Working frequency: 900/1800Mhz;SIM900A module (development board) onboard resources as follows: GSM module: SIM900A;1 x RTC backup battery;1 x microphone interface;1 x headphone jack;1 x RS232 interface selection;1 x RS232 serial port;1 x lithium battery Interface;1 x power input interface;1 x power indicator (blue);1 x power switch;1 x clamshell SIM card;1 x SMA antenna connector and antenna supporting small pepper;1 x power on / off button;1 x network status indicator (red);SIM900A modules were used for all IO port pin leads, easy to use; ATK-SIM900A module (development board) using industry-standard design, features include:Onboard RS232 serial port (supports hardware flow control), convenient and PC / IPC and other devices;Onboard 3.5mm headphone and microphone stand, to facilitate voice communication development;Leads all the IO port SIM900A modules, and communications section IO port compatibility design made for easy connection 3.3V / 5V SCM system;Onboard efficient synchronous buck circuit, the conversion efficiency up to 90%, support for wide voltage range (5~24V), ideal for industrial applications;Onboard power anti-reverse protection, TVS power protection and SIM ESD protection, the protection function;Board RTC backup battery (XH414H-IV01E), without worrying about the power-down problem;Onboard peppers antenna, can effectively improve the signal reception;Adoption of international A-level PCB material, immersion gold processing technology, stable and reliable;With a new component machining, copper plated pin, durable;Humanized design, each interface has silkscreen labels, use a glance; connector location and reasonable arrangements designed to facilitate smoothly.PCB size is 80 x 58mm, and with mounting holes, small and exquisite;