| The onboard two set power supply interface VCC5 5V power supply, VCC4 interface, 3.5--4.5V power supply, optional power on self starting (default) and control start. |
| The onboard SMA (default) and IPXmini antenna interface, SIM900A interface reserved reset. |
| The computer can give early computer debugging USB module power supply. |
| A very large 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 power. Support 2. mobile phone 3.4G card. |
| The serial port circuit: support for 3.3V single chip microcomputer. |
| TTL serial port support3.3 and 5V single chip microcomputer. |
| The SIM card circuit to increase the SMF05C ESD chip. |
| Antenna circuit: guarantee short and straight, so as to ensure the signal strength. |
| PCB display screen printing mark: each interface, convenient development two times. |
| The SIM900/A hardware is completely follow the design when the design manual. |
| 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 - GNDSIMR SIM900A RXD, TTL level. |
| Can not be directly connected to the 232 levelSIMT SIM900A TXD, TTL level. |
| Can not be directly connected to the 232 levelRST - SIM900A reset. |
| Active lowVCC_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. |