Wired comms
Ethernet, RS-232, RS-485/Modbus, CAN, and PoE all ride wires but solve different problems at different distances. Pick the bus and distance first, then the converter or shield.
W5100/W5500 Ethernet shields, LAN8720 RMII PHY boards, MAX3243 RS-232 level shifters, isolated USB-to-RS485 converters, CAN FD bridges, and passive or active PoE injectors and splitters.
- W5100/W5100S/W5500 Ethernet shields put a hardwired TCP/IP stack on SPI for Arduino-class boards; the LAN8720 ETH board is a bare RMII PHY that needs a MAC-capable host such as an ESP32.
- RS-232 is point-to-point: Adafruit's MAX3243 full-pinout breakouts and two-channel RS232 Pal level-shift UARTs. RS-485 is multi-drop: FT4232HL/CH344L isolated USB converters, RS485 hubs, and repeaters — plus industrial DC-monitoring and PWM I/O modules that speak Modbus RTU over the bus.
- PoE gear runs from passive cable sets to a 30 W Mode-B midspan injector, 5 V 2.4 A and 12 V splitters, and a gigabit Type-C splitter — power and data over one Cat5e/Cat6 run.
- Waveshare's CAN FD converters bridge CAN 2.0A/2.0B and CAN FD to Ethernet, RS232, or RS485; an isolated Raspberry Pi expansion board adds 2x RS485, RS232, CAN, and CAN FD in one board.
