Feature:1. Standard antenna, very good signal, comparable to non‑low cost spring antenna.2. The onboard highefficiency DCDC buck circuit can stabilize the 518V power supply at about 3.8V.3. The audio interface includes earphone and microphone interface, and the 2.54mm pitch pin leads out for easy external connection.4. The device supports multiple models of mobile phone cards, and supports 2G networks, as long as the card is an ordinary mobile phone card, whether it is a 4G or 2G card.5. The SIM card static electricity protects the IC and prevents the SIM card from being damaged by static electricity. Even so, it is necessary to develop the habit of plugging in the card or patch cord when the device is powered off.6. The onboard TTL to RS232 interface circuit can be debugged through the 9‑pin 2325. At the same time, the interface also leads to the power supply pin to power the board.7. Onboard TTL level serial port, the serial port level is matched, and it can be directly connected with 5V or 3.3V system without conversion.Specification:Item Type: SIM 900A ModuleProduct Details: 1. Power Supply Requirements: 5V-18V power supply, current needs to provide 1A or above;2. TTL level serial port is compatible with 3.3V and 5V microcontrollers.3. It can truly communicate directly with 51/STM32/MP430 and other single-chip computers;4. When debugging with a computer in the initial stage, it is recommended to use the CP2102 USB-TTL module to power the module and communicate5. When using the single-chip microcomputer control module, you can also monitor the return data of the instruction through the USB-232 monitoring module, which greatly facilitates finding the problem, especially suitable for small partners who use 51 single-chip microcomputers.6. The standby is about 30MA, and the sleep state can be se