1. Three power input interface: DC044 interface and V_IN and a lithium battery interface.
Note that: The range of DC044 and the V_IN pin voltage input is 5 - 26V, when using the 5V as the power, be sure that the power supply can provide 2A current. The range of voltage of Lithium battery input power is 3.5 - 4.2V.
2. Switch: It is used to open/close the input power supply for the module. When in use, please confirm the toggle switched to the OPEN state (near the board inside).
3. SMA antenna interface: there is a GSM antenna interface, a GPS antenna interface onboard and a BT antenna interface.
4. Start button: When the board is power on, the LED (PWR) will light up. After a long press (about 2 seconds) on this button, the other three LEDs will be light. And one of them starts to flash; this suggests that SIM808 is beginning to work now. When the power supply, GSM and GPS antenna and SIM card are connected to the module correctly, the LED will be flash slowly (3Second de 1second light), that indicates that the module is registered to the network, and you can make a call or do something else.
5. TTL serial interface: a TTL level interface. Notice that: The pin of VMCU is used to control the high level of TTL UART, so as to realize to match between 1.25V/3.3V/5V systems. For example, if you want to use the 51 MCU to control this board, the pin of VMCU should be connected the DC5V. And if use the STM32 MCU, the pin of VMCU should be connected the DC3.3V. The pins of RXD is the RXD of SIM808 and the pins of TXD is the TXD of SIM808. The pin of V_IN can connect the Power, the function of this pin has the same function of DC044.
6. USB interface: This interface is just used to update the firmware of SIM808 module.
In the application of GPS function, we can send AT+CGPSINF=* (* represent specific figures, please see the AT instruction set) command to get the longitude and latitude information through the GPRS TTL interface level, we also can obtain NEMA data through the GPS TTL level interface, so as to obtain the information of latitude and longitude.
Notice that: the SIM808 module is turned off GPS function by default. When we use the GPS function, please send two AT commands to open the GPS function, and the commands are AT+CGPSPWR=1 and AT+CGPSRST=1 respectively, two instructions are used to powered GPS and reset GPS. And then, the GPS TTL level interface will send data out, and the baud rate is 115200 by default (we can send the AT command to change).
