Standard Raspberry Pi 40PIN GPIO header, supports Raspberry Pi 3B+/4B PoE (Power Over Ethernet) capability，802.3af-compliant; Fully isolated switched-mode power supply (SMPS) Integrates PCF8574 IO expander for I2C bus, providing pin P0 for directly fan control, and more spare IO pins 0.91" OLED, for monitoring processor temperature, IP address, and fan status in real-time; Onboard cooling fan, allows auto running on powerup OR programmable control, configured by switch Resources download: www.waveshare.com/wiki/PoE_HAT_(B)