The GSM modem, phones provides a low cost, long range, wireless communication channel for embedded, microcontroller based applications that need connectivity rather than high data rates. Machinery such as industrial refrigerators, freezers, HVAC, monitoring and vending machines, vehicle service, warning system, security system, remote control etc. could benefit from being connected to a GSM modem.

This tutorial describes how to use an AVR to control a GSM modem using AT commands. The interface between modem and host is a textual protocol called AT-Commands. These commands enable GSM modem setup, dialing, text messaging etc. This particular application connects an AVR ATmega8 and SIM300, SIM900 module using a RS232 connection. Most GSM modems have same AT commands. Continue reading GSM modem interfacing →