Module SIM900A GSM GPRS Shield Serial Modem for Arduino

Two power supply interface: VCC5, 5V DC above 1A. Computer 5V power supply can be early computer USB. DC long data circuit over larger recommended 5V1A. VCC4, 3.5--4.5V power supply, ibid., suitable for lithium battery.
Control pin all leads.
A TTL level, compatible with 3.3V and 5V.
The two antenna interface, the default SMA straight head, connector for IPXmini antenna.
One way of speech interface, the way Mike interface.
The control interface of each pin description:
GND - GND
SIMR SIM900A RXD, TTL level, can not be directly connected to the 232 level
SIMT SIM900A TXD, TTL level, can not be directly connected to the 232 level
RST - SIM900A reset, active low
VCC_MCU when the SIM900A module and 5V TTL level communication, this pin is connected to DC 5V; when the level of communication of SIM900A and 3.3V TTL, this pin is connected to DC 3.3V.
VCC5----DC 5V input.
VCC4------DC3.5--4.5 input
Onboard Resources:
Serial port circuit(with protection)
Antenna interface circuit(SMA bend female port)
SIM card circuit(flip SIM slot)
4*3.5 fixture hole 4pcs
SIM900A serial port output terminal
Specifications:
Size:49mm x 47mm
Net Weight:28g
Weight: 38g
Package Included:
1 x SIM900A V4.0 kit
1x Power Cable
1x Antenna