additional
functions associated with them based upon the context of their usage.
PORT P2 (pins 21 to 28): PORT P2 can also be used as a general purpose 8 bit port when no
external memory is present, but if external memory access is required then PORT P2 will act
as an address bus in conjunction with PORT P0 to access external memory. PORT P2 acts as
A8-A15, as can be seen from fig 1.1
PORT P3 (Pins 10 to 17): PORT P3 acts as a normal IO port, but Port P3 has additional
functions such as, serial transmit and receive pins, 2 external interrupt pins, 2 external
counter inputs, read and write pins for memory access.
PIN 9: PIN 9 is the reset pin which is used reset the microcontroller’s internal registers and
ports upon starting up. (Pin should be held high for 2 machine cycles.)
PINS 18 & 19: The 8051 has a built-in oscillator amplifier hence we need to only connect a
crystal at these pins to provide clock pulses to the circuit.
PIN 40 and 20: Pins 40 and 20 are VCC and ground respectively. The 8051 chip needs +5V
500mA to function properly, although there are lower powered versions like the Atmel 2051
which is a scaled down version of the 8051 which runs on +3V.
PINS 29, 30 & 31: As described in the features of the 8051, this chip contains a built-in flash
memory. In order to program this we need to supply a voltage of +12V at pin 31. If external
memory is connected then PIN 31, also called EA/VPP, should be connected to ground to

indicate the presence of external memory. PIN 30 is called ALE (address latch enable), which
is used when multiple memory chips are connected to the controller and only one of them
needs to be selected. We will deal with this in depth in the later chapters. PIN 29 is called
PSEN. This is "program store enable". In order to use the external memory it is required to
provide the low voltage (0) on both PSEN and EA pins.
ARCHITECTURE OF 8051
Fig 15: Architecture of 8051

Data and Program Memory
The 8051 Microprocessor can be programmed in PL/M, 8051 Assembly, C and a number of
other high-level languages. Many compilers even have support for compiling C++ for an
8051.
Program memory in the 8051 is read-only, while the data memory is considered to be
read/write accessible. When stored on EEPROM or Flash, the program memory can be
rewritten when the microcontroller is in the special programmer circuit.
Program Start Address
The 8051 starts executing program instructions from address 0000 in the program memory.
Direct Memory
The 8051 has 256 bytes of internal addressable RAM, although only the first 128 bytes are
available for general use by the programmer. The first 128 bytes of RAM (from 0x00 to
0x7F) are called the Direct Memory, and can be used to store data.
Special Function Register
The Special Function Register (SFR) is the upper area of addressable memory, from address
0x80 to 0xFF. A, B, PSW, DPTR are called SFR. This area of memory cannot be used for
data or program storage, but is instead a series of memory-mapped ports and registers. All
port input and output can therefore be performed by memory move operations on specified
addresses in the SFR. Also, different status registers are mapped into the SFR, for use in
checking the status of the 8051, and changing some operational parameters of the 8051.
SPECIAL FUNCTION REGISTER (SFR) ADDRESSES:
ACC ACCUMULATOR 0E0H
B B REGISTER 0F0H
PSW PROGRAM STATUS WORD 0D0H

SP STACK POINTER 81H
DPTR DATA POINTER 2 BYTES
DPL LOW BYTE OF DPTR 82H
DPH HIGH BYTE OF DPTR A0H
P3 PORT3 0B0H
TMODTIMER/COUNTER MODE CONTROL 89H
TCON TIMER COUNTER CONTROL 88H
TH0 TIMER 0 HIGH BYTE 8CH
TLO TIMER 0 LOW BYTE 8AH
TH1 TIMER 1 HIGH BYTE 8DH
TL1 TIMER 1 LOW BYTE 8BH
SCON SERIAL CONTROL 98H
SBUF SERIAL DATA BUFFER 99H
PCON POWER CONTROL 87H
Both timers are the 89c51 share the one register TMOD. 4 LSB bit for the timer 0 and 4 MSB
for the timer 1.

In each case lower 2 bits set the mode of the timer
Upper two bits set the operations.
GATE: Gating control when set. Timer/counter is enabled only while the INTX pin is
high and the TRx control pin is set. When cleared, the timer is enabled
whenever the TRx control bit is set
C/T: Timer or counter selected cleared for timer operation (input from internal
system clock)
M1 Mode bit 1
M0 Mode bit 0
M1 M0 MODEOPERATING MODE
0 0 0 13 BIT TIMER/MODE
0 1 1 16 BIT TIMER MODE
1 0 2 8 BIT AUTO RELOAD
1 1 3 SPLIT TIMER MODE
PSW (PROGRAM STATUS WORD)
CY PSW.7 CARRY FLAG
AC PSW.6 AUXILIARY CARRY
F0 PSW.5 AVAILABLE FOR THE USER FRO

GENERAL PURPOSE
RS1 PSW.4 REGISTER BANK SELECTOR BIT 1
RS0 PSW.3 REGISTER BANK SELECTOR BIT 0
0V PSW.2 OVERFLOW FLAG
-- PSW.1 USER DEFINABLE BIT
P PSW.0 PARITY FLAG SET/CLEARED BY HARDWARE

PCON REGISTER (NON BIT ADDRESSABLE)
If the SMOD = 0 (DEFAULT ON RESET)
TH1 = CRYSTAL FREQUENCY
256___________________
384 X BAUD RATE
If the SMOD IS = 1
CRYSTAL FREQUENCY
TH1 = 256--------------------------------------
192 X BAUD RATE
There are two ways to increase the baud rate of data transfer in the 8051
1. To use a higher frequency crystal
2. To change a bit in the PCON register
PCON register is an 8 bit register. Of the 8 bits, some are unused, and some are used for the
power control capability of the 8051. The bit which is used for the serial communication is
D7, the SMOD bit. When the 8051 is powered up, D7 (SMOD BIT) OF PCON register is
zero. We can set it to high by software and thereby double the baud rate BAUD RATE
COMPARISION FOR SMOD = 0 AND SMOD =1
TH1 (DECIMAL) HEX SMOD =0 SMOD =1
-3 FD 9600 19200
-6 FA 4800 9600
-12 F4 2400 4800
-24 E8 1200 2400

XTAL = 11.0592 MHZ
IE (INTERRUPT ENABLE REGISTER)
EA IE.7 Disable all interrupts if EA = 0, no interrupts is acknowledged
If EA is 1, each interrupt source is individually enabled or disabled
By sending or clearing its enable bit.
IE.6 NOT implemented
ET2 IE.5 enables or disables timer 2 overflag in 89c52 only
ES IE.4 Enables or disables all serial interrupt
ET1 IE.3 Enables or Disables timer 1 overflow interrupt
EX1 IE.2 Enables or disables external interrupt
ET0 IE.1 Enables or Disables timer 0 interrupt.
EX0 IE.0 Enables or Disables external interrupt 0
INTERRUPT PRIORITY REGISTER
If the bit is 0, the corresponding interrupt has a lower priority and if the bit is 1 the
corresponding interrupt has a higher priority
IP.7 NOT IMPLEMENTED, RESERVED FOR FUTURE USE.
IP.6 NOT IMPLEMENTED, RESERVED FOR FUTURE USE

PT2 IP.5 DEFINE THE TIMER 2 INTERRUPT PRIORITY LELVEL
PS IP.4 DEFINES THE SERIAL PORT INTERRUPT PRIORITY LEVEL
PT1 IP.3 DEFINES THE TIMER 1 INTERRUPT PRIORITY LEVEL
PX1 IP.2 DEFINES EXTERNAL INTERRUPT 1 PRIORITY LEVEL
PT0 IP.1 DEFINES THE TIMER 0 INTERRUPT PRIORITY LEVEL
PX0 IP.0 DEFINES THE EXTERNAL INTERRUPT 0 PRIORITY LEVEL
SCON: SERIAL PORT CONTROL REGISTER, BIT ADDRESSABLE
SCON
SM0 : SCON.7 Serial Port mode specified
SM1 : SCON.6 Serial Port mode specified
SM2 : SCON.5
REN : SCON.4 Set/cleared by the software to Enable/disable reception
TB8 : SCON.3 the 9th
bit that will be transmitted in modes 2 and 3, Set/cleared
By software
RB8 : SCON.2 In modes 2 &3, is the 9th
data bit that was received. In mode 1,
If SM2 = 0, RB8 is the stop bit that was received. In mode 0
RB8 is not used
T1 : SCON.1 Transmit interrupt flag. Set by hardware at the end of the 8th
bit

Time in mode 0, or at the beginning of the stop bit in the other modes. Must be cleared by
software
R1 SCON.0 Receive interrupt flag. Set by hardware at the end of the 8th
bit time in mode 0, or
halfway through the stop bit time in the other modes must be cleared by the software.
TCON TIMER COUNTER CONTROL REGISTER
This is a bit addressable
TF1 TCON.7 Timer 1 overflows flag. Set by hardware when the Timer/Counter 1
Overflows. Cleared by hardware as processor
TR1 TCON.6 Timer 1 run control bit. Set/cleared by software to turn Timer
Counter 1 On/off
TF0 TCON.5 Timer 0 overflows flag. Set by hardware when the timer/counter 0
Overflows. Cleared by hardware as processor
TR0 TCON.4 Timer 0 run control bit. Set/cleared by software to turn timer counter 0
on/off.
IE1 TCON.3 External interrupt 1 edge flag
ITI TCON.2 Interrupt 1 type control bit
IE0 TCON.1 External interrupt 0 edge
IT0 TCON.0 Interrupt 0 type control bit.
General Purpose Registers
The 8051 has 4 selectable banks of 8 addressable 8-bit registers, R0 to R7. This means that
there are essentially 32 available general purpose registers, although only 8 (one bank) can be
directly accessed at a time. To access the other banks, we need to change the current bank
number in the flag status register.

A and B Registers
The A register is located in the SFR memory location 0xE0. The A register works in a similar
fashion to the AX register of x86 processors. The A register is called the accumulator, and by
default it receives the result of all arithmetic operations. The B register is used in a similar
manner, except that it can receive the extended answers from the multiply and divide
operations. When not being used for multiplication and Division, the B register is available as
an extra general-purpose register.

ADRESSING MODE:
Definition:
The CPU can access data in various way. The data could be in registers, in memory or could
be provided as an immediate data. The various way of accessing data are called addressing
mode.
Instruction = Mnemonics or opcode + operand
The way by which the address of the operand (source and destination operand) are specified
in the instruction is known as addressing mode
Note: - The various addressing mode of microprocessor are determined when it was designed
and therefore it can not be changed by programmer.
Various addressing mode in 8051
1. Register addressing
2. Direct addressing
3. In direct addressing
4. Register specific addressing
5. Immediate addressing
6. Indexed addressing

1. Register Addressing Mode
In register addressing operands are in registers.
The register addressing modes occur between Register A and R0 to R7. the programmer can
select a register bank by modifying bits 4 and 3 in the PSW.
For example:
MOVA, R0 : copy data from register R0 to register A
ADDA, R1 : Add the content of R1 and A. Store the result in A
ANL A, R2 : AND each bit of A with the same bit of register 2.
2. Direct Addressing Mode
In direct addressing mode the address of operand is specified by an 8-bit address in the
instruction.
Using this instruction one can access internal data RAM and SFRs, directly. Internal RAM
uses address from 00H to 7FH to address each byte. The SFR addresses exits from 80Hto
FFH
For example:-
MOVA, 80H : copy data from the port 0 to register A
MOV 80H, A : copy data from register A to port 0
MOV 0F0, 12H: copy data from RAM location 12H to register B
3. Indirect Addressing Mode

In indirect addressing mode instruction specifies a register which holds address of the
operand.
In this mode only register R0 or R1 may be used to hold the address of one of the data
location RAM from address 00H to FFH.
For example:-
MOV A, @ R0 : copy content of memory location, whose address is specified in R0
select bank to accumulator
ADDA, @ R0 : add the content of memory location, whose address is specified in R1
and accumulator .Store the result in A.
ANLA, @ R0 : AND each bit of A with same bit of contents of the address contained in R0.
Store result in A.
4. Register Specific Addressing Mode
In the register specific mode, the operand is specified by certain specific registers such as
accumulator or DPTR.
For example:-
SWAP A : SWAP nibbles within the accumulator.
DAA : Decimal Adjust Accumulator
RR A : Rotate the content of accumulator to the right.
5. Immediate Addressing Mode
In immediate addressing mode the operand is specified within the instruction itself. In this
“DATA” is the part of instruction.
For examples:
MOV A, # 30H : move data 30H immediately to accumulator.

MOV B, #50H : move data 50H immediately to accumulator.
MOV P1, # 00H : move data 00H immediately to port1.
6 .Indexed Addressing Mode
In the indexed addressing mode only the program memory can be accessed. The program
memory can only be read.
This addressing mode can only be preferred for reading looks up tables in the program
memory.
Either the DPTR or PC can be used as INDEX register.
For example:-
MOVC A, @ A+ DPTR : copy the code byte, found at the ROM address formed by adding
A and the DPTR, to A.
MOVC A, @ A +C : copy the code byte, found at the ROM address formed by adding A
and the PC, to A
CODE:
#include <REG2051.H>.
#define stepper P1
void delay();
void main(){
while(1){
stepper = 0x0C;
delay();
stepper = 0x06;
delay();
stepper = 0x03;
delay();
stepper = 0x09;

delay();
}
}
void delay(){
unsigned char i,j,k;
for(i=0;i<6;i++)
for(j=0;j<255;j++)
for(k=0;k<255;k++);
}
►Assembly Programming
CODE:
org 0H
stepper equ P1
main:
mov stepper, #0CH
acall delay
mov stepper, #06H
acall delay
mov stepper, #03H
acall delay
mov stepper, #09H
acall delay
sjmp main
delay:
mov r7,#4

wait2:
mov r6,#0FFH
wait1:
mov r5,#0FFH
wait:
djnz r5,wait
djnz r6,wait1
djnz r7,wait2
ret
end
The working of the above code can be seen in the demo below.
Fig 16: Interfacing of stepper
motor with micro-controller
►Programming Half step Sequence
►C Programming
Just the main routine changes rest everything remains same, we mean same delay routine.
CODE:

void main(){
while(1){
stepper = 0x08;
delay();
stepper = 0x0C;
delay();
stepper = 0x04;
delay();
stepper = 0x06;
delay();
stepper = 0x02;
delay();
stepper = 0x03;
delay();
stepper = 0x01;
delay();
stepper = 0x09;
delay();
}
}
Here also the main routine changes rest everything remains same.
CODE:
main:
mov stepper, #08H
acall delay
mov stepper, #0CH
acall delay
mov stepper, #04H
acall delay
mov stepper, #06H
acall delay

mov stepper, #02H
acall delay
mov stepper, #03H
acall delay
mov stepper, #01H
acall delay
mov stepper, #09H
acall delay
sjmp main
The working of the above code can be seen in the demo animation below.
Fig 17: Interfacing of unipolar stepper motor with microcontroller
►Programming for 2-wire connection of Unipolar Stepper Motor
►C Programming
CODE:
void main(){
while(1){
stepper = 0x03;

delay();
stepper = 0x01;
delay();
stepper = 0x00;
delay();
stepper = 0x02;
delay();
}
}
CODE:
main:
mov stepper, #03H
acall delay
mov stepper, #01H
acall delay
mov stepper, #00H
acall delay
mov stepper, #02H
acall delay
sjmp main
The working of the above code can be seen in the demo animation below.

Fig 18:interfacing of bipolar stepper motor with microcontroller
►Programming for Bipolar Stepper Motor
►C Programming
CODE:
void main(){
while(1){
stepper = 0x08;
delay();

stepper = 0x02;
delay();
stepper = 0x04;
delay();
stepper = 0x01;
delay();
}
}
CODE:
main:
mov stepper, #08H
acall delay
mov stepper, #02H
acall delay
mov stepper, #04H
acall delay
mov stepper, #01H
acall delay
sjmp main
4.10 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.

Electronic voltage regulators are found in devices such as computer power supplies where
they stabilize the DC voltages used by the processor and other elements.
In electronics, a linear regulator is a voltage regulator based on an active device (such as a
bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear
region" (in contrast, a switching regulator is based on a transistor forced to act as an on/off
switch) or passive devices like zener diodes operated in their breakdown region. The
regulating device is made to act like a variable resistor, continuously adjusting a voltage
divider network to maintain a constant output voltage. It is very inefficient compared to a
switched-mode power supply, since it sheds the difference voltage by dissipating heat.
Overview of Regulator
The transistor (or other device) is used as one half of a potential divider to control the output
voltage, and a feedback circuit compares the output voltage to a reference voltage in order to
adjust the input to the transistor, thus keeping the output voltage reasonably constant. This is
inefficient: since the transistor is acting like a resistor, it will waste electrical energy by
converting it to heat. In fact, the power loss due to heating in the transistor is the current
times the voltage dropped across the transistor.
Linear regulators exist in two basic forms: series regulators and shunt regulators.
• Series regulators are the more common form. The series regulator works by providing
a path from the supply voltage to the load through a variable resistance (the main
transistor is in the "top half" of the voltage divider). The power dissipated by the
regulating device is equal to the power supply output current times the voltage drops
in the regulating device.
• The shunt regulator works by providing a path from the supply voltage to ground
through a variable resistance (the main transistor is in the "bottom half" of the voltage
divider). The current through the shunt regulator is diverted away from the load and
flows uselessly to ground, making this form even less efficient than the series
regulator. It is, however, simpler, sometimes consisting of just a voltage-reference
diode, and is used in very low-powered circuits where the wasted current is too small
to be of concern. This form is very common for voltage reference circuits.

All linear regulators require an input voltage at least some minimum amount higher than the
desired output voltage. That minimum amount is called the dropout voltage. For example, a
common regulator such as the 7805 has an output voltage of 5V, but can only maintain this if
the input voltage remains above about 7V, before the output voltage begins sagging below
the rated output. Its dropout voltage is therefore 7V - 5V = 2V. When the supply voltage is
less than about 2V above the desired output voltage, as is the case in low-voltage
microprocessor power supplies, so-called low dropout regulators (LDOs) must be used.
When one wants an output voltage higher than the available input voltage, no linear regulator
will work (not even an LDO). In this situation, a switching regulator must be used.
Fixed Regulator
"Fixed" three-terminal linear regulators are commonly available to generate fixed voltages of
plus 3 V, and plus or minus 5 V, 6V, 9 V, 12 V, or 15 V when the load is less than 1.5
amperes.
The "78xx" series (7805, 7812, etc.) regulate positive voltages while the "79xx" series (7905,
7912, etc.) regulate negative voltages. Often, the last two digits of the device number are the
output voltage; eg, a 7805 is a +5 V regulator, while a 7915 is a -15 V regulator. There are
variants on the 78xx series ICs, such as 78L and 78S, some of which can supply up to 1.5
Amps.

Adjusting fixed regulators:
Several ways are used to make fixed IC regulators adjustable.
A zener diode or resistor is added between the IC's ground terminal and ground. Resistors are
acceptable where ground current is constant, but are ill-suited to regulators with varying
ground current. Switching in different zeners, diodes or resistors can be used to obtain
stepwise adjustment.
A potentiometer can be placed in series with the ground terminal to variably increase the
output voltage. This degrades regulation, and is not suitable for regulators with varying
ground current.
Fig 19: Common IC’s
Operation
For output voltages not provided by standard fixed regulators and load currents of less than 7
amperes, commonly available "adjustable" three-terminal linear regulators may be used. An
adjustable regulator generates a fixed low nominal voltage between its output and its 'adjust'
terminal (equivalent to the ground terminal in a fixed regulator). The "317" series (+1.25V)
regulates positive voltages while the "337" series (-1.25V) regulates negative voltages.
Adjustable voltage regulator circuit showing 'adjust' terminal
The adjustment is performed by constructing a potential divider with its ends between the
regulator output and ground, and its centre-tap connected to the 'adjust' terminal of the
regulator. The ratio of resistances determines the output voltage using the same feedback
mechanisms described earlier.

Complex power requirements (e.g., op-amp circuits needing matched positive and negative
DC supplies) are more difficult, but single IC dual tracking adjustable regulators are
available. Some even have selectable current limiting as well. An example is the 419x series.
Note that some regulators, like the LM317, require a minimum load.
Component List
• 7805 regulator IC
• 1000uF electrolytic capacitor, at least 25V voltage rating
• 10 uF electrolytic capacitor, at least 6V voltage rating
• 100 nF ceramic or polyester capacitor
Fig 20: Operation of a regulator

Fig 21: Pin out of the 7805 regulator IC.
1. Unregulated voltage in
2. Ground
3. Regulated voltage out
Protection
Linear IC voltage regulators may include a variety of protection methods:
• current limiting
• fold back
• thermal shutdown
• safe area protection
Sometimes external protection is used, such as crowbar protection.
4.11 SWITCH
In electronics, a switch is an electrical component that can break an electrical circuit,
interrupting the current or diverting it from one conductor to another. The most familiar form
of switch is a manually operated electromechanical device with one or more sets of electrical
contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts

are touching and electricity can flow between them, or 'open', meaning the contacts are
separated and non conducting.
A switch may be directly manipulated by a human as a control signal to a system, such as a
computer keyboard button, or to control power flow in a circuit.
The simplest type of switch is one where two electrical conductors are brought in contact
with each other by the motion of an actuating mechanism. Other switches are more complex,
containing electronic circuits able to turn on or off depending on some physical stimulus
(such as light or magnetic field) sensed. In any case, the final output of any switch will be (at
least) a pair of wire-connection terminals that will either be connected together by the
switch's internal contact mechanism ("closed"), or not connected together ("open").
Any switch designed to be operated by a person is generally called a hand switch, and they
are manufactured in several varieties:
Fig 22: Symbol of toggle switch
The common light switch used in household wiring is an example of a toggle switch. Most
toggle switches will come to rest in any of their lever positions, while others have an internal
spring mechanism returning the lever to a certain normal position, allowing for what is called
"momentary" operation.
Fig 22: Symbol of pushbutton switch
Pushbutton switches are two-position devices actuated with a button that is pressed and
released. Most pushbutton switches have an internal spring mechanism returning the button
to its "out," or "unpressed," position, for momentary operation. Some pushbutton switches
will latch alternately on or off with every push of the button. Other pushbutton switches will

stay in their "in," or "pressed," position until the button is pulled back out. This last type of
pushbutton switches usually has a mushroom-shaped button for easy push-pull action.
Fig 24: Symbol of selector switch
Selector switches are actuated with a rotary knob or lever of some sort to select one of two or
more positions. Like the toggle switch, selector switches can either rest in any of their
positions or contain spring-return mechanisms for momentary operation.
Fig 25: Symbol of joystick switch
A joystick switch is actuated by a lever free to move in more than one axis of motion. One or
more of several switch contact mechanisms are actuated depending on which way the lever is
pushed, and sometimes by how far it is pushed. The circle-and-dot notation on the switch
symbol represents the direction of joystick lever motion required to actuate the contact.
Joystick hand switches are commonly used for crane and robot control.
Some switches are specifically designed to be operated by the motion of a machine rather
than by the hand of a human operator. These motion-operated switches are commonly called
limit switches, because they are often used to limit the motion of a machine by turning off the
actuating power to a component if it moves too far. As with hand switches, limit switches
come in several varieties:
Fig 26: Symbol of lever actuator limit switch

These limit switches closely resemble rugged toggle or selector hand switches fitted with a
lever pushed by the machine part. Often, the levers are tipped with a small roller bearing,
preventing the lever from being worn off by repeated contact with the machine part.
Fig 27: Symbol of proximity switch
Proximity switches sense the approach of a metallic machine part either by a magnetic or
high-frequency electromagnetic field. Simple proximity switches use a permanent magnet to
actuate a sealed switch mechanism whenever the machine part gets close (typically 1 inch or
less). More complex proximity switches work like a metal detector, energizing a coil of wire
with a high-frequency current, and electronically monitoring the magnitude of that current. If
a metallic part (not necessarily magnetic) gets close enough to the coil, the current will
increase, and trip the monitoring circuit. The symbol shown here for the proximity switch is
of the electronic variety, as indicated by the diamond-shaped box surrounding the switch. A
non-electronic proximity switch would use the same symbol as the lever-actuated limit
switch.
Another form of proximity switch is the optical switch, comprised of a light source and
photocell. Machine position is detected by either the interruption or reflection of a light beam.
Optical switches are also useful in safety applications, where beams of light can be used to
detect personnel entry into a dangerous area.
In many industrial processes, it is necessary to monitor various physical quantities with
switches. Such switches can be used to sound alarms, indicating that a process variable has
exceeded normal parameters, or they can be used to shut down processes or equipment if
those variables have reached dangerous or destructive levels. There are many different types
of process switches:

Fig 28: Symbol of speed switch
These switches sense the rotary speed of a shaft either by a centrifugal weight mechanism
mounted on the shaft, or by some kind of non-contact detection of shaft motion such as
optical or magnetic.
Fig 29: Symbol of pressure switch
Gas or liquid pressure can be used to actuate a switch mechanism if that pressure is applied to
a piston, diaphragm, or bellows, which converts pressure to mechanical force.
Fig 30: Symbol of temperature switch
An inexpensive temperature-sensing mechanism is the "bimetallic strip:" a thin strip of two
metals, joined back-to-back, each metal having a different rate of thermal expansion. When
the strip heats or cools, differing rates of thermal expansion between the two metals causes it
to bend. The bending of the strip can then be used to actuate a switch contact mechanism.
Other temperature switches use a brass bulb filled with either a liquid or gas, with a tiny tube
connecting the bulb to a pressure-sensing switch. As the bulb is heated, the gas or liquid
expands, generating a pressure increase which then actuates the switch mechanism.
Fig 31: Symbol of liquid level switch

A floating object can be used to actuate a switch mechanism when the liquid level in an tank
rises past a certain point. If the liquid is electrically conductive, the liquid itself can be used
as a conductor to bridge between two metal probes inserted into the tank at the required
depth. The conductivity technique is usually implemented with a special design of relay
triggered by a small amount of current through the conductive liquid. In most cases it is
impractical and dangerous to switch the full load current of the circuit through a liquid.
Level switches can also be designed to detect the level of solid materials such as wood chips,
grain, coal, or animal feed in a storage silo, bin, or hopper. A common design for this
application is a small paddle wheel, inserted into the bin at the desired height, which is slowly
turned by a small electric motor. When the solid material fills the bin to that height, the
material prevents the paddle wheel from turning. The torque response of the small motor than
trips the switch mechanism. Another design uses a "tuning fork" shaped metal prong, inserted
into the bin from the outside at the desired height. The fork is vibrated at its resonant
frequency by an electronic circuit and magnet/electromagnet coil assembly. When the bin
fills to that height, the solid material dampens the vibration of the fork, the change in
vibration amplitude and/or frequency detected by the electronic circuit.
Fig 32: Symbol of liquid flow switch
Inserted into a pipe, a flow switch will detect any gas or liquid flow rate in excess of a certain
threshold, usually with a small paddle or vane which is pushed by the flow. Other flow
switches are constructed as differential pressure switches, measuring the pressure drop across
a restriction built into the pipe.
Another type of level switch, suitable for liquid or solid material detection, is the nuclear
switch. Composed of a radioactive source material and a radiation detector, the two are
mounted across the diameter of a storage vessel for either solid or liquid material. Any height
of material beyond the level of the source/detector arrangement will attenuate the strength of
radiation reaching the detector. This decrease in radiation at the detector can be used to
trigger a relay mechanism to provide a switch contact for measurement, alarm point, or even
control of the vessel level.

Switch Contact Design
A switch can be constructed with any mechanism bringing two conductors into contact with
each other in a controlled manner. This can be as simple as allowing two copper wires to
touch each other by the motion of a lever, or by directly pushing two metal strips into contact.
However, a good switch design must be rugged and reliable, and avoid presenting the
operator with the possibility of electric shock. Therefore, industrial switch designs are rarely
this crude.
The conductive parts in a switch used to make and break the electrical connection are called
contacts. Contacts are typically made of silver or silver-cadmium alloy, whose conductive
properties are not significantly compromised by surface corrosion or oxidation. Gold contacts
exhibit the best corrosion resistance, but are limited in current-carrying capacity and may
"cold weld" if brought together with high mechanical force. Whatever the choice of metal,
the switch contacts are guided by a mechanism ensuring square and even contact, for
maximum reliability and minimum resistance.
Contacts such as these can be constructed to handle extremely large amounts of electric
current, up to thousands of amps in some cases. The limiting factors for switch contact
ampacity are as follows:
• Heat generated by current through metal contacts (while closed).
• Sparking caused when contacts are opened or closed.
• The voltage across open switch contacts (potential of current jumping across the gap).
One major disadvantage of standard switch contacts is the exposure of the contacts to the
surrounding atmosphere. In a nice, clean, control-room environment, this is generally not a
problem. However, most industrial environments are not this benign. The presence of
corrosive chemicals in the air can cause contacts to deteriorate and fail prematurely. Even
more troublesome is the possibility of regular contact sparking causing flammable or
explosive chemicals to ignite.
When such environmental concerns exist, other types of contacts can be considered for small
switches. These other types of contacts are sealed from contact with the outside air, and
therefore do not suffer the same exposure problems that standard contacts do.

A common type of sealed-contact switch is the mercury switch. Mercury is a metallic
element, liquid at room temperature. Being a metal, it possesses excellent conductive
properties. Being a liquid, it can be brought into contact with metal probes (to close a circuit)
inside of a sealed chamber simply by tilting the chamber so that the probes are on the bottom.
Many industrial switches use small glass tubes containing mercury which are tilted one way
to close the contact, and tilted another way to open. Aside from the problems of tube
breakage and spilling mercury (which is a toxic material), and susceptibility to vibration,
these devices are an excellent alternative to open-air switch contacts wherever environmental
exposure problems are a concerm.
Push Button Switches
A push-button (also spelled pushbutton) (press-button in the UK) or simply button is a simple
switch mechanism for controlling some aspect of a machine or a process. Buttons are
typically made out of hard material, usually plastic or metal. The surface is usually flat or
shaped to accommodate the human finger or hand, so as to be easily depressed or pushed.
Buttons are most often biased switches, though even many un-biased buttons (due to their
physical nature) require a spring to return to their un-pushed state. Different people use
different terms for the "pushing" of the button, such as press, depress, mash, and punch.
Fig 32: Contact (Normal) State & Make/Break Sequence
Any kind of switch contact can be designed so that the contacts "close" (establish continuity)
when actuated, or "open" (interrupt continuity) when actuated. For switches that have a
spring-return mechanism in them, the direction that the spring returns it to with no applied

force is called the normal position. Therefore, contacts that are open in this position are called
normally open and contacts that are closed in this position are called normally closed.
For process switches, the normal position, or state, is that which the switch is in when there is
no process influence on it. An easy way to figure out the normal condition of a process switch
is to consider the state of the switch as it sits on a storage shelf, uninstalled. Here are some
examples of "normal" process switch conditions:
• Speed switch: Shaft not turning
• Pressure switch: Zero applied pressure
• Temperature switch: Ambient (room) temperature
• Level switch: Empty tank or bin
• Flow switch: Zero liquid flow
It is important to differentiate between a switch's "normal" condition and its "normal" use in
an operating process. Consider the example of a liquid flow switch that serves as a low-flow
alarm in a cooling water system. The normal, or properly-operating, condition of the cooling
water system is to have fairly constant coolant flow going through this pipe. If we want the
flow switch's contact to close in the event of a loss of coolant flow (to complete an electric
circuit which activates an alarm siren, for example), we would want to use a flow switch with
normally-closed rather than normally-open contacts. When there's adequate flow through the
pipe, the switch's contacts are forced open; when the flow rate drops to an abnormally low
level, the contacts return to their normal (closed) state. This is confusing if you think of
"normal" as being the regular state of the process, so be sure to always think of a switch's
"normal" state as that which it's in as it sits on a shelf.
The schematic symbology for switches vary according to the switch's purpose and actuation.
A normally-open switch contact is drawn in such a way as to signify an open connection,
ready to close when actuated. Conversely, a normally-closed switch is drawn as a closed
connection which will be opened when actuated. Note the following symbols:

Fig 33: Push button switch in open and closed situation
Uses
The "push-button" has been utilized in calculators, push-button telephones, kitchen
appliances, and various other mechanical and electronic devices, home and commercial.
In industrial and commercial applications, push buttons can be linked together by a
mechanical linkage so that the act of pushing one button causes the other button to be
released. In this way, a stop button can "force" a start button to be released. This method of
linkage is used in simple manual operations in which the machine or process have no
electrical circuits for control.
Pushbuttons are often color-coded to associate them with their function so that the operator
will not push the wrong button in error. Commonly used colors are red for stopping the
machine or process and green for starting the machine or process.
Red pushbuttons can also have large heads (called mushroom heads) for easy operation and
to facilitate the stopping of a machine. These pushbuttons are called emergency stop buttons
and are mandated by the electrical code in many jurisdictions for increased safety. This large
mushroom shape can also be found in buttons for use with operators who need to wear gloves
for their work and could not actuate a regular flush-mounted push button. As an aid for
operators and users in industrial or commercial applications, a pilot light is commonly added
to draw the attention of the user and to provide feedback if the button is pushed. Typically
this light is included into the center of the pushbutton and a lens replaces the pushbutton hard
center disk. The source of the energy to illuminate the light is not directly tied to the contacts
on the back of the pushbutton but to the action the pushbutton controls. In this way a start
button when pushed will cause the process or machine operation to be started and a

secondary contact designed into the operation or process will close to turn on the pilot light
and signify the action of pushing the button caused the resultant process or action to start.
In popular culture, the phrase "the button" (sometimes capitalized) refers to a (usually
fictional) button that a military or government leader could press to launch nuclear weapons.
4.12 CRYSTALS
Pin no 18 and 19 is connected to external crystal oscillator to provide a clock to the circuit.
Whenever ever we are using crystals we need to put the capacitor behind it to make it free
from noises. It is good to go for a 33pf capacitor.
Fig 34: A Crystal
We can also resonators instead of costly crystal which are low cost and external capacitor can
be avoided. But the frequency of the resonators varies a lot. And it is strictly not advised
when used for communications projects.
4.13 DIODE
In electronics, a diode is a two-terminal electronic component that conducts electric current in
only one direction. The term usually refers to a semiconductor diode, the most common type
today. This is a crystalline piece of semiconductor material connected to two electrical
terminals. A vacuum tube diode (now little used except in some high-power technologies) is
a vacuum tube with two electrodes: a plate and a cathode.
The most common function of a diode is to allow an electric current to pass in one direction
(called the diode's forward direction), while blocking current in the opposite direction (the
reverse direction). Thus, the diode can be thought of as an electronic version of a check

valve. This unidirectional behavior is called rectification, and is used to convert alternating
current to direct current, and to extract modulation from radio signals in radio receivers.
However, diodes can have more complicated behavior than this simple on-off action. This is
due to their complex non-linear electrical characteristics, which can be tailored by varying the
construction of their P-N junction. These are exploited in special purpose diodes that perform
many different functions. For example, specialized diodes are used to regulate voltage (Zener
diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio
frequency oscillations (tunnel diodes), and to produce light (light emitting diodes). Tunnel
diodes exhibit negative resistance, which makes them useful in some types of circuits.
Diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying
abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor
diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals
such as galena. Today most diodes are made of silicon, but other semiconductors such as
germanium are sometimes used.
Semiconductor diodes
Figure 35: A typical packages in same alignment as diode symbol. Thin bar depicts the
cathode.
A modern semiconductor diode is made of a crystal of semiconductor like silicon that has
impurities added to it to create a region on one side that contains negative charge carriers
(electrons), called n-type semiconductor, and a region on the other side that contains positive
charge carriers (holes), called p-type semiconductor. The diode's terminals are attached to
each of these regions. The boundary within the crystal between these two regions, called a
PN junction, is where the action of the diode takes place. The crystal conducts a current of
electrons in a direction from the N-type side (called the cathode) to the P-type side (called the
anode), but not in the opposite direction; that is, a conventional current flows from anode to
cathode (opposite to the electron flow, since electrons have negative charge).

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