Air Pollution Monitoring - Seminar Paper


Air Pollution Monitoring
 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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