The onboard two set power supply interface VCC5 5 V power supply, VCC4 interface, 3.5-4.5 V power supply, optional power on self start (default) and control start.The onboard SMA (standard) and IPXmini antenna interface, SIM900A interface reserved The size of the module is 49 * 50.The computer can give early computer debugging USB module power, a amount of data under the condition of the recommended current more than 1A. Standby dozens of MA data can be set to dormancy, dormancy of 10MA low power. 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: short and straight, in order to the signal strength.PCB screen printing : any interface, convenient development twice, the SIM900 / ONE hardware is fully the design when the design manual.Two power supply interface: VCC5, 5 V DC above 1A. Computer 5 V power supply can be early computer USB. DC long data circuit over larger recommended 5V1A. VCC4, 3.5-4.5 V power 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-GNDSIMR SIM900A RXD, TTL level, cannot be connected directly to the 232 levelSIMT SIM900A TXD, TTL level, cannot be connected directly to the 232 level-SIM900A reset, active lowVCC_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 inputOnboard Resources:Serial port circuit (with protection)Antenna interface circuit (SMA bend port female) circuit (flip SIM slot)4 * 3.5 fixture hole 4 pcsSIM900A serial port outputColour:blackMaterial:metal+PCPackage Contents:1 x SIM900A Wireless module1 Cable1 x AntennaOnly 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.