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;