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A MAJOR PROJECT SYNOPSISON

SERIAL PORT OPERATE FORHOME APPLIANCES

USING COMPUTERSubmitted to: Submitted by:Mr. Ashish Awasthi Arvind Kumar Verma

H.O.D Roll No. 0922131008(Department of Electroics & Abhishek Singh YadavCommunication Engg.) Roll No. 0922131001

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Triloki Chand

Roll No. 0922131047

Acknowledgement

First of all, I express my deep sense of gratitude

and devotion of God almighty without whose help andwish everything were just impossible .

My present report is the result blessings and well wishes of my teachers. I

wish to express my grateful thanks to teacher Mr. ASHISH AWASTHI, H.O.D of

E&C.I.E.T Sitapur under whose enlighten guidance and supervision. I could

able to complete the report.

Finally, I am hearty obliged to my teacher Mr. ASHISH AWASTHI for

their constant operation and patience .

SUBMITTED BY

Krishna Kumar Yadav

Roll no. 0922131021

Pramit Srivastava

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Roll no. 0922131027

Date.. I.E.T Resora, Sitapur

ABSTRACT

Traditionally electrical appliances in a home are controlled

via switches that regulate the electricity to these devices. As the

world gets more and more technologically advanced, we find

new technology coming in deeper and deeper into our personal

lives even at home. Home automation is becoming more andmore popular around the world and is becoming a common

practice. The process of home automation works by making

everything in the house automatically controlled using

technology to control and do the jobs that we would normally

do manually. Home automation takes care of a lot of different

activities in the house. this project we propose a unique System

for Home automation utilizing Dual Tone Multi Frequency

(DTMF) that is paired with a wireless module to provideseamless wireless control over many devices in a house. The

block diagram is a shown below. This user console has many

keys , each corresponding to the device that needs to be

activated. The encoder encodes the user choice and sends via a

FM transmitter. The FM receiver receives the modulated signal

and demodulates it and the user choice is determined by the

DTMF decoder. Based upon this the required appliance is

triggered.

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Table of Contents

Chapter 1

I. INTRODUCTION..8

II. COMPONENTS.11

III. CIRCUIT DIAGRAM OF INDUSTRIALAUTOMATION.13

IV. BLOCK DIAGRAM OF INDUSTRIAL

AUTOMATION.14

Chapter 2

I. A BRIEF INTRODUCTION TO 8051

MICROCONTROLLER.15II. AT89S5215

III. PIN DIAGRAM..17

IV. BLOCK DIAGRAM...19

V. PIN DESCRIPTION...20

Chapter 3

I. Printed circuit board ...24

II. Reliment pin with base25

Chapter 4

I. MT 8870...27

II. PIN DIAGRAM27

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I. CAPICITOR

II. 1000 F 25 V.47

III. 470 F 25 V...49

IV. 10 F 25 V.49V. 0.1 F 25 V50

VI. 33 pF Cap..50

VII. 22 pF Cap..51

Chapter 9

I. RESISTOR53

II. UNITS54III. ELECTRONIC SYMBOLS AND NOTATION55

IV. THEORY OF OPERATION..56

V. POWER DISSIPATION.59

VI. 10 K pot...61

VII. CRYSTAL...62

VIII. CRYSTAL STRUCTURE ..62

IX. 2 PIN MICRO SWITCHS64

X. CONSTRUCTION AND OPERATION..65

XI. APPLICATION....66

XII. DIODE..67

Chapter 10

POWER SUPPLY..71

REFERENCES 82

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INTRODUCTION

The aim of the proposed system is to develop a cost effective

solution that will provide controlling of industral appliances remotely

and enable industrial security against intrusion in the absence of

industry. The system provides availability due to development of a

low cost system. The industrial control system with an affordable

cost was thought to be built that should be mobile providing remote

access to the appliances and allowing industrial security. Though

devices connected as industrial and office appliances consume

electrical power. These devices should be controlled as well as turn

on/off if required. Most of the times it was done manually. Now it is

a necessity to control devices more effectively and efficiently at

anytime from anywhere.

In this system, we are going to develop a cellular phone based

industrial /office appliance. This system is designed for controlling

arbitrary devices, it includes a cell phone (not included with the

system kit, end user has to connect his/her cell phone to the system)

which is connect to the system via head set. To active the cellular

phone unit on the system a call is to be made and as the call is

answered, in response the user would enter a two/three digit

password to access the system to control devices. As the caller press

the specific password, it results in turning ON or OFF specific

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device. The device switching is achieved by Relays. Security

preserved because these dedicated passwords owned and known by

selected persons only. For instance, our system contains an alarm

unit giving the user a remote on/off mechanism, which is capable ofinforming up to five different numbers over telephony network about

the nature of the event.

The underlying principle mainly relies up on the ability of DTMF

(Double Tune Multi Frequency) ICs to generate DTMF

corresponding to a number or code in the number pad and to detect

the same number or code from its corresponding DTMF. In detail, a

DTMF generator generates two frequencies corresponding to anumber or code in the number pad which will be transmitted through

the communication networks, constituting the transmitter section

which is simply equivalent to a mobile set. In the receiver part, the

DTMF detector IC, for example IC MT 8870 detects the number or

code represented by DTMF back, through the inspection of the two

transmitted frequencies. The DTMF frequencies representing the

number/ codes are shown below.Imagine a high-end home security system with no monthly

maintenance fees, made possible using an list of automatically

contacted phone numbers, synthetic speech and dual-tone detection

to interface with the owner via a phone connection. The

implementation of such a system requires a home phone line, a cell

phone or touch-tone phone, and a power supply to reliably monitor a

home utilizing motion, door, window, and fire sensors.

The home industrial line is used to contact trusted parties at specified

phone numbers in the event of a fire alarm or security issue. For

example, if the window sensor gets tripped and no password is

entered at the keypad, the system will call the owner and indicate

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that the window sensor was tripped. The owner can then listen to

what is happening inside the industrial with microphones near each

sensor that transmit through the phone line when that sensor is

triggered. The owner can then communicate with whomever is insidethe house through the use of a speaker phone built into the system. If

the security system cannot contact the owner, it will use an internal

ordered list of other numbers to make further backup calls. The

contacted party can then take immediate action, such as calling a

neighbor or the police. When there is a security problem the owner

will be the first to know and have the ability to have control of the

situation with the use of their cell phone.

Settings on the security system or industrial automation system can

be changed at home or by cell phone. The base system at the

industrial includes a keypad and LCD screen for on-site use. Internal

menus are displayed on the screen and can be navigated once the

admin password has been verified. Non-admin passwords can only

be used to arm and disarm the system. Options with an admin

password include adding, deleting and reordering phone numbers inthe call list, adding or deleting passwords, changing the admin

password, arming or disarming the system, and adjusting automatic

temperature controls.

Industrial automation is closely related to a security system such as

this, and is intended to be added to the base package. With

automation features a homeowner can remotely toggle appliances

such as air conditioning and heating units, lamps or porch lights,landscape sprinkler timers, snow-melt systems, outdoor property

lighting, and safety lighting. Any of these features could be added

using the existing relays in this system.

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COMPONENTS

NAME QUANTITYPCB 1

Reliment 2 pin with base 2

Reliment 16 pin with base 2

40 pin IC base 118 pin IC base 1

16 pin IC base 1

14 pin IC base 1

MT 8870 1

AT 89C51 1

ULN 2003 1

7404 1

7805 11000F 25V 1

470F 25V 1

10F 25V 1

0.1F Ceramic 2

33pF Cap 2

22pF Cap 2

Resistor 1M 1

Resistor 100K 1

Resistor 330K 1

Resistor 1K 6

Resistor 10K 6

10K pot 1

3.5795MHz Crystal 1

12MHz Crystal 1

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LCD 16*2 1

2pin micro switch 1

Transformer 0-12, 1A 1

5pin relay 12volt 4

Relay external conectors 4diodeIN4007 4

led 6

Headphone 3.5mm 1

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CIRCUIT DIAGRAM

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A BRIEF INTRODUCTION TO 8051

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MICROCONTROLLER:

When we have to learn about a new computer we have to familiarize

about the machine capability we are using, and we can do it by

studying the internal hardware design (devices architecture), and alsoto know about the size, number and the size of the registers.

A microcontroller is a single chip that contains the processor (the

CPU), non-volatile memory for the program (ROM or flash), volatile

memory for input and output (RAM), a clock and an I/O control unit.

Also called a "computer on a chip," billions of microcontroller units

(MCUs) are embedded each year in a myriad of products from toys

to appliances to automobiles. For example, a single vehicle can use70 or more microcontrollers. The following picture describes a

general block diagram of microcontroller.

AT89S52:The AT89S52 is a low-power, high-performance

CMOS 8-bit microcontroller with 8K bytes of in-system

programmable Flash memory. The device is manufactured using

Atmels high-density nonvolatile memory technology and is

compatible with the industry-standard 80C51 instruction set and pin

out. The on-chip Flash allows the program memory to be

reprogrammed in-system or by a conventional nonvolatile memory

programmer. By combining a versatile 8-bit CPU with in-system

programmable Flash on a monolithic chip, the Atmel AT89S52 is a

powerful microcontroller, which provides a highly flexible and cost-

effective solution to many, embedded control applications. The

AT89S52 provides the following standard features: 8K bytes of

Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two datapointers, three 16-bit timer/counters, a six-vector two-level interrupt

architecture, a full duplex serial port, on-chip oscillator, and clock

circuitry. In addition, the AT89S52 is designed with static logic for

operation down to zero frequency and supports two software

selectable power saving modes. The Idle Mode stops the CPU while

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allowing the RAM, timer/counters, serial port, and interrupt system

to continue functioning. The Power-down mode saves the RAM con-

tents but freezes the oscillator, disabling all other chip functions until

the next interrupt.

The hardware is driven by a set of program instructions, or software.

Once familiar with hardware and software, the user can then apply

the microcontroller to the problems easily.

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The pin diagram of the 8051 shows all of the input/output

pins unique to microcontrollers:

The following are some of the capabilities of 8051 microcontroller.

1. Internal ROM and RAM

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2. I/O ports with programmable pins

3. Timers and counters

4. Serial data communication

The 8051 architecture consists of these specific features:

16 bit PC &data pointer (DPTR)

8 bit program status word (PSW)

8 bit stack pointer (SP)

Internal ROM 4k

Internal RAM of 128 bytes.

4 register banks, each containing 8 registers

80 bits of general purpose data memory

32 input/output pins arranged as four 8 bit ports: P0-P3

Two 16 bit timer/counters: T0-T1

Two external and three internal interrupt sources Oscillator and

clock circuits.

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Printed circuit board

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

electrically connect electronic components using conductive

pathways, tracks or signal traces etched from copper sheets

laminated onto a non-conductive substrate. When the board has only

copper tracks and features, and no circuit elements such as

capacitors, resistors or active devices have been manufactured into

the actual substrate of the board, it is more correctly referred to as

printed wiring board (PWB) or etched wiring board. Use of the term

PWB or printed wiring board although more accurate and distinct

from what would be known as a true printed circuit board, hasgenerally fallen by the wayside for many people as the distinction

between circuit and wiring has become blurred. Today printed wiring

(circuit) boards are used in virtually all but the simplest

commercially produced electronic devices, and allow fully

automated assembly processes that were not possible or practical in

earlier era tag type circuit assembly processes.

A PCB populated with electronic components is called a printed

circuit assembly (PCA), printed circuit board assembly or PCB

Assembly (PCBA). In informal use the term "PCB" is used both for

bare and assembled boards, the context clarifying the meaning.

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

construction. PCBs must initially be designed and laid out, but

become cheaper, faster to make, and potentially more reliable forhigh-volume production since production and soldering of PCBs can

be automated. Much of the electronics industry's PCB design,

assembly, and quality control needs are set by standards published by

the IPC organization.

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Reliment pin with base

An electrical connector is an electro-mechanical device for joining

electrical circuits as an interface using a mechanical assembly. The

connection may be temporary, as for portable equipment, require a

tool for assembly and removal, or serve as a permanent electrical

joint between two wires or devices.[1]

There are hundreds of types of electrical connectors. Connectors mayjoin two lengths of flexible copper wire or cable, or connect a wire or

cable or optical interface to an electrical terminal.

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MT 8870

PIN DIAGRAM:

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BLOCK DIAGRAM:

Features

Complete DTMF Receiver

Low power consumption

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Internal gain setting amplifier

Adjustable guard time

Central office quality

Power-down mode

Inhibit mode

Backward compatible with MT8870C/MT8870C-1

Applications

Receiver system for British Telecom (BT) or CEPT Spec(MT8870D-1)

Paging systems

Repeater systems/mobile radio

Credit card systems

Remote control

Personal computers

Telephone answering machine

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Description

The MT8870D/MT8870D-1 is a complete DTMF receiver

integrating both the band -split filter and digital decoder functions.

The filter section uses switched capacitor techniques for high andlow group filters; the decoder uses digital counting techniques to

detect and decode all 16 DTMF tone-pairs into a 4-bit code. External

component count is minimized by on chip provision of a differential

input amplifier, clock oscillator and latched three-state bus interface.Pin Description

1. IN+ Non-Inverting Op-Amp (Input).

2. IN- Inverting Op-Amp (Input).

3. GS Gain Select. Gives access to output of front end

differential amplifier for connection of feedback resistor.

4. V-Ref Reference Voltage (Output).Nominally VDD/2 is used

to bias inputs at mid-rail .

5. INH Inhibit (Input). Logic high inhibits the detection of tones

representing characters A, B, C and D. This pin input is internallypulled down.

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6. PWDN Power Down (Input). Active high. Powers down the

device and inhibits the oscillator. This pin input is internally pulled

down.

7. OSC1 Clock (Input).

8. OSC2 Clock (Output). A 3.579545 MHz crystal connected

between pins OSC1 and OSC2 completes the internal oscillatorcircuit.

9. VSS Ground (Input). 0 V typical.

10. TOE Three State Output Enable (Input). Logic high enables

the outputs Q1-Q4. This pin is pulled up internally.

11-14. Q1-Q4Three State Data (Output). When enabled by TOE,

provide the code corresponding to the last valid tone-pair received

(see Table 1). When TOE is logic low, the data outputs are high

impedance.

15. StD Delayed Steering (Output).Presents a logic high when a

received tone-pair has been registered and the output latch updated;returns to logic low when the voltage on St/GT falls below VTSt.

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16. ESt Early Steering (Output). Presents a logic high once the

digital algorithm has detected a valid tone pair (signal condition).

Any momentary loss of signal condition will cause ESt to return to alogic low.

17. St/GT Steering Input/Guard time (Output) Bidirectional. A

voltage greater than VTSt detected at St causes the device to register

the detected tone pair and update the output latch. A voltage less than

VTSt frees the device to accept a new tone pair. The GT output acts

to reset the external steering time-constant; its state is a function of

ESt and the voltage on St.

18. VDD Positive power supply (Input). +5 V typical.

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ULN2003 RELAY DRIVER:

PIN DIAGRAM:

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LOGIC DIAGRAM:

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DESCRIPTION :

series base resistor for each darlington pair for operation directly

with TTL or 5V CMOS devices.The ULN2003 is a monolithic

high voltage and high current Darlington transistor arrays. It consistsof seven NPN Darlington pairs that features high-voltage outputs

with common-cathode clamp diode for switching inductive loads.

The collector-current rating of a single Darlington pair is 500mA.

The Darlington pairs may be paralleled for higher current capability.

Applications include relay drivers, hammer drivers, lampdrivers,

display drivers (LED gas discharge),line drivers, and logic buffers.The ULN2003 has a 2.7k.

FEATURES :

* 500mA rated collector current (Single output)

* High-voltage outputs: 50V

* Inputs compatible with various types of logic.

* Relay driver application.

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7404

7404 is a NOT gate IC. It consists of six inverters which perform

logical invert action. The output of an inverter is the complement of

its input logic state, i.e., when input is high its output is low and vice

versa.

Pin Diagram

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Pin Description:

Pin No Function Name

1Input/output of 1

stinverter Input1

2 Output13

Input/output of 2nd

inverter Input24 Output25

Input/output of 3rd inverter Input36 Output37 Ground (0V) Ground8

Output/input of 4th

inverter Output49 Input410

Output/input of 5th

inverter Output511 Input512

Output/input of 6

th

inverter Output6

13 Input614

Supply voltage; 5V (4.75 - 5.25

V)Vcc

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Description :

7404,a NOT gate IC with six inverters that perform logical invert

action.

I/P-O/P Table:

Pin Configuration:

Input Output

1 0

0 1

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7805

7805 is a voltage regulator integrated circuit. It is a member of 78xx

series of fixed linear voltage regulator ICs. The voltage source in a

circuit may have fluctuations and would not give the fixed voltage

output. The voltage regulator IC maintains the output voltage at a

constant value. The xx in 78xx indicates the fixed output voltage it is

designed to provide. 7805 provides +5V regulated power supply.

Capacitors of suitable values can be connected at input and output

pins depending upon the respective voltage levels.

Pin Diagram:

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Pin Description:

PinNo

Function Name

1 Input voltage (5V-18V) Input

2 Ground (0V) Ground

3 Regulated output; 5V (4.8V-5.2V) Output

The 7805 is a family of self-contained fixed linear voltage regulator

integrated circuits. The 7805 family is commonly used in electronic

circuits requiring a regulated power supply due to their ease-of-use

and low cost. For ICs within the family, the xx is replaced with two

digits, indicating the output voltage (for example, the 7805 has a 5

volt output, while the 7812 produces 12 volts). The 7805 line are

positive voltage regulators: they produce a voltage that is positive

relative to a common ground. There is a related line of 7805 devices

which are complementary negative voltage regulators. 7805 ICs can

be used in combination to provide positive and negative supply

voltages in the same circuit.

7805 ICs have three terminals and are commonly found in the

TO220 form factor, although smaller surface-mount and larger TO3

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packages are available. These devices support an input voltage

anywhere from a couple of volts over the intended output voltage, up

to a maximum of 35 to 40 volts depending on the make, and typically

provide 1 or 1.5 amperes of current (though smaller or largerpackages may have a lower or higher current rating).

Advantages

7805 series ICs do not require additional components to

provide a constant, regulated source of power, making them

easy to use, as well as economical and efficient uses of space.

Other voltage regulators may require additional components to

set the output voltage level, or to assist in the regulation

process. Some other designs (such as a switched-mode power

supply) may need substantial engineering expertise to

implement.

7805 series ICs have built-in protection against a circuit

drawing too much power. They have protection againstoverheating and short-circuits, making them quite robust in

most applications. In some cases, the current-limiting features

of the 7805 devices can provide protection not only for the

7805 itself, but also for other parts of the circuit.

Disadvantages

The input voltage must always be higher than the output

voltage by some minimum amount (typically 2 volts). This can

make these devices unsuitable for powering some devices from

certain types of power sources (for example, powering a circuit

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that requires 5 volts using 6-volt batteries will not work using a

7805).

As they are based on a linear regulator design, the input current

required is always the same as the output current. As the inputvoltage must always be higher than the output voltage, this

means that the total power (voltage multiplied by current)

going into the 7805 will be more than the output power

provided. The extra input power is dissipated as heat. This

means both that for some applications an adequate heatsink

must be provided, and also that a (often substantial) portion of

the input power is wasted during the process, rendering them

less efficient than some other types of power supplies. When

the input voltage is significantly higher than the regulated

output voltage (for example, powering a 7805 using a 24 volt

power source), this inefficiency can be a significant issue.

Even in larger packages, 7805 integrated circuits cannot supply

as much power as many designs which use discrete

components, and are generally inappropriate for applications

requiring more than a few amperes of current.

Each specific model of 7805 is designed to produce only one

fixed voltage output, so they may not be suitable for

applications requiring a configurable or varying output (For

such applications, the LM317 series of ICs are available, which

are similar to 7805 ICs but can produce a configurable voltage).

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1000 F 25 V

A capacitor (originally known as condenser) is a passive two-

terminal electrical component used to store energy in an electricfield. The forms of practical capacitors vary widely, but all

contain at least two electrical conductors separated by a dielectric

(insulator); for example, one common construction consists of

metal foils separated by a thin layer of insulating film. Capacitors

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are widely used as parts of electrical circuits in many common

electrical devices.

When there is a potential difference (voltage) across the

conductors, a static electric field develops across the dielectric,causing positive charge to collect on one plate and negative charge

on the other plate. Energy is stored in the electrostatic field. An

ideal capacitor is characterized by a single constant value,

capacitance, measured in farads. This is the ratio of the electric

charge on each conductor to the potential difference between

them.

The capacitance is greatest when there is a narrow separation

between large areas of conductor, hence capacitor conductors are

often called plates, referring to an early means of construction. In

practice, the dielectric between the plates passes a small amount

of leakage current and also has an electric field strength limit,

resulting in a breakdown voltage, while the conductors and leads

introduce an undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking

direct current while allowing alternating current to pass, in filter

networks, for smoothing the output of power supplies, in the

resonant circuits that tune radios to particular frequencies, in

electric power transmission systems for stabilizing voltage and

power flow, and for many other purposes.

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470 F 25 V

10 F 25 V

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0.1 F Ceramic

33 pF Cap

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22 pF Cap

Description: This is a very common 22pF capacitor. Used with

crystals for loading purposes. 0.1" spaced leads make this a perfect

candidate for breadboarding and perf boarding. Rated at 200V.

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Resistor

A resistor is a passive two-terminal electrical component that

implements electrical resistance as a circuit element.

The current through a resistor is in direct proportion to the voltage

across the resistor's terminals. This relationship is represented by

Ohm's law:

where I is the current through the conductor in units of amperes, V is

the potential difference measured across the conductor in units of

volts, and R is the resistance of the conductor in units of ohms.

The ratio of the voltage applied across a resistor's terminals to the

intensity of current in the circuit is called its resistance, and this can

be assumed to be a constant (independent of the voltage) for ordinary

resistors working within their ratings.

Resistors are common elements of electrical networks and electronic

circuits and are ubiquitous in electronic equipment. Practical

resistors can be made of various compounds and films, as well as

resistance wire (wire made of a high-resistivity alloy, such as nickel-

chrome). Resistors are also implemented within integrated circuits,

particularly analog devices, and can also be integrated into hybrid

and printed circuits.

The electrical functionality of a resistor is specified by its resistance:

common commercial resistors are manufactured over a range of

more than nine orders of magnitude. When specifying that resistance

in an electronic design, the required precision of the resistance may

require attention to the manufacturing tolerance of the chosen

resistor, according to its specific application. The temperature

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coefficient of the resistance may also be of concern in some

precision applications. Practical resistors are also specified as having

a maximum power rating which must exceed the anticipated power

dissipation of that resistor in a particular circuit: this is mainly ofconcern in power electronics applications. Resistors with higher

power ratings are physically larger and may require heat sinks. In a

high-voltage circuit, attention must sometimes be paid to the rated

maximum working voltage of the resistor.

Practical resistors have a series inductance and a small parallel

capacitance; these specifications can be important in high-frequency

applications. In a low-noise amplifier or pre-amp, the noisecharacteristics of a resistor may be an issue. The unwanted

inductance, excess noise, and temperature coefficient are mainly

dependent on the technology used in manufacturing the resistor.

They are not normally specified individually for a particular family

of resistors manufactured using a particular technology.[1] A family

of discrete resistors is also characterized according to its form factor,

that is, the size of the device and the position of its leads (orterminals) which is relevant in the practical manufacturing of circuits

using them.

Units

The ohm (symbol: ) is the SI unit of electrical resistance, named

after Georg Simon Ohm. An ohm is equivalent to a volt per ampere.

Since resistors are specified and manufactured over a very large

range of values, the derived units of milliohm (1 m = 103 ),

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kilohm (1 k = 103 ), and megohm (1 M = 106 ) are also in

common usage.

The reciprocal of resistance R is called conductance G = 1/R and is

measured in siemens (SI unit), sometimes referred to as a mho.Hence, siemens is the reciprocal of an ohm: . Although the concept

of conductance is often used in circuit analysis, practical resistors are

always specified in terms of their resistance (ohms) rather than

conductance.

Electronic symbols and notation

The symbol used for a resistor in a circuit diagram varies from

standard to standard and country to country. Two typical symbols areas follows;

American-style symbols IEC-style resistor symbol

(a) resistor,

(b) rheostat (variable resistor),

and

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(c) potentiometer

The notation to state a resistor's value in a circuit diagram varies, too.

The European notation avoids using a decimal separator, and

replaces the decimal separator with the SI prefix symbol for the

particular value. For example, 8k2 in a circuit diagram indicates a

resistor value of 8.2 k. Additional zeros imply tighter tolerance, for

example 15M0. When the value can be expressed without the need

for an SI prefix, an 'R' is used instead of the decimal separator. For

example, 1R2 indicates 1.2 , and 18R indicates 18 . The use of aSI prefix symbol or the letter 'R' circumvents the problem that

decimal separators tend to 'disappear' when photocopying a printed

circuit diagram.

Theory of operation

Ohm's law

The behavior of an ideal resistor is dictated by the relationshipspecified by Ohm's law:

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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:

This formulation states that the current (I) is proportional to the

voltage (V) and inversely proportional to the resistance (R). This is

directly used in practical computations. For example, if a 300 ohm

resistor is attached across the terminals of a 12 volt battery, then a

current of 12 / 300 = 0.04 amperes (or 40 milliamperes) flowsthrough that resistor.

In a series configuration, the current through all of the resistors is the

same, but the voltage across each resistor will be in proportion to its

resistance. The potential difference (voltage) seen across the networkis the sum of those voltages, thus the total resistance can be found as

the sum of those resistances:

As a special case, the resistance of N resistors connected in series,

each of the same resistance R, is given by NR.

Resistors in a parallel configuration are each subject to the same

potential difference (voltage), however the currents through them

add. The conductances of the resistors then add to determine the

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conductance of the network. Thus the equivalent resistance (Req) of

the network can be computed:

The parallel equivalent resistance can be represented in equations by

two vertical lines "||" (as in geometry) as a simplified notation.Occasionally two slashes "//" are used instead of "||", in case the

keyboard or font lacks the vertical line symbol. For the case of two

resistors in parallel, this can be calculated using:

As a special case, the resistance of N resistors connected in parallel,

each of the same resistance R, is given by R/N.

A resistor network that is a combination of parallel and seriesconnections can be broken up into smaller parts that are either one or

the other. For instance,

However, some complex networks of resistors cannot be resolved in

this manner, requiring more sophisticated circuit analysis. For

instance, consider a cube, each edge of which has been replaced by a

resistor. What then is the resistance that would be measured between

two opposite vertices? In the case of 12 equivalent resistors, it can beshown that the corner-to-corner resistance is 56 of the individual

resistance. More generally, the Y- transform, or matrix methods

can be used to solve such a problem.[2][3][4]

One practical application of these relationships is that a non-standard

value of resistance can generally be synthesized by connecting a

number of standard values in series or parallel. This can also be used

to obtain a resistance with a higher power rating than that of the

individual resistors used. In the special case of N identical resistors

all connected in series or all connected in parallel, the power rating

of the individual resistors is thereby multiplied by N.

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Power dissipation

The power P dissipated by a resistor is calculated as:

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:

Resistors are rated according to their maximum power dissipation.

Most discrete resistors in solid-state electronic systems absorb much

less than a watt of electrical power and require no attention to their

power rating. Such resistors in their discrete form, including most of

the packages detailed below, are typically rated as 1/10, 1/8, or 1/4

watt.

Resistors required to dissipate substantial amounts of power,

particularly used in power supplies, power conversion circuits, and

power amplifiers, are generally referred to as power resistors; this

designation is loosely applied to resistors with power ratings of 1

watt or greater. Power resistors are physically larger and may not use

the preferred values, color codes, and external packages described

below.

If the average power dissipated by a resistor is more than its powerrating, 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

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it can burn the circuit board or adjacent components, or even cause a

fire. There are flameproof resistors that fail (open circuit) before they

overheat dangerously.

Since poor air circulation, high altitude, or high operatingtemperatures may occur, resistors may be specified with higher rated

dissipation than will be experienced in service.

Some types and ratings of resistors may also have a maximum

voltage rating; this may limit available power dissipation for higher

resistance values.

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10 K pot

Description:

An adjustable potentiometer can open up many interesting user

interfaces. Turn the pot and the resistance changes. Connect VCC to

an outer pin, GND to the other, and the center pin will have a voltagethat varies from 0 to VCC depending on the rotation of the pot. Hook

the center pin to an ADC on a microcontroller and get a variable

input from the user!

This is a center-tap linear type potentiometer. The outer two pins will

always show 10K resistance, the center pin resistance to one of the

outer pins will vary from 10K Ohm to about 50 Ohm. The pot is

linear meaning the resistance will vary linearly with its position. This

is a good choice for general user interfaces.

This pot works great in a breadboard but on a few breadboards, you

may have to trim off the large metal anchors.

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Crystal

A crystal or crystalline solid is a solid material whose constituentatoms, molecules, or ions are arranged in an ordered pattern

extending in all three spatial dimensions. In addition to their

microscopic structure, large crystals are usually identifiable by their

macroscopic geometrical shape, consisting of flat faces with specific,

characteristic orientations.[citation needed]

The scientific study of crystals and crystal formation is known as

crystallography. The process of crystal formation via mechanisms ofcrystal growth is called crystallization or solidification. The word

crystal is derived from the Ancient Greek word

(krustallos), meaning both ice and rock crystal,[1] from

(kruos), "icy cold, frost".[2][3]

Common crystals include snowflakes, diamonds, and table salt;

however, most common inorganic solids are polycrystals. Crystals

are often symmetrically intergrown to form crystal twins.

Crystal structure (microscopic)

The scientific definition of a "crystal" is based on the microscopic

arrangement of atoms inside it, called the crystal structure. A crystal

is a solid where the atoms form a periodic arrangement.

(Quasicrystals are an exception, see below.)

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Not all solids are crystals. For example, when liquid water starts

freezing, the phase change begins with small ice crystals that grow

until they fuse, forming a polycrystalline structure. In the final block

of ice, each of the small crystals (called "crystallites" or "grains") is atrue crystal with a periodic arrangement of atoms, but the whole

polycrystal does not have a periodic arrangement of atoms, because

the periodic pattern is broken at the grain boundaries. Most

macroscopic inorganic solids are polycrystalline, including almost all

metals, ceramics, ice, rocks, etc. Solids that are neither crystalline

nor polycrystalline, such as glass, are called amorphous solids, also

called glassy, vitreous, or noncrystalline. These have no periodic

order, even microscopically. There are distinct differences between

crystalline solids and amorphous solids: most notably, the process of

forming a glass does not release the latent heat of fusion, but forming

a crystal does.

A crystal structure (an arrangement of atoms in a crystal) is

characterized by its unit cell, a small imaginary box containing one

or more atoms in a specific spatial arrangement. The unit cells arestacked in three-dimensional space to form the crystal.

The symmetry of a crystal is constrained by the requirement that the

unit cells stack perfectly with no gaps. There are 219 possible crystal

symmetries, called crystallographic space groups. These are grouped

into 7 crystal systems, such as cubic crystal system (where the

crystals may form cubes or rectangular boxes, such as halite shown

at right) or hexagonal crystal system (where the crystals may formhexagons, such as ordinary water ice).

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2 pin micro switch

A miniature snap-action switch, also trademarked and frequentlyknown as a micro switch, is an electric switch that is actuated by

very little physical force, through the use of a tipping-point

mechanism, sometimes called an "over-center" mechanism.

Switching happens reliably at specific and repeatable positions of the

actuator, which is not necessarily true of other mechanisms. They are

very common due to their low cost and durability, greater than 1

million cycles and up to 10 million cycles for heavy duty models.This durability is a natural consequence of the design.

The defining feature of micro switches is that a relatively small

movement at the actuator button produces a relatively large

movement at the electrical contacts, which occurs at high speed

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(regardless of the speed of actuation). Most successful designs also

exhibit hysteresis, meaning that a small reversal of the actuator is

insufficient to reverse the contacts; there must be a significant

movement in the opposite direction. Both of these characteristicshelp to achieve a clean and reliable interruption to the switched

circuit.

Construction and operation

K In one type of microswitch, internally there are two conductive

springs. A long flat spring is hinged at one end of the switch (the left,

in the photograph) and has electrical contacts on the other. A small

curved spring, preloaded (i.e., compressed during assembly) so it

attempts to extend itself (at the top, just right of center in the photo),

is connected between the flat spring near the contacts. A fulcrum is

near the midpoint of the flat spring. An actuator nub presses on the

flat spring near its hinge point.

Because the flat spring is anchored and strong in tension the curved

spring cannot move it to the right. The curved spring presses, or

pulls, the flat spring upward, that is away, from the anchor point.

Owing to the geometry, the upward force is proportional to the

displacement which decreases as the flat spring moves downward.

(Actually, the force is proportional to the sine of the angle, which is

approximately proportional to the angle for small angles.)

As the actuator depresses it flexes the flat spring while the curved

spring keeps the electrical contacts touching. When the flat spring is

flexed enough it will provide sufficient force to compress the curved

spring and the contacts will begin to move.

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As the flat spring moves downward the upward force of the curved

spring reduces causing the motion to accelerate even in the absence

of further motion of the actuator until the flat spring impacts the

normally-open contact. Even though the flat spring unflexes as itmoves downward, the switch is designed so the net effect is

acceleration. This "over-center" action produces a very distinctive

clicking sound and a very crisp feel.

In the actuated position the curved spring provides some upward

force. If the actuator is released this will move the flat spring

upward. As the flat spring moves, the force from the curved spring

increases. This results in acceleration until the normally-closedcontacts are hit. Just as in the downward direction, the switch is

designed so that the curved spring is strong enough to move the

contacts, even if the flat spring must flex, because the actuator does

not move during the changeover.

Applications

Common applications of micro switches include the door interlockon a microwave oven, levelling and safety switches in elevators,

vending machines, and to detect paper jams or other faults in

photocopiers. Micro switches are commonly used in tamper switches

on gate valves on fire sprinkler systems and other water pipe

systems, where it is necessary to know if a valve has been opened or

shut.

Micro switches are very widely used; among their applications areappliances, machinery, industrial controls, vehicles, and many other

places for control of electrical circuits. They are usually rated to

carry current in control circuits only, although some switches can be

directly used to control small motors, solenoids, lamps, or other

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devices. Special low-force versions can sense coins in vending

machines, or with a vane attached, air flow. Micro switches may be

directly operated by a mechanism, or may be packaged as part of a

pressure, flow, or temperature switch, operated by a sensingmechanism such as a Bourdon tube. In these latter applications, the

repeatability of the actuator position when switching happens is

essential for long-term accuracy. A motor driven cam (usually

relatively slow-speed) and one or more micro switches form a timer

mechanism. The snap-switch mechanism can be enclosed in a metal

housing including actuating levers, plungers or rollers, forming a

limit switch useful for control of machine tools or electrically-driven

machinery.

Diode

In electronics, a diode is a two-terminal electronic component with

an asymmetric transfer characteristic, with low (ideally zero)

resistance to current flow in one direction, and high (ideally infinite)

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resistance in the other. A semiconductor diode, the most common

type today, is a crystalline piece of semiconductor material with a p

n junction connected to two electrical terminals.[5] A vacuum tube

diode is a vacuum tube with two electrodes, a plate (anode) andheated 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 viewed as an electronic version of a check

valve. This unidirectional behavior is called rectification, and is used

to convert alternating current to direct current, including extractionof modulation from radio signals in radio receiversthese diodes are

forms of rectifiers.

However, diodes can have more complicated behavior than this

simple onoff action. Semiconductor diodes begin conducting

electricity only if a certain threshold voltage or cut-in voltage is

present in the forward direction (a state in which the diode is said to

be forward-biased). The voltage drop across a forward-biased diodevaries only a little with the current, and is a function of temperature;

this effect can be used as a temperature sensor or voltage reference.

Semiconductor diodes' nonlinear currentvoltage characteristic can

be tailored by varying the semiconductor materials and doping,

introducing impurities into the materials. These are exploited in

special-purpose diodes that perform many different functions. For

example, diodes are used to regulate voltage (Zener diodes), to

protect circuits from high voltage surges (avalanche diodes), to

electronically tune radio and TV receivers (varactor diodes), to

generate radio frequency oscillations (tunnel diodes, Gunn diodes,

IMPATT diodes), and to produce light (light emitting diodes).

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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 Germanphysicist 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.

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POWER SUPPLY:

A power supply is a device that supplies electric powerto

an electrical load. The term is most commonly applied to electric

power converters that convert one form of electrical energy to

another, though it may also refer to devices that convert another form

of energy (mechanical, chemical, solar) to electrical energy.

A regulated power supply is one that controls the output voltage or

current to a specific value; the controlled value is held nearly

constant despite variations in either load current or the voltage

supplied by the power supply's energy source.

Every power supply must obtain the energy it supplies to its load, as

well as any energy it consumes while performing that task, from an

energy source. Depending on its design, a power supply may obtain

energy from:

Electrical energy transmission systems. Common examples of this

include power supplies that convert AC line voltage to DC voltage.

Energy storage devices such as batteries and fuel cells.

Electromechanical systems such as generators and alternators.

Solar power.

A power supply may be implemented as a discrete, stand-alone

device or as an integral device that is hardwired to its load. Examples

of the latter case include the low voltage DC power supplies that arepart ofdesktop computers and consumer electronics devices.

Commonly specified power supply attributes include:

The amount ofvoltage and current it can supply to its load.

http://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Electrical_loadhttp://en.wikipedia.org/wiki/Electric_power_converterhttp://en.wikipedia.org/wiki/Electric_power_converterhttp://en.wikipedia.org/wiki/Regulated_power_supplyhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Energy_storagehttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Electrical_generatorshttp://en.wikipedia.org/wiki/Alternatorhttp://en.wikipedia.org/wiki/Solar_powerhttp://en.wiktionary.org/wiki/hardwiredhttp://en.wikipedia.org/wiki/Desktop_computerhttp://en.wikipedia.org/wiki/Consumer_electronicshttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Consumer_electronicshttp://en.wikipedia.org/wiki/Desktop_computerhttp://en.wiktionary.org/wiki/hardwiredhttp://en.wikipedia.org/wiki/Solar_powerhttp://en.wikipedia.org/wiki/Alternatorhttp://en.wikipedia.org/wiki/Electrical_generatorshttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Energy_storagehttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Regulated_power_supplyhttp://en.wikipedia.org/wiki/Electric_power_converterhttp://en.wikipedia.org/wiki/Electric_power_converterhttp://en.wikipedia.org/wiki/Electrical_loadhttp://en.wikipedia.org/wiki/Electric_power

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How stable its output voltage or current is under varying line and

load conditions.

How long it can supply energy without refueling or recharging

(applies to power supplies that employ portable energy sources).

Power supply is a reference to a source of electrical power. A

device or system that supplies electrical or other types of energy to

an output load or group of loads is called a power supply unit or

PSU. The term is most commonly applied to electrical energy

supplies, less often to mechanical ones, and rarely to others. Here inour application we need a 5v DC power supply for all electronics

involved in the project. This requires step down transformer,

rectifier, voltage regulator, and filter circuit for generation of 5v DC

power. Here a brief description of all the components is given as

follows:

TRANSFORMER:

A transformer is a static electrical device that transfers energy by

inductive coupling between its winding circuits. A varying current in

the primary winding creates a varying magnetic flux in the

transformer's core and thus a varying magnetic flux through the

secondary winding. This varying magnetic flux induces a varying

electromotive force (emf)or voltage in the secondary winding.

Transformers range in size from thumbnail-sized used inmicrophones to units weighing hundreds of tons interconnecting the

power grid. A wide range of transformer designs are used in

electronic and electric power applications. Transformers are essential

for the transmission, distribution, and utilization of electrical energy.

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Transformer is a device that transfers electrical energy from one

circuit to another through inductively coupled conductors the

transformer's coils or "windings". Except for air-core transformers,

the conductors are commonly wound around a single iron-rich core,or around separate but magnetically-coupled cores. A varying current

in the first or "primary" winding creates a varying magnetic field in

the core (or cores) of the transformer. This varying magnetic field

induces a varying electromotive force (EMF) or "voltage" in the

"secondary" winding. This effect is called mutual induction.

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Classification parameters:

Transformers can be classified in many ways, such as the following:

Duty of a transformer: Continuous, short-time, intermittent,periodic, varying.

Frequency range: Power-frequency, audio-frequency, or radio-

frequency.

Voltage class: From a few volts to hundreds of kilovolts.

Cooling type: Dry and liquid-immersed - self-cooled, forced

air-cooled; liquid-immersed - forced oil-cooled, water-cooled.

Circuit Application: Such as power supply, impedance

matching, output voltage and current stabilizer or circuit isolation.

Utilization: Pulse, power, distribution, rectifier, arc furnace,

amplifier output, etc..

Basic magnetic form: Core form, shell form.

Consant-Potential transformer descriptor: Step-up, step-down,

isolation.

General winding configuration: By EIC vector group - various

possible two-winding combinations of the phase designations delta,

wye or star, and zigzag or interconnected star;[i] other -

autotransformer, Scott-T,zigzag grounding transformer winding.

Rectifier phase shift configuration: 2-winding, 6-pulse; 3-

winding, 12-pulse; . . . n-winding, [n-1]*6-pulse; polygon; etc..

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OUTPUT SMOOTHING:

For many applications, especially with single phase AC where the

full-wave bridge serves to convert an AC input into a DC output, theaddition of a capacitor may be desired because the bridge alone

supplies an output of fixed polarity but continuously varying or

"pulsating" magnitude.

The function of this capacitor, known as a reservoir capacitor (or

smoothing capacitor) is to lessen the variation in (or 'smooth') the

rectified AC output voltage waveform from the bridge. One

explanation of 'smoothing' is that the capacitor provides a low

impedance path to the AC component of the output, reducing the AC

voltage across, and AC current through, the resistive load. In lesstechnical terms, any drop in the output voltage and current of the

bridge tends to be canceled by loss of charge in the capacitor. This

charge flows out as additional current through the load. Thus the

change of load current and voltage is reduced relative to what would

occur without the capacitor. Increases of voltage correspondingly

store excess charge in the capacitor, thus moderating the change in

output voltage / current.

The simplified circuit shown has a well-deserved reputation forbeing dangerous, because, in some applications, the capacitor can

retain a lethal charge after the AC power source is removed. If

supplying a dangerous voltage, a practical circuit should include a

reliable way to safely discharge the capacitor. If the normal load

cannot be guaranteed to perform this function, perhaps because it can

be disconnected, the circuit should include a bleeder resistor

connected as close as practical across the capacitor. This resistor

should consume a current large enough to discharge the capacitor ina reasonable time, but small enough to minimize unnecessary power

waste.

Because a bleeder sets a minimum current drain, the regulation of the

circuit, defined as percentage voltage change from minimum to

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maximum load, is improved. However in many cases the

improvement is of insignificant magnitude.

The capacitor and the load resistance have a typical time constant =

RC where C and R are the capacitance and load resistance

respectively. As long as the load resistor is large enough so that thistime constant is much longer than the time of one ripple cycle, the

above configuration will produce a smoothed DC voltage across the

load.

In some designs, a series resistor at the load side of the capacitor is

added. The smoothing can then be improved by adding additional

stages of capacitorresistor pairs, often done only for sub-supplies to

critical high-gain circuits that tend to be sensitive to supply voltage

noise.The idealized waveforms shown above are seen for both voltage and

current when the load on the bridge is resistive. When the load

includes a smoothing capacitor, both the voltage and the current

waveforms will be greatly changed. While the voltage is smoothed,

as described above, current will flow through the bridge only during

the time when the input voltage is greater than the capacitor voltage.

For example, if the load draws an average current of n Amps, and the

diodes conduct for 10% of the time, the average diode current during

conduction must be 10n Amps. This non-sinusoidal current leads to

harmonic distortion and a poor power factor in the AC supply.

In a practical circuit, when a capacitor is directly connected to the

output of a bridge, the bridge diodes must be sized to withstand the

current surge that occurs when the power is turned on at the peak of

the AC voltage and the capacitor is fully discharged. Sometimes a

small series resistor is included before the capacitor to limit this

current, though in most applications the power supply transformer's

resistance is already sufficient.Output can also be smoothed using a choke and second capacitor.

The choke tends to keep the current (rather than the voltage) more

constant. Due to the relatively high cost of an effective choke

compared to a resistor and capacitor this is not employed in modern

equipment.

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Some early console radios created the speaker's constant field with

the current from the high voltage ("B +") power supply, which was

then routed to the consuming circuits, (permanent magnets were then

too weak for good performance) to create the speaker's constant

magnetic field. The speaker field coil thus performed 2 jobs in one: itacted as a choke, filtering the power supply, and it produced the

magnetic field to operate the speaker.

REGULATOR IC:

Here we can used the 3 pin IC for voltage regulator as we call the

name 78XX. Now we consider the IC of 3pin for this voltageregulator.

It is a three pin IC used as a voltage regulator. It converts

unregulated DC current into regulated DC current.

Normally we get fixed output by connecting the voltage regulator at

the output of the filtered DC (see in above diagram).It can also be

used in circuits to get a low DC voltage from a high DC voltage (for

example we use 7805 to get 5V from 12V). There are two types ofvoltage regulators 1. fixed voltage regulators (78xx, 79xx) 2. variable

voltage regulators(LM317) In fixed voltage regulators there is

another classification 1. +ve voltage regulators 2. -ve voltage

regulators POSITIVE VOLTAGE REGULATORS This include

78xx voltage regulators. The most commonly used ones are 7805 and

7812. 7805 gives fixed 5V DC voltage if input voltage is in (7.5V,

20V).

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The Capacitor Filter:

Filter capacitors are capacitors used for filtering of undesirable

frequencies. They are common in electrical and electronic

equipment, and cover a number of applications, such as:

Glitch removal on Direct current (DC) power rails

Radio frequency interference (RFI) removal for signal or power

lines entering or leaving equipment

Capacitors used after a voltage regulatorto further smooth dc

power supplies

Capacitors used in audio, intermediate frequency (IF) orradio

frequency (RF) frequency filters (e.g. low pass, high pass, notch,

etc.)

Arc suppression, such as across the contact breakeror 'points' in

a spark-ignition engine

Filter capacitors are not the same as reservoir capacitors, the tasks

the two perform are different, albeit related.

The simple capacitor filter is the most basic type of power supply

filter. The application of the simple capacitor filter is very limited. It

is sometimes used on extremely high-voltage, low-current powersupplies for cathode-ray and similar electron tubes, which require

very little load current from the supply. The capacitor filter is also

used where the power-supply ripple frequency is not critical; this

frequency can be relatively high. The capacitor (C1) shown in figure

4-15 is a simple filter connected across the output of the rectifier in

parallel with the load.

http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Radio_frequency_interferencehttp://en.wikipedia.org/wiki/Voltage_regulatorhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Intermediate_frequencyhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Electronic_filterhttp://en.wikipedia.org/wiki/Arc_suppressionhttp://en.wikipedia.org/wiki/Contact_breakerhttp://en.wikipedia.org/wiki/Spark-ignition_enginehttp://en.wikipedia.org/wiki/Reservoir_capacitorhttp://en.wikipedia.org/wiki/Reservoir_capacitorhttp://en.wikipedia.org/wiki/Spark-ignition_enginehttp://en.wikipedia.org/wiki/Contact_breakerhttp://en.wikipedia.org/wiki/Arc_suppressionhttp://en.wikipedia.org/wiki/Electronic_filterhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Intermediate_frequencyhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Voltage_regulatorhttp://en.wikipedia.org/wiki/Radio_frequency_interferencehttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Capacitor

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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 isnecessary 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.

A type of relay that can handle the high power required to directlycontrol an electric motor or other loads is called a contactor. Solid-

state relays control power circuits with no moving parts, instead

using a semiconductor device to perform switching. Relays with

calibrated operating characteristics and sometimes multiple operating

coils are used to protect electrical circuits from overload or faults; in

modern electric power systems these functions are performed by

digital instruments still called "protective relays".

The relay takes advantage of the fact that when electricity flowsthrough a coil, it becomes an electromagnet. The electromagnetic

coil attracts a steel plate, which is attached to a switch. So the

switch's motion (ON and OFF) is controlled by the current flowing to

the coil, or not, respectively.

A very useful feature of a relay is that it can be used to electrically

isolate different parts of a circuit. It will allow a low voltage circuit

(e.g. 5VDC) to switch the power in a high voltage circuit (e.g. 100

VAC or more).

The relay operates mechanically, so it can not operate at high speed.

https://en.wikipedia.org/wiki/Electrichttps://en.wikipedia.org/wiki/Switchhttps://en.wikipedia.org/wiki/Electromagnethttps://en.wikipedia.org/wiki/Contactorhttps://en.wikipedia.org/wiki/Solid-state_relayhttps://en.wikipedia.org/wiki/Solid-state_relayhttps://en.wikipedia.org/wiki/Moving_partshttps://en.wikipedia.org/wiki/Protective_relayhttps://en.wikipedia.org/wiki/Protective_relayhttps://en.wikipedia.org/wiki/Moving_partshttps://en.wikipedia.org/wiki/Solid-state_relayhttps://en.wikipedia.org/wiki/Solid-state_relayhttps://en.wikipedia.org/wiki/Contactorhttps://en.wikipedia.org/wiki/Electromagnethttps://en.wikipedia.org/wiki/Switchhttps://en.wikipedia.org/wiki/Electric

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Internal circuit of Relay:

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.

There are many kind of relays. You can select one according to your

needs. The various things to consider when selecting a relay are its

size, voltage and current capacity of the contact points, drive voltage,

impedance, number of contacts, resistance of the contacts, etc. The

resistance voltage of the contacts is the maximum voltage that can be

conducted at the point of contact in the switch. When the maximum

is exceeded, the contacts will spark and melt, sometimes fusingtogether. The relay will fail. The value is printed on the relay.

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REFERENCES

8051 and embedded system by Mazidi andMazidi

All datasheets from www.datasheetcatalog.com

About AT89s8252 from www.atmel.com

Andwww.triindia.co.in

ESTIMATED COST: Rs.7000

http://www.triindia.co.in/http://www.triindia.co.in/http://www.triindia.co.in/