- Adopts SIM900 quad-band GSM/GPRS module, expands GSM/GPRS function for Arduino main control board; With this expansion board, Arduino can send / receive messages as well as achieve GPRS data communication;

- Switch on board for ports option: SIM900 serial port or SIM900 debug port; If choose Debug, then you must use Arduino hardware serial port to control, analog serial port is invalid; Farad capacitors on board are designed to supply power for RTC;

- Toggle Debug switch, can setup the SIM900 Debug port to connect to Arduino or setup it to connect to PC through the ATMEGA8U2/FT232 on Arduino;

- 3.3V and 5.5V automatic level compatible, self-adaptive to 3.3V or 5V main control boards, supports development boards based on other 3.3V platforms, such as leaf maple and Chipkit;

- After connecting to the Arduino board, you must use a 9V/2A DC power supply; Otherwise, it can not work;

- Quad-band supported: GSM/GPRS 850/900/1800/1900MHz (Supports China Unicom, China Mobile; Not for China Telecom).