INTRODUCTION
Over the past quarter century, there has been an exponential
increase of industries, and these industries have caused complex and
serious problems to the environment. The first and the foremost is the severe
environmental pollution which has caused deterioration of atmosphere, climate
change, stratospheric ozone depletion, loss of biodiversity, changes in
hydrological systems and the supplies of fresh water, land degradation and
stresses on systems of food producing, acid rain, and global warming.
The motivation of the project is to build an air pollution
monitoring system, so a detection system for multiple information of
environment is designed in this project. There is a growing demand for the
environmental pollution monitoring and control systems. In view of the
ever-increasing pollution sources with toxic chemicals, these systems should
have the facilities to detect and quantify the sources rapidly. This project is
built for low cost, quick response, low maintenance, ability to produce
continuous measurements etc. The main goal of this project is to control the
air pollution, hazardous gases and increase awareness about pollution by using
air pollution monitoring system. The work is to measure the air pollutants
level and temperature range. Then the Acquired air pollutant level from the
sensors array will report to the PC. This system is used for acquiring the
real-time data from the sensors-array and the physical location, time and date
of the sampled pollutants from the GPS module. This information is then
encapsulated into a data frame by the microcontroller. Finally the acquired
data will report to the PC.
In addition to industries, automobiles, agricultural
activities, and even ordinary homes contribute towards the environmental
pollution. It is well known that some of these chemical pollutants have
increased Environmental pollution has several aspects.
The most serious aspect of environmental pollution is the air pollution, while
two other aspects are water and soil pollution. Most of the above air pollution
and quality
monitoring systems are based on sensors that report the pollutants levels to a
server via wired modem, router, or short-range wireless access points. In this
paper, we propose a system that integrates a single-chip microcontroller and
several air pollution sensors. The integrated unit is a sensor, Analog to
digital converter and a Microcontroller. This unit can be placed on the top of
any moving device such as a public transportation vehicle. While the vehicle is
on the move, the microcontroller generates a frame consisting of the acquired
air pollutant level from the sensors array and the physical location that is
reported to the PC. Future work of this paper is pollutants frame uploaded to
the ZIGBEE Modem and transmitted to the Pollution-Server via the public mobile
network.
Many
air pollution systems in urban and rural areas that utilize smart sensor
networks and wireless systems. Most of the above air pollution and quality
monitoring systems are based on sensors that report the pollutants levels to a
server via wired modem, router, or short-range wireless access points. We propose
a system that integrates a single-chip microcontroller, several air pollution
sensors, GPRS-Modem, and a general positioning systems (GPSs) module. The
integrated unit is a mobile and a wireless data acquisition unit that utilizes
the wireless mobile public networks. The pollutants frame is then uploaded to
the General Packet Radio Service Modem (GPRS-Modem) and transmitted to the
Pollution-Server via the public mobile network. A database server is attached to the
Pollution-Server for storing the pollutants level for further usage by
interested clients such as environment production agencies and vehicles
regeneration authorities. The acquired air
pollutant level from the sensors array will report to the PC. This system is
used for acquiring the real-time data from the sensors-array and the physical
location, time and date of the sampled pollutants from the GPS module. This
information is then encapsulated in to a data frame by the microcontroller.
Finally the acquired data will report to the PC. This project is built for low
cost, quick response, low maintenance etc.
BLOCK DIAGRAM DESCRIPTION
OVERVIEW
This chapter mainly includes the
detailed explanation of different blocks included in the block diagram
representation of Air Pollution Monitoring. To satisfy the system’s functional and non functional
requirements, two major building blocks are needed, namely: a Mobile
Data-Acquisition Unit (Mobile-DAQ) and a fixed Internet-Enabled Pollution
monitoring Server (Pollution-Server). The Mobile-DAQ consists of a 16-bit
single-chip microcontroller integrated with a sensor array using analog ports.
The Mobile-DAQ is also connected to a GPS module and a GPRS-Modem using the
RS-232 interface.
The blocks
mainly included in the block diagram representation of Air Pollution Monitoring
system are ATMEGA 16-8 Bit Microcontroller, Sensors, Amplifiers, GPS Module, GSM Modem, LCD Display, RS
232, Pollution Server. The sensors will collect the level of pollutants and
then amplify it with the help of amplifiers. This data will be in the form of
analog. In order to make this into digital form we feed this analog data to an
ADC unit, which will convert the data to digital form. A microcontroller will
store this information. Along with GPS details a GPRS modem will packs the
digital data and then transmits to the receiver part. The transmitted signal
will be received by another GSM modem which is interfaced to the PC with RS232
interface. Finally the data will be displayed on PC.
BLOCK DIAGRAM EXPLANATION
This section gives the explanation about the
different blocks represented in the block diagram of air pollution monitoring
system. ATMEGA 16 is explained first. It is followed by the signal CO2 sensor,
CO sensor, LPG sensor,NO2 sensor, amplifier, GPS module, GSM modem, LCD
display, RS 232, pollution server.
ATMEGA16-8 BIT MICROCONTROLLER
AT mega 16 is a low-power CMOS 8-bit microcontroller
based on the AVR enhanced RISC architecture. By executing powerful instructions
in a single clock cycle, the AT mega achieves throughputs approaching 1 MIPS
per MHz allowing the system designer to optimize power consumption versus
processing speed.
The AT mega 16 provides the following features: 16K
bytes of In-system Programmable Flash Program memory with Read-While-Write
capabilities, 512 bytes EPROM, 1Kbyte SRAM, 32 general purpose I/O lines, 32
general purpose working registers, a JTAG interface for Boundary-scan, On-chip
Debugging support and programming, three flexible Timer/Counters with compare
modes, Internal and External Interrupts, a serial programmable USART, a byte
oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional
differential input stage with programmable gain (TQFP package only), a
programmable watchdog Timer with internal oscillator, an SPI serial port, and
six software selectable power saving modes. Idle mode stops the CPU while
allowing the USART, Two-wire interface, A/D converter, SRAM; Timer/Counters,
SPI port, and interrupt system to continue functioning. The power-down mode
saves the register but freezes the oscillator disabling all other chip
functions until the next external interrupt or hardware reset. In power-saver
mode, the asynchronous timer continues to run, allowing the user to maintain a
timer base while the rest of the device is sleeping.
The ADC Noise Reduction mode stops the CPU and all
I/O modules except asynchronous timer and ADC, to minimize switching noise
during ADC conversions.
In
standby mode, the crystal/resonator oscillator is running while the rest of the
device is sleeping. This allows very fast start-up combined with low-power
consumption. In extended standby mode, both the main oscillator and the
asynchronous timer continue to run.
SOFTWARE – C
The
program used to implement AIR POLLUTION MONITORING systems is written in C
language. C is an imperative (procedural) language. It was designed
to be compiled using a relatively straightforward compiler, to provide low-level access
to memory, to provide language constructs that map efficiently to machine
instructions, and to require minimal run-time
support. C was therefore useful for many applications that had formerly been
coded in assembly language, such
as in system programming. Despite
its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant and portably written C program can be compiled for
a very wide variety of computer platforms and operating systems with few
changes to its source code. The language has become available on a very wide
range of platforms, from embedded microcontrollers
to supercomputers. Embedded C programming requires nonstandard extensions
to the C language in order to support exotic features such as fixed-point
arithmetic, multiple distinct memory banks, and basic I/O operations.
The
C language also exhibits the following more specific characteristics:
There are a
small, fixed number of keywords, including a full set of flow
of control primitives: for, if, while, switch, and do..While. There is
basically one namespace, and user-defined names are not distinguished from
keywords by any kind of sigil.
There are a
large number of arithmetical and logical operators, such as
+, +=, ++, &, ~, etc.
More than
one assignment may be performed in a single statement.
Function
return values can be ignored when not needed.
Typing is static, but weakly
enforced: all data has a type, but implicit
conversions can be performed; for instance, characters can be used as integers.
Declaration syntax mimics usage context. C has no "define" keyword;
instead, a statement beginning with the name of a type is taken as a
declaration.
SIGNAL CONVERSION UNIT ( ADC)
DC signals are often used as analog representations
of physical measurements such as temperature, pressure, flow, weight, and
motion. Most commonly, DC current signal is used in preference to DC voltage
signals, because current signals are exactly equal in magnitude throughout the
series circuit loop carrying current from the source(measuring device) to the
load(indicator ,recorder, or controller), whereas voltage signals in a parallel
circuit may vary from one end to the other due to resistive wire losses.
Furthermore, current sensing instruments typically have low impedances (while
voltage-sensing instruments have high impedances), which gives current-sensing
instruments greater electrical noise immunity.
In order to use current as an analog representation
of a physical quantity, we have to have some way of generating a precise amount
of current within the signal circuit .To generate a precise current signal when
we might not know the resistance of the loop, we use an amplifier that is
designed to hold current to a prescribed value, applying as much or as little
voltage as necessary to the load circuit to maintain that value. Such an
amplifier performs the function of a current source. An op-amp with negative
feedback is a perfect candidate for such a task.
LPG SENSOR
Ideal sensor for use to detect the presence of a dangerous LPG
leak in your 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.
FEATURES:
High
Sensitivity
Detection Range: 100 - 10,000 ppm iso-butane propane
Fast Response Time: <10s
Heater Voltage: 5.0V
Dimensions: 18mm Diameter, 17mm High excluding pins, Pins - 6mm High
CO SENSOR
A carbon monoxide sensor or CO
sensor is a device that detects
the presence of the carbon
monoxide (CO) gas in order to prevent carbon monoxide positioning. In the
late 1990s Underwriters Laboratories (UL) changed their definition of a single
station CO detector with a sound device in it to a carbon monoxide (CO) alarm.
This applies to all CO safety alarms that meet UL 2034; however for passive
indicators and system devices that meet UL 2075 UL refers to these as carbon
monoxide detectors. This difference is not well known by the public. CO is a
colorless, tasteless and odorless compound produced by incomplete combustion of
carbon containing materials. It is often referred to as the "silent
killer" because it is virtually undetectable without using detection
technology and most do not realize they are being poisoned. Elevated levels of CO can be dangerous
to humans depending on the amount present and length of exposure. Smaller
concentrations can be harmful over longer periods of time while increasing
concentrations require diminishing exposure times to be harmful.
CO
detectors are designed to measure CO levels over time and sound an alarm before
dangerous levels of CO accumulate in an environment, giving people adequate warning
to safely ventilate the area or evacuate. Some system-connected detectors also
alert a monitoring service that can dispatch emergency services if necessary.
CO2 SENSOR
A carbon dioxide
sensor or CO2 sensor is an instrument for the measurement of carbon
dioxide gas. The most common principles for CO2 sensors are infrared
gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important
in monitoring indoor air quality and many industrial processes.
The CO2 sensor is a chemical
optical sensor utilizing the acidic nature of CO2 for detection. It
consists of a gas-permeable membrane in which a pH-sensitive luminescence dye
is immobilized together with a buffer and an inert reference luminescent dye.
CO2 permeating into the membrane changes the internal pH of the
buffer. With this changes the luminescence of the pH-sensitive dye. Together
with the inert reference dye internal referencing is made for detection of the
luminescence lifetime of the sensor. The measurement signal detected by the pCO2
mini correlates to the partial pressure of CO2 ambient.
AMPLIFIERS
An
operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.
An op-amp produces an output voltage that is typically hundreds or thousands of
times larger than the voltage difference between its input terminals.
Operational amplifiers had their origins in analog
computers where they were used to
do mathematical operations in many linear, non-linear and frequency-dependent
circuits. Characteristics of a circuit using an op-amp are set by external
components with little dependence on temperature changes or manufacturing
variations in the op-amp itself, which makes op-amps popular building blocks
for circuit design.
Op-amps
are among the most widely used electronic devices today, being used in a vast
array of consumer, industrial, and scientific devices. Many standard IC op-amps
cost only a few cents in moderate production volume; however some integrated
or hybrid operational amplifiers with special performance specifications may
cost high in small quantities. Op-amps
may be packaged as components, or used as elements of more complex integrated
circuits.
The
op-amp is one type of differential
amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two
outputs), the instrumentation amplifier (usually built from three op-amps),
the isolation amplifier (similar to the instrumentation
amplifier, but with tolerance to common-mode voltages that would destroy an
ordinary op-amp), and negative
feedback amplifier (usually built
from one or more op-amps and a resistive feedback network).
The power supply pins (VS+ and VS−)
can be labeled in different ways. Despite different labeling, the function
remains the same — to provide additional power for amplification of the signal.
Often these pins are left out of the diagram for clarity, and the power
configuration is described or assumed from the circuit.
GPS MODULE
The Global
Positioning System (GPS) is a satellite-based navigation system made up of a
network of 24 satellites placed into orbit by the U.S. Department of Defense.
GPS was originally intended for military applications, but in the 1980s, the
government made the system available for civilian use. GPS works in any weather
conditions, anywhere in the world, 24 hours a day. There are no subscription
fees or setup charges to use GPS. GPS satellites circle the earth twice a day
in a very precise orbit and transmit signal information to earth. GPS receivers
take this information and use triangulation to calculate the user's exact
location. Essentially, the GPS receiver compares the time a signal was
transmitted by a satellite with the time it was received. The time difference
tells the GPS receiver how far away the satellite is. Now, with distance
measurements from a few more satellites, the receiver can determine the user's
position and display it on the unit's electronic map.
A GPS receiver
must be locked on to the signal of at least three satellites to calculate a 2D
position (latitude and longitude) and track movement. With four or more satellites
in view, the receiver can determine the user's 3D position (latitude, longitude
and altitude). Once the user's position has been determined, the GPS unit can
calculate other information, such as speed, bearing, track, trip distance,
distance to destination, sunrise and sunset time and more. The features of GPS
module is given below
Ability to receive both
the presently available L1 frequency and the L5 frequency to be introduced in
the future
Interoperability with
the Galileo system would allow receiver manufacturer to utilize this antenna
Vehicle mounting of
antenna would allow navigational tracking capability for any vehicle
GSM MODEM
The general packet radio
service (GPRS) is a packet-oriented mobile data service used in 2G and 3G
cellular communication systems global system for mobile communications (GSM).
The proposed system uses a GPRS-Modem as a communication device to transmit
time, date, physical location and level of air pollutants. The modem used for
the proposed system has an embedded communication protocol that supports
Machine-to-Machine (M2M) intelligent wireless Transmission Control Protocol
(TCP/IP) features such as Simple Mail Transfer (SMTP) E mail, File Transfer
Protocol (FTP), and Simple Messaging Service (SMS) services Protocol.
The
GSM net used by cell phones provides a low cost, long range, wireless
communication channel for applications that need connectivity rather than high
data rates. Machinery such as industrial refrigerators and freezers, HVAC,
vending machines, vehicle service etc. could benefit from being connected to a
GSM system. The protocol used by GSM modems for setup and control is based on
the Hayes AT-Command set. The GSM modem specific commands are adapted to the
services
offered by a GSM modem
such as: text messaging, calling a given Phone number, deleting memory
locations etc. Since the main objective for this application note is to show
how to send and receive text messages, only a subset of the AT-Command set
needs to be implemented.
RS 232
In telecommunications, RS 232 is a standard for serial binary data interconnection
between a DTE (Data terminal equipment) and a DCE (Data
Circuit-terminating Equipment). It is commonly used in computer serial ports.
The Electronic Industries Alliance (EIA) standard RS-232-C [3] as of 1969
defines:
Electrical
signal characteristics such as voltage levels, signaling rate, timing and
slew-rate of signals, voltage withstand level, short-circuit behavior,
maximum stray capacitance and cable length
Interface
mechanical characteristics, pluggable connectors and pin identification
Functions
of each circuit in the interface connector
Standard
subsets of interface circuits for selected telecom applications
The standard does not define such elements as
character encoding (for example, ASCII, Baudot or EBCDIC), or the framing of
characters in the data stream (bits per character, start/stop bits, parity).
The standard does not define protocols for error detection or algorithms for
data compression.
The standard does not define bit rates for
transmission, although the standard says it is intended for bit rates lower
than 20,000 bits per second. Many modern devices can exceed this speed (38,400
and 57,600 bit/s being common, and 115,200 and 230,400 bit/s making occasional
appearances) while still using RS-232 compatible signal levels.
Details of character format and transmission bit
rate are controlled by the serial port hardware, often a single integrated
circuit called a UART that converts data from
parallel
to serial form. A typical serial port includes specialized driver and receiver
integrated circuits to convert between internal logic levels and RS-232
compatible signal levels.
LCD
Liquid crystal displays (LCDs)
have materials which combine the properties of both liquids and
crystals. Rather than having a melting point, they have a temperature range
within which the molecules are almost as mobile as they would be in a liquid,
but are grouped together in an ordered form similar to a crystal. An LCD
consists of two glass panels, with the liquid crystal material sand witched in
between them. The inner surface of the glass plates are coated with transparent
electrodes which define the character, symbols or patterns to be displayed
polymeric layers are present in between the electrodes and the liquid crystal,
which makes the liquid crystal molecules to maintain a defined orientation
angle.
The
LCDs used exclusively in watches, calculators and measuring instruments are the
simple seven-segment displays, having a limited amount of numeric data. The
recent advances in technology have resulted in better legibility, more
information displaying capability and a wider temperature range. These have
resulted in the LCDs being extensively used in telecommunications and entertainment
electronics. The LCDs have even started replacing the cathode ray tubes (CRTs)
used for the display of text and graphics, and also in small TV applications.
POLLUTION SERVER
The Pollution-Server is an
off-the-shelf standard personal computer with accessibility to the Internet.
The Pollution-Server connects to the GPRS-Modem via TCP/IP through the Internet
and the public mobile network. The server requires a private IP address for the
GPRS-Modem and communicates over a pre-configured port. The Pollution-Server connects to a database
management system (MySQL) through a local area network (LAN). Clients such as
the municipality, environmental protection agencies, travel agencies, insurance
companies and tourist companies can connect to the Pollution-Server through the
Internet and check the real-time air pollutants level using a normal browser on
a standard PC or a mobile device.
CIRCUIT
DIAGRAM DESCRIPTION
OVERVIEW
The proposed air pollution monitoring & control
system comprises of sensor nodes and a communications system which allows the
data to reach a server. The sensor nodes gather data autonomously and the data
network is used to pass data to one or more base stations, which forward it to
a sensor network server. The air quality information from other node also
received by the node to control pollution level
There are many types of pollutant gas sensors, such as Co2 sensor, Co
sensor, LPG sensor. These can be used for gas detection. It means that we will
discuss sensors, which mainly operate on the base of surface reactions. Of
course these sensors have some disadvantages. However, these sensors in
comparison with other ones have excellent sensitivity, very short response
time, low cost, and very good suitability for design of portable instruments,
which compensate their disadvantages. The information Manipulate the air
quality information, the data is been stored in memory and transmitted to base
station, received data also stored into the memory. It performs important
manipulation which reduces power and time. A level comparator accepts the data
compare it with allowable pollutant level, and categories into low, medium high
& critical level.Various display methods can be used to indicate pollution
level. The pollution level can be display via SMS, GPRS at the vehicle, or LED
display at every square.
CIRCUIT DIAGRAM EXPLANATION
This
section gives a detailed explanation of ATMEGA 16-8 bit microcontroller which
is a 40-pin wide Dual In Line Package chip. It is followed by the explanation
of sensors, power supply, GSM, logic level converter and GPS.
ATMEGA 16-8 BIT MICROCONTROLLER
A microcontroller often serves the “brain” of a
mechatronic system. Like a mini, self contained computer, it can be programmed
to interact with both the hardware of the system and the user. Even the most
basic microcontroller can perform simple math operations, control digital
outputs, and monitor digital inputs. As the computer industry has evolved, so
that the technology is associated with microcontrollers.
Newer microcontrollers are much faster, have more memory, and have a host of
input and output features that dwarf the ability of earlier models. Most modern
controllers have analog-to-digital converters, high-speed timers and counters,
interrupt capabilities, output that can be pulse-width modulated, serial
communication ports etc.
The AT mega 16 microcontroller shown above in figure
4.1 is a 40-pin wide DIP (Dual Inline) Package chip. This chip is robust, and
the DIP package interfaces with prototyping supplies like solder less bread
boards and solder-type perf-boards. This same microcontroller is available in a
surface mount package, about the size of a dime. Surface mount devices are more
useful for circuit boards built for mass production.
The AVR
core combines a rich instruction set with 32 general purpose working registers.
All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU),
allowing two independent registers to be accessed in one single instruction
executed in one clock cycle. The resulting architecture is more code efficient
while achieving throughputs up to ten times faster than conventional CISC
microcontrollers. The ATmega16 provides the following features: 16K bytes of
In-System Programmable Flash Program memory with Read-While-Write capabilities,
512 bytes EEPROM, 1K byte SRAM, 32 general purpose I/O lines, 32 general
purpose working registers, a JTAG interface for Boundary-scan, On-chip
Debugging support and programming, three flexible Timer/Counters with compare
modes, Internal and External Interrupts, a serial programmable USART, a byte
oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional
differential input stage with programmable gain (TQFP package only), a
programmable Watchdog Timer with Internal Oscillator, an SPI serial port, and
six software selectable power saving modes. The Idle mode stops the CPU while
allowing the USART, Two-wire interface, A/D Converter, SRAM, Timer/Counters,
SPI port, and interrupt system to continue functioning. The Power-down mode
saves the register contents but freezes the Oscillator, disabling all
other chip functions until the next External Interrupt or Hardware Reset. In
Power-save mode, the Asynchronous Timer continues to run, allowing the user to
maintain a timer base while the rest of the device is sleeping. The ADC Noise
Reduction mode stops the CPU and all I/O modules except Asynchronous Timer and
ADC, to minimize switching noise during ADC conversions. In Standby mode, the
crystal/resonator Oscillator is running while the rest of the device is
sleeping. This allows very fast start-up combined with low-power consumption.
In Extended Standby mode, both the main Oscillator and the Asynchronous Timer
continue to run. The device is manufactured using Atmel’s high density non-volatile
memory technology. The On-chip ISP Flash allows the program memory to be
reprogrammed in-system through an SPI serial interface, by a conventional non-volatile
memory programmer, or by an On-chip Boot program running on the AVR core. The
boot program can use any interface to download the application program in the
Application Flash memory. Software in the Boot Flash section will continue to
run while the Application Flash section is updated, providing true
Read-While-Write operation. By combining an 8-bit RISC CPU with In-System
Self-Programmable Flash on a monolithic chip, the Atmel ATmega16 is a powerful
microcontroller that provides a highly-flexible and cost-effective solution to many
embedded control applications. The ATmega16 AVR is supported with a full suite
of program and system development tools including: C compilers, macro
assemblers, program debugger/simulators, in-circuit emulators, and evaluation
kits.
CO SENSOR
The H-550 CO2 module is a world’s
smallest sensor and can be integrated into wide range of application product
from small wall-pads to building ventilation controller. Its main application
area is Indoor Air Quality, HVAC, Automotive, Stove, Air-conditioner, Vehicle
drowsiness, Gas Equipment.
CO2 SENSOR
The LM358/LM358A
consist of two independent, high gain, internally frequency compensated
operational amplifiers which were designed specifically to
operate from a single power
supply over a wide range of voltage. 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
amplifier, DC gain blocks and all the conventional OP-AMP circuits which now can
be easily implemented in single power supply systems.
LPG SENSOR
The
gas sensor is the special sensor which designed for sense the gas leakage. In
the gas sensor the supply voltage is given to input terminal. The gas sensor
output terminals are connected to non inverting input terminal of the
comparator.
Here
the comparator is constructed with operational amplifier LM 358. The reference
voltage is given to inverting input terminal. The reference voltage is depends
on the desired gas intensity. When there is no leakage the non inverting input
is grater then inverting input so the output of the comparator is positive
voltage which is given to the base of the switching transistor BC 547. Hence
the transistor is conducting. Here the
transistor is act as switch so the collector and emitter will be closed. The
output is taken from collector terminal. Now the output is zero which is given
to hex inverter 40106.Figure 4.5 shows the circuit diagram of LPG sensor
When there is gas leakage the inverting input
voltage is greater than non inverting input. Now the comparator output is -12V
so the transistor is cutoff region. The 5v is given to hex inverter 40106 IC.
Then the final output data is directly given to microcontroller to determine
the gas leakage.Each circuit of the HEF40106B
functions as an inverter with Schmitt-trigger action. The Schmitt-trigger
switches at different points for the positive and negative-going input signals.
The difference between the positive-going voltage (VP) and the negative-going
voltage (VN) is defined as hysteresis voltage (VH). This device may be used for
enhanced noise immunity or to “square up” slowly changing waveforms.
POWER SUPPLY
The
ac voltage, typically 220V rms, is connected to a transformer, which steps that
ac voltage down to the level of the desired dc output. A diode rectifier then
provides a full-wave rectified voltage that is initially filtered by a simple
capacitor filter to produce a dc voltage. This resulting dc voltage usually has
some ripple or ac voltage variation.
A
regulator circuit removes the ripples and also remains the same dc value even
if the input dc voltage varies, or the load connected to the output dc voltage
changes. This voltage regulation is usually obtained using one of the popular
voltage regulator IC units.
TRANSFORMER
The
potential transformer will step down the power supply voltage (0-230V) to
(0-6V) level. Then the secondary of the potential transformer will be connected
to the precision rectifier, which is constructed with the help of op–amp. The
advantages of using precision rectifier are it will give peak voltage output as
DC, rest of the circuits will give only RMS output.
BRIDGE
RECTIFIER
When four diodes are
connected as shown in figure, the circuit is called as bridge rectifier. The
input to the circuit is applied to the diagonally opposite corners of the
network, and the output is taken from the remaining two corners.
Let us assume that the transformer
is working properly and there is a positive potential, at point A and a
negative potential at point B. the positive potential at point A will forward
bias D3 and reverse bias D4.
The
negative potential at point B will forward bias D1 and reverse D2. At this time
D3 and D1 are forward biased and will allow current flow to pass through them;
D4 and D2 are reverse biased and will block current flow.
The path for current flow is from point B
through D1, up through RL, through D3, through the secondary of the transformer
back to point B. this path is indicated by the solid arrows. Waveforms (1) and
(2) can be observed across D1 and D3.
One-half cycle later the polarity
across the secondary of the transformer reverse, forward biasing D2 and D4 and
reverse biasing D1 and D3. Current flow will now be from point A through D4, up
through RL, through D2, through the secondary of T1, and back to point A. This
path is indicated by the broken arrows. Waveforms (3) and (4) can be observed
across D2 and D4. The current flow through RL is always in the same direction.
In flowing through RL this current develops a voltage corresponding to that
shown waveform (5). Since current flows through the load (RL) during both half
cycles of the applied voltage, this bridge rectifier is a full-wave rectifier.
One advantage of a bridge rectifier over a conventional
full-wave rectifier is that with a given transformer the bridge rectifier
produces a voltage output that is nearly twice that of the conventional
full-wave circuit.
This may be shown
by assigning values to some of the components shown in views A and B. assume
that the same transformer is used in both circuits. The peak voltage developed
between points X and y is 1000 volts in both circuits. In the conventional
full-wave circuit shown—in view A, the peak voltage from the center tap to
either X or Y is 500 volts. Since only one diode can conduct at any instant,
the maximum voltage that can be rectified at any instant is 500 volts.
The maximum voltage that
appears across the load resistor is nearly-but never exceeds-500 v0lts, as
result of the small voltage drop across the diode. In the bridge rectifier shown
in view B, the maximum voltage that can be rectified is the full secondary
voltage, which is 1000 volts. Therefore, the peak output voltage across the
load resistor is nearly 1000 volts. With both circuits using the same
transformer, the bridge rectifier circuit produces a higher output voltage than
the conventional full-wave rectifier circuit.
IC VOLTAGE
REGULATORS
Voltage
regulators comprise a class of widely used ICs. Regulator IC units contain the
circuitry for reference source, comparator amplifier, control device, and
overload protection all in a single IC. IC units provide regulation of either a
fixed positive voltage, a fixed negative voltage, or an adjustably set voltage.
The regulators can be selected for operation with load currents from hundreds
of milli amperes to tens of amperes, corresponding to power ratings from milli
watts to tens of watts.
A fixed three-terminal voltage regulator has an
unregulated dc input voltage, Vi, applied to one input terminal, a regulated dc
output voltage, Vo, from a second terminal, with the third terminal connected
to ground.
The series 78 regulators provide fixed positive
regulated voltages from 5 to 24 volts. Similarly, the series 79 regulators
provide fixed negative regulated voltages from 5 to 24 volts.
·
For ICs,
microcontroller, LCD --------- 5 volts
·
For alarm circuit,
op-amp, relay circuits ---------- 12 volts
GSM MODEM
The GSM net used by cell phones provides a low
cost, long range, wireless communication channel for applications that need
connectivity rather than high data rates. Machinery such as industrial
refrigerators and freezers, HVAC, vending machines, vehicle service etc. could
benefit from being connected to a GSM system.
The protocol used by GSM modems for setup and control is based on
the Hayes AT-Command set. The GSM modem specific commands are adapted to the
services offered by a GSM modem such as: text messaging, calling a given Phone
number, deleting memory locations etc. Since the main objective for this
application note is to show how to send and receive text messages, only a
subset of the AT-Command set needs to be implemented.
The European Telecommunication Standard Institute (ETSI) GSM 07.05
defines the AT-Command interface for GSM compatible modems. From this document
some selected commands are chosen, and presented briefly in this section. This
command subset will enable the modem to send and receive SMS messages.
LOGIC LEVEL CONVERTER
Logic level converter is
an asynchronous communication protocol that lets you transfer data between
electronic devices. It uses a serial transmission method where bytes of data are output one
bit at a time onto a single wire.
In this circuit the MAX
232 IC used as level logic converter. The MAX232 is a dual driver/receiver that
includes a capacive voltage generator to supply EIA 232 voltage levels from a
single 5v supply. Each receiver converts EIA-232 to 5v TTL/CMOS levels. Each
driver converts TLL/CMOS input levels into EIA-232 levels.
GPS MODEM
GPS is arguably one of
the most important inventions of our time, and has so many different
applications that many technologies and ways of working are continually being
improved in order to make the most of it.To understand exactly why it is so
useful and important, we should first look at how GPS works. More importantly,
looking at what technological achievements have driven the development of this
fascinating positioning system.In order for GPS to work, a network of
satellites was placed into orbit around planet Earth, each broadcasting a
specific signal, much like a normal radio signal. This signal can be received
by a low cost, low technology aerial, even though the signal is very weak.
Rather than carrying an
actual radio or television program, the signals that are broadcast by the
satellites carry data that is passed from the aerial, decoded and used by to
the GPS software.The information is specific enough that the GPS software can
identify the satellite, it’s location in space, and calculate the time that the
signal took to travel from the satellite to the GPS receiver.Using different signals
from different
satellites, the GPS software is able to calculate
the position of the receiver. The principle is very similar to that which is
used in orienteering – if you can identify three places on your map, take a
bearing to where they are, and draw three lines on the map, then you will find
out where you are on the map.The lines will intersect, and, depending on the
accuracy of the bearings, the triangle that they form where they intersect will
approximate your position, within a margin of error.GPS software performs a
similar kind of exercise, using the known positions of the satellites in space,
and measuring the time that the signal has taken to travel from the satellite
to Earth.
PRINCIPLE
OF OPERATION
The proposed system consists of a Mobile Data-Acquisition
Unit (Mobile-DAQ) and a fixed Internet-Enabled Pollution Monitoring Server
(Pollution-Server). The Mobile-DAQ unit integrates a single-chip
microcontroller, air pollution sensors array, a General Packet Radio Service
Modem (GPRS-Modem), and a Global Positioning System Module (GPS-Module). The
Pollution-Server is a high-end personal computer application server with
Internet connectivity. The Mobile-DAQ unit gathers air pollutants levels (CO,
NO2, and SO2), and packs them in a frame with the GPS physical location, time,
and date. The frame is subsequently uploaded to the GPRS-Modem and transmitted
to the Pollution-Server via the public mobile network. A database server is
attached to the Pollution- Server for storing the pollutants level for further
usage by various clients such as environment protection agencies, vehicles
registration authorities, and tourist and insurance companies. The
Pollution-Server is interfaced to Google Maps to display real-time pollutants levels
and locations in large metropolitan areas. The system software architecture is divided into two
layers structure: physical layer and application layer.
Physical
layer is responsible for acquiring the real-time data from the sensors-array
and the physical location, time and date of the sampled pollutants from the GPS
module. This information is then encapsulated into a data frame by the
microcontroller. The microcontroller then sends each frame to the GPRS-Modem
through the RS-232 interface. The GPRS-Modem, in turn, sends each data frame to
the Pollution-Server using the publicly available mobile network and the
Internet.
The physical layer is implemented
using C language which is compiled to native microcontroller code. The software
implementing the physical layer is composed of five functions, namely: Port-Read()
function, Sensor-acquisition() function, GPS-position() function, Data-Frame() function,
and GPRS-Transit() function.
The
application layer consists of socket-server whcih collects and stores pollutant
data from all the Mobile-DAQs. Air pollution-index calculates pollution
categories based on The application layer consists of three primary modules.
They are local pollution policies and regulations. Finally, Google Mapper, makes this pollution information
available over the Internet. Each module is described in the following.Multithreaded
Java program that uses Berkeley sockets to listen to a pre-configured port for
socket connections from the various remote Mobile-DAQs. Upon connecting with a
Mobile-DAQ, the Socket-Server spawns a software thread that parses the data
frame containing pollutant data along with the sampling time and location,
stores the data frame in a database using the
database management system and closes the connection.PHP program running
on the Apache web-server that reads the pollutant data from the mySQL database
and plots it on a Google Map using the Google Maps API. In specific, an
instance of a GMap object from is created using a JavaScript call.AGPolygon
object based on latitude, longitude and the level of the pollutant is created for
each region in the Map being shown.
PCB LAYOUT
OVERVIEW
This chapter gives the detailed explanation of
design and fabrication of PCB. Design of PCB is concerned as the last step of
electronic circuit design as well as first step in the production of PCBs. It
includes the major steps for assembling it in a printed circuit board. The
different steps included are processing the film, standard requirements,
cleaning, artwork transfer, etching, drilling and varnish coating. These steps
are explained in detail in this chapter. It also includes the PCB layout of
relay circuit, power supply and microcontroller circuit.
INTRODUCTION TO PCB
A printed circuit is a
wiring arrangement that is fabricated by means of foil runs on the circuit
board. Printed circuit can be mass produced inexpensively and efficiently.
Printed circuits allow extreme miniaturization and high reliability. Most
electronic devices are built printed circuit technology, although high power
circuits still use point to point wiring method. Printed circuits are
fabricated by first drawing and etching pattern. This pattern is then
photographed and reproduced on clear plastic sheets. The plastic sheet is
placed over a copper coated glass epoxy or phenol board, and the assemble
undergoes photochemical process.
Alternatives to PCB’s
include wire wrap and point-to-point construction. PCB’s are often less expensive
and more reliable than these alternatives, though they require more layout
effort and higher initial cost. PCB’s are much cheaper and faster for
high-volume production since production and soldering of PCB’s can be done by
automated equipment. Most of the electronics industry’s PCB design, assembly,
and quality control needs are set by standards that are published by the IPC
organization. The vast majority of printed circuit boards are made by bonding a
layer of copper over the entire substrate, sometimes on both sides,(creating a
“blank PCB”) then removing unwanted copper after applying a temporary mask( by
etching).
PROCESSING THE FILM
The layout is printed in a butter paper using a laser printer. The
layout is transferred to copper clad sheet using the screen print procedure.
First a negative screen of the layout is prepared with the help of a
professional screen printer. The copper clad sheet is kept under the screen.
The screen printing ink is poured on the screen and brushed through the top of
the screen. The printed board is kept under shade for few hours till the ink
become dry.
Etching medium is prepared with the un-hydrous ferric chloride and
water. The printed board is kept in this medium till the exposed copper
dissolves in the solution completely. After that the board is taken out and
rinsed in flowing water under a tap. The ink is removed with the help of NC
thinner. The board is coated with soldering in order to prevent oxidation.
Another screen, which contains component side layout, is prepared and
the same is printed on the component side of the board. A paper epoxy laminate
is used in the board.
STANDARD REQUIREMENTS
The minimum conductor width of finished PCB shall not be less than
0.05mm for signal and 0.4mm for power line. The standard ratio is taken as 1:1,
5:2 for signal power and ground respectively.
CLEANING
Surface of copper clad may contain oxides greases, oils or solid. They
should be removed by the following procedure.
·
Wipe with cotton wool soaked with tricolor
ethylene.
·
Dip in 10% HCl solution at room temperature.
·
Scrap with powder.
ARTWORK TRANSFER
Art work transfer can be done in many ways and the procedure used in
work is named fabrication process, usually used methods are:
·
Silk screen printing
·
Photographic method
·
Direct method
First methods are used for industrial and professional applications.
In direct method artwork is transferred to clad sheet in 1:1 ratio using paint
or permanent ink. This method is used where a single PCB is needed.
ETCHING
Etching is the process of removing unwanted copper from the processed
board using etching solution. For this the PCB is dipped into the etching
solution. Usually ferric chloride solution is used. It is stirred for the
speedy action. After etching the board is cleaned using Is propylene alcohol.
DRILLING
The holes for mounting components are drilled using a high speed of
drilling machine. The size of the holes to drill will be specified during the
layout designing depending upon the component lead diameter. For drilling we
use the mm drill bit.
VARNISH COATING
If the
board is unprotected copper oxides are formed over the conductor and it affects
arability and neatness of the board. For this insulation coating such as
varnish can be used.
PCB LAYOUT
Polychlorinated
Biphenyls are a class of synthetic organic chemicals. Since 1930 PCBs are used
for a variety of industrial uses (mainly as dielectric fluids in capacitors and
transformers but also as flame retardants, ink solvents, plasticizers, etc.)
because of their chemical stability. PCBs are fire resistance, have a low
electrical conductivity, high resistance to thermal breakdown and a high
resistance to oxidants and other chemicals.
Figure
6.1 is the PCB layout of RS232
CONCLUSION
The overarching goal of this project is to
dramatically increase the resolution of air pollution information and maximize its
impact on public life. As discussed in
this paper, recent technological developments in the miniaturization of
electronics and wireless communication technology have led to the emergence of
Environmental Sensor Networks. These will greatly enhance monitoring of the
natural environment and in some cases open up new techniques for taking
measurements or allow previously impossible deployments of sensors. WSN for air
pollution and monitoring will be very beneficial for monitoring different high
risk regions of the country. It will provide real-time information about the
level of air pollution in these regions, as well as provide alerts in cases of
drastic change in quality of air. Our
pollution monitoring system operates deeply embedded in the physical
environment. We have designed mobile nodes to sense known air pollutants as
well as environmental conditions and communicate this data to a central server,
providing continuous real time data feeds over a web interface. Finally, the
system provides an intuitive method of data retrieval using web-based visualization
with a number of other novel applications still under development, such as a
"Green Trip Planner”. which takes into account regional air quality data
and calculates trip paths minimizing exposure to pollution. We currently
provide two approaches for widespread dissemination of our information. First,
the project web site displays sensor and pollution data and allows users to
download pollution information from individual or groups of nodes. Secondly, we
have received permission from the EPA to publish our pollution data on their
AIRNow web site, thus providing widespread access to our data as a free
service.
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