The GSM/GPRS Modem-RS232 is built with Dual Band GSM/GPRS engine- SIM900A, it delivers 900/ 1800 MHz performance.

This Modem is coming with an RS232 interface, which allows you to connect PC as well as a microcontroller with RS232 Chip(MAX232).

The baud rate (the rate at which information is transferred in a communication channel) is configurable from 9600-115200 through AT command.

This Modem is having internal TCP/IP stack to enable you to connect with the internet via GPRS. It is suitable for SMS, Voice as well as DATA transfer application in the M2M (machine to machine) interface.

Using this modem, you can make audio calls, SMS, Read SMS, attend the incoming calls and use the internet through simple AT commands.


This Modem can work with any of the GSM network operator SIM card, just like a mobile phone with its own unique phone number.

The SIM900A GSM/GPRS modem is plug and plays modem with RS232 serial communication supported. Hence Advantage of using this modem will be that its RS232 port can be used to communicate and develop embedded applications.

Applications related to SMS Control, data transfer, remote control, and logging can be developed. The GSM/GPRS modem supports features like voice call, SMS, Data/Fax, GPRS, etc.

GSM/GPRS modem uses AT commands to work with supported features.

Note that the modem requires a SIM card provided by a network provider, for connection to a cellular network.

SIM900A Pinout

The SIM900A module typically features a set of pins that serve different functions, such as power supply input, communication interfaces like UART, GPIO pins for controlling external devices, and antenna connections for signal reception.

By referring to the datasheet or documentation provided by the manufacturer, users can easily identify each pin’s purpose and ensure correct wiring during setup. It is essential to connect the required pins to their respective components accurately to avoid any issues with functionality.

sim900a pinout


  • Dual-Band GSM/GPRS 900/ 1800 MHz.
  • The RS232 interface for direct communication with computer or MCU kit.
  • Configurable baud rate.
  • Power controlled using 29302WU IC.
  • ESD Compliance.
  • Enable with MIC and SPeaker socket.
  • With slid in SIM card tray.
  • With a Stub antenna and SMA connector.
  • Input Voltage: 12V DC.

How to Connect and Use the Module

To connect and use the SIM900A GSM/GPRS Module effectively, start by identifying the pinout configuration. Ensure you have all the necessary components such as a power source, antenna, and a microcontroller for communication.

Next, carefully refer to the datasheet or module documentation to understand each pin’s function. Connect power supply pins following the specified voltage requirements to avoid damaging the module.

After connecting power, establish communication between your microcontroller and SIM900A using UART or SPI interface based on your application needs. Configure baud rate settings according to your project requirements for seamless data transfer.

Don’t forget to connect an external antenna securely to ensure reliable reception and transmission of GSM signals. Test your setup by sending AT commands through the serial monitor tool in your programming environment.

With proper connections in place, explore different functionalities of SIM900A like making calls, sending SMS messages, or establishing a GPRS connection for data transmission over cellular networks.

Applications of SIM900A

The SIM900A GSM/GPRS Module is a versatile tool that finds applications in various industries.

  • One common use for the module is in IoT devices, enabling them to communicate over cellular networks. Its ability to send and receive SMS messages makes it ideal for remote monitoring and control systems.
  • In the automotive sector, the SIM900A can be integrated into vehicle tracking systems for real-time location updates.
  • Additionally, it is utilized in security systems to alert users of unauthorized access or emergencies through text notifications.
  • Moreover, the module is popular in smart agriculture solutions, providing farmers with data on soil moisture levels or weather conditions via GPRS connectivity.
  • It also plays a role in vending machines by facilitating cashless transactions through mobile payments.

Alternatives to SIM900A

When considering alternatives to the SIM900A GSM/GPRS module, there are a few options worth exploring. One popular choice is the SIM800L module, which offers similar functionality and features but in a smaller form factor. Another alternative is the Quectel M95 module, known for its reliability and performance.

The best option will depend on your specific project requirements and budget constraints. It’s recommended to research each alternative thoroughly before making a decision to ensure it aligns with your needs.

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