GSM Module – SIM900

By on January 4, 2011

This is a GSM/GPRS-compatible Quad-band cell phone, which works on a frequency of 850/900/1800/1900MHz and which can be used not only to access the Internet, but also for oral communication (provided that it is connected to a microphone and a small loud speaker) and for SMSs. Externally, it looks like a big package (0.94 inches x 0.94 inches x 0.12 inches) with L-shaped contacts on four sides so that they can be soldered both on the side and at the bottom. Internally, the module is managed by an AMR926EJ-S processor, which controls phone communication, data communication (through an integrated TCP/IP stack), and (through an UART and a TTL serial interface) the communication with the circuit interfaced with the cell phone itself.
The processor is also in charge of a SIM card (3 or 1,8 V) which needs to be attached to the outer wall of the module.
In addition, the GSM900 device integrates an analog interface, an  A/D converter, an RTC, an  SPI bus, an I²C, and a PWM module. The radio section is GSM phase 2/2+ compatible and is either class   4 (2 W) at 850/ 900 MHz or class 1 (1 W) at 1800/1900 MHz.
The TTL serial interface is in charge not only of communicating all the data relative to the SMS already received and those that come in during TCP/IP sessions in GPRS (the data-rate is determined by GPRS class 10: max. 85,6 kbps), but also of receiving the circuit commands (in our case, coming from the PIC governing the remote control) that can be either AT standard or AT-enhanced SIMCom type.
The module is supplied with continuous energy (between 3.4 and 4.5 V) and absorbs a maximum of 0.8 A during transmission.


 Pinout SIM900

Pinout SIM900

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  • somnath

    Hi Boris

    I tried but i am not able to get 50Ohm impedance in RF trace.

    Can i use the same characteristic as your design to get 50Ohm impedance for antenna trace?

    Ideally it should work but just to get confirmation from your side will be very helpful.
    Waiting for your reply!


  • Nidhi Joshi

    hello there,
    I am using GSM to interface it with Arduino uno. It worked other times perfectly but now if I try to interface them and check it in serial monitor of arduino software, it types crap.
    please help.

    • saqib

      i am going to do the same project that is to interface GSM SIM900 module with arduino uno r3. what things should i have in mind before starting? can you please tell me… Thanks


    i have a sim 900 gprs module i want to program it to send a message to a mobile no when the module is on . how do i do this . i cannot use an arduino board here .
    my email id is