Features: The serial port is a TTL serial port, which can be directly linked with the micro controller. No need of MAX232. Onboard signal lights all the way. It flashes slowly when there is a signal, it flashes quickly when there is no signal. Module power-on automatically starts, automatically finds the network. Small size, no other GSM module is smaller than this module. Full machine chip processing, reflow soldering and stable performance. The power supply can be powered directly from a lithium battery or from a 5V supply. By default, the pin header is not welded, and leaving more space for customers to expand. Specification: Condition: 100% Brand New Material: Plastic Module Size: Approx. 2.5*2.3 cm / 1*0.9 in Module Model: latest module, performance exceeds SIM900/M590 Working Voltage: 3.7~4.2V (current peak 1A, please handle it) Support Network: Support for China Mobile/China Unicom/Global Guad-band Network Type: without Antenna, with Antenna (optional) Package list: (optional) 1 * GPRS Board GSM Module MicroSIM Card TTL Serial Port 1 * Spring-shaped Antenna 2 * Pin Header or 1 * GPRS Board GSM Module MicroSIM Card TTL Serial Port 1 * Spring-shaped Antenna 2 * Pin Header 1 * Wire Connecting Antenna .