Arduino SIM Card Module

This module is designed to allow GPRS and GSM communication with an Arduino. You put a SIM card into the SIM card slot on the device and communicate with the SIM900 using serial commands.

Included in my broadband package is a mobile phone plan, which includes 500MB of data, 200 minutes and unlimited texts. Perfect for experimenting with, using an Arduino and this module.

So far I have been able to send text messages using the module, with the code below:

#include <SoftwareSerial.h>;
#include <String.h>;
 
SoftwareSerial SIM900(7, 8); // Set the SoftwareSerial pins.
 
char incoming_char = 0;
 
void setup()
{
 SIM900.begin(19200); // Set the baud rate.
 Serial.begin(19200); // Set the baud rate.
 delay(500); // Give the module time to establish a serial connection.
}
 
void loop()
{
 /* When sending a 't' to the module, it runs the script
 to send a text message, configured below. The switch statement has
 been used early on so that other options can easily be added. */
 if (Serial.available())
 switch (Serial.read())
 {
 case 't':
 SendTextMessage();
 break;
 }
 /* When the module sends something back to the Arduino,
 it runs it's own function. This is so the responses can
 be processed later on. */
 if (SIM900.available())
 RecievedMessage();
}
 
// This function is to send an SMS message.
void SendTextMessage()
{
 SIM900.print("AT+CMGF=1\r"); // Because we want to send the SMS in text mode.
 delay(100);
 SIM900.println("AT + CMGS = \"+447755544321\"");// Send the AT command to the module, include the phone number with country code.
 delay(100);
 SIM900.println("Hi, I sent this using my Arduino!");// Message contents.
 delay(100);
 SIM900.println((char)26);// The ASCII code of the CTRL+Z is 26, this tells the module to send the text.
 delay(100);
 SIM900.println();
}
 
void RecievedMessage()
{
 /* Here we're checking if information is available from the module. Running
 the data through a char makes it easier to process later on. The module
 only sends one character at a time. Later on we will look at combining
 the characters into a string of text for parsing. */
 if (SIM900.available() > 0)
 {
 incoming_char = SIM900.read(); // Get the character from the serial port.
 Serial.print(incoming_char); // Print the incoming character to the serial monitor.
 // The characters will keep coming through until there aren't any left to send.
 }
}

I am now working on being able to receive a text message and parsing information out of it (e.g. phone number message sent from and message contents).

If you’re interested in a sketch I wrote that sends the lyrics of Rick Astley – Never Gonna Give You Up to a number of choice, the sketch can be found here.

If you have any questions about this project, or any others on my site get in touch!