The onboard dual power supply interfaces include VCC5 for 5V supply and VCC4 for 3.5-4.5V supply, supporting optional self-start (default) or controlled start. The module features onboard SMA (standard) and IPX mini antenna interfaces, with a reserved reset pin for SIM900A. Module dimensions are 49 x 50 mm.This USB interface module supports computer debugging and is recommended to use a power supply with current over 1A for optimal data transmission performance. Standby current is in the range of tens of mA, with sleep mode current as low as 10mA. Supports 2G, 3G, and 4G mobile communication networks.Serial port circuit supports 3.3V and 5V microcontrollers with TTL level compatibility. Includes SMF05C ESD protection chip. Antenna circuit is designed to be short and direct to enhance signal strength.PCB features clear silkscreen markings for all interfaces, enabling convenient secondary development. Hardware design is fully compatible with SIM900 / ONE series reference design guidelines.Dual power input options: - VCC5: 5V DC input, recommended current over 1A. Can be powered via computer USB port. For long cable runs, 5V/1A power supply is recommended. - VCC4: 3.5-4.5V DC input, suitable for lithium battery power sources.All control pins are fully accessible. TTL level signals are compatible with both 3.3V and 5V microcontrollers. Dual antenna interfaces include standard SMA straight connector and IPX mini connector. Includes audio interface with microphone input.Control interface pinout: GND – Ground SIMR – SIM900A RXD, TTL level, not compatible with RS232 SIMT – SIM900A TXD, TTL level, not compatible with RS232 RST – SIM900A reset, active low VCC_MCU – Connect to 5V when interfacing with 5V TTL; connect to 3.3V when interfacing with 3.3V TTL VCC5 – 5V DC power input VCC4 – 3.5-4.5V DC power input Onboard features: - Protected serial port circuit - Antenna interface circuit (SMA female connector) - SIM card holder (flip-type) - 4 x 3.5mm mounting holes (4 pieces) - SIM900A serial output interface Color: Black Material: Metal + PC Package Includes: 1 x SIM900A Wireless Module 1 x Cable 1 x Antenna Note: The package includes only the items listed above. Other accessories are not included. Note: Lighting and display differences may cause slight color variations between the image and the actual item. Measurement tolerance is +/- 1-3 cm.