GSM Module Modem – SIM900A


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  • Single supply voltage: 3.4V – 4.5V
  • Power saving mode: Typical power consumption in SLEEP mode is 1.5mA
  • Frequency bands:SIM900A Dual-band: EGSM900, DCS1800. The SIM900A can search the two frequency bands automatically. The frequency bands also can be set by AT command.
  • GSM class: Small MS
  • GPRS connectivity:GPRS multi-slot class 10 (default) , GPRS multi-slot class 8 (option)
  • Transmitting power: Class 4 (2W) at EGSM 900, Class 1 (1W) at DCS 1800
  • Operating Temperature: -30ºC to +80ºC
  • Storage Temperature: -5ºC to +90ºC
  • DATA GPRS: download transfer max is 85.6KBps, Upload transfer max 42.8KBps
  • Supports CSD, USSD, SMS, FAX
  • Supports MIC and Audio Input
  • Speaker Input
  • Features keypad interface
  • Features display interface
  • Features Real Time Clock
  • Supports UART interface
  • Supports single SIM card
  • Firmware upgrade by debug port
  • Communication by using AT commands

The SIM900A is a readily available GSM/GPRS module,used in many mobile phones and PDA. The module can also be used for developing IOT (Internet of Things) and Embedded Applications. SIM900A is a dual-band GSM/GPRS engine that works on frequencies EGSM 900MHz and DCS 1800MHz. SIM900A features GPRS multi-slot class 10/ class 8 (optional) and supports the GPRS coding schemes CS-1, CS-2, CS-3 and CS-4.

The communication with this module is done through UART or RS232 Interface. The data is sent to the module or received from the module though UART interface. The module is typically connected to +4.0V standard power supply. It can work on +4.5V regulated power and any higher voltage may damage the module. And the power source should be able to deliver a peak current of 2A. The UART interface is established as shown in figure. All you need to do is connect RXD of module to TXD of Arduino and TXD is connected to RXD of ARDUINO. The ground of controller and module must be connected for voltage reference. Here AUDIO IN is connected to MIC and AUDIO OUT is connected to a speaker or headset. And at last we need to connect a working GSM SIM card to the module. On powering the module the NETLIGHT LED will blink periodically to state successful connection.

After all connections are done,we need to write a program for the microcontroller to exchange data with module. Since data exchange sequence between controller and module is really complex we will use libraries prewritten for the module. You can download libraries for controller or module through their websites. Using these libraries makes the communication easy. All you need to do is download these libraries and call them in programs. Once the header file is included, you can use simple commands in the program to tell the controller to send or receive data. The controller sendsthe data to the module through UART Interface based on protocol setup in libraries. The module sends this data to another GSM user using cellular network. If the module receives any data from the cellular network (or another GSM user) it will transmit it to controller through UART serial communication.


  • Cellular Communication
  • Robotics
  • Mobile Phone Accessories
  • Servers
  • Computer Peripherals
  • Automobile
  • USB Dongles

Technical Specifications

Weight 45 g
Dimensions 120 × 84 × 24 mm
Main Chip SIM900A
Input Voltage 7V-12V
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