SIM900 GPRS Shield Development Board Quad-Band GSM/GPRS Module Compatible with Arduino SMS/Voice/GPRS Wireless Data Transmission

SIM900 module Product Overview

The SIM900 GPRS Shield is an Arduino-compatible expansion board based on the SIM900 quad-band GSM/GPRS module, supporting global GSM networks (850/900/1800/1900MHz). It communicates with host boards via UART serial interface using AT commands (GSM 07.07, 07.05, and SIMCOM enhanced commands), enabling SMS, voice calls, GPRS data transmission, and TCP/UDP communication. Onboard features include Speaker and Headphone jacks, a microphone interface, a SIM card slot, and RTC support. It is ideal for M2M applications, remote device control, wireless sensor networks, and vehicle GPS tracking systems.

SIM900 module Core Features

Quad-Band Global Coverage： Supports 850/900/1800/1900MHz for use on GSM networks worldwide.

GPRS Multi-slot Class 10/8： Supports GPRS Class 10/8, Mobile Station Class B, with embedded TCP/UDP stack for web server data upload.

AT Command Control： Controlled via standard UART interface using AT commands (GSM 07.07, 07.05, and SIMCOM enhanced commands).

SMS Service： Supports SMS messaging (ASCII or raw hexadecimal) for small data transfer.

Voice Functionality： Onboard Speaker, Headphone jacks, and microphone interface for voice calls.

GPIO/PWM/ADC Breakout： Exposes 2 GPIOs, 2 PWMs, and 1 ADC from the SIM900 module (2.8V logic).

Low Power Consumption： 1.5mA in sleep mode.

Industrial Temperature Range： -40℃ to +85℃ for harsh environments.

Selectable Serial Port： Switchable between hardware serial (D0/D1) and software serial (D7/D8).

RTC Support： Onboard real-time clock.

Status LEDs： Power and network status indicators.

SIM900 module Applications

M2M (Machine to Machine) Communication： Remote monitoring and data transmission for industrial equipment

Remote Device Control： Control appliances and industrial devices via SMS or GPRS

Wireless Sensor Networks： Remote weather stations, environmental monitoring nodes

Vehicle Tracking Systems： GPS-based vehicle positioning and tracking

Smart Home： Remote security alarms, access control

IoT Gateways： Upload sensor data to cloud platforms via GPRS

SIM900 module Key Advantages

The SIM900 GPRS Shield is a proven, mature solution for global 2G IoT applications. Based on the industrial-grade SIMCom SIM900 module, it offers quad-band global coverage, low power consumption, and a wide industrial temperature range. The complete onboard design integrates a SIM card slot, audio interfaces, antenna connector, and status LEDs for out-of-the-box use. The UART serial interface can be switched between hardware serial (D0/D1) and software serial (D7/D8) via jumpers for seamless compatibility with Arduino and other mainstream development boards. The SIM900 module uses AT commands for flexible control, supporting SMS, voice, and GPRS communication, while also breaking out GPIO, PWM, and ADC pins for easy peripheral expansion. Mature open-source libraries and a rich community ecosystem further lower the development barrier. For projects requiring global GSM network coverage, low power consumption, and reliability, this shield offers outstanding value.

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FAQ

1. What is the SIM900 GPRS Shield, and what is it used for?
It is a quad‑band GSM/GPRS communication module based on the SIM900 chip, designed as an Arduino expansion board (Shield). It plugs directly onto standard Arduino Uno, Mega, or compatible boards, giving your device independent SMS send/receive, voice calling, and GPRS wireless data transmission. Using simple AT commands, you can implement remote alarms, wireless meter reading, asset tracking, and IoT gateways—ideal for outdoor equipment that needs connectivity beyond Wi‑Fi coverage.

2. Which frequency bands does the module support? Can it be used worldwide?
It is a quad‑band module supporting GSM 850 MHz, EGSM 900 MHz, DCS 1800 MHz, and PCS 1900 MHz. This means it can operate on most 2G networks worldwide. However, before deploying, please verify that a 2G network is still available in your region, as some countries have already shut down their 2G infrastructure. The module typically scans and registers on the strongest available band automatically.

3. How do I install it onto an Arduino? Are extra jumpers or circuits needed?
Installation is straightforward: align the shield’s male headers with the Arduino’s female headers and press them together. Power is supplied from the Arduino’s 5V pin. Be aware, however, that the SIM900 can draw current spikes of up to 2 A during GPRS transmission or voice calls. If your Arduino’s power supply is insufficient, the module will repeatedly restart. It is strongly recommended to power the Arduino with an external 9–12 V adapter via the DC barrel jack, rather than relying solely on the USB port, to ensure adequate current delivery.

4. How can I debug and send my first AT command?
The most common method is to use the on‑board “soft serial” jumpers to connect the module’s TX/RX to Arduino pins D7 and D8 (or other digital pins) and communicate through the SoftwareSerial library. Write a simple Arduino sketch that transparently bridges the USB serial monitor to the module’s serial port. You can then type AT commands directly in the serial monitor—for example, sending `AT` should return `OK`, and `AT+CPIN?` queries the SIM card status—allowing manual debugging and verification.

5. Why does the module’s LED stay off after power‑up, or why does it keep restarting?
This almost always indicates insufficient power. The SIM900’s instantaneous current requirement during transmission far exceeds what a USB port can provide. Check the following: ① always use a rated 9–12 V external power supply (2 A or higher) through the Arduino’s DC jack; ② ensure the power cables and jumper wires are not too thin or too long; ③ if the shield has its own power switch, verify it is turned on; ④ a rapidly blinking network LED means it is searching for a network; a slow blink indicates it has registered on a network.

6. What communication protocols does the SIM900 support? Can it send HTTP requests or MQTT?
The SIM900 has a built‑in TCP/IP stack accessible via AT commands, allowing you to establish TCP or UDP connections. This means you can manually construct HTTP requests to upload sensor data to a cloud platform, or connect to a TCP‑based MQTT server. However, the SIM900 does not natively support HTTPS (SSL/TLS encryption). If encrypted transmission is required, you must perform encryption in software on the MCU side before sending, or upgrade to a module with hardware SSL (such as the SIM800 family).

7. Can the onboard microphone and headset jack be used for voice calls? What is the voice quality like?
Yes. The shield usually breaks out a 3.5 mm audio jack or an electret microphone input and a speaker output. By plugging in a standard mobile phone headset, you can make voice calls with the `ATD;` command and answer with `ATA`. Voice quality is adequate for call alarms and remote monitoring, but keep in mind it uses traditional 2G voice codecs and is not suitable for transmitting high‑fidelity music.

8. Why do Chinese SMS messages display garbled characters, and how can this be fixed?
This is caused by incorrect SMS encoding settings. The SIM900 defaults to GSM 7‑bit encoding, which only supports English. To send Chinese, you must first switch the character set to UCS2 using `AT+CSCS="UCS2"` and then send the message via `AT+CMGS` in UCS2‑encoded hexadecimal. Most Arduino libraries already handle this conversion automatically—you simply call `SMS.send(phone, message)` and the library transparently manages the encoding without manual code‑point calculation.

9. How fast is the GPRS data rate? Can it transmit images or video?
The SIM900’s downlink rate is up to 85.6 kbps, with an uplink of about 42.8 kbps—comparable to early dial‑up speeds. It is well suited for transmitting sensor data, GPS coordinates, short audio clips, or highly compressed low‑resolution images. Transmitting video or high‑resolution photos is impractical due to both speed and data consumption. For image‑heavy applications, consider compressing images locally on the MCU and uploading thumbnails or feature values over GPRS.

10. What is the power consumption of the SIM900 in standby and during communication? Is it suitable for long‑term battery operation?
In sleep mode, current consumption can drop to around 1.5 mA, making it very suitable for battery‑powered devices that need long standby times. During GPRS data transmission, the current typically ranges from 200 to 400 mA, with instantaneous peaks up to 2 A. For long‑term outdoor deployment, it is recommended to pair the module with a high‑capacity lithium battery and a solar charging panel. In your software, maximize the use of sleep modes and short connection bursts to reduce average power consumption.