Specification
1. Auto-adaption to 3.3V and 5V main board, supports 3.3V platforms such as leaf maple and Chipkit;
2. After connecting the SIM900 shield to Arduino, 9V/2A DC power supply is needed. Otherwise, there may be malfunction;
3. Quad-Band GSM/GPRS 850/900/1800/1900MHz (Support 2G card of UNICOM, China Mobile, does not support Telecom card).