bus tracking using gps & gsm system
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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
GPS/GSMSELECTOR
GPSReceiver
GSMMODEM RS232
Micro Controller (AT89S52)
Power Supply
Trans former
Rectifier Filter
Regulator(7805)
Memory
RTC
RTC OSC
Battery Backup
LCD (Display)
LCD Glass
LCD Driver
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 - Freq-1 to 18 kHz (5v-12Vdc)
GSM modem (900/1800 MHz)
GPS receiver (with licence).
SOFTWARE USED:
Embedded C.
Visual basics (VB)
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.
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
DC OutputAC Power
AC/DC Adapter
Regulator (7805)
Filter
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 highly-flexible 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 low-
power 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 mid-
1991, 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<nb> where <nb> 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<nb>; where <nb> 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 <speed> 10,11,12, ifthe call succeeds,
for data calls only,
13,14,15 <speed> 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 OK
Note: Characters are not echoed Note:
Done
ATE1 OK
Note: Characters are echoed 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=<service>
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 OK
Set TEXT mode
New message indication +CNMI
Description:
This command selects the procedure for message reception from the
network.
Syntax:
Command Syntax: AT+CNMI=<mode>,<mt>,<bm>,<ds>,<bfr>
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”,”98/1
0/01,
12:3000+00”,129,4,32
,240,
“15379”,129,5<CR>
<LF>
Read message +CMGR
Description:
This command allows the application to read stored messages.
Syntax:
Command Syntax: AT+CMGR=<index>
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”,”0146290
800”,
”98/10/01,18:22
:11+00”,<CR><LF>
ABCdefGHI
OK
Note: read the message
Send message +CMGS
Description:
The <address> field is the address of the terminal to which the message is
sent. To send he message, simply type, <ctrl-Z> character (ASCII 26). The text
can contain all existing characters except <ctrl-Z> and <ESC> (ASCII 27).
This command can be aborted using the <ESC> character when entering
text.
In PDU mode, only hexadecimal characters are used (‘0’…’9’,’A’…’F’).
Syntax:
Command syntax in text mode:
AT+CMGS= <da> [ ,<toda> ] <CR>
text is entered <ctrl-Z / ESC >
COMMAND POSSIBLE
RESPONSES
AT+CMGS=”+33146290800”<CR> +CMGS: <mr>
Please call me soon, Fred. <ctrl-Z> OK
Note: Send a message in text mode Note: Successful
transmission
The message reference, <mr>, 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,<startmode>
Examples:
$PFST,START<CR><LF>
Starts navigation using the fastest possible start mode.
$PFST,START,2<CR><LF>
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,<1|0>
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,<N|S>,yyymm.dddd,<E|W>,v,
ss,d.d,h.h
,M,g.g,M,a.a,xxxx*hh<CR><LF>
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
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