This GPS/GPRS/GSM all-in-one board uses an embedded SIM908 chip from SIMCOM.
Featuring an industry-standard interface and GPS function, the combination of both technologies allows goods, vehicles and people to be tracked seamlessly at any location and anytime with signal coverage.
Although the module is capable of dual UART , only a single UART is used in this board.Through AT commands the GPS Engine is switched ON to get the NMEA sentence.GSM is controlled through same UART by AT commands.
Individual Antennas are provided , a STUB Antenna for GSM & an external Magnetic PATCH Antenna for the GPS.The position of Antennas is important , the one near the LM317 regulator is for GSM & the one in middle is for GPS.
The board must be powered by an external adapter of 12v 1.5amps.Do not try to power this board from your Arduino or any uC board.
The board is best suited for Microcontrollers like 89S52 or PIC16F877A which have only single UART.
With SIM908 you can avail both GSM & GPS on a single UART.
To test the board with PC , we make use of a USB-UART board built on CP2102 Silicon Labs IC .The M908 board is connected to USB-UART board with a STAIGHT type of RS232 cable.
On connecting the USB cable to PC , a COM port is allotted ( which you can note down from the Device Manager) .This port number is used to communicate from PC to SIM9908 using a Terminal Software like PUTTY or HyperTerminal or TERATERM.
In this demo we shall use PUTTY on serial Baud Rate 9600.
Following snapshot shows the setup for testing.Note that the GPS Antenna should be left outside window .GPS gets a FIX immediately only when the Antenna faces SKY directly.Otherwise it takes more time to get a FIX.
Insert a valid SIM to the SIMHOLDER on the back of the board.On powering up the SIM908 , the SIGNAL LED blinks fast initially & after short time it stops & then blinks slowly.
This indicates that the NETWORK is received.
Now from your mobile , dial the number of the SIM you’ve inserted on the SIM908 board.You get the Ring Back tone & the RING LED on the board glows.
Note the COM Port allotted under the Device Manager & then open the PUTTY.
Select Serial , feed in the COM Port ( here its COM11) & baud rate as 9600.
Type in AT , the SIM908 module will respond with OK.
AT+CPIN? returns the SIM STATUS . +CPIN: READY indicates SIM is inserted.
AT+CSQ returns the SIGNAL QUALITY. 31 is the maximum level.
AT+COPS? returns the SERVICE PROVIDER of your SIM.
AT+CGSN gives the IMEI number of the SIM908 module which is Unique to every module.
The default BAUD RATE is 9600.
If you wish to change baud , use the command AT+IPR
To dial a number
ATD944xxxxx; ATD followed by the number to be called & then a semicolon ; is a must.
ATH to terminate the call
If you call the SIM number from another mobile , you get RING , RING display.
ATA To attend the call & ATH to terminate the call.
If you want the caller ID to be displayed
AT+CLIP=1 enables caller ID.
To send a message , first enable TEXT MODE ,
Now assign the target number to which message has to be sent
A > symbol appears , after which you’ve type the Message to be sent.
CTRL+Z has to be pressed to send the message . 0x1A is the Hex code used to represent CTRL+Z within your C code.
GPS AT COMMANDS
AT+CGPSPWR=1 enables GPS engine
AT+CGPSRST=0 COLD starts GPS.
AT+CGPSINF=0 returns a single NMEA sentence
AT+CGPSSTATUS? indicates whether GPS has got a FIX. If ERROR is the response , then relocate the GPS Antenna , wait for some time & then retry.
AT+CGPSINF=32 returns the GPRMC NMEA sentence , from which you can parse the latitude,longitude
Generally the CGPSINF is assigned value 2 ( 2 power 1) to get GPGGA sentence
4 ( 2 power 2 ) to get GPGLL sentence
32 ( 2 power 5) to get GPRMC sentence.
Widely used value for CGPSINF is 32 which returns the GPRMC Sentence.
In your C code , look out for the value 32 & then count the occurrence of comma .After second comma is the FIX data ( A means FIX , V means VOID- no fix) ,after 3rd comma is the longitude, etc..
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