Arduino GSM shield

By on March 21, 2011
Pin It






This is a very low cost and simple Arduino GSM and GPRS shield. We use the module SIMCom SIM900. It’s the cheaper module now avalaible in the market. The module is not simple to mount by an hobbyst, so we use the Breakboard TDGGSM_900 that we presented in this post.

You can buy the GSM module premounted from our cart.

To connect this module to Arduino we make a PCB that include a LM317 some capacitor filter and no more.

The LM317 give to module about 3.9V.
There is a switch to select the way to comunicate with arduino:
– throw serial hardware (pin 0 and 1)
– throw serial software (pin 4 and 5)

R1: 470 ohm
R2: 1 kohm
C1-C3: 100 nF
C2-C4: 470 µF 25 VL
U1: LM317
GSM: TDGGSM_900 module

SW1: switch
P1: Microswitch

Selecting the serial hardware there are no problem with the baudrate (the default module baudrate is 115200) but there are problem programming the module (the serial is also used to upload the sketch).
Using instead the pin 4 and 5 there aren’t problems to upload the sketch but the maximum baudrate for NewSoftSerial (the serial library) is 57600.
We performed a GSM library to controll easly the module. The GSM library is a modified version of the library of HWKitchen.
With our version we controll the module throw the pin 4 and 5 (so normal digital pin) and our GSM libray include also the NewSoftSerial, so you can easy control the module, send and read SMS, make call, control the GSM state ecc.

Download GSM_Shield_Library

New GSM/GPRS library




This is the GSM_shield library documentation:

Download GSM_Shield_Library

New GSM/GPRS library





In this page you can find some example.

Example to test library


Example to network registration



Example to test call



Download GSM_Shield_Library

New GSM/GPRS library




Bigger example




Test AT command



GPRS Client


GPRS Server


Test SMS without GPRS function

About Boris Landoni

Boris Landoni is the technical manager of Skilled in the GSM field, embraces the Open Source philosophy and its projects are available to the community.


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