gas leakage alarm with power failure system
TRANSCRIPT
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.