A PROJECT REPORT ON
“GAS LEAKAGE PROTECTION
&
AUTO ON-OFF SYSTEM”
For partial fulfillment of requirement for the award of the degree of “Bachelor of Technology”
SUBMITTED BY:





UNDER THE GUIDANCE OF:
GEETANJALI SINGH
PRATIBHA SINGH
RAHUL KUMAR
RAKESH YADAV
SANDEEP KUMAR VERMA
Er. AYUSH ANAND SRIVASTAVA
(H.O.D., Electronics & Comm. Engg.)
Department of Electronics & Communication Engg.
SAROJ INSTITUTE OF TECHNOLOGY AND MANAGEMENT
SESSION 2009-10
(Affiliated to Uttar Pradesh Technical University, Lucknow)
1
SAROJ INSTITUTE OF TECHNOLOGY AND MANAGEMENT, LUCKNOW
DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGG
.
(Affiliated to Uttar Pradesh Technical University, Lucknow)
Certificate
This is to certify that Miss. GEETANJALI SINGH, Miss. PRATIBHA SINGH, Mr. RAHUL KUMAR, Mr.
RAKESH YADAV & Mr. SANDEEP KUMAR VERMA students of Bachelor of Technology in Electronics &
Comm. Engg., of Uttar Pradesh Technical University, Lucknow has successfully completed their project work
entitled “GAS LEAKAGE PROTECTION & AUTO ON-OFF SYSTEM” under my supervision during the
academic session 2009-10. The project report embodies result of original work and studies carried out by student
themselves and the contents of the report do not form the basis for the award of any other degree to the candidate
or to anybody else.
I wish them a bright and prosperous career and life.
Date:
Er. Ayush Anand Srivastava
Place: Lucknow
(H.O.D. Electronics & Comm.Engg.)
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ACKNOWLEDGEMENT
We take this opportunity to express our gratitude & thanks to respected Er. AYUSH ANAND
SRIVASTAVA, HOD, Department of Electronics & Communication , for his valuable technical
suggestions & encouragement throughout the work.
A special thanks to our team also. Our team has proven to be great team without any
misunderstandings. Our team members played awesome role in completing the duties whichever
were assigned to them.
And on a personal note, there was a worldwide network of friends and family who offered their
support and encouragement on a daily basis, which we couldn’t do.
DATE:
GEETANJALI SINGH
(0612331024)
PLACE: LUCKNOW
PRATIBHA SINGH
(0612331048)
RAHUL KUMAR
(0612331054)
RAKESH YADAV
(0612331057)
SANDEEP KUMAR VERMA
(0612331064)
3
CHAPTER 1
INTRODUCTION
1.1. Introduction
The primary objective of the present project to provide a novel means for safely detecting any
malfunction of a pressurized gas system in order to prevent accumulation of combustible gases so that
damage or explosion due to such an accumulation of gases is prevented.
It detects the leakage of gas into the area of an appliance when the appliance is in a shutdown condition
and/or not in operation.
Yet another objective of the present project is to provide a gas detection and monitoring system which is
economical to manufacture and may be readily installed in conventional trailers, boats or the like which
are normally dependent upon a stored supply of pressurized gas.
Sensors are used to detect the presence of dangerous LPG leak in our car or in a service station, storage
tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a
visual indication of the LPG concentration. The sensor has excellent sensitivity combined with a quick
response time. The sensor can also sense iso-butane, propane, LNG and cigarette smoke. Stepper motor
is used to turn-off the appliance by rotating the knob if the leakage is due to knob of gas kit being ON.
1.2. Advantages
 The sensor has excellent sensitivity combined with a quick response time
 High sensitivity to LPG, iso-butane, propane
 Small sensitivity to alcohol, smoke
 Fast response
 Wide detection range
 Stable performance and long life
 Simple drive circuit
4
1.3. Limitations

It sensitivity is less in presence of smoke.

Current system works only when at 5V power supply is given though it can modified for other
supply voltages.

Its sensitivity depends on humidity and temperature.
1.4. Applications
 It is used in house as LPG leakage detection.
 It also detects alcohol so it is used as liquor tester.
 It can be used in vehicles employing LPG/CNG kit.
 For safety from gas leakage in heating gas fired appliances like boilers, domestic water heaters.
 For safety from gas leakage in cooking gas fired appliances like ovens, stoves etc.
 Large industries which uses gas as their production.
 Provided with stepper motor it can be used to turn off gas supply in normal gas cylinders and
also in large industrial pipelines using knobs.
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CHAPTER 2
PRINCIPLE OF OPERATION & COMPONENTS
2.1. Circuit Diagram
Figure 2.1. Circuit Diagram
6
2.2. Block Diagram
BUZZER
LPG/CNG
GAS
SENSOR
MICROCONTROLLER
STEPPER
MOTOR
DRIVER
DISPLAY
UNIT
Figure 2.2.Block Diagram
This project has microcontroller, gas sensor, buzzer, LCD display, stepper motor and power supply as its
key elements. Whenever there is leakage of gas due to any reason it is initially sensed by the gas sensor
“MQ6”. This sensor transmits corresponding signal to the microcontroller which controls the working of
all devices in the project.
Microcontroller then generates a signal which makes the pin corresponding to the buzzer low. Therefore
buzzer rings and sounds alert indicating leakage of gas and need of appropriate action to be taken by the
user. If the gas leakage is due to the fact that its knob is in ON position then stepper motor comes into
action. As the knob of the cylinder or pipeline is rotated to turn it ON and OFF , the stepper motor
rotates the knob so as to turn the gas supply or leakage OFF. If the knob is in ON position then the
cylinder or pipeline is turned OFF and the buzzer stops alarming. If the knob is already in OFF position
then stepper motor makes no effect on the knob position and buzzer continues to sound alert.
An LCD display is also used in the project. It continuously displays leakage or no leakage condition
depending on the fact that there is leakage or not.
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2.3. Working
The systematic working of the project involves following steps:

Switch on the module with the help of toggle switch.

Display Unit (LCD) displays “NO LEAKAGE” on the display board. It is connected to the
PCB with the 16 pin connector. LCD contrast is controlled by the variable resistance which
can be varied to change the contrast on display.

12 V dc battery is used to provided the power supply to following units:
 PCB containing microcontroller, comparator IC etc.
 PCB containing stepper motor driver
 Toggle switch

All the components in the module work on 5 V power supply. For this purpose a 7805 voltage
regulator is used on both the PCB’s . This voltage regulator IC performs the conversion of 12
V into 5 V and supplies the 5 V output to all the components which include microcontroller at
pin no. 40, comparator IC LM 324 at pin no. 4, stepper motor driver IC, LCD, gas sensor
MQ6, variable resistor, buzzer etc.

A crystal oscillator which provides the timing clock to the microcontroller is connected to pin
no. 18 and 19. Pin 19 is XTAL 1 and is used for input to the inverting oscillator amplifier and
to the internal clock operating circuit. Pin 18 is XTAL 2 and is used for output from inverting
oscillator amplifier.

The gas sensor MQ6 senses the LPG and CNG gas leakage. The sensor’s output is connected
to the microcontroller PCB through 3 pin connector in which one wire is use for +5 V power
supply, second wire is used for GND (ground), third wire is connected to pin 5 of IC LM 324.

A preset resistor of 10 K is connected to pin no. 6 of IC LM 324. This resistance provides
reference voltage for gas section. This reference voltage can be varied according to different
situations by changing the value of preset resistance.

Pin no. 7 of IC LM 324 is output pin and is connected to pin no. 4 of the microcontroller
which is SS (slave part select input) of port 1.

If gas sensor output is greater than the reference voltage microcontroller stars performing
control action.

LCD displays “LPG leakage on the screen”. A variable resistance is used to change the
contrast of the display by varying the resistance. The LCD is connected to the pin no.
21,22,23,24,25,26,31 and 40 of the microcontroller. Pin no. 31 is EA/VPP (External Access
Enable), EA must be strapped to ground in order to enable the device to fetch code from
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external program memory location starting at 0000H upto FFFFH and EA should be strapped
to Vcc for internal program executions. Pin no. 21 to 26 acts as a address line of port 2.

Microcontroller also activates the buzzer which is connected to the pin no. 1 of the
microcontroller which is T2 (External count input to the timer (counter 2), clock out) of port 1.
This buzzer continues to sound alert till the leakage is sensed by the gas sensor which causes
the pin corresponding to the buzzer remain active low which otherwise i.e. in no leakage
condition remains active high.

Microcontroller also generates four bit control output which is connected to the stepper motor
driver PCB through 4 pin connector. The four pin connector is connected to the pin no.
36,37,38,39 of the microcontroller which are used as Address/Data multiplexed line. The
stepper motor driver IC LM 293 drives the stepper motor which rotates until the knob of the
cylinder or the gas pipeline is turned off.
2.4. List of Components
1. Gas Sensor – MQ6
2. Microcontroller – AT89S8253
3. Comparator IC - LM324
4. Stepper Motor
5. Stepper Motor Driver IC L293
6. Reset Switch
7. LCD
8. Buzzer
9. Crystal oscillator
10. Capacitors
11. Resistors
12. Battery
2.5. Description of Components
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2.5.1. Gas Sensor
The LPG Gas Sensor is used in gas detection equipment for detecting Propane gas in home, automotive
or industrial settings. This sensor is compatible with all Parallax microcontrollers, and would be a good
addition to any projects needing to sense the presence of propane.
Gas sensors based on nickel oxide come in various types. Gas sensors can be either optical or electrical.
The principle of most gas sensors is that a reaction of the sensor with the gas causes changes in the
surface of the sensor, which results in changes of the optical and/or electrical properties.
a. Optical Sensors
In optical sensors, the colour of the sensor varies with the concentration of the detected gas. Optical
sensors are mainly used in detection of CO.
b. Electrical Sensors
Electrical sensors come in two types. In the first type the resistance of the sensor varies with the
concentration of the gas. In the other type the output voltage depends on the concentration. The
resistance-type sensors operate due to a reaction of the gas with chemisorbed oxygen at the surface of the
sensor. This changes the amount of electrons at the surface and thereby the conductivity.
The voltage-type sensors use nickel oxide as thermoelectric (TE) material. By applying a temperature
gradient to a thermoelectric material, a small voltage is generated. This temperature gradient can be
provided by a chemical reaction at one side of the TE material.
Figure 2.3.Principle of a thermoelectric gas sensor
MQ-6 GAS SENSOR
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Sensitive material of MQ-6 gas sensor is SnO2 with lower conductivity in clean air. When the target
combustible gas exist the sensor’s conductivity is increases along with the gas concentration rising.
Simple electrocircuit is used to convert change of conductivity into corresponding output signal of the
gas concentration.
MQ-6 gas sensor has high sensitivity to Propane, Butane and LPG. It also response to Natural gas. The
sensor could be used to detect different combustible gas, especially Methane. It has low cost and is
suitable for different applications.
Features

High sensitivity to LPG, iso-butane and propane

Small sensitivity to alcohol and smoke

Fast response

Wide detection range

Stable performance and long life

Simple drive circuit
Figure 2.4.MQ-6 Gas Sensor
Specifications:
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Parameter
Value
Unit
Target Gas
iso-butane, Propane, LPG
Detection Range
100 to 10000
Calibrated Gas
1000ppm iso-butane
Sensitivity
R in air/Rin typical gas≥5
Sensing Resistance
40 to 400KΩ in air
Ω Ohms
Response Time
≤10s
Seconds
Resume Time
≤30s
Seconds
Heating Resistance
31Ω±3Ω
Ω Ohms
Heating Current
≤180Ma
mA
Heater Voltage
5V±0.2V
Volts
Heating Consumption
≤900mW
mW
Circuit Voltage
≤15V
Volts
Standard Working
Condition
Storage Condition
Temperature: -10ºC to 65 ºC Humidity:
≤95%RH
Temperature: -20ºC to 70 ºC Humidity:
≤70%RH
ppm(part per
millions)
Structure And Circuit:
Figure 2.5. Structure & Measuring Circuit of MQ-6 Gas Sensor
Cross-Sectional View:
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Figure 2.6. Cross Sectional View of MQ-6 Gas Sensor
Following conditions must be prohibited

Exposure to organic silicon steam

Organic silicon steam cause sensors to be invalid, sensors must avoid exposure to silicon bond,
silicon latex, putty or plastic contain silicon environment.

High Corrosive gas


If the sensors are exposed to high concentration corrosive gas it will not only result in corrosion
of sensors structure, also it cause sincere sensitivity attenuation.
Touch water

Sensitivity of the sensors will be reduced when spattered or dipped in water.

Freezing

Do avoid icing on sensor’s surface, otherwise sensor would lose sensitivity.

Higher applied voltage

Applied voltage on sensor should not be higher than stipulated value, otherwise it causes heater
damage and sensor’s sensitivity characteristic changes badly.

Voltage on wrong pins

Water Condensation

Indoor conditions, slight water condensation will affect sensors performance lightly.

Used in high gas concentration

If long time placed in high gas concentration, it will affect sensors characteristic.
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
Long time storage

The sensors resistance produce reversible drift if it’s stored for long time without electrify.
Sensors should be stored in airproof place.

Long time exposed to adverse environment

No matter the sensors electrified or not, if exposed to adverse environment for long time, such as
high humidity, temperature, or pollution etc will affect the sensors performance badly.

Vibration Continual

Vibrations will result in sensors down-lead response then rupture, concussion. If sensors meet
strong concussion, it may lead its lead wire to get disconnected.
2.5.2. Microcontroller
Description:
The AT89S8253 is a low-power, high-performance CMOS 8-bit microcontroller. The device is
manufactured using Atmel’s high-density non-volatile memory technology and is compatible with the
industry-standard MCS-51instruction set and pin out. The on-chip downloadable Flash allows the
program memory to be reprogrammed in-system through an SPI serial interface or by a conventional non
volatile memory programmer. In addition, the AT89S8253 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 allowing the RAM, timer/counters, serial port, and interrupt system to continue
functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all
other chip functions until the next external interrupt or hardware reset.
Figure 2.7.Microcontroller IC
Features:
 12K Bytes of In-System Programmable (ISP) Flash Program Memory
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 Endurance: 10,000 Write/Erase Cycles
 2K Bytes EEPROM Data Memory
 Endurance: 100,000 Write/Erase Cycles
 64-byte User Signature Array
 2.7V to 5.5V Operating Range
 Fully Static Operation: 0 Hz to 24 MHz (in x1 and x2 Modes)
 Three-level Program Memory Lock
 256 x 8-bit Internal RAM
 32 Programmable I/O Lines
 Three 16-bit Timer/Counters
 Nine Interrupt Sources
 Enhanced UART Serial Port with Framing Error Detection and Automatic
 Address Recognition
 Enhanced SPI (Double Write/Read Buffered) Serial Interface
 Low-power Idle and Power-down Modes
 Interrupt Recovery from Power-down Mode
 Programmable Watchdog Timer
 Dual Data Pointer
 Power-off Flag
 Flexible ISP Programming (Byte and Page Modes)
 Page Mode: 64 Bytes/Page for Code Memory, 32 Bytes/Page for Data Memory
 Four-level Enhanced Interrupt Controller
 Programmable and Fuseable x2 Clock Option
 Internal Power-on Reset
 42-pin PDIP Package Option for Reduced EMC Emission
Pin Configurations:
15
Figure 2.8. Pin Diagram of AT89S8253 Microcontroller IC
 VCC (Pin no.40)
Supply voltage
 GND (Pin no.20)
Ground
 Port 0 (Pin no.39 to 32)
Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink six TTL inputs.
When 1s are written to port 0 pins, the pins can be used as high-impedance inputs. Port 0 can also be
configured to be the multiplexed low-order address/data bus during accesses to external program and
data memory. In this mode, P0 has internal pull-ups.
 Port 1 (Pin no.1 to 8)
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can
sink/source six TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the weak
internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low
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will source current (IIL,150 μA typical) because of the weak internal pull-ups. Some Port 1 pins
provide additional functions. P1.0 and P1.1 can be configured to be the timer/counter 2 external count
input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX) respectively.
 Port 2(Pin no.21 to 28)
Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can sink/source
six TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the weak internal pull-ups
and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current
(IIL,150 μA typical) because of the weak internal pull-ups. Port 2 emits the high-order address byte
during fetches from external program memory and during accesses to external data memory that use 16bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting
1s. During accesses to external data memory that use 8-bit addresses, Port 2 emits the contents of the P2
Special Function Register.
 Port 3(Pin no.10 to 17)
Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output buffers can sink/source
six TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the weak internal pull-ups
and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current
(IIL,150 μA typical) because of the weak internal pull-ups. Port 3 receives some control signals for Flash
programming and verification. Port 3 also serves the functions of various special features of the
AT89S8253, as shown in the following table.
17
 RST(Pin no. 9)
Reset input. A high on this pin for at least two machine cycles while the oscillator is running resets the
device.
 ALE/PROG(Pin no. 30)
Address Latch Enable. ALE/PROG is an output pulse for latching the low byte of the address (on its
falling edge) during accesses to external memory. This pin is also the program pulse input (PROG)
during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator
frequency and may be used for external timing or clocking purposes.
 PSEN(Pin no. 29)
Program Store Enable. PSEN is the read strobe to external program memory (active low). When the
AT89S8253 is executing code from external program memory, PSEN is activated twice each machine
cycle, except that two PSEN activations are skipped during each access to external data memory.
 EA/VPP(Pin no. 31)
External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from
external program memory locations starting at 0000H up to FFFFH.EA should be strapped to VCC for
internal program executions.
 XTAL1(Pin no.19)
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
 XTAL2(Pin no.18)
Output from the inverting oscillator amplifier.
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2.5.3. Operational Amplifier: LM 324
Description:
The LM124 series consists of four independent, high gain, internally frequency compensated operational
amplifiers which were designed specifically to operate from a single power supply over a wide range of
voltages. Operation from split power supplies is also possible and the low power supply current drain is
independent of the magnitude of the power supply voltage.
Application areas include transducer amplifiers, DC gain blocks and all the conventional op amp circuits
which now can be more easily implemented in single power supply systems. For example, the LM124
series can be directly operated off of the standard +5V power supply voltage which is used in digital
systems and will easily provide the required interface electronics without requiring the additional ±15V
power supplies.
Features:
 Internally frequency compensated for unity gain.
 Large DC voltage gain upto 100 dB.
 Wide bandwidth (unity gain) 1 MHz (temperature compensated).
 Wide power supply range: Single supply 3V to 32V or dual supplies ±1.5V to ±16V.
 Very low supply current drain (700 μA)—essentially independent of supply voltage.
 Low input biasing current 45 Na (temperature compensated).
 Low input offset voltage 2 mV and offset current: 5 nA.
 Input common mode voltage range includes ground.
 Differential input voltage range equal to the power supply voltage.
 Large output voltage swing 0V to ±1.5V.
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Unique Characteristics:
 In the linear mode the input common-mode voltage range includes ground and the output voltage
can also swing to ground, even though operated from only a single power supply voltage.
 The unity gain cross frequency is temperature compensated.
 The input bias current is also temperature compensated.
Figure 2.9. IC LM 324
Connection Diagram:
Figure 2.10. Connection Diagram of IC LM 324
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Advantages:
 Eliminates need for dual supplies.
 Four internally compensated op amps in a single package.
 Allows directly sensing near GND and VOUT also goes to GND.
 Compatible with all forms of logic.
 Power drain suitable for battery operation.
2.5.4. Stepper Motor
Introduction:
A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a full rotation
into a large number of steps. The motor's position can be controlled precisely, without any feedback
mechanism (Open-loop controller). Stepper motors are similar to switched reluctance motors (which are
very large stepping motors with a reduced pole count and generally are closed-loop commutated.)
Fundamentals of Operation:
Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their
terminals. Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets
arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external
control circuit, such as a micro controller. To make the motor shaft turn, first electromagnet is given
power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth.
When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next
electromagnet. So, when the next electromagnet is turned on and the first is turned off, the gear rotates
slightly to align with the next one and from there the process is repeated. Each of those slight rotations is
called a "step", with an integer number of steps making a full rotation. In that way, the motor can be
turned by a precise angle.
Figure below illustrates one complete rotation of a stepper motor. At position 1, we can see that the
rotor is beginning at the upper electromagnet, which is currently active (has voltage applied to it). To
move the rotor clockwise (CW), the upper electromagnet is deactivated and the right electromagnet is
activated, causing the rotor to move 90 degrees CW, aligning itself with the active magnet. This process
21
is repeated in the same manner at the south and west electromagnets until we once again reach the
starting position.
A quick way to determine if the stepper motor is working is to short circuit every two pairs and try
turning the shaft, whenever a higher than normal resistance is felt, it indicates that the circuit to the
particular winding is closed and that the phase is working.
Figure 2.11. Stepper motor operation
22
Stepper Motor Characteristics:
1. Easy Angle and Speed Control
Stepper motors move by rotating in steps of predetermined degrees called the step angle. The degrees
rotated and the speed of rotation are easily controlled using electrical signals called pulses.
Figure 2.12. Step Angles of Stepper Motor
2. Pulses
A pulse is an electrical signal that repeats ON and OFF voltages as shown in the illustration below. Each
cycle of ON and OFF (1 cycle) is called a “pulse.” Normally, a 5 volt is used. ON is high and OFF is
low.
3. High Torque/Good Response
Stepping motors are compact, but produce high torque. This provides excellent acceleration and fast
movement.
23
4. High Resolution/High Positioning Precision
There are two types of stepping motors: the 5-phase stepping motor, which rotates 0.72° for each pulse,
and the 2-phase stepping motor, which rotates 1.8° for each pulse. The angular distance moved
corresponds to the number of pulses input, with a stopping accuracy of 0.05° with no load.
5. Holding Torque
Stepping motors produce high holding torque even while stopped. The stop position can be held without
relying on a mechanical brake.
Other Features:

Stepper motors are constant power devices.

As motor speed increases, torque decreases.

The torque curve may be extended by using current limiting drivers and increasing the driving
voltage.

Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the rotor
from one position to another.

This vibration can become very bad at some speeds and can cause the motor to lose torque.

The effect can be mitigated by accelerating quickly through the problem speeds range, physically
damping the system, or using a micro-stepping driver.
Types:
There are three main types of stepper motors:
A. Permanent Magnet (PM) Stepper Motor:
The permanent-magnet stepper motor operates on the reaction between a permanent-magnet rotor
and an electromagnetic field. Figure below shows a basic two-pole PM stepper motor. The rotor
shown in figure (a) has a permanent magnet mounted at each end. Both the stator and rotor are
shown as having teeth. The teeth on the rotor surface and the stator pole faces are offset so that there
will be only a limited number of rotor teeth aligning themselves with an energized stator pole. The
number of teeth on the rotor and stator determine the step angle that will occur each time the polarity
of the winding is reversed. The greater the number of teeth, smaller the step angle.
24
Figure 2.13.Components of a PM stepper motor: (a) Rotor (b)stator
B. Variable -Reluctance (VR) Stepper Motor:
The variable-reluctance (VR) stepper motor differs from the PM stepper in that it has no permanentmagnet rotor and no residual torque to hold the rotor at one position when turned off. When the stator
coils are energized, the rotor teeth will align with the energized stator poles. This type of motor operates
on the principle of minimizing the reluctance along the path of the applied magnetic field. By alternating
the windings that are energized in the stator, the stator field changes, and the rotor is moved to a new
position.
The stator of a variable-reluctance stepper motor has a magnetic core constructed with a stack of steel
laminations. The rotor is made of unmagnetized soft steel with teeth and slots.
25
Figure 2.14. Variable-reluctance stepper motor and switching sequence
C. Hybrid stepper Motor:
The hybrid step motor consists of two pieces of soft iron, as well as an axially magnetized, round
permanent-magnet rotor. The term hybrid is derived from the fact that the motor is operated under the
combined principles of the permanent magnet and variable-reluctance stepper motors. The stator core
structure of a hybrid motor is essentially the same as its VR counterpart. The main difference is that in
the VR motor, only one of the two coils of one phase is wound on one pole, while a typical hybrid motor
will have coils of two different phases wound on one the same pole.
The two coils at a pole are wound in a configuration known as a bifilar connection. Each pole of a hybrid
motor is covered with uniformly spaced teeth made of soft steel. The teeth on the two sections of each
pole are misaligned with each other by a half-tooth pitch. Torque is created in the hybrid motor by the
interaction of the magnetic field of the permanent magnet and the magnetic field produced by the stator.
26
Torque versus Steps:
Figure below shows a plot of the relationship between pull-in torque versus pulses per second for a
typical stepper motor. From this curve, it is apparent that torque is greatest at zero steps per second and
decreases as the number of steps increases.
Figure 2.15. Torque versus steps per second for a stepper motor
The direction of rotation is determined by applying the pulses to either the clockwise or counter
clockwise drive circuits. Rotor displacement can be very accurately repeated with each succeeding pulse.
Stepping motors are generally operated without feedback, which simplifies the control circuit
considerably. One of the most common stepper motor drive circuits is the unipolar drive. This circuit
uses bifilar windings and four Darlington transistors to control the direction of rotation and the stepping
rate of the motor.
Two Phase Stepper Motor:
Unipolar Motor:
A unipolar stepper motor has two windings per phase, one for each direction of magnetic field. In this
arrangement a magnetic pole can be reversed without switching the direction of current. Typically, given
a phase, one end of each winding is made common: giving three leads per phase and six leads for a
typical two phase motor. Often, these two phase commons are internally joined, so the motor has only
five leads.
27
Figure 2.16. Unipolar Stepper Motor Drive
Bipolar Motor:
Bipolar motors have a single winding per phase. The current in the winding needs to be reversed in order
to reverse a magnetic pole, so the driving circuit must be more complicated. There are two leads per
phase. Because windings are better utilised, they are more powerful than a unipolar motor of the same
weight.
Applications:
 Factory Automation
X-Y plotters, laser processors, electric discharge processors, NC machines, sewing machines, etc.
 Semiconductor fabrication equipment
Wafer processing devices, wafer conveyors, IC bonders, dicing machines, IC inspection devices, etc.
 Automation and labour-saving devices
ATMs, ticket machines, laboratory systems, bill counters, vending machines, etc.
 Medical equipment
28
Analytical instruments, blood pumps, centrifuges, spectrographs etc.
 Office automation
Copiers, faxes, word processors, printers, optical and magnetic disk devices etc.
2.5.5. Stepper Motor Driver: IC L 293
The L293D contains two H-bridges for driving small DC motors. It can also be used to drive stepper
motors because stepper motors are, in fact, two (or more) coils being driven in a sequence, backwards
and forwards. One L293D can, in theory, drive one bi-polar 2 phase stepper motor.
The L293D chip has 16 pins:
Pin 1, 9: Enable pins. They are hooked together and can either keep them high and run the motor all the time, or
can control them with own controller.
Pin 3, 6, 11, 14: We plug in the two coils at these pins. To tell which wires correspond to each coil, we
can use a multimeter to measure the resistance between the wires. The wires corresponding to the same
coil has a much lower resistance than wires corresponding to the different coils. (This method only
applies to bipolar stepper motors. For unipolar stepper motors, we have to refer to the specification sheet
to tell which wires correspond to each coil).We can then get one coil hooked up to pin 3,6 and another
one hooked up to pin 11, 14.
Pin 4, 5, 12, 13: These pins are hooked to ground.
Pin 8: It is used for motor voltage, for the motors we are using, it is 12V.
Pin 16: +5V supply is given to this pin. It is the power supply of the chip and its a good idea to keep this
power supply separate from motor power.
Pin 2, 7, 10, 15: Control signal pins. Here the pulse sequence is supplied. The following is how we pulse
them for a single-cycle (to move the motor in the opposite direction, just reverse the steps. i.e. from step
4 to step1):
Figure 2.17. IC L293
29
2.5.6. Voltage Regulator IC-7805
Description:
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level.
It may use an electromechanical mechanism or passive or active electronic components. Depending on
the design, it may be used to regulate one or more AC or DC voltages. With the exception of passive
shunt regulators, all modern electronic voltage regulators operate by comparing the actual output voltage
to some internal fixed reference voltage. Any difference is amplified and used to control the regulation
element in such a way as to reduce the voltage error. This forms a negative feedback control loop;
increasing the open-loop gain tends to increase regulation accuracy but reduce stability (avoidance of
oscillation, or ringing during step changes).
If the output voltage is too low the regulation element is commanded, up to a point, to produce a higher
output voltage - by dropping less of the input voltage if the output voltage is too high, the regulation
element will normally be commanded to produce a lower voltage. However, many regulators have overcurrent protection, so that they will entirely stop sourcing current (or limit the current) if the output
current is too high, and some regulators may also shut down if the input voltage is outside a given range.
Figure 2.18. Schematic of IC7805
Advantages:
The 7805 series has several key advantages over many other voltage regulator circuits which have
resulted in its popularity:
30

7805 series ICs do not require any additional components to provide a constant, regulated source
of power, making them easy to use, as well as economical. By contrast, most other voltage
regulators require several additional components to set the output voltage level, or to assist in the
regulation process.

78xx series ICs have built-in protection against a circuit drawing too much power. They also
have protection against overheating and short-circuits, making them quite robust in most
applications. In some cases, the current-limiting features of the 78xx devices can provide
protection not only for the 78xx itself, but also for other parts of the circuit it is used in,
preventing other components from being damaged as well.
Disadvantages:
The 78xx devices have a few drawbacks which can make them unsuitable or less desirable for some
applications:

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 which requires 5 volts using 6volt 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 input voltage must always be higher than the output voltage, this means
that the total power (voltage multiplied by current) going into the 78xx 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 heat sink must be provided.
2.5.7. Crystal Oscillator
A crystal
oscillator is
an electronic
circuit that
uses
the
mechanical resonance of
a
vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency.
This
frequency is
commonly used
to
keep track of time,
to
provide
a stable clock
signal for digital integrated circuits and to stabilize frequencies for radio transmitters and receivers.
31
A crystal oscillator is an electronic circuit that produces electrical oscillations at a particular designed
frequency determined by the physical characteristics of one or more crystals, generally of quartz,
positioned in the circuit feedback loop. A piezoelectric effect causes a crystal such as quartz to vibrate
and resonate at a particular frequency. The crystal oscillator is generally used in various forms such as a
frequency generator, a frequency modulator and a frequency converter.
Figure 2.19. Crystal Oscillator
The crystal oscillator utilizes crystal having excellent piezoelectric characteristics, in which crystal
functions as a stable mechanical vibrator. There are many types of crystal oscillators. One of them is a
crystal oscillator employing an inverting amplifier including a CMOS (complementary metal oxide
semiconductor) circuit. Temperature-compensated crystal oscillators in which variation in oscillation
frequency arises from the frequency-temperature characteristic of the quartz-crystal unit is compensated.
A surface mounting crystal oscillator is used mainly as a frequency reference source particularly for a
variety of portable electronic devices such as portable telephones because of its compact size and light
weight.
32
Operation:
When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by
applying a voltage to an electrode near or on the crystal. This property is known as piezoelectricity.
When the field is removed, the quartz will generate an electric field as it returns to its previous shape,
and this can generate a voltage. The result is that a quartz crystal behaves like a circuit composed of
an inductor, capacitor and resistor, with a precise resonant frequency.
Crystal Oscillator Circuit used in Mocrocontroller:
A microcontroller is disclosed that includes a crystal oscillator circuit that is programmable to provide
multiple different levels of startup current.. XTAL1 and XTAL2 are the input and output, respectively,
of an inverting amplifier that can be configured for use as an on-chip oscillator. Either a quartz crystal or
ceramic resonator may be used. For frequencies above 16MHz it is recommended that C1 be replaced
with R1 for improved startup performance.
Figure 2.20.Oscillator Connections
33
To drive the device from an external clock source, XTAL2 should be left unconnected while
XTAL1 is driven.
Figure 2.21. External Clock Drive Configuration
Advantages:
 High stability
 Exhibit very low phase noise
 Good temperature stability
Limitation:
 Environmental changes of temperature, humidity, pressure, and vibration can change the resonant
frequency.
34
2.5.8. LCD (Liquid Crystal Display)
A liquid crystal display (LCD) is a thin, flat panel used for electronically displaying information such
as text, images and moving pictures. Its uses include monitors for computers, televisions, gaming
devices, watches, calculators etc.It consumes low electrical power and is an electronically-modulated
optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light
source (backlight) or reflector to produce images in colour or monochrome.
Specifications:
Important factors to be considered while evaluating an LCD monitor are:
 Resolution: The horizontal and vertical screen size expressed in pixels (e.g., 1,024×768).
 Dot pitch: The distance between the centres of two adjacent pixels. The smaller the dot pitch size,
the less granularity is present resulting in a sharper image.
 Viewable size: The size of an LCD panel measured on the diagonal (more specifically known as
active display area).
 Response time: The minimum time necessary to change a pixel's colour or brightness.
 Input lag - A delay between the moment monitor receives the image over display link and the
moment the image is displayed. Input lag is caused by internal digital processing such as image
scaling, noise reduction and details enhancement.
 Refresh rate: The number of times per second in which the monitor draws the data it is being given.
 Matrix type: Active TFT or Passive.
 Brightness: The amount of light emitted from the display (more specifically known as luminance).
 Contrast ratio: The ratio of the intensity of the brightest bright to the darkest dark.
 Aspect ratio: The ratio of the width to the height (for example, 4:3, 5:4, 16:9 or 16:10).
35
Colour Display:
In colour LCDs each individual pixel is divided into three cells, or sub pixels, which are coloured red,
green, and blue, respectively.LCD and CRT monitors are direct applications of the RGB colour model
and give the illusion of representing a continuous spectrum of hues as a result of the trichromatic nature
of human vision.
Figure 2.22. Colour Display in LCD
Colour components may be arrayed in various pixel geometries, depending on the monitor's usage. If the
software knows which type of geometry is being used in a given LCD, this can be used to increase the
apparent resolution of the monitor through sub pixel rendering. This technique is especially useful for
text anti-aliasing.
Passive Matrix Addressed LCDs:
LCDs with a small number of segments have individual electrical contacts for each segment.An external
dedicated circuit supplies an electric charge to control each segment. Small monochrome displays have a
passive-matrix structure employing Super Twisted Nematic (STN) or Double Layer STN (DSTN)
technology and colour-STN (CSTN)—wherein colour is added by using an internal filter.
Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time
by row and column addresses. This type of display is called passive-matrix addressed because the pixel
36
must retain its state between refreshes without the benefit of a steady electrical charge. As the number of
pixels (and, correspondingly columns and rows) increases, this type of display becomes less feasible.
Very slow response times and poor contrast are typical of passive-matrix addressed LCDs.
Active Matrix Addressed LCDs:
High-resolution colour displays such as modern LCD computer monitors and televisions use an active
matrix structure.A matrix of thin-film transistors (TFTs) is added to the polarizing and colour filters.
Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row
line is activated, all of the column lines are connected to a row of pixels and the correct voltage is driven
onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the
row lines are activated in sequence during a refresh operation. Active-matrix addressed displays look
"brighter" and "sharper" than passive-matrix addressed displays of the same size, and generally have
quicker response times, producing much better images.
Figure 2.23. LCD
2.5.9.Battery
The battery used here has following specifications:
MODEL NUMBER: 12V 1.3AH 20HR
TYPE: VRLA BATEERY
NOMINAL VOLTAGE: 12V
NOMINAL CAPACITY: 1.3AH
37
A VRLA battery (valve-regulated lead-acid battery) is the designation for low-maintenance lead-acid
rechargeable batteries. Because of their construction, VRLA batteries do not require regular addition of
water to the cells.
These batteries are often colloquially called sealed lead-acid batteries, but they always include a safety
pressure relief valve. As opposed to vented (also called flooded) batteries, a VRLA cannot spill its
electrolyte if it is inverted because VRLA batteries use much less electrolyte (battery acid) than
traditional lead-acid batteries.
Construction:
 Sealant: Epoxy resin
 Positive: Lead dioxide
 Negative: Lead
 Terminal: Copper
 Separator: Fibre Glass
 Electrolyte: Sulphuric Acid
General Features:
 Sealed and maintenance free operation
 Non spill able construction design
 Safety valve installation for explosion proof
 High quality and reliability
 Exceptional deep discharge recovery performance
 Low self discharge characteristics
 Flexible design for multiple install positions
38
Figure 2.24. Battery
2.5.10. Buzzer
A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical
or electronic. Typical uses of buzzers and beepers include alarms, timers and confirmation of user input
such as a mouse click or keystroke.In electronic buzzer a piezoelectric element may be driven by
an oscillating electronic circuit or other audio signal source. Sounds commonly used to indicate that a
button has been pressed are a click, a ring or a beep.
Uses:
 Annunciation panels
 Electronic metronomes
 Game shows : The buzzer is also used to signal wrong answers and when time expires on many
game shows.
 Microwave ovens and other household appliances
Figure 2.25.Symbol of Buzzer
Figure 2.26. Buzzer
39
2.5.11. Resistors
The resistor's function is to reduce the flow of electric current. This symbol
is used to indicate a
resistor in a circuit diagram, known as a schematic. Resistance value is designated in units called the
"Ohm." There are two classes of resistors:
 Fixed resistors
 Variable resistors
They are also classified according to the material from which they are made. The typical resistor is made
of either carbon film or metal film. The resistance value of the resistor is not the only thing to consider
when selecting a resistor for use in a circuit. The "tolerance" and the electric power ratings of the resistor
are also important. The maximum rated power of the resistor is specified in Watts. Power is calculated
using the square of the current ( I2 ) x the resistance value ( R ) of the resistor. If the maximum rating of
the resistor is exceeded, it will become extremely hot, and may even burn. Generally, it's safe to choose a
resistor which has a power rating of about twice the power consumption needed. The resistance value is
displayed using the colour code.
A. Fixed Resistors:
A fixed resistor is one in which the value of its resistance cannot change.
Carbon film resistor : This is the most general purpose, cheap resistor. Usually the tolerance of the
resistance value is ±5%. Power ratings of 1/8W, 1/4W and 1/2W are frequently used. This resistor is
called a Single-In-Line(SIL) resistor network. It is made with many resistors of the same value, all in one
package. One side of each resistor is connected with one side of all the other resistors inside.
Figure 2.27. Fixed Resistance
Metal film resistors: Metal film resistors are used when a higher tolerance (more accurate value) is
needed. They are much more accurate in value than carbon film resistors. They have about ±0.05%
tolerance. They have about ±0.05% tolerance .Ni-Cr (Nichrome) used for the material of resistor. The
metal film resistor is used for bridge circuits, filter circuits, and low-noise analog signal circuits.
40
B. Variable Resistors:
There are two general ways in which variable resistors are used. One is the variable resistor which value
is easily changed, like the volume adjustment of Radio. The other is semi-fixed resistor that is not meant
to be circuit by the technician. Semi-fixed resistors are used to compensate for the inaccuracies of the
resistors, and to fine-tune a circuit. The rotation angle of the variable resistor is usually about 300
degrees. Some variable resistors must be turned many times to use the whole range of resistance they
offer. This allows for very precise adjustments of their value.
Figure 2.28. Variable Resistance
Resistances used in the Project:
 A resistance of 2.2k (RRR)
 A resistance of 1k(BBO)
 Two resistance of 10k(BBR)
 Two variable resistance of 10k
 A network resistance of 10k each
Figure 2.29. Network Resistance
41
Resistor colour code:
Colour
Value
Multiplier
Tolerance
(%)
Black
0
0
-
Brown
1
1
±1
Red
2
2
±2
Orange
3
3
±0.05
Yellow
4
4
-
Green
5
5
±0.5
Blue
6
6
±0.25
Violet
7
7
±0.1
Gray
8
8
-
White
9
9
-
Gold
-
-1
±5
Silver
-
-2
±10
None
-
-
±20
Table 2.1. Resistor Colour Code
42
2.5.12. Capacitors
The capacitor's function is to store electricity, or electrical energy. The capacitor also functions as a
filter, passing alternating current (AC) and blocking direct current (DC). This symbol
is used to
indicate a capacitor in a circuit diagram. The capacitor is constructed with two electrode plates facing
each other but separated by an insulator.
When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the
capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully
charged.
The most used capacitors are mica, paper, electrolytic and ceramic capacitors. Electrolytic capacitors use
a molecular thin oxide film as the dielectric resulting in large capacitance values. There is no polarity
required, since either side can be the most positive plate, except for electrolytic capacitors. These are
marked to indicate which side must be positive to maintain the internal electrolytic action that produces
the dielectric required to form the capacitance. It should be noted that the polarity of the charging source
determines the polarity of the capacitor voltage.
Capacitance:
This is a measure of a capacitor's ability to store charge. Capacitance is measured in farads, symbol F.
However 1F is very large, so prefixes are used to show the smaller values. Three prefixes (multipliers)
are used, µ (micro), n (nano) and p (pico).
Types of Capacitors:
There are various types of capacitors available in the market. Some of them are as follows:
 Mica Capacitor
 Paper Capacitor
 Ceramic Capacitor
 Variable Capacitor
 Electrolytic Capacitor
 Film Capacitor
 Polystyrene Capacitor
43
Polarised Capacitors (large values, 1µF +):
Examples:
:
Figure 2.30. Polarised Capacitor
Electrolytic Capacitors:
Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of
their leads will be marked + or -. The construction consists of two metal electrodes, usually Aluminium,
in an electrode of Borax, Phosphate or Carbonate. Between the two aluminium strips, absorbent gauze
soaks up to provide the required electrolysis.
Figure 2.31. Electrolytic Capacitor
44
Unpolarised Capacitors (small values, up to 1µF):
Examples:
:
Figure 2.32.Unpolarised Capacitors
Small value capacitors are unpolarised and may be connected either way round. They are not damaged
by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at
least 50V, usually 250V or so.
Capacitor Number Code:
A number code is often used on small capacitors where printing is difficult:
 The 1st number is the 1st digit,
 The 2nd number is the 2nd digit,
 The 3rd number is the number of zeros to give the capacitance in pF.
Ignore any letters - they just indicate tolerance and voltage rating.
For example: 102 means 1000pF = 1nF (not 102pF!)
Capacitor Colour Code:
A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there
are many still around. The colours should be read like the resistor code, the top three colour bands giving
the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating). For example:
45
Colour
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Number
0
1
2
3
4
5
6
7
8
9
Table 2.2.Capacitor Colour Codes
Ceramic Capacitor:
The ceramic dielectric materials are made from earth under extreme heat. By use of titanium dioxide or
several types of silicates, very high values of dielectric constant can be obtained.
Figure 2.33.Ceramic Capacitor
.
46
CHAPTER 3
PCB DESIGNING
3.1. PCB Layout
Figure3.1. Layout of PCB containing Microcontroller
47
Figure3.2.Layout of PCB containing Stepper Motor Driver
48
3.2. PCB Making
A printed circuit board or PCB, is used to mechanically support and electrically connect electronic
components using conductive pathways, tracks, or traces, etched from copper sheets laminated onto a
non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. A
PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed
circuit board assembly (PCBA).
In past PCB was build on photosensitive resin coated ceramic or FR4 substrates, exposing the board to
UV light with a mask or stencil between the light source and the board with the purpose of setting the
features included in the mask (the design) into the resin. Next the material was developed using a
chemical agent to attack the non-reacted resin. Then copper or aluminium plating was done to create the
circuitry on the channels created. An optional step to cover again with a second step of photosensitive
resin could be done to protect the metal traces and leave exposed only the areas for component
attachment. Only one layer of circuitry was allowed with this process; in many ways this is still
sufficient if the application is not too demanding: low number of components, relatively moderate
requirements for power and heat dissipation.
More complex designs require that this basic process be repeated several times to create a multilayered
board, where alternate coatings with resin, exposure, development, etching, plating and recoating are
conducted to grow metal and isolator layers. This is required to enable sufficient escape lines for all
signals and enough input lines for power and ground.
Material used:
Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically
laminated together with epoxy resin . The board is typically coated with a solder mask that is green in
colour. Other colours that are normally available are blue and red. There are quite a few different
dielectrics that can be chosen to provide different insulating values depending on the requirements of the
circuit. Some of these dielectrics are polytetrafluroethylene (Teflon).The board used in original form for
the making of PCB is called as Copper Clad Sheet on which various operations are performed. Typical
density of a raw PCB (an average amount of traces, holes with no components) is 2.15g / cm3.
49
Steps Involved in Making PCB:
PROCESSING
CLEANING
PRINTING
ETCHING
DRILLING
SOLDERING
MASKING
TESTING
Processing:
The layout of a PCB has to incorporate all the information on the board before one can go on to the
artwork preparation. The detailed circuit diagram is very important for the layout designer and he must
also be familiar with the design concept and with the philosophy behind the equipment. The general
considerations are:
Layout scale:
Depending on the accuracy required, artwork should be produced at a 1:1 or 2:1 or even 4:1 scale. The
layout is best prepared on the same scale as the artwork
50
Board Types:
There are two sides of a PCB board – Component side and Solder side. Depending on these PCB boards
are classified as:
 Single-sided Boards: These are used where cost has to be kept at a minimum and a particular circuit
can be accommodated on such board. To jump over conductor tracks, components have to be
utilized. If this is not feasible jumper wires are used.
 Double-sided Boards: These are made with or without plated through holes. Plated through holes
are fairly expensive.
Cleaning:
The cleaning of the copper surface prior to resist application is an essential step for any type of PCB
process using etches or plating resist.
After scrubbing with the abrasive, a water rinse will remove most of the remaining slurry.
Etching:
Etching is a process of removing unwanted copper after applying mask on the copper clad sheet. There
are three common "subtractive" methods (methods that remove copper) used for the production of
printed circuit boards:
1)
Silk Screen Printing
2)
Photoengraving
3)
PCB Milling
It is of utmost importance to choose a suitable Etchant Systems. There are many factors to be
considered: Etching speed
 Copper solving capacity
 Etchant price
 Pollution character
We have used FeCl3 (Conc. 120 g/litre 0.1 M) for etching.
51
Reactions Involved:
FeCl3
+
3H 2O
Fe(OH)3
+
FeCl3
+
FeCl3
CuCl2
3HCl (Free acid attack to copper)
Cu
FeCl2
+
CuCl
+
CuCl
FeCl2
+
CuCl2
+
Cu
2CuCl
Drilling:
Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling
is performed by automated drilling machines with placement controlled by a drill tapeor drill file. These
computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files".
These holes are often filled with annular rings (hollow rivets) to create vias. Vias allow the electrical and
thermal connection of conductors on opposite sides of the PCB.
The following hole diameter tolerances have been generally accepted wherever no other specifications
are mentioned.
Hole Diameter
(D) <= 1mm
+ / - 0.05 mm
Hole Diameter
(D) > 3 mm
+ / – 0.1 mm
Drill bits are made up of high-speed steel (HSS), Glass epoxy material, Tungsten Carbide.
Figure 3.3. Drilling Machine
52
Soldering:
Solder is a fusible metal alloy with a melting point or melting range of 90 to 450 °C (200 to 840 °F),
used in a process called soldering where it is melted to join metallic surfaces. Alloys that melt between
180 and 190 °C are the most commonly used.
Lead Solder:
Tin/lead solders, also called soft solders, are commercially available with tin concentrations between 5%
and 70% by weight. The greater the tin concentration, the greater the solder’stensile and shear strengths.
Hard Solder:
Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or
silver are the most common.
Flux Core Solder:
Flux is a reducing agent designed to help remove impurities (specifically oxidised metals) from the
points of contact to improve the electrical connection and mechanical strength. The two principal types
of flux are acid flux, used for metal mending and plumbing, and rosin flux, used in electronics.
Lead Free Solder:
Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony,
and traces of other metals.
Figure 3.4. Solder Iron
Figure 3.5. Solder Wire
53
Masking:
It is done for the protection of conductor track from oxidation. Solder mask or solder resist provides a
permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder
from bridging between conductors, thereby preventing short circuits. It also provides some protection
from the environment.
The lowest cost solder mask is epoxy liquid that is silk screened through the pattern on to the PCB.
Other types are the liquid photoimageable solder mask (LPSM) inks and dry film photoimageable solder
mask (DFSM).
Testing:
After assembling the circuit components on the PCB and soldering them according to the layout, testing
is the next step to be taken. Testing includes measurement of the parameters such as current, voltage,
clock frequency and comparing them with the standard values provided with the circuit. Any sort of
deviation from the actual values should be measured and corrected accordingly. Unpopulated boards
may be subjected to a bare-board test where each circuit connection (as defined in a netlist) is verified as
correct on the finished board.
Designing of PCB Layout:
A PCB layout is required to place components on the PCB so that the component area can be minimized
and the components can be placed in an efficient manner. The components can be placed in two ways,
either manually or by software. The manual procedure is quiet cumbersome and is very inefficient. The
other method is by the use of computer software. This method is advantageous as it saves time and
valuable copper area. There are various softwares available for this purpose like Express PCB
 Pad to Pad
 Protel PCB
 PCB design etc
Many of them are loaded with auto routing and auto placement facility. The software that we have used
here is EXPRESS PCB.
54
Express PCB
Express PCB is a very easy to use with Windows application for laying out printed circuit boards. There
are two parts Express SCH for drawing schematics and Express PCB for designing circuit boards. We
downloaded the software from the website www.expresspcb.com.
There are lots of functions available in the software. This software is free of cost and also it is very easy
to use. The different layers of the PCB can be viewed by just a click of a button on the interface. And we
easily get its print on paper which is utilized for further processing. We can design single sided PCB as
well as Double Sided PCB with this Software.
55
CHAPTER 4
CONCLUSION &FUTURE SCOPE
Conclusion
Every project is meant for sake of betterment of daily life. Wide application range of our project
includes industries, vehicles, household etc making it a life and property saving project. Thus
revealing its high importance. Its installation at desired location is very easy and so is its operation.
Though this project has few limitations as any other project would have but they could be easily
avoided or overcome by taking suitable precautionary measures.
Considering its uses in different fields, its applicability to all sections of society and its property of
averting casualties makes it a feasible project in terms of cost. Thus we hope to see it being used
widely.
4.1. Future Scope
Current project uses gas sensors for the detection of LPG and CNG leakage. This project can be
further modified by the use of various other sensors which are sensitive for the detection of
presence of other gases as well.
In its current form this project finds application in various household and industrial departments.
Incorporated with more and powerful sensors it can be used on large scale to monitor presence of
various gases in atmosphere and sound alert when a particular level of gas exceeds. Therefore it
can be used by various research agencies where atmospheric constituents matters a lot be it
biological field or some space program.
A fire sensor can also be incorporated in the project which can used to sense fire. Microcontroller
can be programmed to a particular temperature at which it will trigger the buzzer to sound alert in
case it gets a signal from the fire sensor indicating that the temperature had risen above the
programmed temperature.
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A fire extinguisher can also be installed with the module so that in case of fire a preventive action
is taken automatically by the device. After sensing the fire microcontroller can automatically
trigger the fire extinguisher to release the nitrogen gas.
Another possible modification in the project can be installation of a transmitter in the module so
that a receiver section with mobile user or monitoring station at a remote place can help to
constantly supervise the operation.
This project proves out to be very useful when it comes to avert tragedies which may occur due to
gas leakage or fire that may occur. Thus it saves life and property as well. Conceptually being
simple, its implementation on large scale is also easily feasible.
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REFERENCES
1. The 8085 Microcontroller and Embedded Systems
Muhammad Ali Mazidi
2. OP- AMPs and Linear ICs
R.A.Gayakwad
3. Integrated Electronics
J.Milliman and Halkiyas
4. www.extremeelectronics.co.in
5. www.howstuffworks.com
6. www.allaboutcircuits.com
7. www.stepperstuff.com
8. www.wikipedia.com
9. www.electronics-lab.com
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