lpg1.5.docx
TRANSCRIPT
Chapter 1
INTRODUCTION
1.1 overview
In human’s daily life, environment gives the most significant impact to their health
issues. Therefore, environment and industry air quality issues are critically discussed to
increase the awareness and responsibility regarding the threat on the environment towards
public and workers health. Most of the dangerous gas such as carbon monoxide (CO),
refrigerant gas and liquefied petroleum gas (LPG) are colourless and odourless compound
that are produced by incomplete combustion. Therefore, gas detector device is needed in
order to inform the safety situation continuously.
An embedded system is a computer system with a dedicated function within a larger
mechanical or electrical system, often with real-time computing constraints. It is embedded
as part of a complete device often including hardware and mechanical parts. By contrast, a
general-purpose computer, such as a personal computer (PC), is designed to be flexible and to
meet a wide range of end-user needs. Embedded systems control many devices in common
use today.
An embedded system is a special-purpose computer system designed to perform one
or a few dedicated functions, sometimes with real-time computing constraints. In contrast, a
general-purpose computer, such as a personal computer, can do many different tasks
depending on programming. Embedded systems have become very important today as they
control many of the common devices we use. A modern example of embedded system is
shown in fig 1.1
Fig 1.1 modern example of embedded system
This project also comes under embedded system. This project is designed to detect
dangerous gases in mines. If human being exposed to these gases then their health will be
damaged. So we will send a robot instead of human beings. Robot consists of gas sensor.
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Robot movements can be controlled wirelessly using RF communication . As a
solution for the problem, a monitoring system of gas detector by wireless system needs to be
developed in order to solve the problem. By monitoring system wirelessly, user can remotely
view the condition of the required place without them being there themselves. Therefore we
send a robot for prior checking the area.
A robot is an electromechanical device that can perform autonomous or predefined
programmed tasks. A robot may work under a human or according to the tasks defined.
Robots may be used to perform the tasks that are too dangerous or harmful for the humans. A
robot is designed and constructed with associated electronic circuits to move into an
unknown location and transport the details to the home place. The robots will have inbuilt
sensors to achieve this. The robot is equipped with the gas sensor, buzzer and a wireless
transmission and a reception module. Whenever the system detects the increase in the
concentration of the LPG it will stop there and immediately alerts by activating the buzzer.
1.2 Problem outline
Sensing technology has been widely investigated and utilized for gas detection. The
advancement of smart sensor technology has allowed us to design and development of a
flexible reliable smart gas detection system to detect gases such as combustible and LPG in
the real life. Gas sensing technology has become more significant because of its widespread
and common applications in the following areas:
(1) Automobile industry (e.g., detection of polluting gases from vehicles),
(2) Industrial production (e.g., methane detection in mines),
(3) Medical applications,
(4) Detection of indoor carbon monoxide,
(5) Greenhouse gas monitoring,
(6) Detection of LPG.
Gas detection systems became a concern after the effects of harmful gases on human
health were discovered. Gas detection systems are systems which identify potentially
hazardous gas leaks within an area by means of various sensors based electronic systems.[1]
These systems also employ an audible alarm to alert people whenever a dangerous gas is
detected. These gas detection systems are of immense use because they can be used to detect
a wide range of combustible, flammable and toxic gases which have hazardous effects on
human health.
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In general the gas leakage detection system is classified based on operating mode of the
sensor, one is based on direct contact, where the monitoring station and sensing unit are
wired or could be wireless, enabling their integration with a wireless module . The other type
is based on wireless transducers utilizing the change of electrical indicators to indicate the
variation of physical parameters, such as gas concentration. While most sensors belong to the
first type, we think that the latter type of sensor could be regarded as a new type of
reconfigurable antenna. Unlike conventional reconfigurable antennas, the reconfigurable part
is controlled by the gas concentration. The wireless sensor networks are very popular and are
studied widely on the hardware and software configurations.
1.3 Proposed idea
In this project we use wireless RF technology:
The project is to design and develop an intelligence robot to detect smoke/gas by
using an 8 bit microcontroller.
The robot acts according to the command given by the controller.
To move in all the directions like forward, backward, right and left.
If any smoke/gas is detected the robot will give a buzzer sound.
In this prototype project we design in such a way that the robot can be moved anywhere
with the user commands. This project is very much useful in the places where a human
cannot go into the places like ground canals, smoke oriented caves, coal mines etc., and this
project is very much useful in such situations
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Chapter 2
WIRELESS RF TECHNOLOGY
2.1 What is wireless?
Wireless is a term used to describe telecommunications in which electromagnetic
waves (rather than some form of wire) carry the signal over part or all of the communication
path. Some monitoring devices, such as intrusion alarms, employ acoustic waves at
frequencies above the range of human hearing; these are also sometimes classified as
wireless. Wireless technology is rapidly evolving, and is playing an increasing role in the
lives of people throughout the world. In addition, ever-larger numbers of people are relying
on the technology directly or indirectly.
Examples of Wireless devices:
Baby monitors
These devices are simplified radio transmitter/receiver units with limited range.
Cellular phones and pagers
These provides connectivity for portable and mobile applications, both personal and
business.
Two way radios
This includes Amateur and Citizens Radio Service, as well as business, marine, and
military Communications.
Satellite television
Allows viewers in almost any location to select from hundreds of channels. Etc.,
Global positioning system (GPS)
GPS allows drivers of cars and trucks, captains of boats and ships, and pilots of
aircraft to ascertain their location anywhere on earth.
2.2 wireless communications
Wireless communication is the transfer of information between two or more points
that are not connected by an electrical conductor. The most common wireless technologies
use radio. With radio waves distances can be short, such as a few meters for television or as
far as thousands or even millions of kilometers for deep-space radio communications. It
encompasses various types of fixed, mobile, and portable applications, including two-way
radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other
examples of applications of radio wireless technology include GPS units, garage door
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openers, wireless computer mice, keyboards and headsets, headphones, radio receivers,
satellite television, broadcast television and cordless telephones.
Fig 2.1 Wireless communication
Wireless operations permit services, such as long-range communications, that are
impossible or impractical to implement with the use of wires. The term is commonly used in
the telecommunications industry to refer to telecommunications systems (e.g. radio
transmitters and receivers, remote controls etc.) which use some form of energy (e.g. radio
waves, acoustic energy, etc.) to transfer information without the use of wires. Information is
transferred in this manner over both short and long distances. The term "wireless" came into
public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter
device), establishing its usage in the field of wireless telegraphy early on; now the term is
used to describe modern wireless connections such as in cellular networks and wireless
broadband Internet. It is also used in a general sense to refer to any type of operation that is
implemented without the use of wires, such as "wireless remote control" or "wireless energy
transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) used.
2.2.1Types of wireless communications:
The different types of wireless communication technologies include:
Infrared (IR) wireless communication:
IR wireless communication communicates data or information in devices or systems
through infrared (IR) radiation. Infrared is electromagnetic energy at a wavelength that is
longer than that of red light.IR wireless is used for short and medium-range communications
and security control. For IR communication to work, the systems mostly operate in line-of-
sight mode which means that there must be no obstruction between the transmitter (source)
and receiver (destination). Infrared is used in television remote controls and security
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systems. The source and/or destination can be laptops, mobile phones, televisions, security
systems and any other device that supports wireless communication.
Broadcast Radio
Basically an audio broadcasting service, radio broadcasts sound through the air as radio
waves. It uses a transmitter to transmit radio waves to a receiving antenna. To broadcast
common programming, stations are linked to the radio networks. The broadcast occurs either
in syndication or simulcast (simultaneous broadcast) or both. Radio broadcasting can also be
done via cable FM, the internet and satellites. A radio broadcast sends data over long
distances (across countries) at up to 2 megabits per second (AM/FM Radio).
Microwave Radio
Microwave transmission involves the transfer of voice and data through the
atmosphere as super high-frequency radio waves called microwaves. Microwave transmission
is mainly used to transmit messages between ground-based stations and satellite
communications systems.
Microwave transmission mainly uses radio waves whose wavelengths are
conveniently measured in small units such as centimeters. Microwaves belong to the radio
spectrum ranges of roughly 1.0 gigahertz (GHz) to 30 GHz. Antennas used in microwave
transmissions are of convenient sizes and shapes. Microwave transmission depends on line-
of-sight in order to work properly. The main drawback of microwave signals is that they can
be affected by bad weather, especially rain.
Communications Satellites
A communication satellite is an artificial satellite used specifically as a
communication transmitter/receiver in orbit. It behaves like a radio relay station above the
earth to receive, amplify, and redirect analog and digital signals carried on a specific radio
frequency. The huge capability makes communication satellites an ideal medium for
transmitting and receiving all kinds of content, including audios and videos.
Applications of Wireless Communication
Television Remote Control
Modern televisions use wireless remote control. Currently radio waves are also used.
Wi-fi
This is a wireless local area network that establishes internet connection with the
portable computers.
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Security systems
For homes and office buildings, hard wired implementation security systems are
replaced by the Wireless technology.
Cellular Telephone
Radio waves are used to facilitate the operator to make phone calls from any place on
the earth. CDMA, GSM, and 3G are examples of the advancement made by wireless
communication in the domain.
Wireless energy transfer
A process where a power source transmits electrical energy to electrical load which
does not have built-in power source wirelessly.
2.3 Wireless network
A wireless network is any type of computer network that uses wireless data
connections for connecting network nodes. Wireless networking is a method by which
homes, telecommunications networks and enterprise (business) installations avoid the costly
process of introducing cables into a building, or as a connection between various equipment
locations. Wireless telecommunications networks are generally implemented and
administered using radio communication. This implementation takes place at the physical
level (layer) of the OSI model network structure.
The following situations justify the use of wireless technology:
To span a distance beyond the capabilities of typical cabling,
To provide a backup communications link in case of normal network failure,
To link portable or temporary workstations,
To overcome situations where normal cabling is difficult or financially impractical, or
To remotely connect mobile users or networks.
Developers need to consider some parameters involving Wireless RF technology for
better developing wireless networks:
Sub-GHz versus 2.4 GHz frequency trends,
Operating range and battery life,
Sensitivity and data rate,
Network topology and node intelligence.
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2.4 Radio Frequency
Radio frequency is the rate of oscillation in the range of about 3Hz to 300GHz which
corresponds to the frequency of radio waves, and the alternating currents which carry the
radio signals. In general any frequency < 300 GHz is termed as radio waves. The radio waves
are the very starting point of the EM spectrum. The Radio Wave Wavelength lies in 1mm to
100,000km. And the Radio Wave Frequency lies between as low as 3 Hz to as high as 300
GHz. The radio waves are generally used in communication systems.
2.5 Radio communication
To receive radio signals an antenna must be used. However, since the antenna will pick
up thousands of radio signals at a time, a radio tuner is necessary to tune into a particular
frequency (or frequency range). This is typically done via a resonator – in its simplest form, a
circuit with a capacitor and an inductor form a tuned circuit. The resonator amplifies
oscillations within a particular frequency band, while reducing oscillations at other
frequencies outside the band. Another method to isolate a particular radio frequency is by
oversampling (which gets a wide range of frequencies) and picking out the frequencies of
interest, as done in software defined radio.
The distance over which radio communications is useful depends significantly on
things other than wavelength, such as transmitter power, receiver quality, type, size, and
height of antenna, mode of transmission, noise, and interfering signals. Ground waves,
tropospheric scatter and sky waves can all achieve greater ranges than line-of-sight
propagation. The study of radio propagation allows estimates of useful range to be.
The Radio Wave Frequency band is generally divided into several categories
according to their wavelength and uses. Table 2.1 shows the radio-frequency spectrum
broken down into nine bands.
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Table 2-1.—Radio-Frequency Spectrum
Frequency Description
30 GHZ - 300 GHZ Extremely high frequency
3 GHZ - 30 GHZ Super high frequency
300 MHZ - 3 GHZ Ultra high frequency
30 MHZ - 300 MHZ Very high frequency
3 MHZ - 30 MHZ High frequency
300 KHZ - 3 MHZ Medium frequency
30 KHZ - 300 KHZ Low frequency
3 KHZ - 30 KHZ Very low frequency
300 HZ - 3 KHZ Voice frequency
Up to 300 HZ Extremely low frequency
A radio frequency (RF) signal refers to a wireless electromagnetic signal used as a
form of communication, if one is discussing wireless electronics. Radio waves are a form of
electromagnetic radiation with identified radio frequencies that range from 3Hz to 300 GHz.
Frequency refers to the rate of oscillation (of the radio waves.) RF propagation occurs at the
speed of light and does not need a medium like air in order to travel. RF waves occur
naturally from sun flares, lightning, and from stars in space that radiate RF waves as they age.
Humankind communicates with artificially created radio waves that oscillate at various
chosen frequencies.
RF communication is used in many industries including television broadcasting,
radar systems, computer and mobile platform networks, remote control, remote
metering/monitoring, and many more. While individual radio components such as mixers,
filters, and power amplifiers can be classified according to operating frequency range, they
cannot be strictly categorized by wireless standard (e.g. Wi-Fi, Bluetooth, etc.) because these
devices only provide physical layer (PHY) support. In contrast, RF modules, transceivers,
often include data link layer support for one or more wireless communication protocols.
Propagation of radio waves varies widely at different frequencies. Frequencies and equipment
are chosen to meet the communications application desired.
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2.6 RF Module
An RF module (radio frequency module) is a (usually) small electronic device used
to transmit and/or receive radio signals between two devices. In an embedded system it is
often desirable to communicate with another device wirelessly. This wireless communication
may be accomplished through optical communication or through Radio Frequency (RF)
communication. For many applications the medium of choice is RF since it does not require
line of sight. RF communications incorporate a transmitter and/or receiver. RF Modules are
widely used in consumer applications such as garage door openers, wireless alarm systems,
industrial remote controls, smart sensor applications, and wireless home automation systems.
They are often used instead of infrared remote controls as they have the advantage of not
requiring line-of-sight operation.
Main factor affecting RF modules performance
As with any other radio-frequency device, the performance of an RF Module will
depend on a number of factors. For example, by increasing the transmitter power, a larger
communication distance will be achieved. However, this will also result in a higher electrical
power drain on the transmitter device, which will cause shorter operating life for battery
powered devices. Also, using a higher transmit power will make the system more prone to
interference with other RF devices.
Chapter 3
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IDENTIFICATION OF HAZARDOUS GAS (LPG) IN
UNDERGROUND APPLICATIONS
3.1 Mine Gases
Based on Occupational Safety and Health Administration (OSHA), the definition of
hazardous gas is defined as those chemical present in the workplace which are capable of
causing harm. From the definition of the hazardous gas, the chemical term refer to dust,
mixtures and common materials such as paints, fuels and solvents. According to the
limitation of the LPG gas, OSHA mentioned that exposes over 1000ppm of LPG gas will
cause hazard to the human respiration system
The goal of mining is to obtain coal from the ground. The gases most commonly
found in mines are oxygen, nitrogen, carbon dioxide, and methane. In connection with gob
fires, blasting operations, and explosions, carbonmonoxide is very common, while in these
and cases hydrogen sulphide, hydrogen, ethylene, nitrous oxide, etc., sometimes occur.
The staggering data reveals that huge number of accidents occur in a coal mine during
and after a disaster. The main reasons being, gas accidents, caving, flood, etc. This really asks
for the development of a system that can help minimize the human and material loss
that happens during rescue operations. Gas explosion is the most serious one in all mine
disasters for after the gas explosion, the scene becomes extremely complex. Thus gas sensors
are mandatory in the robot to be deployed.
3.2 LIQUIFIED PETROLEUM GAS (LPG)
LPG is derived from fossil fuels which on burning releases carbondioxide, a
greenhouse gas. The reaction also produces some carbon monoxide. LPG does, however,
release less CO2 per unit of energy than does coal or oil. It emits 81% of the CO2 per kWh
produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated
electricity distributed via the grid. Being a mix of propane and butane, LPG emits less carbon
per joule than butane but more carbon per joule than propane. LPG can be considered to burn
more cleanly than heavier molecule hydrocarbons, in that it releases very few particulates.
3.3 LPG composition & characteristics
The main composition of LPG are hydrocarbons containing three or four hydrocarbons . LPG is a mixture of gas, mainly propane (C3H8 ) and butane (C4H10 ). LPG is commonly
used as a fuel in homes for cooking and heating and as a transportation fuel. It is normally
created as a by-product of petroleum refining and from the production of Natural Gas. LPG
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is non-toxic and flammable gas which is heavier than air. Liquefied petroleum gas is a
flammable mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles.
Varieties of LPG bought and sold include mixtures that are primarily propane (C3H8),
primarily butane (C4H10) and, most commonly, includes both propane and butane,
depending on the application.
Fig 3.1 chemical composition of LPG
Significant characteristics of LPG
LPG has three significant characteristics:
LPG allows efficient cooking.
LPG is heavier than air.
LPG is odourless and colourless.
Properties of LPG
Table 3.1 properties of LPG
LEL is the Lower Explosive Limit and UEL is the Upper Explosive Limit. Any amount
of gas between the two limits is explosive. The explosion of LPG may happen if the
following conditions are fulfilled:
• The concentration of gas is between LEL.
• A sufficient amount of Oxygen exists.
• There is a source of ignition.
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The technical specifications of LPG are:
Table 3.2 technical specifications of LPG
GENERAL
Confirming to Indian Standards specification IS476
Vapour Pressure at 65 deg.(max) kg/sq-cm 16.76
Volatility evaporation temp. in celsius For 95% volume at NTP
2
Copper strip corission at 38celsius Not Worse Than 1 Dryness No free entrained water
Odour Level 2CHEMICAL COMPOSITIONEthane % 1 max
Propane % 38 maxIs-Butane % 19 max
Not-Butane % 41 min
Iso-Pentane and Olefins % 1 max
Volatile sulphur % 0.003 max
LIQUID
Density at 15celsius kg/litre 0.557
Volume of liquid per kg at 15celsius litres 1.85
Vapour pressure at 15celsius Bar 5.3
Gross Calorific Value Kcal/kg 11840
Net Calorific Value Kcal/kg 10920
Boiling Point at atm. Pressure 0
VAPOUR
Density at 15celsius kg/cube-metre 2.21
Volume of gas per kg at 15celsius cube-metre
0.48
Latent Heat of Vapourization at 15celsius kcal/kg
86
Gross Calorific Value Kcal/Nm^3 26200
Net Calorific Value Kcal/Nm^13 24100
Air required for combustion metre-cube/metre- cube
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Unlike natural gas, LPG is heavier than air, and thus will flow along floors & tend to
settle in lower spots, such as basements. There are two main dangers from this.
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• Possible explosion if mixture of LPG & air is right & if there is an ignition
source.
• Suffocation due to LPG displacing air, causing a decrease in oxygen
concentration
LP Gas vapour, being heavier than air, may, in the event of a leak, accumulate in
confined spaces and low-lying areas. The means of ventilation and meteorological conditions
will influence the movement and dispersion of the LP Gas vapour. Uncontrolled release of
LP Gas is inherently hazardous. A liquid LP Gas leak is considered more hazardous in that it
will expand to vapour form with volume in excess of 200 times that of the original liquid
volume leak. Being heavier than air, vapour will tend to lie, or drift, close to the ground with
a risk that it will find a source of ignition while it remains within its flammable limits.
Persons exposed to high level of LPG experiences Central Nervous System (CNS)
depression. There is a range of symptoms with increasing concentration from the onset CNS
effects, hypoxia and asphyxiation: disorientation, light headedness, dizziness, drowziness,
loss of physical coordination, impaired judgement, drunkenness, unconsciousness and death.
3.4 Gas Detection sensors
A gas detector is a device which detects the presence of various gases within an area,
usually as part of a safety system. This type of equipment is used to detect a gas leak and
interface with a control system so a process can be automatically shut down. A gas detector
can also sound an alarm to operators in the area where the leak is occurring, giving them the
opportunity to leave the area. This type of device is important because there are many gases
that can be harmful to organic life, such as humans or animals. Gas detectors can be used to
detect combustible, flammable and toxic gases, and oxygen depletion. This type of device is
used widely in industry and can be found in a variety of locations such as on oil rigs.
Gas detectors can be classified according to the operation mechanism
(semiconductors, oxidation, catalytic, infrared, etc.). Gas detectors come in two main types:
portable devices and fixed gas detectors.
Portable detectors are used to monitor the atmosphere around personnel and are
worn on clothing or on a belt/harness. These gas detectors are usually battery operated. They
transmit warnings via a series of audible and visible signals such as alarms and flashing
lights, when dangerous levels of gas vapors are detected. As detectors measure a gas
concentration, the sensor responds to a calibration gas, which serves as the reference point or
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scale. As a sensor’s detection exceeds a preset alarm level, the alarm or signal will be
activated
Fixed type gas detectors may be used for detection of one or more gas types. Fixed
type detectors are generally mounted near the process area of a plant or control room.
Generally, they are installed on fixed type mild steel structures, and a cable connects the
detectors to a SCADA system for continuous monitoring.
Semiconductor sensors detect gases by a chemical reaction that takes place when
the gas comes in contact with the sensor. Tin dioxide is the most common material used in
semiconductor sensors and the electrical resistance in the sensor is decreased when it comes
in contact with the monitored gas. The resistance of the tin dioxide is typically around 50 kΩ
in air but can drop to around 3.5 kΩ in the presence of 1% methane. This change in
resistance is used to calculate the gas concentration. Semiconductor sensors are commonly
used to detect hydrogen, oxygen, alcohol, and harmful gases such as carbon monoxide. The
sensor must come in contact with the gas in order to detect it, semiconductor sensors work
over a smaller distance than infrared point or ultrasonic detectors. There are different
semiconductor sensors for flammable gas, plastic or metal cover. Few of them are given
below in table 3.3
Table 3.3 semiconductor gas sensors
Model Target gas voltage
MQ-2 Methane,butane,LPG,
smoke,flammable,combustible
gases
5V
MQ-3 Alcohol, ethanol, smoke 5V
MQ-4 Methane, CNG 5V
MQ-5 Natural gas, LPG 5V
MQ-6 LPG, butane gas 5V
MQ-7 carbonmonoxide 5V-1.4V
MQ-8 Hydrogen gas 5V
MQ-9 Carbonmonoxide, flammable
gases
5V-1.5V
MQ-131 Ozone 6V
MQ-135 Benzene, alcohol, smoke 5V
Model Target gas VoltageMQ214 Methane, natural gas 6V
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MQ216 Natural gas, coal gas
MQ303A Alcohol, ethanol, smoke 0.9V
MQ306A LPG, butane gas 0.9V
MQ136 Hydrogen sulphide 5V
MQ137 Ammonia 5V
MQ138 Benzene, toluene, alcohol,
propane, hydrogen gas
5V
Features
High sensitivity
Fast response
Wide detection range
Stable performance and long life
Simple drive circuit
3.5 Emergency Plan, Procedures
Expert hazard evaluation and quantification should form the basis of the emergency plan
by:
Identifying the on-site and off-site hazards
Assessing the ability for the emergency plans to mitigate the impact of the accident or
incident
Quantifying the on-site and off-site impact of credible accident scenarios.
Gas detection instruments may be portable (or semi-portable) gas measuring
instruments or fixed installed gas detection systems. The safety of an area potentially being
affected by dangerous gases and vapours to a high degree depends on the reliability of the gas
detection system, and especially on the quality of the sensors being used. In opposite to
sensors of portable devices fixed installed sensors including their electronics are continuously
in operation for years to detect the random gas release. There are certain gas detection
transmitters having so excellent measuring performance characteristics that today they even
show up more and more as analysing instruments in the field of process instrumentation.
3.6 LPG detection by MQ-2 sensor
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LPG is detected by using MQ-2 sensor. It can also detect i-butane, propane, methane,
alcohol, Hydrogen, smoke. Sensitive material of MQ-2 gas sensor is SnO2, which with lower
conductivity in clean air. When the target combustible gas exist, the sensors conductivity is
more higher along with the gas concentration rising.
Character of MQ-2
High sensitivity to Combustible gas in wide range
High sensitivity to LPG, Propane and Hydrogen
Fast response
Wide detection range
Stable performance, long life, low cost
Simple drive circuit
Fig 3.2 MQ2 sensor
The externals of a standard gas sensor module consists of a steel mesh, copper
clamping ring and connecting leads. The top part is a stainless steel mesh which takes care of
the following:
Filtering out the suspended particles so that only gaseous elements are able to
pass inside of the sensor.
Protecting the insides of the sensor.
Exhibits an anti explosion network that keeps the sensor module intact at high
temperatures and gas pressures.
In order to manage above listed functions efficiently, the steel mesh is made into two
layers. The mesh is bound to rest of the body via a copper plated clamping ring. The
connecting leads of the sensor are thick so that sensor can be connected firmly to the circuit
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and sufficient amount of heat gets conducted to the inside part. They are casted from copper
and have tin plating over them. Four of the six leads are for signal fetching while two are
used to provide sufficient heat to the sensing element. The pins are placed on a Bakelite base
which is a good insulator and provides firm gripping to the connecting leads of the sensor.
The internal structure has hollow sensing element which is made up from Aluminum Oxide
based ceramic and has a coating of tin oxide. Using a ceramic substrate increases the heating
efficiency and tin oxide, being sensitive towards adsorbing desired gas components suffices
as sensing coating.
Fig 3.3 internal structure of gas sensor
The leads responsible for heating the sensing element are connected through Nickel-
Chromium, well known conductive alloy. Leads responsible for output signals are connected
using platinum wires which convey small changes in the current that passes through the
sensing element. The platinum wires are connected to the body of the sensing element while
Nickel-Chromium wires pass through its hollow structure.
Fig 3.4 ceramic sensing element
The above image shows the ceramic with tin dioxide on the top coating that has
good adsorbing property. Any gas to be monitored has specific temperature at which it
ionizes. The task of the sensor is to work at the desired temperature so that gas molecules get
ionized. Through Nickel-chromium wire, the ceramic region of the sensing element is
subjected to heating current. The heat is radiated by the element in the nearby region where
gases interact with it and get ionized. Once, ionized, they are absorbed by the tin dioxide.
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Adsorbed molecules change the resistance of the tin dioxide layer. This changes the current
flowing through the sensing element and is conveyed through the output leads to the unit that
controls the working of the gas sensor.
If the sensors exposed to high concentration corrosive gas (such as H2Sz,
SOX，Cl2，HCl etc), it will not only result in corrosion of sensors structure, also it cause
sincere sensitivity attenuation. The sensors performance will be changed badly if sensors be
sprayed polluted by alkali metals salt especially brine, or be exposed to halogen such as
fluorine. Do avoid icing on the sensor surface and dipping of sensor in water which may
result in loss of sensitivity of the sensor.
Chapter 4
SYSTEM ARCHITECTURE AND DESIGN APPROACH
4.1 Block diagram
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The main aim of this project is to design a wireless RF controlled LPG detecting
robot for underground and mining applications. Therefore the project is divided into two parts
which are hardware and software. For the software implementation, it involves writing code
and programming the PIC microcontroller. Meanwhile, hardware implementation involves
designing the circuit of the project and PCB development. Each part of the project will be
discussed in details in this chapter.
Transmitter:
fig 4.1 tra
fig 4.1 transmitter
Receiver:
fig 4.2 receiver
Hardware requirements:
Microcontrollers
IR Modules
Driver IC
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PIC16F877A
MICRO
CONTROLLER
RF
RECEIVER
DECODER
BUZZER
L293D
DRIVER
IC
M1
M2GAS SENSOR
SWITCHES
PIC16F877A
MICRO
CONTROLLERENCODER
RF
TRANSMITTER
Motors
Gas sensor
Software requirements:
MPLAB IDE.
Embedded C Programming.
4.2 PIC microcontroller
The microcontroller that is been used is the PIC 16F877A controller. PICs are
popular with both industrial developers and hobbyists alike due to their low cost, wide
availability, large user base, extensive collection of application notes, availability of low
cost or free development tools, and serial programming ( and re-programming with flash
memory) capability. The microcontroller is used to collect the parameter value from the
sensor unit and compare it with the set point (safer level of gases) and transfer the
corresponding data to the CPU. It also receives commands from the CPU and transfers
it to the robot unit for its movement. The Microcontroller is the core of the surveillance
robot.
4.3 PIC16F877A
PIC microcontrollers (Programmable Interface Controllers) are electronic circuits that
can be programmed to carry out a vast range of tasks. They can be programmed to be timers
or to control a production line and much more. They are found in most electronic devices
such as alarm systems, computer control systems, phones, in fact almost any electronic
device. Many types of PIC microcontrollers exist, although the best are probably found in the
GENIE range of programmable microcontrollers. These are programmed and simulated by
Circuit Wizard software.
PIC is the most popular 8-bit chip in the world, used in a wide variety of
applications.The PIC16F877A devices have a 13-bit program counter capable of addressing
an 8K word x 14 bit program memory space. This memory is used to store the program after
we burn it to the microcontroller. The PIC16F877A device has 8K words x 14 bits of Flash
21
program memory that can be electrically erased and reprogrammed. Each time we burn
program into the micro, we erase an old program and write a new one.
Pin diagram
4.4 Pin diagram of PIC16F877A
Features of PIC
Table 4.1 features of PIC
Program Memory Type FLASHRAM bytes 368Data EEPROM 256Timers 2*8 bit,1*16 bitADC 8 ch,10 bitComparators 2Program Memory 14CPU Speed 5Capture/compare PWM peripherals 2 CCPTemperature range -40 to 125Operating voltage range 2 to 5.5Pin count 40
Advantages of PIC
Small instruction set to learn
RISC architecture
Built in oscillator with selectable speeds
22
Inexpensive microcontrollers
Wide range of interfaces including I²C, SPI, USB, USART, A/D, programmable
comparators, PWM, LIN, CAN, PSP, and Ethernet.
Availability of processors in DIL package make them easy to handle for hobby use.
4.3 PCB
PCB stands for “PRINTED CIRCUIT BOARD”. Printed circuit board (PCB)
provides both the physical structure for mounting and holding the components as well as the
electrical interconnection between the components. That means a PCB or PWB (printed
wiring board) is the platform upon which electronic components such as integrated circuit
chips and other components are mounted. A PCB consists of anon-conducting substrate
(typically fibre glass with epoxy as resin) upon which the conductive pattern or circuitry is
formed. Copper is the most prevalent conductor although nickel, silver and tin are also used
in some cases.
4.3.1 Types of PCB
PCB may be of different types:-
1) Single-sided
2) Double-sided
3) Multilayer
Single sided PCBs
As the name suggest in these designs the conductive pattern is only at in one side.
And also the size is large in these case but these are cheap.
Double sided PCBs
These are the PCBs on which the conductive pattern is in on both sides. The size of
board is small in this case but it is costlier than that of single sided PCB.
Multilayer PCBs
In this case the board consists of alternating layers of conducting pattern and
insulating material. The conductive Material is connected across the layers through plated
Through holes. The size of this PCB is smaller than that of double sided PCB but it is very
costly.
But in our project we use a single sided PCB. In some applications, a single sided PCB
design may be desired to reduce cost. While a single sided design reduces cost, it also creates
additional design limitations that may affect performance. Performance parameter affected by
the layout can include EMI, EMC, spurious radiation, reliability of the over production
23
spread, temperature, supply voltage and sensitivity of the design to its environment (e.g. FOB
handheld-effect..).However, in many applications with less stringent requirements the
performance of a single sided PCB may be acceptable.
4.5 Single sided PCB
PCBs may also be either rigid, flexible, or the combination of two (rigid-flex).
When the electronic components have been mounted on the PCB, the combination of PCB
and components is an electronic assembly, also called PRINTED CIRCUIT ASSEMBLY.
This assembly is the basic building block for all the electronic appliances such as television,
computer and other goods.
Function of PCB
Printed circuited boards are dielectric substrates with metallic circuitry formed on
that. They are sometimes referred to as the base line in electronic packaging. Electronic
packaging is fundamentally an inter connection technology and the PCB is the baseline
building block of this technology.
4.4 RF Transmitter STT433
The STT-433 is ideal for remote control applications where low cost and longer range is
required. The transmitter operates from a 1.5-12V supply, making it ideal for battery-
powered applications. The transmitter employs a SAW-stabilized oscillator, ensuring
accurate frequency control for best range performance. Output power and harmonic
emissions are easy to control, making FCC and ETSI compliance easy. The manufacturing-
friendly SIP style package and low-cost make the STT-433 suitable for high volume.
24
(A) (B) Front view Back view
Fig 4.6 RF transmitter STT433
4.4.1 Operation
OOK (On Off Keying) modulation is a binary form of amplitude modulation. When a
logical 0 (data line low) is being sent, the transmitter is off, fully suppressing the carrier. In
this state, the transmitter current is very low, less than 1mA. When a logical 1 is being sent,
the carrier is fully on. In this state, the module current consumption is at its highest, about
11mA with a 3V power supply. OOK is the modulation method of choice for remote control
applications where power consumption and cost are the primary factors. Because OOK
transmitters draw no power when they transmit a 0, they exhibit significantly better power
consumption than FSK transmitters. OOK data rate is limited by the start-up time of the
oscillator. High-Q oscillators which have very stable centre frequencies take longer to start-
up than low-Q oscillators. The start-up time of the oscillator determines the maximum data
rate that the transmitter can send.
4.4.2 Features and Applications
The features of 433MHz RF Transmitter are:
433.92 MHz Frequency
Low Cost
1.5-12V operation
11mA current consumption at 3V
Small size
4 dBm output power at 3V
25
The applications of 433MHz RF Transmitter are:
Remote Keyless Entry (RKE)
Remote Lighting Controls
On-Site Paging
Asset Tracking
Wireless Alarm and Security Systems
Long Range RFID
Automated Resource Management
4.5 RF Receiver STR433
The STR-433 is ideal for short-range remote control applications where cost is a
primary concern. The receiver module requires no external RF components except for the
antenna. It generates virtually no emissions, making FCC and ETSI approvals easy. The
super-regenerative design exhibits exceptional sensitivity at a very low cost. The
manufacturing-friendly SIP style package and low-cost make the STR-433 suitable for high
volume applications.
(A) (B)Front view Back view
Fig 4.7 RF receiver STR433
4.5.1 Operation
The STR-433 uses a super-regenerative AM detector to demodulate the incoming
AM carrier. A super regenerative detector is a gain stage with positive feedback greater than
unity so that it oscillates. An RC-time constant is included in the gain stage so that when the
gain stage oscillates, the gain will be lowered over time proportional to the RC time constant
until the oscillation eventually dies. When the oscillation dies, the current draw of the gain
stage decreases, charging the RC circuit, increasing the gain, and ultimately the oscillation
starts again. In this way, the oscillation of the gain stage is turned on and off at a rate set by
the RC time constant. This rate is chosen to be super-audible but much lower than the main
oscillation rate. Detection is accomplished by measuring the emitter current of the gain stage.
Any RF input signal at the frequency of the main oscillation will aid the main oscillation in
26
restarting. If the amplitude of the RF input increases, the main oscillation will stay on for a
longer period of time, and the emitter current will be higher. Therefore, we can detect the
original base-band signal by simply low-pass filtering the emitter current.
4.5.2 Features and Applications:
Features of STR433MHz Receiver are:
Low Cost
5V operation
3.5mA current drain
No External Parts are required
Receiver Frequency: 433.92 MHZ
Typical sensitivity: -105dBm
IF Frequency: 1MHz
Applications of STR433MHz Receiver are:
Car security system
Sensor reporting
Automation system
Remote Keyless Entry (RKE)
Remote Lighting Controls
Asset Tracking
Wireless alarm and security systems.
4.6 Voltage Regulator
A voltage regulator (also called a ‘regulator’) with only three terminals appears to be a
simple device, but it is in fact a very complex integrated circuit. It converts a varying input
voltage into a constant ‘regulated’ output voltage. Voltage Regulators are available in a
variety of outputs like 5V, 6V, 9V, 12V and 15V. The LM78XX series of voltage regulators
are designed for positive input. For applications requiring negative input, the LM79XX series
is used. Using a pair of ‘voltage-divider’ resistors can increase the output voltage of a
regulator circuit.
4.6.1 LM7805
7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed
linear voltage regulator ICs. The voltage source in a circuit may have fluctuations and would
not give the fixed voltage output. The voltage regulator IC maintains the output voltage at a
27
constant value. The xx in 78xx indicates the fixed output voltage it is designed to provide.
7805 provides +5V regulated power supply. Capacitors of suitable values can be connected at
input and output pins depending upon the respective voltage levels.
Fig 4.8 LM7805
Pin Description:
Table 4.2 pin description of LM7805
Pin No Function Name1 Input voltage (5V-18V) Input2 Ground (0V) Ground3 Regulated output; 5V (4.8V-5.2V) Output
4.6.2 LM7812
7812 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed linear
voltage regulator ICs. The voltage source in a circuit may have fluctuations and would not
give the fixed voltage output. The voltage regulator IC maintains the output voltage at a
constant value. The xx in 78xx indicates the fixed output voltage. It is a positive voltage
regulator capable of delivering 12V@1Amps.
Specifications:
Input Voltage Max: 14-36V
Maximum Output current: 1A
Maximum Power dissipation :15W(at 25degree C)
Package Type: TO22
Fig 4.9 LM7812
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4.7 Driver IC L293D
The L293D is a popular motor driver IC that is usable from 6 to12V, at up to 1A total
output current. By itself, the IC is somewhat diffcult to wire and use, but the Compact L293D
Motor Driver makes it much more convenient to use. L293D is a dual H-bridge motor driver
integrated circuit (IC). Motor drivers act as current amplifiers since they take a low-current
control signal and provide a higher-current signal. This higher current signal is used to drive
the motors.
L293D contains two inbuilt H-bridge driver circuits. In its common mode of
operation, two DC motors can be driven simultaneously, both in forward and reverse
direction. The motor operations of two motors can be controlled by input logic at pins 2 & 7
and 10 & 15. Input logic 00 or 11 will stop the corresponding motor. Logic 01 and 10 will
rotate it in clockwise and anticlockwise directions, respectively.
Enable pins 1 and 9 (corresponding to the two motors) must be high for motors to
start operating. When an enable input is high, the associated driver gets enabled. As a result,
the outputs become active and work in phase with their inputs. Similarly, when the enable
input is low, that driver is disabled, and their outputs are off and in the high-impedance state.
Fig 4.10 pin diagram OF L293D
4.8 HT12E
The 2^12 encoders are a series of CMOS LSIs for remote control system applications.
They are capable of encoding information which consists of N address bits and 12-N data
bits. Each address/ data input can be set to one of the two logic states. The programmed
addresses/data are transmitted together with the header bits via an RF or an infrared
transmission medium upon receipt of a trigger signal. The capability to select a TE trigger on
29
the HT12E further enhances the application flexibility of the 2^12 series of encoders. The
HT12A additionally provides a 38KHz carrier for infrared systems.
Fig 4.11 pin diagram of HT12E
Features
HT12E: 18-pin DIP/20-pin SOP package
Operating voltage - 2.4V~12V for the HT12E
Low power and high noise immunity CMOS technology
Low standby current: 0.1uA (typ.) at VDD=5V
Minimum transmission word -four words for the HT12E
Built-in oscillator needs only 5% resistor
Data code has positive polarity
Minimal external components
Applications
Burglar alarm system
Smoke and fire alarm system
Garage door controllers
Car door & alarm controllers
Security system
Other remote control systems
4.9 HT12D
The 2^12 decoders are a series of CMOS LSIs for remote control system
applications. The decoders receive serial addresses and data from a programmed 2^12 series
of encoders that are transmitted by a carrier using an RF or an IR transmission medium. They
compare the serial input data three times continuously with their local addresses. If no error
or unmatched codes are found, the input data codes are decoded and then transferred to the
output pins. The VT pin also goes high to indicate a valid transmission. The 212 series of
30
decoders are capable of decoding information that consist of N bits of address and 12-N bits
of data. Of this series, the HT12D is arranged to provide 8 address bits and 4 data bits. The
features and applications of HT12D are similar to that of HT12E.
Fig 4.12 pin diagram of HT12D
4.10 GAS SENSOR MQ-2
The Grove - Gas Sensor (MQ2) module is useful for gas leakage detecting (in home,
industry, mining). It can detect LPG, i-butane, methane, alcohol, Hydrogen, smoke and so on.
Based on its fast response time, measurements can be taken as soon as possible. Also the
sensitivity can be adjusted by the potentiometer.
Fig 4.13 MQ2 gas sensor
Working principle
When a gas interacts with the sensor, it is first ionized into its constituents and is then
adsorbed by the sensing element. This adsorption creates a potential difference on the
element which is conveyed to the processor unit through output pins in form of current.
The gas sensor module consists of a steel exoskeleton under which a sensing element
is housed. This sensing element is subjected to current through connecting leads. This current
is known as heating current through it, the gases coming close to the sensing element get
31
ionized and are absorbed by the sensing element. This changes the resistance of the sensing
element which alters the value of the current going out of it.
Electronic characteristics
Table 4.3: Electronic Characteristics of MQ-2:
Sensitivity Adjustment
Resistance value of MQ-2 is difference to various kinds and various concentration
gases. So, When using this components, sensitivity adjustment is very necessary. we
recommend that you calibrate the detector for 1000ppm liquified petroleum gas<LPG>,or
1000ppm iso-butane<i-C4H10>concentration in air and use value of Load resistance
that( RL) about 20 KΩ(5KΩ to 47 KΩ). When accurately measuring, the proper alarm point
for the gas detector should be determined after considering the temperature and humidity
influence.
Fig 4.14 sensitivity characteristics
Power of Sensitivity body(Ps):
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Items Parameter
nameMin Type
Max
Unit
System Characteristics
VCC Working Voltage
4.9 5 5.1 V
PH Heating
consumption
0.5 - 800 mW
RL Load
resistance can
adjust
RH Heater
resistance- 33 - Ω
RsSensing
Resistance 3 - 30 kΩ
Ps=Vc2×Rs/(Rs+RL)2
Resistance of sensor(Rs):
Rs=(Vc/VRL-1)×RL
Features
Wide detecting scope
Stable and long life
Fast response and High sensitivity
Application Ideas
Gas leakage detecting
a) Domestic gas leakage detector
b) Industrial Combustible gas detector
c) Portable gas detector
toys
4.11 Buzzer
A buzzer or beeper is an audio signalling device, which may be mechanical,
electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm
devices, timers and confirmation of user input such as a mouse click or keystroke. We use a
piezo buzzer. This buzzer requires no external oscillation, simply place a voltage of between
9V & 15V DC, across the terminals and it will make noise.
Fig 4.15 buzzer
4.12 LED
A light emitting diode (LED) as shown in Figure 2.12 is a semiconductor light source.
LED is used as the indicator lamp in the many devices and is increasingly used for lighting.
The LED is based on the semiconductor diode.
33
Fig 4.16 LED
When a diode is forward biased which is switch on, electron are able to recombine
with holes within the devices, releasing energy in the form of photon. This effect is called
electroluminescence and the colour of the light is determined by the energy gap of the
semiconductor. LED are usually integrated optical components are used to shape its radiation
pattern and assist in the reflection.
4.13 Bridge full wave rectifier
The Bridge rectifier converts an ac voltage to dc voltage using both half cycles of
the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four
diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite
ends of the bridge. The load resistance is connected between the other two ends of the bridge.
For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct,
whereas diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series
with the load resistance RL and hence the load current flows through RL.
For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct
whereas, D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the
load resistance RL and hence the current flows through RL in the same direction as in the
previous half cycle. Thus a bi-directional wave is converted into a unidirectional wave.
34
Fig 4.17 Bridge rectifier
4.14 Battery
A battery is a type of linear power supply that offers benefits that traditional line-
operated power supplies lack: mobility, portability and reliability. A battery consists of
multiple electrochemical cells connected to provide the voltage desired.
Fig 4.18 Hi battery
4.15 capacitors
The Capacitor or sometimes referred to as a Condenser is a passive device, and one
which stores energy in the form of an electrostatic field which produces a potential (static
voltage) across its plates. In its basic form a capacitor consists of two parallel conductive
plates that are not connected but are electrically separated either by air or by an insulating
material called the Dielectric. When a voltage is applied to these plates, a current flows
charging up the plates with electrons giving one plate a positive charge and the other plate an
equal and opposite negative charge this flow of electrons to the plates is known as the
Charging Current and continues to flow until the voltage across the plates (and hence the
capacitor) is equal to the applied voltage Vcc.
35
Fig 4.19 capacitor
4.16 Resistor
A resistor is a two-terminal electronic component that produces a voltage across its
terminals that is proportional to the electric current passing through it in accordance with
Ohm's law:
V = IR
The primary characteristics of a resistor are the resistance, the tolerance, maximum
working voltage and the power rating. Other characteristics include temperature coefficient,
noise, and inductance. Resistors can be made to control the flow of current, to work as
Voltage dividers, to dissipate power and it can shape electrical waves when used in
combination of other components.
4.20 Resistor
36
Chapter 5
WORKING OF RF MODULE
5.1 Interfacing of RF Module with PIC
The term wireless is very much hyped! Whenever we hear the term wireless, stuffs
like Mobile telecommunication (GSM), Wi-Fi, Bluetooth, RF Communication, Wireless
networks, Zigbee, I2C, SPI,DTMF, etc.. Well, fortunately or unfortunately, all of these
protocols can be interfaced with a microcontroller in one way or the other. But what matters
is, the level of complexity. To start off, RF (Radio Frequency) Communication is the most
preferred and low cost solution. All we need is a RF Module (Transmitter-Receiver Pair). RF
Communication works on the principle of Serial Communication. Thus, we need either of the
things to convert the conventional n-bit (4-bit, 8-bit, 16-bit, etc.) data into serial data. For
this, we have two choices:
Use a microcontroller to convert the n-bit data into serial data and vice-versa
Use serial encoders/decoders to do the same.
A general RF communication block diagram is shown above. Since most of the
encoders/decoders/microcontrollers are TTL compatible, most of the inputs by the user will
be given in TTL logic level. Thus, this TTL input is to be converted into serial data input
using an encoder or a microcontroller. This serial data can be directly read using the RF
Transmitter, which then performs ASK (in some cases FSK) modulation on it and transmit
the data through the antenna.
In the receiver side, the RF Receiver receives the modulated signal through the
antenna, performs all kinds of processing, filtering, demodulation, etc and gives out a serial
data. This serial data is then converted to a TTL level logic data, which is the same data that
the user has input. RF Modules are used wireless transfer data. This makes them most
suitable for remote control applications, as in where we need to control some machines or
robots without getting in touch with them Now depending upon the type of application, we
choose an ASK RF Transmitter-Receiver Module of frequency 433 MHz which is the most
suitable.
5.2 How Do RF Transmitters and Receivers Work?
An RF transmitter generates radio frequency waves in its circuits, and to this
carrier signal, it adds the information part by modulating the carrier signal. This composite
37
signal (carrier plus information) is then fed to an antenna (aerial). The aerial induces a
corresponding signal into the atmosphere, by altering the Electric and Magnetic fields at
(obviously) the same frequency. The impedance of 'free space' is few tens of Ohms to a few
hundreds of Ohms. [Impedance may be considered analogous to resistance, but with reactive
properties as well.] The power emitted by the transmitter can vary from a megawatt or so (for
VLF signals) to a few watts for handheld devices.
An RF receiver receives the signal from the atmosphere, from its own aerial. The
receiver aerial is often quite simple, and the signal level is typically of a few microvolts. This
it tunes in (gets rid of unwanted signals and amplifies only the wanted ones). The receiver
circuits then strip the information part of the signal from the carrier part, and amplify this to a
useful level for audio. The actual signal into the loudspeaker will be a few tens of volts. In
spite of the Inefficiency of loudspeakers, (often only a few %) the signal eventually appears
at a level that may be heard.
5.3 Circuit implementation
A wireless radio frequency (RF) transmitter and receiver can be easily made using
HT12D Decoder, HT12E Encoder and ASK RF Module. Wireless transmission can be done
by using 433MHz ASK RF Transmitter and Receiver modules. In these modules digital data
is represented by different amplitudes of the carrier wave, hence this modulation is known as
Amplitude Shift Keying (ASK). Radio Frequency (RF) transmission is more strong and
reliable than Infrared (IR) transmission due to following reasons:
Radio Frequency signals can travel larger distances than Infrared.
Only line of sight communication is possible through Infrared while radio frequency
signals can be transmitted even when there are obstacles.
Infrared signals will get interference by other IR sources but signals on one frequency
band in RF will not interference by other frequency RF signals.
38
5. 3.1 Power supply circuit
Fig 5.1 power supply circuit diagram
The heavier the load (higher current), the faster the capacitor discharges, thus the more
ripple there will be. We want an input voltage (to the load) as smooth as possible because
sometimes a device acts weird due to a power supply with too large of a ripple. When the
load is so heavy that the ripple is too large, you can use a bigger capacitor, because that
smoothens the line more. Therefore, it depends on the load what value you need for a
capacitor.
On each cycle, the capacitor charges to the peak voltage. Then, it discharges as the
regulator draws current from it. The capacitor must be large enough that when the regulator
draws current from it between the charge cycles, the voltage will not drop below the
minimum voltage specified for that regulator.
5. 3.2 Transmitter circuit diagram
39
Fig 5.2 Transmitter circuit diagram
HT12E Encoder IC will convert the 4 bit parallel data given to pins D0 – D3 to serial
data and will be available at DOUT. This output serial data is given to ASK RF Transmitter.
Address inputs A0 – A7 can be used to provide data security and can be connected to GND
(Logic ZERO) or left open (Logic ONE). Status of these Address pins should match with
status of address pins in the receiver for the transmission of the data. Data will be transmitted
only when the Transmit Enable pin (TE) is LOW. 1.1MΩ resistor will provide the necessary
external resistance for the operation of the internal oscillator of HT12E.
5.3.3 Receiver circuit diagram
Fig 5.3 Receiver circuit diagram
ASK RF Receiver receives the data transmitted using ASK RF Transmitter. HT12D
decoder will convert the received serial data to 4 bit parallel data D0 – D3. The status of these
address pins A0-A7 should match with status of address pin in the HT12E at the transmitter
for the transmission of data. 51KΩ resistor will provide the necessary resistance required for
the internal oscillator of the HT12D.The VT pin (pin 17) of HT12D is connected to the RC7
(pin 26) of PIC.
From the figure we can conclude that the DC Motor is not interfaced directly to the
micro controller. It is interfaced through its driver L293D .As shown in the above figure
40
L293D is a 16 pin IC in which the two motors are connected to pins 3,6,11,14of L293D and
in turn the L293D is connected to Microcontroller to its Pins 34,35,39,40(Port B).
If the both the inputs to the Motor Driver is Low and high the motor is in halt
position. If the first output is high, Second output is low then DC Motor moves forward .If
the first output is low, second output is high then DC Motor moves reverse.
Here the pins of motor driver that is four input pins i/p1, i/p2, i/p3, i/p4 and heat sink
pin and enable1 and enable2 pins and ground pin and vs pins are connected to micro
controller pins respectively, here L293D is the motor driver and its having one ‘H’ bridge
inbuilt to handle two motors by using two enable pins.
41
Chapter 6
RESULT ANALYSIS
The circuit for “Wireless RF controlled LPG detection in underground and mining
applications” has been set up. The software program for our project is written in MATLAB
IDE (Integrated Development Environment) that helps us to write, compile and debug
embedded programs. Circuit diagram was laid out in PROTEUS software. This has been
successfully interfaced with the microcontroller.
The PIC microcontroller acts as a central controlling unit. This module is capable of
communicating with the input and the output modules. The output module is formed by the
motors used for controlling the direction of the motor i.e. the forward and backward
movement of the robot. The microcontroller reads the mobile sensor continuously to take any
action.
The robot has two DC Motors respectively. The DC motor generates torque directly
from DC power supplied to the motor by using internal commutation, stationary permanent
magnets, and rotating electrical magnets. It works on the principle of Lorentz force, which
states that any current carrying conductor placed within an external magnetic field
experiences a torque or force known as Lorentz force. The controller is interfaced with DC
motors, that are fixed to the Robot to control the direction of the Robot.
The project has five switches that helps the robot to move in forward, backward, left
and right directions. The fifth switch is used for stop/ run of the robot.
42
Fig 6.1 remote control
Whenever the switch in the remote control is pressed, the robot follows the
commands that are given to it for that switch in the microcontroller. The remote control board
is connected to the transmitter section. Since the switches are in active low state (i.e. low
signal is sent when the switch is pressed), we need to add external pull-up resistors as shown,
so as to provide a high signal by default. The Transmitter Enable (TE, pin 14) pin is an active
low pin. Thus, it is permanently grounded, so as to enable the transistor always. The output
serial data DOUT is fed to the RF Transmitter Module directly.
The most important thing lies in the address pins (A0-A7, pin1-8) of HT12D and
HT12E. There are 8 address pins, thus giving us an opportunity to have 8! (8 factorial)
different and independent ways to connect to a device, so that there is no interference. The
address pins MUST have the same address in both transmitter and receiver, or else the data
won’t be transferred. Thus we have made the first five address pins (A0-A4) to active high
and the rest to active low (grounded).
Fig 6.2 Transmitter section
The data from DOUT pin is transferred to data pin of STT433.The antenna transmits
the data to the receiver module. Pin 17 (VT) is enabled whenever the receiver receives any
data. The STR433 receives the data from the transmitter module. The serial data received by
43
the RF Receiver module is directly fed to pin 14 (DIN), which is then converted into 4-bit
parallel data (D0-D3). A 33k ohm resistor is connected in between OSC1 and OSC2.
The receiver section is fixed to the robot. The controller is interfaced with DC
motors, that are fixed to the Robot to control the direction of the Robot. The gas sensor is
connected to the RC6 (pin26) of microcontroller. Whenever the sensor detects the leakage in
LPG it sends the signal to the microcontroller. Then automatically it stops there and sounds
the buzzer.
Fig 6.3 Receiver section
The sensors and the connection are tested for their performance and to conduct
the test, LPG or any other source of smoke is brought near to the MQ-02 sensor. As a
result the sensor has detected the smoke/LPG stopped the robot and alarmed the buzzer with
a beep sound.
44
CONCLUSION & FUTURE SCOPE
Conclusion
The project is aimed at providing human safety for the rescue team in hazardous
environments such as coal mines. In this paper we have proposed a wireless sensor network
which employs smart gas sensors to be used in mining and underground applications to detect
the combustible gases. This system is built to help user to feel comfortable in a work place
and easy to monitor the range of air quality in the environment. This system device also gives
an advantage to the user to easily get the information about the air quality in their building or
industrial area or in their work place.
It provides information about gas leakage and it alerts the consumer about it
through wireless transmission. The base station can be enabled manually and also
automatically by a remote. If there is no gas leakage that is when the system is normal, the
buzzer does not give a beep sound. And if there is any abnormality occurs, then the gas
leakage detection system is enabled and it is indicated by a beeping sound of the buzzer and
corresponding preventive action has been taken. This system can be used in home, industry,
storage yard safety systems, coal mines and other underground applications to detect any
combustible gas leakage which can alert the personnel apart from taking required safety
measures.
The system proposed is reasonably simple with low power consumption and
can be deployed in short span of time without entailing considerable maintenance cost. Also
use of wireless RF technology made it easy to manage the wireless sensor network.
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Future scope
This project can be advanced due to requirement of the consumer. This device can
also be made to target the domestic need, by using the required sensors for required specific
application.
As an advance modification this device may include several gas sensors such as
carbon monoxide nitrogen dioxide etc. since those sensors do not consume much current
comparing to LPG sensor. Furthermore gas level can be detected according to hazards ppm
level and can be transmit for further processing according to industrial need.
In the future work the robot can be fixed with a wireless camera that can shot the
pictures and send the data to the controller or the user. This can also be functioned using
GSM technology.
As our future work we will employ Zigbee transceiver so that the coverage area will
be increasing. This can be developed by the use of higher transmission range transceivers so
that it can travel for a greater distance and can be used in different environments based on the
transmission range.
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APPENDIX
PIC16F877A is a microcontroller which without a programming code is as dumb as
a plastic stuff. To make the PIC as our project CPU we do write a program code in
EMBEDDEDC using MATLAB as a compiler.
Source code for PIC on Transmitter module
#pragma config |= 0x3F32
#pragma bit s1 = PORTC.0
#pragma bit s2 = PORTC.1
#pragma bit s3 = PORTC.2
#pragma bit s4 = PORTC.3
#pragma bit s5 = PORTC.4
#pragma bit s6 = PORTC.5
#pragma bit s7 = PORTC.6
#define rf PORTD
#pragma bit te = PORTD.7
void delay()
{
unsigned int i,j;
for(i=0;i<250;i++)
for(j=0;j<30;j++);
}
void main()
{
TRISC = 0xFF;
TRISD = 0x00;
while(1)
{
if(s1==0)
{
rf = 0x01;
te = 0;
delay();
te = 1;
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delay();
}
else if(s2==0)
{
rf = 0x02;
te = 0;
delay();
te = 1;
delay();
}
else if(s3==0)
{
rf = 0x03;
te = 0;
delay();
te = 1;
delay();
}
else if(s4==0)
{
rf = 0x04;
te = 0;
delay();
te = 1;
delay();
}
else if(s5==0)
{
rf = 0x05;
te = 0;
delay();
te = 1;
delay();
}
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else if(s6==0)
{
rf = 0x06;
te = 0;
delay();
te = 1;
delay();
}
else if(s7==0)
{
rf = 0x07;
te = 0;
delay();
te = 1;
delay();
}
}
}
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Source code for PIC on Receiver module
#pragma config|=0x3F32
#pragma bit en1 = PORTB.0
#pragma bit in1 = PORTB.1
#pragma bit in2 = PORTB.2
#pragma bit en2 = PORTB.5
#pragma bit in3 = PORTB.6
#pragma bit in4 = PORTB.7
#pragma bit sen = PORTC.6
#pragma bit buz = PORTB.3
#define rf PORTC
#pragma bit vt = PORTC.7
void delay()
{
unsigned int i,j;
for(j=0;j<250;j++)
for(i=0;i<250;i++);
}
void forward()
{
en1 = en2 = 1;
in1 = in3 = 1;
in2 = in4 = 0;
}
void backward()
{
en1 = en2 = 1;
in1 = in3 = 0;
in2 = in4 = 1;
}
void right()
{
en1 = en2 = 1;
in1 = in4 = 1;
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in2 = in3 = 0;
}
void left()
{
en1 = en2 = 1;
in1 = in4 = 0;
in2 = in3 = 1;
}
void main()
{
unsigned int i,j;
unsigned char x;
TRISC = 0xFF;
TRISB = 0x00;
delay();
buz=1;
while(1)
{
while(vt==0)
{
if(sen==0)
{
buz = 0;
en1 = en2 = 0;
while(1);
}
}
x = rf;
x = x & 0x0F;
switch(x)
{
case 0x01:forword();
break;
case 0x02:backword();
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break;
case 0x03:left();
break;
case 0x04:right();
break;
case 0x05:en1 = en2 = 0;
break;
}
}
}
52
BIBILIOGRAPHY
PIC Microcontroller Notes - NetMax Technologies.
http://www.all datasheets.com
www.wireless communications.com
“liquefied petroleum gas” ,Wikipedia
www.wikipedia.com
Development of wireless sensor network for combustible gas monitoring. Sensors &
Actuators: A. Physical, 1-8
Health, E., & Elements, L. (2012). Liquefied Petroleum Gas (Canada) Section 1:
Identification of the substance or mixture and of the supplier
59
Section 2 : Hazard ( s ) Identification Section 3 : Composition / Information on Ingredients
Section 4 : First Aid Measures
53