This SIM800A V4 module has a set of TTL level serial interface, two sets of power supply interface, and only one power interface can make the module work well. And SIM800A V4
Basic features
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Arduino 51 STM32 AVR MCU compatible
3.5mm speech and Mike interface
Prototype expand
Quad-band 850/900/1800/1900MHz
Size:48*51mm
Power requirements: 5V-18V power supply, the current need to provide 1.5A or above;
TTL level serial port is compatible with 3.3V and 5V microcontrollers. Really can communicate directly with 51 / STM32 / MP430 microcontroller such;
Beginning with the computer debugging, it recommended CP2102 USB-TTL module to module power supply and communications;
When using single-chip control module, also through USB - 232 Monitoring module returns to the instruction data, greatly facilitate find the problem, especially for a small microcontroller with 51 partners.
Standby around 30MA, you can set the sleep state is about 10MA low power consumption.
Support SMS, GPRS data transmission, send MMS, DTMF, HTTP, FTP, PPP dial and other functions.
At the same time containing all the way to the hardware reset pin. When there is a problem module, this pin can be used to reset to resolve.
Development board supports 2G / 3G / 4G or China Unicom mobile phone card