Relays
A GPIO-driven Gravity relay and a 16-channel Modbus TCP PoE module both switch loads. The real difference is the control path — GPIO pin, USB port, RS485 bus, Ethernet packet or a 433MHz key fob.
Gravity and Grove single-relay modules, Pi relay HATs, USB-RLY16 boards, Sonoff Wi-Fi smart switches, and Waveshare Modbus RTU/TCP industrial modules — matched by control interface and contact rating.
- GPIO tier: Gravity Digital 5A/10A/16A relay modules, the Grove 2-Channel SPDT and Adafruit's STEMMA non-latching mini relay switch from a single pin — check contact ratings before touching mains.
- Wi-Fi tier: Sonoff BasicR2, Mini and Dual smart switches add app or home-automation control with no microcontroller wiring required; they ship pre-flashed and accept custom firmware via the header.
- Industrial tier: Waveshare's Modbus RTU 8/16-ch RS485 modules and Modbus TCP PoE Ethernet relays add isolation circuits, rail-mount cases and 30A contacts; DFRobot's 8-channel PoE Ethernet controller plays the same role.
- Some need no microcontroller at all: USB-RLY16 boards switch 8 channels of up to 16A from a PC, Seeed's 315/433MHz codec-adaptive wireless relays pair directly with a key fob, and Waveshare's latching Modbus RTU module holds state through power loss.
