6D4 SIM900 GSM GPRS Module Mini V4.0 Serial Wireless Development Board With Antenna

First, you must add the library. Download the Zip file, and add the file to Arduino IDE. Go to Sketch tab, Include library and Add ZIP Library. If it is the first time you are using an Arduino board, just follow these steps:

• Go to www.arduino.cc/en/Main/Software and download the Arduino software compatible to your OS. Install the IDE software as instructed.
• Run the Arduino IDE and clear the text editor and copy the following code in the text editor.
• Choose the board in tools and boards, select your Arduino Board.
• Connect the Arduino to your PC and set the COM port in tools and port.
• Press the Upload (Arrow sign) button.
• You are all set!
• Necessary Files and Downloads: SIM900 Arduino Shield

#include "SIM900.h"
#include "SoftwareSerial.h"
//#include "inetGSM.h"
//#include "sms.h"
//#include "call.h"

//To change pins for Software Serial, use the two lines in GSM.cpp.

//GSM Shield for Arduino
//this code is based on the example of Arduino Labs.

//Simple sketch to communicate with SIM900 through AT commands.

//InetGSM inet;
//CallGSM call;
//SMSGSM sms;

int numdata;
char inSerial[40];
int i=0;


void setup()
{
     //Serial connection.
     Serial.begin(9600);
     Serial.println("GSM Shield testing.");
     //Start configuration of shield with baudrate.
     //For http uses is raccomanded to use 4800 or slower.
     if (gsm.begin(9600))
          Serial.println("\nstatus=READY");
     else Serial.println("\nstatus=IDLE");
};

void loop()
{
     //Read for new byte on serial hardware,
     //and write them on NewSoftSerial.
     serialhwread();
     //Read for new byte on NewSoftSerial.
     serialswread();
};

void serialhwread()
{
     i=0;
     if (Serial.available() > 0) {
          while (Serial.available() > 0) {
               inSerial[i]=(Serial.read());
               delay(10);
               i++;
          }

          inSerial[i]='\0';
          if(!strcmp(inSerial,"/END")) {
               Serial.println("_");
               inSerial[0]=0x1a;
               inSerial[1]='\0';
               gsm.SimpleWriteln(inSerial);
          }
          //Send a saved AT command using serial port.
          if(!strcmp(inSerial,"TEST")) {
               Serial.println("SIGNAL QUALITY");
               gsm.SimpleWriteln("AT+CSQ");
          } else {
               Serial.println(inSerial);
               gsm.SimpleWriteln(inSerial);
          }
          inSerial[0]='\0';
     }
}

void serialswread()
{
     gsm.SimpleRead();
}

It’s simple to communicate with SIM900 through AT commands.

AT commands are commands for controlling modems. AT commands are actually derived from Hayes Command. All commands AT commands start with AT.

Be careful that AT is a prefix that receives a syntax and is not a command name. For example, one of the CMC + CMCAM commands is called AT + CMGS. There is another command called D that is sent to the modem as ATD.

Many GSM, GPRS, Bluetooth, and some other modules use AT commands for communication with computers and microcontrollers.

You can download all AT commands from Here.

Necessary Files and Downloads: SIM900 AT Commands

AT+CGATT =1 

AT+SAPBR =3,1,"CONTYPE","GPRS"
AT+SAPBR =3,1,"APN","RCMNET"
AT+SAPBR=1,1
AT+SAPBR=2,1

AT+CIPGSMLOC=1,1