SIM900A GSM Module and Arduino: Sending and Receiving SMS Using AT Commands

This tutorial is a complete guide to the SIM900 GSM GPRS Shield with the Arduino. Learn how to send and receive SMS using arduino and SIM900A.

The SIM900A is a complete Dual-band GSM/GPRS solution in a SMT module which can be embedded in the customer applications. Featuring an industry-standard interface, the SIM900A delivers GSM/GPRS 900/1800MHz performance for voice, SMS, Data, and Fax in a small form factor and with low power consumption.

GSM stands for Global System for Mobile Communications and is the global standard for mobile communications.

GPRS stands for General Packet Radio Service. GPRS is a mobile service on the 2G and 3G cellular communication

Applications:

The GSM GPRS shield is particularly useful as it allows to:

Connect to the Internet over GPRS network
Send and receive SMS
Place and receive phones calls

Its capabilities make it perfect for projects with Arduino like:

Remote control of electronic appliances – sending an SMS to turn something on;
Receive notifications – send SMS to your cell phone if movement is detected in your house;
Receive sensor data – send periodic SMS to your cell phone with daily weather data.

Features

Here’s some of the most important features of the shield:

Compatible with Arduino and clones
Based on SIM900 module from SIMCOM
Allows you to send SMS, MMS, GPRS and Audio via UART using AT commands.
It has 12 GPIOs, 2 PWMs and buit-in ADC of the SIM900 module
Quad Band: 850; 900; 1800 and 1900 MHZ, so it should work in all countries with GSM (2G) networks
Control via AT commands

Preliminary steps

Before getting started with your SIM900 GSM GPRS module, you need to consider some aspects about the SIM card and the shield power supply.

GSM coverage

Ensure you have coverage on a GSM 850 MHz, GSM 900 MHz, DCS 1800 MHz or PCS 1900 MHz network. By GSM we mean 2G.

Prepaid SIM Card

We recommend that you use a prepaid plan or a plan with unlimited SMS for testing purposes. Otherwise, if something goes wrong, you may need to pay a huge bill for hundreds of SMS text messages sent by mistake. In this tutorial we’re using a prepaid plan with unlimited SMS.

The shield uses the original SIM card size, not micro or nano.

Getting the right power supply

To power up the shield, it is advisable to use a 5V power supply that can provide 2A as the one shown below

Getting started

1) Insert the SIM card into the SIM card holder – make sure you’ve read the preliminary steps in the previous section.

2) Make sure the antenna is well connected.

Connection with Arduino uno

Arduino uno GSM Module

RX ========> GPIO 10

TX ========> GPIO 9

GND =======> GND

Power the shield using an external 12V & 2amp power supply.

The Status LED will light up and the NetLight LED will blink every 800 ms until it finds the network. When it finds the network, the NetLight LED will start blinking every three seconds.

CODE

Copy and upload this code to your arduino uno board.


 
 #include <SoftwareSerial.h>

SoftwareSerial mySerial(9, 10);

void setup()
{
  mySerial.begin(9600);   // Setting the baud rate of GSM Module  
  Serial.begin(9600);    // Setting the baud rate of Serial Monitor (Arduino)
  delay(100);
}


void loop()
{
  if (Serial.available()>0)
   switch(Serial.read())
  {
    case 's':
      mySerial.println("AT+CMGF=1");    //Sets the GSM Module in Text Mode
     delay(1000);  // Delay of 1 second
     mySerial.println("AT+CMGS=\"+91xxxxxxxxxx\"\r"); // Replace x with mobile number
     delay(1000);
     mySerial.println("Technolab creation");// The SMS text you want to send
     delay(100);
     mySerial.println((char)26);// ASCII code of CTRL+Z for saying the end of sms to  the module 
      delay(1000);
      break;



      
    case 'r':
      mySerial.println("AT+CNMI=2,2,0,0,0"); // AT Command to receive a live SMS
      delay(1000);
      break;
  }

 if (mySerial.available()>0)
   Serial.write(mySerial.read());
}

SIM900A GSM Module and Arduino: Sending and Receiving SMS Using AT Commands