GSM Module



One of the best-known examples of wireless technology is the mobile phone, also known as a cellular phone. These wireless phones use radio waves to enable their users to make phone calls from many locations worldwide using techniques like CDMA, GSM etc.

GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second-generation (2G) digital cellular networks used by mobile phones. GSM supports voice calls and data transfer speeds of up to 9.6 kbps, together with the transmission of SMS (Short Message Service). 

Using AT Commands

AT commands are instructions used to control a modem. AT is the abbreviation for attention. Every command line starts with AT.

Table1: AT Commands for Calling

ATD <Number>; To dial a number
ATA To attend a call
AT DL To redial the last number
ATH To Hold the call


Table2: AT commands for Messaging


TEXT mode

To enter text mode
AT+CMGS = < Recipient Number>


(Then press Crtl+Z)

To send a message
AT+ CMGR= N To read Nth message
AT+CMGD = N To delete  Nth  message