Description : Model: SIM800L (over SIM900) Working voltage: 3.7~4.2V(peak current 2A, please handle) Support network: China Mobile, China Unicom Module size: 2.2cmx1.8cm The serial port is TTL serial port, which can be directly connected to the microcontroller. Don #39;t need a MAX232 When the module is powered on, it automatically starts up and searches for the network Onboard signal indicator (blinking slowly if there is a signal, blinking at short intervals if there is no signal)