The GSM module has the SIM900A microcontroller, a SIM slot, a 12V input, RS232 (Serial) interface and Pin outs for interfacing with other controllers like Arduino. The module can be interfaced with serial commands from a PC/laptop to get started with understanding the module. Since our laptop does not come with a serial port, we use a prolific USB to Serial converter and use it to communicate with the GSM module.
The connections done are
TX from Prolific converter => RX of GSM
RX from Prolific converter => TX of GSM
GND of GSM to GND of Prolific converter
12V from AC adapter
Refer the below picture for connections.
The putty (or other serial terminal software like TeraTerm) is downloaded and installed.
The prolific USB->Serial is connected to the laptop and necessary drivers are installed
From the device manager note down the Serial port of the converter (see below)
This port is given when launching putty (see below). Also note that the baud rate is kept at 9600 (default of the module)
Then, in the serial terminal, give the first command as AT
You should get OK as response to it. If you don’t get it then anything could be wrong (like connections, power, baud rate, etc)
After this initial OK you can proceed to give other commands (like ATD for calling, etc). See below
The last command was sending SMS. The message has to be terminated with a CTRL + Z to be sent.
The message and the call before that were successfully received in the target mobile as can be seen below