Bus Tracking Using Gps & Gsm System

BTS BUS TRACKING USING GPS & GSM SYSTEM

INTRODUCTION This project is based on VTU syllabus. The proposed system is based on ATMEL 89C52 µcontroller, which is in our syllabus. For doing this project we use some of the software like 

Embedded C for programming the application software to the microcontroller.

 Protel schematic software is used for designing the circuit diagram for this project.  Express PCB software is used for designing the PCB for this project. (Since PCB making is a big process and involves lot of machineries, which are expensive. So we are going to outsource this to the manufacture.)

ABSTRACT: The main aim of this project is to map the vehicles and find out the speed of the

vehicles;

this

system

uses

GPS

receiver/transmitter,

GSM

receiver/transmitter with a micro controller. Imagine the vehicle has left Bangalore at 6 o clock in the morning. If the officer in charge for that vehicle wants to know where this bus is, he will send an SMS to that particular bus number. The SMS, which has sent, by the officer will reach the vehicle, which is traveling and there it will compare the password and the command. If every thing matches then it will perform the request required by the officer. In this way we can easily map the vehicle position or speed of the vehicle from the place where they are sitting. In our project the PCB is designed by using Express PCB & the circuit is designed by using Proteus software. WORKING PRINCIPLE: The project consists of GPS receiver and GSM modem with a micro controller. The whole system is attached to the vehicle. In the other end (main vehicle station) one GSM mobile phone is attached to the computer with VB application. So the GPS system will send the longitudinal and altitude values corresponding to the position of vehicle to GSM Modem. Imagine the bus has left Bangalore at 6 o clock in the morning. If the officer in charge for that vehicle wants to know where the vehicle is, he will come to the computer and click on the vehicle number on the VB program .The VB program will send an SMS to the vehicle number. The SMS sent would come through the GSM service provider and then reach the vehicle, which is traveling, because the vehicle has a GSM device with sim

card. This GSM modem will receive the SMS and send to the microcontroller in the vehicle. The microcontroller will receive this SMS and compare the password and the command. If every thing matches then it will perform the request required by the office. A place name is assigned for each longitude & latitude. The GSM receiver in the vehicle office receives these data & gives to the PC through serial port. The VB program in the PC checks this data with its database & displays the details of the vehicle on the screen. The device is password controlled i.e. person who knows the device password only able to operate.

BLOCK DIAGRAM Transmitter

LCD (Display) LCD Driver

GPS Receiver

GSM MODEM

LCD Glass

GPS/GSM SELECTOR

RS232

Micro Controller (AT89S52)

RTC RTC OSC

Power Supply Trans former Rectifier

Regulator (7805) Filter

Memory

Battery Backup

COMPONENTS USED:  Power Supply 5v DC

- 7805

 Micro controller

- AT89S52-Atm(www.Atmel.Com)

 External EEPROM memory - AT24C02/4/8/16/32A  LCD

- (Liquid crystal display) 2 x16

 Real Time Clock (RTC)

- DS1307 (www.Dallas.Com)

 Serial Communication

- MAX 232

 Buzzer

-

 GSM modem (900/1800 MHz)  GPS receiver (with licence).

SOFTWARE USED:  Embedded C.  Visual basics (VB)

Freq-1 to 18 kHz (5v-12Vdc)

COMPONENT APPLICATIONS: Power supply: The microcontroller and other devices get power supply from AC to Dc adapter through voltage regulator. The adapter output voltage will be 12V DC non-regulated. The 7805 voltage regulators are used to convert 12 V to 5VDC.

AC Power

AC/DC Adapter

Regulator (7805)

Filter

DC Output

Vital role of power supply in ‘BTS BUS TRACKING USING GPS & GSM SYSTEM’. The adapter output voltage will be 12V DC non-regulated. The 7805/7812 voltage regulators are used to convert 12 V to 5V/12V DC. Microcontroller: The

AT89C52

is

a

low-power,

high-performance

CMOS

8-bit

microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry- standard 80C51 instruction set and pin out. Features: 8K Bytes of In-System Programmable (ISP) Flash Memory Endurance: 1000 Write/Erase Cycles 4.0V to 5.5V Operating Range 256 x 8-bit Internal RAM 32 Programmable I/O Lines Full Duplex UART Serial Channel Fully Static Operation: 0 Hz to 33 MHz

Vital role of Micro controller-AT89C52 in ‘Vehicle position tracking using GPS AND GSM receiver with licence’ The microcontroller will receive the SMS, which has sent from the office and compare the password and the command. If every thing matches then it will perform the request required by the office. Memory: These memory devices are used to store the data for off line process. The AT24C02A / 04A/ 08A/ 32/64 provides 2048/4096/8192/32,768/65,536 bits of serial electrically erasable and programmable read only memory (EEPROM) organized as 56/512/1024/4096/8192 words of 8 bits each. The device is optimized for use in many industrial and commercial applications where low power and low voltage operation are essential. The AT24C02A/04A/08A is available in space saving 8-pin PDIP. Features Internally Organized 256 x 8 (2K), 512 x 8 (4K) or 1024 x 8 (8K) 2-Wire Serial Interface (I2C protocol) High Reliability – Endurance: 1 Million Write Cycles – Data Retention: 100 Years – ESD Protection: >3000V Vital role of External EEPROM memory in ‘BTS BUS TRACKING USING GPS & GSM SYSTEM’ is used to store the longitudinal and latitudinal values.

RS 232 CONVERTER (MAX 232N) Serial Port: This is the device, which is used to convert TTL/RS232 vice versa. RS-232Protocol

RS-232 was created for one purpose, to interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. So as stated the DTE is the terminal or computer and the DCE is the modem or other communications device. RS-232 pin-outs for IBM compatible computers are shown below. There are two configurations that are typically used: one for a 9-pin connector and the other for a 25-pin connector.

Real Time Clock (RTC – DS1307): This is used to maintain the current time in off line processing. The DS1307 Serial Real-Time Clock is a low power; full binary-coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially via a 2-wire, bi-directional bus. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307 has a built-in power sense circuit that detects power failures and automatically switches to the battery supply. Features It uses I2C protocol

_ Real-time clock (RTC) counts seconds, minutes, hours, date of the month, month, and day of the week, and year with leap-year compensation valid up to 2100. _Two-wire serial interface Consumes less than 500nA in battery backup mode with oscillator running Vital role of RTC in ‘BTS BUS TRACKING USING GPS & GSM SYSTEM’ is used to get the current time. LCD: LCDs can add a lot to your application in terms of providing an useful interface for the user, debugging an application or just giving it a "professional" look. The most common type of LCD controller is the Hitatchi 44780, which provides a relatively simple interface between a processor and an LCD. Inexperienced designers do often not attempt using this interface and programmers because it is difficult to find good documentation on the interface, initializing the interface can be a problem and the displays themselves are expensive. LCD has single line display, Two-line display, four line display. Every line has 16 characters. Vital role of LCD in ‘BUS TRACKING USING GPS & GSM SYSTEM‘ is used to display the corresponding action in written form.

GSM modem (900/1800 MHz): Semens GSM/GPRS Smart Modem is a multi-functional, ready to use, rugged unit that can be embedded or plugged into any application. The Smart Modem can be controlled and customized to various levels by using the standard AT commands. The modem is fully type-approved, it can speed up the

operational time with full range of Voice, Data, Fax and Short Messages (Point to Point and Cell Broadcast), the modem also supports GPRS (Class 2*) for spontaneous data transfer. Description of the interfaces The modem comprises several interfaces: -

LED Function including operating Status

-

External antenna (via SMA)

-

Serial and control link

-

Power Supply (Via 2 pin Phoenix tm contact)

-

SIM card holder

LED Status Indicator The LED will indicate different status of the modem: -

OFF

Modem Switched off

-

ON

Modem is connecting to the network

-

Flashing Slowly

Modem is in idle mode

-

Flashing rapidly

Modem is in transmission/communication (GSM

only) Vital role of GSM MODEM in ‘BUS TRACKING USING GPS & GSM SYSTEM’ is used to transmit and receive the SMS. GPS RECEIVER: ITRAX02 receiver produces and interprets messages in accordance with the NMEA (National Marine Electronics association) standard (its with licence). The fully autonomous receiver provides high position and speed accuracy performances as well as high sensitivity and tracking capabilities in urban conditions. The solutions enable small form factor devices. The deliver major

advancements in GPS performances, accuracy, integration, computing power and flexibility. They are designed to simplify the embedded system integration process. The NMEA commands used for controlling the basic ITRAX operations. The accuracy of the receiver is 50 to 100 meters. APPLICATIONS - Car navigation - Fleet management/tracking - Palmtop, Laptop, PDA, and Handheld - Location Based Services enabled devices Vital role of GPS RECEIVER in ‘BUS TRACKING USING GPS & GSM SYSTEM’ is used for finding the longitude and latitude values.

COMPONENT DESCRIPTION: Micro controller-AT89C52: The

AT89C52

is

a

low-power,

high-performance

CMOS

8-bit

microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry- standard 80C51 instruction set and pin out. Features: 8K Bytes of In-System Programmable (ISP) Flash Memory Endurance: 1000 Write/Erase Cycles 4.0V to 5.5V Operating Range 256 x 8-bit Internal RAM 32 Programmable I/O Lines Full Duplex UART Serial Channel

Fully Static Operation: 0 Hz to 33 MHz The

AT89C52

is

a

low-power,

high-performance

CMOS

8-bit

microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89C52 is a powerful microcontroller which provides a highlyflexible and cost-effective solution to many embedded control applications. The AT89C52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89C52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. RS 232 CONVERTER (MAX 232N) Serial Port: This is the device, which is used to convert TTL/RS232 vice versa. RS-232Protocol 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 RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels. Valid signals are plus or minus 3 to 15 volts. The range

near zero volts is not a valid RS-232 level; logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance of OFF. RS-232 was created for one purpose, to interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. So as stated the DTE is the terminal or computer and the DCE is the modem or other communications device. RS-232 pin-outs for IBM compatible computers are shown below. There are two configurations that are typically used: one for a 9-pin connector and the other for a 25-pin connector.

LCD: LCDs can add a lot to your application in terms of providing an useful interface for the user, debugging an application or just giving it a "professional" look. The most common type of LCD controller is the Hitatchi 44780, which provides a relatively simple interface between a processor and an LCD. Inexperienced designers do often not attempt using this interface and programmers because it is difficult to find good documentation on the interface, initializing the interface can be a problem and the displays themselves are expensive.

LCD has single line display, Two-line display, four line display. Every line has 16 characters.

EEPROM 24C04: Features • Low-voltage and Standard-voltage Operation – 2.7 (VCC = 2.7V to 5.5V) – 1.8 (VCC = 1.8V to 5.5V) • Internally Organized 128 x 8 (1K), 256 x 8 (2K), 512 x 8 (4K), 1024 x 8 (8K) or 2048 x 8 (16K) • 2-wire Serial Interface • Schmitt Trigger, Filtered Inputs for Noise Suppression • Bi-directional Data Transfer Protocol • 100 kHz (1.8V, 2.5V, 2.7V) and 400 kHz (5V) Compatibility • Write Protect Pin for Hardware Data Protection • 8-byte Page (1K, 2K), 16-byte Page (4K, 8K, 16K) Write Modes • Partial Page Writes are Allowed • Self-timed Write Cycle (10 ms max) • High-reliability – Endurance: 1 Million Write Cycles – Data Retention: 100 Years • Automotive Grade, Extended Temperature and Lead-Free Devices Available • 8-lead PDIP, 8-lead JEDEC SOIC, 8-lead MAP, 5-lead SOT23, 8-lead TSSOP and 8-ball dBGA2™ Packages Description: The AT24C01A/02/04/08/16 provides 1024/2048/4096/8192/16384 bits of serial electrically erasable and programmable read-only memory (EEPROM) organized as128/256/512/1024/2048 words of 8 bits each. The device is

optimized for use in many industrial and commercial applications where lowpower and low-voltage operation are essential. The AT24C01A/02/04/08/16 is available in space-saving 8-lead PDIP, 8-lead JEDEC SOIC, 8-lead MAP, 5-lead SOT23 (AT24C01A/AT24C02/AT24C04), 8-lead TSSOP and 8-ball dBGA2 packages and is accessed via a 2-wire serial interface. In addition, the entire family is available in 2.7V (2.7V to 5.5V) and 1.8V (1.8V to 5.5V) versions.

PIN Diagram:

GSM modem (900/1800 MHz): History of GSM During the early 1980s, analog cellular telephone systems were experiencing rapid growth in Europe, particularly in Scandinavia and the United Kingdom, but also in France and Germany. Each country developed its own system, which was incompatible with everyone else's in equipment and operation. This was an undesirable situation, because not only was the mobile equipment limited to operation within national boundaries, which in a unified Europe were increasingly unimportant, but there was also a very limited market for each type

of equipment, so economies of scale and the subsequent savings could not be realized. The Europeans realized this early on, and in 1982 the Conference of European Posts and Telegraphs (CEPT) formed a study group called the Groupe Spécial Mobile (GSM) to study and develop a pan-European public land mobile system. The proposed system had to meet certain criteria: •

Good subjective speech quality

•

Low terminal and service cost

•

Support for international roaming

•

Ability to support handheld terminals

•

Support for range of new services and facilities

•

Spectral efficiency

•

ISDN compatibility

In

1989,

GSM

responsibility

was

transferred

to

the

European

Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid1991, and by 1993 there were 36 GSM networks in 22 countries. Although standardized in Europe, GSM is not only a European standard. Over 200 GSM networks (including DCS1800 and PCS1900) are operational in 110 countries around the world. In the beginning of 1994, there were 1.3 million subscribers worldwide, which had grown to more than 55 million by October 1997. With North America making a delayed entry into the GSM field with a derivative of GSM called PCS1900, GSM systems exist on every continent, and the acronym GSM now aptly stands for Global System for Mobile communications. The developers of GSM chose an unproven (at the time) digital system, as opposed to the then-standard analog cellular systems like AMPS in the United States and TACS in the United Kingdom. They had faith that advancements in

compression algorithms and digital signal processors would allow the fulfillment of the original criteria and the continual improvement of the system in terms of quality and cost. The over 8000 pages of GSM recommendations try to allow flexibility and competitive innovation among suppliers, but provide enough standardization to guarantee proper interworking between the components of the system. This is done by providing functional and interface descriptions for each of the functional entities defined in the system. Services provided by GSM From the beginning, the planners of GSM wanted ISDN compatibility in terms of the services offered and the control signalling used. However, radio transmission limitations, in terms of bandwidth and cost, do not allow the standard ISDN B-channel bit rate of 64 kbps to be practically achieved. Using the ITU-T definitions, telecommunication services can be divided into bearer services, teleservices, and supplementary services. The most basic teleservice supported by GSM is telephony. As with all other communications, speech is digitally encoded and transmitted through the GSM network as a digital stream. There is also an emergency service, where the nearest emergency-service provider is notified by dialing three digits (similar to 911). A variety of data services is offered. GSM users can send and receive data, at rates up to 9600 bps, to users on POTS (Plain Old Telephone Service), ISDN, Packet Switched Public Data Networks, and Circuit Switched Public Data Networks using a variety of access methods and protocols, such as X.25 or X.32. Since GSM is a digital network, a modem is not required between the user and GSM network, although an audio modem is required inside the GSM network to interwork with POTS. Other data services include Group 3 facsimile, as described in ITU-T recommendation T.30, which is supported by use of an appropriate fax adaptor.

A unique feature of GSM, not found in older analog systems, is the Short Message Service (SMS). SMS is a bidirectional service for short alphanumeric (up to 160 bytes) messages. Messages are transported in a store-and-forward fashion. For point-to-point SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cell-broadcast mode, for sending messages such as traffic updates or news updates. Messages can also be stored in the SIM card for later retrieval . Supplementary services are provided on top of teleservices or bearer services. In the current (Phase I) specifications, they include several forms of call forward (such as call forwarding when the mobile subscriber is unreachable by the network), and call barring of outgoing or incoming calls, for example when roaming in another country. Many additional supplementary services will be provided in the Phase 2 specifications, such as caller identification, call waiting, multi-party conversations.

AT COMMANDS USED: SIM Insertion, SIM Removal SIM card Insertion and Removal procedures are supported. There are software functions relying on positive reading of the hardware SIM detect pin. This pin state (open/closed) ispermanently monitored.When the SIM detect pin indicates that a card is present in the SIM connector, the product tries to set up a

logical SIM session. The logical SIM session will be set up or not depending on whether the detected card is a SIM Card or not. The AT+CPIN? command delivers the following responses: If the SIM detect pin indicates “absent”, the response to AT+CPIN? is “+CME ERROR 10” (SIM not inserted). If the SIM detect pin indicates “present”, and the inserted Card is a SIM Card, the

response to AT+CPIN? is “+CPIN: xxx” depending on SIM PIN

state. If the SIM detect pin indicates “present”, and the inserted Card is not a SIM Card, the response to AT+CPIN? is CME ERROR 10. These last two states are not given immediately due to background initialization. Between the hardware SIM detect pin indicating “present” and the previous results the AT+CPIN? sends “+CME ERROR: 515” (Please wait, init in progress). When the SIM detect pin indicates card absence, and if a SIM Card was previously inserted, an IMSI detach procedure is performed, all user data is removed from the product (Phonebooks, SMS etc.). The product then switches to emergency mode. Call Control commands Dial command D Description: The ATD command is used to set a voice, data or fax call. As per GSM 02.30, the dial command also controls supplementary services. For a data or a fax call, the application sends the following ASCII string to the product (the bearer must be previously selected with the +CBST command): ATD where is the destination phone number. For a voice call, the application sends the following ASCII string to the product: (the bearer may be selected previously, if not a default bearer is used).

ATD; where is the destination phone number. Please note that for an international number, the local international prefix does not need to be set (usually 00) but does need to be replaced by the ‘+’ character. Example: to set up a voice call to Wavecom offices from another country, the AT command is: “ATD+33146290800;” Note that some countries may have specific numbering rules for their GSM handset numbering. The response to the ATD command is one of the following: Verbose result code

Numeric code

Description with ATV0 set OK

0

ifthe call succeeds, for voice call only

CONNECT

10,11,12,

ifthe call succeeds, for data calls only,

13,14,15

takes the value negotiated by the product.

BUSY

7

If the called party I

is Already in communication

NO ANSWER

8

If no hang up is detected

after a fixed

network time-out NO CARRIER

3

Call setup failed or remote user

release Echo E Description: This command is used to determine whether or not the modem echoes characters received by an external application (DTE). Syntax: Command Syntax: ATE COMMAND

POSSIBLE

RESPONSES ATE0 Note: Characters are not echoed

OK Note:

Done ATE1 Note: Characters are echoed

OK Note:

Done 55 Select message service +CSMS Description: The supported services are originated (SMS-MO) and terminated short message (SMSMT) + Cell Broadcast Message (SMS-CB) services. Syntax: Command Syntax: AT+CSMS=

COMMAND

POSSIBLE

RESPONSES AT+CSMS=0

+CSMS: 1,1,1 OK

AT+CSMS=1

+CSMS: 1,1,1

Preferred Message Format +CMGF Description: The message formats supported are text mode and PDU mode.In PDU mode, a complete SMS Message including all header information is given as a binary string (in hexadecimal format). Therefore, only the following set of characters is allowed: {‘0’,’1’,’2’,’3’,’4’,’5’,’6’,’7’,’8’,’9’, ‘A’, ‘B’,’C’,’D’,’E’,’F’}. Each pair or characters is converted to a byte (e.g.: ‘41’ is converted to the ASCII character ‘A’, whose ASCII code is0x41 or 65). In Text mode, all commands and responses are in ASCII characters. Syntax: Command Syntax: AT+CMGF COMMAND

POSSIBLE

RESPONSES AT+CMGF=0

OK

Set PDU mode AT+CMGF=1 Set TEXT mode

OK

New message indication +CNMI Description: This command selects the procedure for message reception from the network. Syntax: Command Syntax: AT+CNMI=,,,,

COMMAND

POSSIBLE

RESPONSES AT+CNMI=2,1,0,0,0

OK AT+CMTI : “SM”,1 Note:message received

AT+CNMI=2,2,0,0,0

OK +CMT“123456”,”98/10

/01, 12:3000+00”,129,4,32, 240, “15379”,129,5< LF> Read message +CMGR

Description: This command allows the application to read stored messages. Syntax: Command Syntax: AT+CMGR= A message read with status “REC UNREAD” will be updated in memory with the status “REC READ”.

COMMAND

POSSIBLE

RESPONSES AT+CMTI: “SM”,1 AT+CMGR=1

+CMGR: “REC UNREAD”,”01462908

00”, ”98/10/01,18:22 :11+00”, ABCdefGHI OK Note: read the message Send message +CMGS Description: The field is the address of the terminal to which the message is sent. To send he message, simply type, character (ASCII 26). The text can contain all existing characters except and (ASCII 27). This command can be aborted using the character when entering text. In PDU mode, only hexadecimal characters are used (‘0’…’9’,’A’…’F’). Syntax: Command syntax in text mode: AT+CMGS= [ , ] text is entered COMMAND

POSSIBLE

RESPONSES AT+CMGS=”+33146290800”

+CMGS:

Please call me soon, Fred.

OK

Note: Send a message in text mode transmission

Note: Successful

The message reference, , which is returned to the application is allocated by the product. This number begins with 0 and is incremented by one for each outgoing message(successful and failure cases); it is cyclic on one byte (0 follows 255). Global Positioning System (GPS): The Global Positioning System (GPS), is the only fully-functional satellite navigation system. More than two dozen GPS satellites orbit the Earth, transmitting radio signals which allow GPS receivers to determine their location, speed and direction. GPS has become indispensable for navigation around the world and an important tool for map-making and synchronization of telecommunications networks.

How it works - simple introduction: A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS radio signal gives the distance to each satellite, since the signal travels at a known speed. The signals also carry information about the satellites' location. By determining the position of, and distance to, at least three satellites, the receiver can compute its location using

trilateration.Receivers do not have perfectly accurate clocks, and must track one extra satellite to correct their clock error. Technical description Satellites and Ground Control: The GPS design calls for 24 satellites to be distributed equally among six circular orbital planes with 55° declination (tilt relative to the equator) and separated by 60° right ascension (angle along the equator). Orbiting at an altitude of 10,988 nautical miles (approximately 20,200 kilometers or 12,600 statute miles), each satellite passes over the same location on Earth twice a day. The orbits are arranged so that at least four satellites are always within line of sight from almost anywhere on Earth.

The satellites also broadcast two forms of clock information, the Coarse / Acquisition code, or C/A which is freely available to the public, and the restricted Precise code, or P-code, usually reserved for military applications. The C/A code is a 1,023 bit long pseudo-random code broadcast at 1.023 MHz, repeating every millisecond. Each satellite sends a distinct C/A code, which allows it to be uniquely identified. The P-code is a similar code broadcast at 10.23 MHz, but it repeats only once a week. In normal operation, the so-called "anti-spoofing mode", the P code is first encrypted into the Y-code, or P(Y), which can only be decrypted by units with a valid decryption key. Frequencies used by GPS include:

•

L1 (1575.42 MHz) - Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code.

•

L2 (1227.60 MHz) - P(Y) code, and a second C/A code on the Block II-R and newer satellites.

•

L3 (1381.05 MHz) - Used by the Defense Support Program to signal detection of missile launches, nuclear detonations, and other high-energy infrared events.

•

L4 (1841.40 MHz) - Being studied for additional ionospheric correction.

•

L5 (1176.45 MHz) - Proposed for use as a civilian safety-of-life (SoL) signal. This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. The first Block IIF satellite that would provide this signal is set to be launched in 2008.

Receivers: In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years such that, as of 2006, receivers typically have between twelve and twenty channels. Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol. NMEA 2000 is a newer and less widely adopted protocol. Both are proprietary and controlled by the US-based National Marine

Electronics Association. References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws. Other proprietary protocols exist as well, such as the SiRF protocol. Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth. General NMEA commands: START – Start Navigation Commands iTrax to start navigation. The command has no effect if called while iTrax is already navigating. After the start command has been given, it takes some time from iTrax to acquire satellites, acquire required navigation data from the signal and calculate a first fix. $PFST,START, Examples: $PFST,START Starts navigation using the fastest possible start mode. $PFST,START,2 Starts navigation using warm start mode if possible. STOP – Stop Navigation: Commands iTrax to stop navigation and enter idle state. At idle state iTrax receiverdoesn’t navigate but still accepts commands. Idle state consumes less power than navigation state, but remarkably more than in the power-down mode. This command also stores the “LastKnownGood” fix, ephemeris and almanac data acquired during navigation to flash memory. $PFST,STOP, NMEA MESSAGES: This is one of the NMEA messages.

GGA – Global Positioning System Fix Data Time, position and fix related data for a GPS receiver. $GPGGA,hhmmss.dd,xxmm.dddd,,yyymm.dddd,,v, ss,d.d,h.h ,M,g.g,M,a.a,xxxx*hh

Example: $GPGGA,111200.02,6016.3092,N,02458.3841,E,1,09,0.8,30.6,M,18.1 ,M,,*5D

APPLICATION OF THIS PROJECT: •

For identification of person, vehicles etc

•

For finding the speed of the vehicles