The onboard two set supply interface VCC5 5 V supply, VCC4 interface, 3.5-4.5 V supply, optional on self start (default) and control start.The onboard SMA (standard) and IPXmini antenna interface, SIM900A interface reserved reset.The size of the module is 49 * 50. The computer can give early computer debugging USB module , a very amount of data under the condition of the recommended current more than 1A. Standby dozens of MA data can be set to provide dormancy, dormancy of 10MA low . Support 2, mobile phone 3,4G card. The serial port circuit: support for 3.3 V single chip microcomputer. TTL serial port support.3.3 and 5 V single chip microcomputer.The circuit increase the SMF05C ESD chip.Antenna circuit: guarantee short and straight, in order to improve the signal strength. PCB screen printing mark: any interface, convenient development twice, the SIM900 / ONE hardware is fully follow the design when the design manual.Two supply interface: VCC5, 5 V DC above 1A. Computer 5 V supply can be early computer USB. DC long data circuit over larger recommended 5V1A. VCC4, 3.5-4.5 V supply, ibid., Suitable for lithium battery. Control pin all leads.ONE ttl level, compatible with 3.3 V and 5 V.The two antenna interface, the standard SMA straight head, connector for IPXmini antenna.A way of speech interface, the way Mike interface. The control interface of each pin description: GND-GND SIMR SIM900A RXD, TTL level, cannot be connected directly to the 232 level SIMT SIM900A TXD, TTL level, cannot be connected directly to the 232 level -SIM900A reset, active low VCC_MCU when the SIM900A module and 5 V TTL level communication, this pin is connected to DC 5 V; When the level of communication of SIM900A and 3.3 V TTL, this pin is connected to DC 3.3 V. VCC5-DC 5V input. VCC4 -DC3.5-4.5 input Onboard Resources: Serial port circuit (with protection) Antenna interface circuit (SMA bend port female) circuit (flip SIM slot) 4 * 3.5 fixture hole 4 pcs SIM900A serial port output Colour:black Material:metal+PC Package Contents: 1 x SIM900A Wireless module 1 x Cable 1 x Antenna Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.