GAS LEAKAGE ALERT WITH

POWER FAILURE SYSTEM

AND AUTO DIAL

TABLE OF CONTENTS

INTRODUCTION

SYNOPSIS

BLOCK DIAGRAM

BLOCK DESCRIPTION

CIRCUIT DIAGRAM

CIRCUIT DESCRIPTION

WORKING PRINCIPLE

FABRICATION OF CIRCUITS

SUGGESTIONS FOR IMPROVEMENTS

APPLICATIONS

CONCLUSION

BIBLIOGRAPHY

INTRODUCTION

INTRODUCTION

The advent of modern digital technology and the surface mount

technology, latest communication technologies and the far reaching

technologies related to instrumentation and remote sensing and all such

developments are contributing to the benefit of the human race so as to make

him live is peace harmony life easy, safe and comfortable.

Everyday new technologies are coming in so that it is hardly possible to

predict as to how and what would be technology of tomorrow. Incoming new

technologies are really, directly and indirectly, creating benefits & challenges as

well to mankind.

Of course LPG gas is a benefit man enjoys as an outcome of science and

technology. The comfort of the gas comes along with the threats of its own

hazards as well because of a possible gas or petrol leakage.

News of dangers of burnings and explosions of gas cylinders due to gas

leakage are also coming in, if not everyday at least now and then. Yes. We

witness both benefits and challenges out of science and technology.

It is obligatory on every human being to face the challenges and threats,

just without giving any way for frustrations that may slowly lead into many

difficulties, if not faced with courage. From time immemorial the war between

the advantages of science which evolve by human error and machine failure is

on. We in this project have attempted to support the theory of being on the

right side to positively and boldly face the menaces of gas leakage hazard

using the latest technologies.

SYNOPSIS

SYNOPSIS

Accidents due to fuel leakage are dangers encountered several times. We

have, therefore, in his project, attempted to develop a system that features the

sensing of gas leakage and giving an alarm.

The ultra modern micro electronics has made opportunities for the

development of such security system with the advent of advanced sensors for

sensing touch and fuel leakage. It is because of the developments in the field of

transducers that leads the way for such projects.

Fuel leakage sensing is developed using a special transducer that uses

highly activated carbon granules. In the vicinity of the activated carbon

enclosure is a heater. There are two electrodes separated by an air gap. If the

flammable fuel particles mixed in air reaches the air gap of the fuel leak sensor

the current between the two electrodes increase and the increase in current is

monitored and used to generate the alarm.

Once a gas leakage is monitored the gadget immediately gives signal to

the alarm device The alarm device is a buzzer that gives a low sounding alarm.

BLOCK DIAGRAM

BLOCK DIAGRAM

BLOCK DESCRIPTION

BLOCK DESCRIPTION

The main blocks of the project are,

1. The fuel leakage sensor. ( Activated carbon leak detector)

2. The alarm device. ( A hooter )

3. The Power supply system.

4,1 The LPG Gas Leakage Sensor. ( Activated carbon leak detector)

The fuel leakage detector system is to smell out the presence of any

dissolved gas particles in the environmental air inside the car. If the density of

gas particles dissolved in the air inside the car is more than a threshold level

the alarm is activated.

The presence of LPG particles in air is monitored in terms of parts per

million. If the parts per million of the LPG elements in air exceeds the set level

the electronic system gives the alarm.

The sensor used for this purpose is of the activated carbon type. It is a

passive transducer. An applied voltage across the two plates of the sensor

causes a nominal current through the circuit and if the density of LPG is high in

the air then the conduction of the sensor increases and the increased current is

responsible to activate the alarm circuit. The activated carbon sensor is

specially designed by its manufacturer to detect Petroleum related leakages

into air.

4,2 The Alarm Device.

( A hooter )

At the event of a gas leakage then a local alarm is activated.. To achieve this

sensor gives logic information to the relay activating circuit and the relay then

closes the buzzer unit. The buzzer is the source of alarm inside the car and the

sound is normally sufficient to draw the attention of the people.

CIRCUIT DIAGRAM

CIRCUIT DIAGRAM

CIRCUIT DESCRIPTION

CIRCUIT DESCRIPTION

6,1Overall Circuit Operation

The project has been designed to serve the objective of sensing and

raising an alarm in the event of a gas leakage. It is supposed to be reliably

useful to make a definite alarm in the event of a gas leakage. The alarm is

supposed to ring at the surroundings of the leakage area say a house or a hotel

or a factory premises.

As such the factor to be monitored is leakage of LPG gas.

To detect any gas leakage we have to install a gas leakage detector.

he gas leakage is detected using an advanced transducer called the

“Activated Carbon LPG detector“. This is a passive transducer and a voltage is

normally impressed actross its terminals and the current through an external

resistor is monitored. If the current through the external resistor is enhanced

severely then it means the sensor is in the presence of air with LPG particles

dispelled in it.

Thus a measure of the current through the external resistor made in

terms of the voltage drop across the resistor is an indirect measure of the gas

leakage dispelled in air.

This voltage is compared in a comparator, against a set point voltage and

if the voltage is more than a threshold value then a logic high level voltage of 5

volts is produced by the comparator.

This logic high level voltage is responsible for turning On the alarm both

at the local larm device and at the remote alarm device

6,2 The LPG Sensor

The Gas leak is detected by the gas leakage detector. The gas leakage

detector is a high technology device that uses the principle of thermionic

emission between two plates held at different electrical potentials.

The amount of current flow between the two electrodes is a function of

the voltage

between the two electrodes, the temperature of one of the two electrodes –

the cathode and the amount of mixture of any inflammable gas particles in

terms of parts per million in the air between the two electrodes.

With reference to the sensor that we use, it consists of a ring of activated

carbon. Inside the ring of carbon particles are two electrodes held apart. There

is a heater inside the unit to heat up the cathode. Electrical connections are

brought out from the Plate or Anode, the Cathode and the heater

An external source of DC potential of say 5 volts is applied to the heater.

The Anode is held at a potential of about 24 volts with respect to the cathode.

The external circuit is completed through a fixed a and a variable resistor. The

voltage drop across the fixed resistor is a measure of conduction between the

anode and cathode of the sensor and therefore the amount of this voltage

drop is used for monitoring the degree of gas leakage.

The two electrodes are enclosed inside a ring of activated hydro carbon.

The property of the hydro carbon is to attract the air particles that are rich in

mixed LPG particles. Thus the concentration of LPG mixture in air is more inside

the carbon ring. Leakages of LPG in the room causes the carbon ring to attract

the LPG mixed air particles and make a concentration of LPG mixed air inside

the ring so as to improve the electrical conduction between the plates of the

Sensor.

While in normal operation the anode is held at a DC potential of 24

volts. The heater is applied with 5 volts. The hot cathode now emits electrons

just like a thermionic valve these electrons are attracted by the positive anode

and thus a current is caused to flow between the cathode and the anode. This

is the cause of the external current as well. The external current flows through

external fixed resistor and a variable resistor.

In the absence of mixture of LPG in air this current is very small and

makes a very small drop across the external fixed resistor. But with increased

LPG mixture richness in air the conduction increases and the current through

the external resistor is also very high and the voltage across the external

resistor is also very high.

The drop across the external resistor is a function of the LPG richness in

air and the relation between the output voltages with respect to the richness of

LPG in air is almost linear.

The variable resistor that comes in series with the fixed resistor is to

adjust the level of detection or sensitivity of LPG leakage detection. This is

essential because in some areas like kitchens etc., the air is normally dispelled

with LPG particles because off the burning of LPG, however this is not a

leakage. Therefore a sensitivity control is essential to set the threshold of

sensing and alarming.

6,3 The Operational Amplifier Comparator

Operational amplifiers are high gain amplifiers in the form of

integrated circuits. They have a number of advantages over conventional

amplifiers that make them suitable for many industrial applications. The

various modes of operation of the operational amplifiers are,

1. Inverting amplifier.

2. Non Inverting amplifier

3. Comparator.

4. Adder.

5. Subtractor.

6. Sign Changer.

7. Scale Changer.

8. Astable Multivibrator.

9. Mono stable Multivibrator and so on..

In our project we have used the operational amplifier in the comparator

mode. The operational amplifier IC 741 has 8 pins and of the 8 pins, 2 are used

for power supply and two are used for input and one pin is used for getting the

output.

In the comparator mode, the operational amplifier is fed with two inputs

and the two inputs are the inverting inputs and the non inverting inputs. While

in the comparator mode of operation, if the potential at the non inverting input

is higher than that at the inverting input then the output will be the same as

the positive operating voltage. Similarly if the potential at the inverting input is

higher than that at the non inverting input then the output will be the same as

the negative operating voltage.

In our project we have used the comparator with two input signals one

from the gas leakage sensor and the other from the sensitivity control unit. The

sensitivity control voltage is is applied to inverting input and the Gas Leakage

Sensor voltage is applied at the non inverting input. At normal condition the

voltage at the sensitivity control input is more than that at the other input

therefore the output of the operational amplifier is a high negative potential

compared to the maximum operating positive voltage. This voltage is not

sufficient to drive the transistor at the output of the operational amplifier.

Whenever there is a gas leakage the Gas Leakage Sensor output is more

than that at the sensitivity control input of the operational amplifier. This

causes the output of the operational amplifier to go high and it drives the

transistor at the output of the operational amplifier and the output of this

transistor goes high. This transistor drives the tone generating astable

multivibrator. The output of the Astable multivibrator is connected to the

transistor ads the modulating signal.

WORKING PRINCIPLE

WORKING PRINCIPLE

The project has been designed to serve the objective of sensing and

raising an alarm in the event of a gas leakage. It is supposed to be

reliably useful to make a definite alarm in the event of a gas leakage. The

alarm is supposed to ring at the surroundings of the leakage area say a

house or a hotel or a factory premises.

As such the factor to be monitored is leakage of LPG gas. To detect

any gas leakage we have to install a gas leakage detector. The gas

leakage is detected using an advanced transducer called the “Activated

Carbon LPG detector”. This is a passive transducer and a voltage is

normally impressed across its terminals and the current through an

external resistor is monitored. If the current through the external resistor

is enhanced severely then it means the sensor is in the presence of air

with LPG particles dispelled in it.

Thus the measure of the current through the external resistor made in

terms of the voltage drop across the resistor is an indirect measure of

the gas leakage dispelled in air. This voltage is compared in a

comparator, against a set point voltage and if the voltage is more than a

threshold value then a logic high level voltage of 5volts is produced by

the comparator. This logic high level voltage is responsible foturning on

the alarm both at the local alarm device and at the remote alarm device.

FABRICATION OF

CIRCUITS

FABRICATION OF CIRCUITS

MICRO CONTROLLER UNIT

8,1 FLASH EPROM

Flash EPROM is electrically erasable, like EEPROM, but most Flash

devices erase all at once, or in a few large blocks, rather than byte-by byte

like EEPROM. Some flash EPROMs require special programming voltages. As

with EPROMs, the number of erase/program cycle is limited.

8,2 CPU

The cpu, or central processing unit, executes program instructions.

Types of instructions include arithmetic (addition, subtraction), logic (AND, OR

NOT), data transfer(move), and program branching(jump) operations. An

external crystal provides a timing reference for clocking the CPU.

8,3 RAM

RAM (random-access memory) is Where programs store information for

temporary use. Unlike ROM, the CPU can write to RAM as well as read it, Any

information stored in RAM is lost when power is removed from the chip. The

PIC has 128 X 8 bytes of RAM. BASIC-52 uses much of this for its own

operations, with a few bytes available to users.

8,4 I/O PORTS

1/0 (Input/output) ports enable the PIC to read and write to external

memory and other components. The PIC has four 8-bit I /O ports (ports 0-3).

As the name suggests, the ports can act as inputs (to be read) or outputs (to be

written to). Many of the port bits have optional, alternate functions relating to

accessing external memory, using the on-chip timer /counters, detecting

external interrupts, and handling serial communications. BASIC-52 assigns

alternate functions to the remaining port bits. Some of these functions are

required by BASIC-52 while others are optional. If you don’t use an alternate

function, you can use the bit for any control, monitoring, or other purpose in

your application.

8,5 TIMERS AND COUNTERS

The PIC has three 16-bit timer/counters, which it easy to generate

periodic signals or count signal transitions. BASIC-52 assigns optional functins

for each of the timer/counters.

Timer 0 controls a real-time clock that increments every 5 milliseconds.

You can use this clock to time events that occur at regular intervals, or as the

base for clock or calendar functions. Timer 1 has several uses in BASIC-52,

including

(PWM) (a series of pulses of programmable width and number); writing

to a line printer or other serial peripheral (LPT); and generating pulses for

EPROM programming (PGM PULSE). Timer 2 generates a baud rate for serial

communications at SER IN and SER OUT. These are all typical applications for

timer / counters in microcontroller circuits.

8,5 SERIAL PORT

The PIC serial port automatically takes care of many of the details of

serial communications. On the transmit side, the serial port translates bytes to

be sent into serial data, including adding start and stop bits and writing the

data in a timed sequence to SER OUT. On the receive side, the serial port

accepts serial data at SER IN and sets a flag to indicate that a byte has been

received. BASIC-52 uses the serial port for communicating with a host

computer.

8,6 EXTERNAL INTERRUPTS

INTO and INT1 are external interrupt inputs, which detect logic levels or

transitions that interrupt the CPU and cause it to branch to a predefined

program location. BASIC-52 uses INTO for its optional direct-memory-access

(DMA) function.

8,7 ADDITIONAL CONTROL INPUTS

Two additional control inputs need to be mentioned. A logic high on

RESET resets the chip and causes it to begin executing the program that begins

at 0 in code memory. In the PIC BASIC chip, this program is the BASIC-52

interpreter. EA (external memory access) determines whether the chip will

access internal or external code memory in the area from 0 to 1FFFh. In BASIC-

52 systems, EA is tied high so that the chip runs the BASIC interpreter in

internal ROM on boot-up.

8,8 POWER SUPPLY CONNECTIONS

And, finally, the chip has two pins for connecting to a+5-volt power

supply (VCC) and ground (VSS). That finishes our tour of the PIC BASIC chip.

We’re now ready to put together a working system. To+5V. or use a jumper as

show in the schematic, to allow you to bypass BASIC-52 and boot to an

assembly-language program in external memory,

8,9 CRYSTAL

XTALI is an 6 MHz crystal that connects to pins 18 and 19 of U2. this

crystal frequency has two advantages. It gives accurate baud rates for serial

communications, due to the way that the PIC timer divides the system clock to

generate the baud rates. Plus, BASIC-52 assumes this frequency when it times

the real-time clock, EPROM programming pulses, and serial printer port.

8,10 CORE FEATURES

High Performance RISC CPU

Only 35 single word instructions to learn

All single cycle instructions except for program branches which are two

cycle

Operating speed : DC – 20 MHz Clock Input

DC – 200 ns Instruction cycle

2K*14 words of FLASH Program Memory

128* 8 bytes of Data Memory (RAM)

64*8 bytes of EEPROM Data Memory

Pinout compatible to the PIC 16CXXX 28 and 40 pin devices

Interrupt capability (upto 11 sources)

Eight level deep hardware stack

Direct, Indirect and relative addressing modes

Power-on Reset

Power-up timer and Oscillator Start-up timer

Watchdog Timer with its own on-chip RC Oscillator for reliable operation

Programmable code-protection

Power saving SLEEP Mode

Selectable Oscillator options

Low-power, high-speed CMOS FLASH/EEPROM technology

Fully static design

In-circuit Serial Programming via two pins

Single 5V In-circuit Serial Programming capability

In-circuit debugging via two pins

Processor read/write access to program memory

Wide Operating voltage range : 2.0 to 5.5V

High Sink/Source Current : 25mA

Commercial and Industrial temperature ranges

Low-power consumption

- Less than 1.6mA typical @ 5V, 4MHz

- 20 micro Amps typical @ 3V, 32 KHz

- Less than 1 Micro Ampere typical standby current

8,11 PERIPHERAL FEATURES

Timer 0 : 8 bit timer /counter with 8-bit prescaler

Timer 1 : 16 bit timer / counter with prescaler, can be incremented

during sleep via external crystal / clock

Timer 2 : 8 bit timer / counter with 8-bit period register, prescaler and

post-scaler

10 bit multi-channel Analog to Digital converter

Universal Synchronous / Asynchronous Receiver, Transmitter with 9 bit

address detection

Parallel slave port 8-bits wide, with external read, write and control

signals

Brown-out Detection circuitry for Brown-out reset

One Capture, Compare, PWM Module

- Capture is 16 bit max, resolution is 12.5 ns

- Compare is 16 bit max, resolution is 200ns

- PWM max resolution is 10-bit

8.12 PIC 16F877

8,13 PIN DIAGRAM

PIC 16F877

PIC 16F877 is available in 40 pin DIP Package. It has five ports

PORT A - IPORT B - 8 Bits

PORT C - 8 Bits

PORT D - 8 Bits

PORT E - 3 Bits

8.14 LCD DISPLAY MODUL

Using an LCD display, the micro controller displays the required information.

The Liquid Controlled Display is a ready-to-use module based on the regular IC

SED1278 manufactured and marketed by SEIKO EPSON Corporation, Japan.

The module has 14 pins as input. The pin 1 is supply ground. The pin 2 is supply

+ve of 5 V DC. The pin 3 is used to vary the contrast of the display. Generally a

10K preset connected across the supply and the center wiper connected to the

pin is the suggested arrangement to vary the contrast. To make the design

simple, the contrast pin is tied to ground for maximum contrast. Pin 4 is for

informing the module, whether the byte given to the module is command word

or ASCII character. This pin is designated as RS – Register select. By making

this low, the data supplied is directed command register. The same way, when

ULM

2003

IN 1

IN 2

IN 3

IN 4

IN 5

IN 6

IN 7

GND

Out1

Vcc

Out7

Out6

Out5

Out4

Out3

Out2

this pin is high, the data supplied is directed to its internal display RAM. The pin

5 is used for writing or reading the registers of the LCD module. But in this

project, this pin is tied to ground. This means the LCD can only be written into

but not read from. The reading of LCD registers is done only to see if the busy

flag is set, so that next data can be sent. This problem is overcome by giving

sufficient gap between data writes to LCD. Pin 6 of the LCD is used to enable

the LCD operation and this pin is pulsed to transfer the DATA into LCD. Pin 7

to pin 14 are used to send D0 to D7 or 8-bits of data. The design of this module

permits the module to be driven by a 4-bit data words. To send 8-bits of data,

first the higher 4-bits are to be sent and then the next lower bits are sent to the

module. Pin 7 to pin 10 are not used in this 4-bit configuration. Pin 11 gets D0

and pin 12 gets D1, pin3 – D2 and pin 14 to D4. In this method, only 6-bits are

required to control LCD display and one of the output port is designated as LCD

port and that port drives the LCD module. This is the sequence of commands to

initialization of LCD module in the project.

8,15 RELAY DRIVER (ULN 2003A)

Driver IC ULM 2003

The ULN2003A is a high voltage, high current, Darlington Arrays each

containing seven open collection Darlington pairs with common emitters. Each

channel rated at 500mA and can withstand peak currents of 600mA. Suppression

diodes are included for inductive load driving and the inputs are pinned opposite

to outputs to simplify layout. It is a 5V TTL, CMOS. This versatile device is useful

for driving a wide range of loads including solenoids, relays, DC motors, LED

displays And high power buffers. Outputs can be paralleled for higher current.

The output of MC is applied to the input of relay driver transistor at its

phase terminals. When the input base voltage is reduced so that the relay is de-

energized, the collector current falls to zero abruptly. This sudden switching off

the relay current induces a very high back emf in the relay coils, which may be

high enough to puncture the collector-emitter junction at the transistor and

damage it. A large capacitor connected in parallel with the relay coil absorbs this

transient and protects the transistor. However large capacitor connected in

parallel with the relay coil absorbs this transient, protects the transistor and

sluggish the relay operations.

In an alternative method, a diode is connected in parallel with relay coil

instead of the capacitor. During normal operation, the diode is reversed biased

and has no effects on circuit performance, but, when the high back emf is

induced, it has the proper polarity for the diode to conduct. The diode there

after conducts heavily and absorbs all the transient voltage. The use of a diode

is parallel with the relay coil is highly recommended.

8,16 RELAY

Reas are switching devices. Switching devices are the heart of

industrial electronic systems. When a relay is energized or activated,

contacts are made or broken. They are used to control ac or dc power.

They are used to control the sequence of events in the operation of a

system such as an electronic heater, counter, welding circuits, and X-ray

equipment, measuring systems, alarm systems and telephony.

Electromagnetic relays are forms of electromagnets in which the coil

current produces a magnetic effect. It pulls or pushes flat soft iron

armatures or strips carrying relay contacts. Several relay contact can be

operated to get several possible ON/OFF combinations.

8,17 OPERATION OF ELECTROMAGNETIC RELAY :

Relays are usually dc operated. When dc is passed to the coil, the

core gets magnetized. The iron armature towards the core contacts 1 and

2 open and contacts 2 and 3 close. When coil current is stopped, the

attraction is not there and hence the spring tension brings 1 and 2 to

closed position, opening the other set 2 and 3.

8.18 ELECTROMAGNETIC RELAY

8,19 RELAY CONTACTS AND IDENTIFICATION :

The heart of the relay is the ‘junction’ of the contact points. The

relay contact points may be flat, spherical, pointed and combination of

all these. Flat contacts require more pressure for perfect contact

closing. Half round contacts are better because the surface

contamination will be minimum. The twin contacts give reliable

operation.

Relay contacts are made of silver and silver alloys in small power

applications. For large relays, contacts are made up of copper. Certain

relays use silver – palladium of platinum – ruthenium alloys for contacts.

The special types mentioned above give long life, carry moderate

currents and keep shape for long time.

To identify relay contacts, some important contact arrangements

must be remembered.

SPST - Single Pole Single Throw

SPDT - Single Pole Double Throw

NO - Normally Opened

NC - Normally Closed

Break - Relay action opens or breaks

contacts

Make - Relay action makes or closes

contacts

Relays are electromagnetic device by which operation of one or

more circuits can be controlled by the operation of some other circuit.

Relay is a type of switch where switching completely depends upon the

electromagnetism. When winding of insulted wire is made on soft iron

rod and apply is given across its end then magnetic field develops

around the rod and due to this magnetic field, magnetism also becomes

magnet. In this way, can be said that on giving supply to the coil winded

over a core, it becomes magnet. This magnet is known as

electromagnet.

Relay is a device which can turn ON/OFF any external circuit in

some special circumstances. The principal relay is a one pole 2 way

switch. The difference is that simple switch is manual switch where as

relay is an automatic switch to some extent. It has a coil in it.

When this coil gets enough supply then it becomes electromagnet

and attracts the strip of pole towards itself and changes the position of

switch. When supply cuts off then coil demagnetizes and thus switch

comes in its normal position. In telephony, the relays are used widely.

The relay that we used in this circuit has two states.

1. Normally closed state (NC)

2. Normally opened state (NO)

The control circuit of the relay transistor is shown in figure. When

the input to transistor is logic 0, the transistor will be open. So the relay

will be holding +12 and which will be in normally closed state.

Relays are electro mechanical switches and are electrically operated power

switches. A relay consists of an electromagnet which when energized pulls the

armature. The armature carries heavy electrical contacts that make or break an

electric circuit. General purpose relays can handle current of five or ten

amperes. Relays that have contact ratings of about 25A or more are known as

contactors. A single relay can make or break a number of contacts

simultaneously.

The amount of electrical power required to drive a relay is very

small. Most

Voltage stabilizers use relay coils of 720mw.It means that 12v relay coil will

have resistance of 200 ohms and operated up to 60mA.The same relay with

450 ohms coil will operate on 18v with 40mA.Transistor circuits can easily

supply this much of power and this much of power and thus control large

amount of power through relay contacts.

When the relay is not activated (ie.) in the reenergized state, Nc

contacts are closed and NO connections are opened. When the relay is

activated (ie.)in the energized state, NC contacts broken and NO contacts are

made. When the relay is de energized the original states of the contacts are

returned. The Above relays are single contact relays. This means that the

relays have one common point, one NO contact and one NC contact.

Double contact relays are also present. These relays have a set of

common points, a set of NO contacts and set of NC contacts. In single contact

relay, only one relay independent load or a series of different loads can be

connected.

In double contact relay, two independent loads can be connected at

two different contacts and these two different and these two loads can be

operated as desired.

8,20 LM78XX

Series Voltage Regulators

General Description

The LM78XX series of three terminal regulators is available

with several fixed output voltages making them useful in a

wide range of applications. One of these is local on card

regulation, eliminating the distribution problems associated

with single point regulation. The voltages available allow

these regulators to be used in logic systems, instrumenta-tion,

HiFi, and other solid state electronic equipment. Al-though

designed primarily as fixed voltage regulators these

devices can be used with external components to obtain ad-justable

voltages and currents.

The LM78XX series is available in an aluminum TO-3 pack-age

which will allow over 1.0A load current if adequate heat

sinking is provided. Current limiting is included to limit the

peak output current to a safe value. Safe area protection for

the output transistor is provided to limit internal power dissi-pation.

If internal power dissipation becomes too high for the

heat sinking provided, the thermal shutdown circuit takes

over preventing the IC from overheating.

Considerable effort was expanded to make the LM78XX se-ries

of regulators easy to use and minimize the number of

external components. It is not necessary to bypass the out-

put, although this does improve transient response. Input by-passing

is needed only if the regulator is located far from the

filter capacitor of the power supply.

For output voltage other than 5V, 12V and 15V the LM117

series provides an output voltage range from 1.2V to 57V.

Features

n Output current in excess of 1A

n Internal thermal overload protection

n No external components required

n Output transistor safe area protection

n Internal short circuit current limit

n Available in the aluminum TO-3 package

8,21 Voltage Range

LM7805C 5V

LM7812C 12V

LM7815C 15V

8,22 PCB DESGNING AND FABRICATION

PROCEDURE FOR MAKING THE PCB

1. PREPARING OF LAYOUT

With the diagram and all the components at hand, draw a complete layout

plan of the circuit on a sheet of a tracing paper. As a model, for laying the

circuit, a thermo Cole base may be used to hold components. Avoid over

crowding of components while making full space utilization. Keep the

ground line on the side of the PCB and the

supply line on other side as far as possible. When all the components have

been mounted on the tracing paper sheet fixed on a piece of thermo Cole

base, take out a Sketch Pen for making in such a way that all the connecting

wires are equal in width, termination rounded off. Re-draw it on a fresh

paper if required.

2. PAINTING OF PCB

The tracing so prepared has to be imposed over the copper printed circuit

board keeping in view that the component would be mounted from the non-clad

side of the board. Take a PCB lamination sheet and cur a piece of required size

of the board by

using hacksaw file edges, put the copper clad sheet on the table keeping side on

the runway the dirt grease and oxide with a sand paper with its marked side

tracing the carbon paper and at her side on top. Since the tracing paper is

transformed you can now reproduce a carbon point over a surface but using ball

pen on a hard pencil over the drawing on the transparent side. When the carbon

print has been obtained over the copper clad board drill ropes in the board using

a hand drill. The holes may be draw with 1/32 bit for

componentleadsandthecarbonshouldberaisedorwipedbymistake.Painttheconnecti

ng lines with the help of an ordinary paint. Edges should be scratched with tip of

razor blade.

3. DEVELOPMENT OF THE PRINTED CIRCUIT DIAGRAM

After painting the board, it will be made by the cool air for

sometime. Now take a plastic tray and get some Fe Cl3 chemical powder. The

ferric chloride salt is then added with 500ml of water. The color of the solution

is pink. Color of the salt is in

yellow. Now we add three to five drops of dilute HCL or H2S04. This is necessary

to quicken the process.

4.ETCHING OF PCB

Now we take the painted copper clad board and dip it in the

solution kept in the tray. After 15 to 25 minutes we see the board, with only

printed pattern portion remaining in other places the copper coating is

removed due to the chemical action. Then

the board is taken out and washes in water. After wash the board by using

thinner solution. Now a printed circuit has been formed on the board.

Take fresh water and mix a few teaspoons of Fe CL3 add a few drops of dilute

HCL to it, as it speeds the etching process. Shake well immerse the PC Bin the

solution for about 20 minutes occasionally altering the solution by giving the

seesaw

reaction to the disk storing reduces the etching time. Observe the changing

color on the copper surface. Take out the PCB only when the un painted

portion of the copper surface

is completely dissolved in the solution wash the PCB with the water. After the

PCB is thoroughly washed remove the paint by soft pieces of the cloth dipped in

thinner or turpenti

5. DRILLING OF HOLES

Then take a drilling machine with 1/32 drill bit to make holes for the

incretion of the components use 1/18 drill bit for inset wires and other thick

components. Now the PCB is ready to use.

ADVANTAGES:

1. Reliability in operation and low cost.

2. Space required becomes less.

DISADVANTAGES:

It can’t withstand larger weight such as transformer.

6.MATERIAL REQUIRED

1. Copper clad sheet [It is made of hylam or nylon board over

which the sheet copper is pressed.]

2. “Paint or “Nail polish” or even “PCB Ink”.

3. Painting brush, tray.

4. Ferric chloride solution and also few drop of dilute

HCL or H2SO4.

5. Thinner or kerosene or p

6. Cotton cloth.

7. Trace paper.

8,23SOLDERING

Solder is an alloy of tin and lead used for using metals relatively low

temperature about 260-315k the point where two metal conductors are to be

fused is heated and then solder is applied so that it can melt and cover the

connection. The reason for soldering connection is that it makes a good blend

between the joined metals.

Covering the joint completely is to prevent oxidation. The coating of solder

provides protection for practically an in definitive period of time.

The trick in soldering is to heat the joint, not the solder. When the join is

not enough to melt the solder the cracks, forming a shifty cover without until

the solder has set, which takes only a few seconds. Either a soldering gun can

be used, rated at 25-

10,000. The gun is convenient for the intermittent operation, since it heats

almost instantaneously when for press the trigger. The small pencilironof25-

4,000ishelpfulor small connections where excessive heat cause damage. This

precaution is particularly important when working on PCB boards, where too

much heat can soften the plastic form and loosen the printed writing, a

soldering iron for F&T devices should have the tip ground to eliminate static

charge.

The three grades of solder, generally used for electronics workare40-60,

50-50, and 60-40 solder. The 60-40 solders costs more but it melts at the

lowest temperature flows more freely takes less time to harder, and generally

makes it easier to do a soldering job.

In addition to the solder there must be flux to move any oxide film on the

metals being joined otherwise they cannot fuse. The flux enables the molten

solder to wet the metals so that the solder can stick. The two types are acid flux

and rosin flux. Acid flux is more active in cleaning metals but is corrosive.

Rosin flux is always used for the light soldering work in making wire

connection.

8,24 POWER SUPPLY

Most electronic circuits require DC voltage sources or power

supplies. If the electronic device is to be portable, then one or more

batteries are usually needed to provide the DC voltage required by

electronic circuits. But batteries have a limited life span and cannot be

recharged. The solution is to convert the alternating current lose hold line

voltage to a DC voltage source.

8,25BLOCK DIAGRAM FOR POWER SUPPLY:

Block diagram of AC to DC power Supply consists,

1. Transformer: Steps the household line voltage up or down

as required.

2. Rectifier : converts ac voltage into dc voltage

3. Filter : smooth the pulsating DC voltage to a varying

dc voltage

4. Regulator : fixed the output voltage to constant value.

FILTER

REGULATOR

TRANSFORMER RECTIFIER

8,26 Transformer:

The basic transformer consists of a primary winding of N1 turns and

secondary winding of N2 turns. When an alternating line voltage V1, is

applied to the primary winding, an alternating current it creates a flux.

The flux flows through the magnetic core, includes an alternating current

I2, which in turn generates an alternating voltage V2 in the secondary

winding. Three important specifications are the secondary winding,

power rating and the regulation factor.

MAGNETIC CORE

FLUX

I1 I2

V1 V2

8,27Rectifiers:

A rectifier circuit converts an AC voltage into a pulsating DC voltage.

This is accomplished by using one or more diodes because diodes

conduct current in only one direction.

8,28 Types Of Rectifiers:

Half-wave Rectifier

Full-wave Rectifier

Full-wave bridge rectifier

Half-wave Rectifier:

The transformer (T1) isolates the household voltage and also

steps down the household voltage to a more useful voltage level. The

diode lets current flow into the load in only one direction. The load

current is unidirectional; therefore, it has a significant dc component (or

average value).When V2 is positive, diode D1 conducts and VL=V2.

When V2 is negative, diode D1 blocks the current flow and VL=0volts.

The load voltage consists of dc voltage along with ripple voltage. In a

half-wave rectifier circuit, the ripple component is lager than the DC

component, which is undesirable.

USEFUL FORMULAS:

VAVG (DC) = 0.637V2

VL (DC) = 0.318V2

VL (AC) = 0.386V2

%RIPPLE = VL (AC)/VL (DC) = 121%

RIPPLE FREQUENCY = SUPPLY FREQUENCY

8,29 Full-wave Rectifier :

The full wave rectifier circuit requires a transformer with two

secondary windings. I.e. a center-tapped secondary winding.

The secondary windings are 180 out of phase.

Diode D1 contacts when V2a is positive, producing a half-wave

rectified voltage across the load. Diode D1 does not conduct when V2a

is negative. Diode D2 contacts when V2b is positive and does not

conduct when V2b is negative. One of the two diodes is conducting at all

times because V2a and V2b are 180 out of phase and thus producing

full-wave rectified voltage. In the Full wave rectifier, Dc component is

larger than ripple.

6,30 USEFUL FORMULAS:

VL (DC) = 0.637V2

VL (AC) = 0.3072

%RIPPLE = VL (AC)/VL (DC) = 48.2%

RIPPLE FREQUENCY = 2 x SUPPLY FREQUENCY

8,31 Full-wave bridge rectifier:

The full-wave bridge rectifier circuit requires four diodes. The

transformer has only one secondary winding.

When V2 is positive, diodes D1 & D3 conduct current through the

load. Diodes D2 and D4 block current flow. When V2 is negative, diodes

D2 and D4 conduct current through the load. Diodes D1 and D3 block

current flow. The full-wave bridge rectifier fully utilizes the transformer

winding during both half cycles.

8,32 USEFUL FORMULAS:

VL (DC) = 0.637V2

VL (AC) = 0.307V2

%RIPPLE = VL (AC)/VL (DC) = 48.2%

RIPPLE FREQUENCY = 2 x SUPPLY FREQUENC

8,33 Filters:

The 121% ripple in the output of the half-wave rectifier and 48% in

the full-wave rectifier is more than can be normally tolerated. In the full

wave filtering, wherein the frequency of the ripple is 100Hz for a 50Hz ac

line voltage. This is an advantage where either an inductor is used to

prevent the passage of the ripple current(due to its high inductive

reactance to ac but quite low resistance to dc), or a capacitor is used to

‘short’ the ripple to ground but leave the dc to appear at the output.

Various combinations of L and C are also used.

8,34 Regulators

The simplest regulator is a large capacitor in parallel with the load.

The capacitor stores DC voltage while the load voltage increases to its

peak value. The capacitor converts the pulsating DC voltage of a rectifier

into a smooth Dc load voltage.

Two important parameters of a capacitor regulator are its working

voltage and its capacitance. The working voltage must be at least equal

to no-load output voltage of power supply. The capacitance determines

the amount of ripple that appears on the Dc output when current is drawn

from the circuit. The amount of ripple decreases with increase in

capacitance.

8,35 Capacitance regulator circuit :

L-regulator circuit :

This circuit consists of a series inductor and a capacitance in parallel

with load. The L-regulator is often used in high-power DC supplies.

MC 7800 and 7900 Regulators standard application circuit:

The Mc 7800 is a 3 terminal, positive, fixed voltage integrated circuit

regulator. These regulators employ internal current limiting, thermal

shutdown and safe area compensation. The Mc 7900 is a 3 terminal,

negative, fixed voltage integrated circuit regulator.

Mc 7800 and Mc 7900 series requires no external components.

The input voltage must be at least two volts higher than the output

voltage capacitor c1 is required if the regulator is located far from the

power supply. Capacitor c2 improve the transient response. Both series

available in To-220 plastic package and T01-3 metal package.

8,36 Block diagram of Mc 7800 and Mc7900 regulator:

The unregulated input voltage is fed to the control element and the

reference voltage. The output voltage is sampled and fed into one of the

error amplifier inputs. The other error amplifier input connected to the

reference voltage. When the error amplifier senses a difference between

the reference and sampling voltages it acts upon the control element to

correct the error by dropping a greater portion of the input voltage across

the control element. The control element is a transistor which acts as a

variable registers, in which the resistance is controlled by the error

amplifier.

The input voltage however must not be large enough to exceed the

regulator power dissipation specification. Both series have an internal

protection circuit, a current limiting circuit, and a safe-area protection

circuit. The safe-area protection circuit limits the regulator output voltage

when the input voltage is too higher ensuring that the pass transistor

control element operates within its allowed voltage and current ranges.

8,37POWER SUPPLY

+5V

-5V

GROUND

IN OUTCOM

7905

25V

25V 25V

25V

DISC

DISC

1

2

3

1

2 3

1A230V/9V-0-9V

IN4007

IN

COM

OUT7805

0.1uF

0.1uF

+

100uF

+

100uF

+1000uF

+1000uFIN4007

SUGGESTIONS FOR

IMPROVEMENTS

SUGGESTIONS FOR IMPROVEMENTS

The project works very well and functions as constrained by the design.

Though the project works satisfactorily, it has to be improved in so many ways

and then it will reach the professional standards.

First of all the system must be built around a dedicated PCB. Dedicated

PCB especially developed for this purpose will improve the efficiency of the

system and will be more reliable.

In our project the range of the sound produced can reach only within a

short distance however by using a transmitter the range can be extended to

long distances.

APPLICATIONS

APPLICATIONS

The Project has been designed with the idea of developing a dedicated

application. Therefore the very application of the project is quite obvious.

However we can think of developing the same project for related other

applications as well.

Inflammable gas leakage is a general hazard that is applicable not just to

moving vehicles such as cars, but the same danger is encountered in many

places like, domestic kitchens, hotel kitchen yards, gas storage go downs, gas

furnace based other industrial process plants etc. Therefore, the project can be

suggested in all such areas. Specific sensors are available to check the presence

of such gas leakages.

CONCLUSION

CONCLUSION

The project work has been completed successfully. The project work

functions satisfactorily as per the design. The project work was developed after

conducting a number of experiments before finalizing the design work, this

reduced the bottle necks and we did not face much difficulty in the final

integration process.

In general the entire development of the project work was educative and

we could gain a lot of experience by way of doing the project practically. We

could understand the practical constraints of developing such systems which of

which we have studied by way of lectures in the theory classes.

It was satisfying to see so many theoretical aspects work before us in real

life practice of which we have heard through lectures and of which we have

studied in the books.

BIBLIOGRAPHY

BIBLIOGRAPHY

1. Electronic Principles Albert Paul Malvino.

2. Communication Engineering George Kennedy.

3. Linear Integrated Circuits Sharma.

4. IC Data Sheets Manufacturers Manuals.