Relay Board
4-channel relay board with mains-rated contacts (10 A / 250 VAC) and onboard AC/DC power supply. Connect to the Sensor Board via USB-C cable, or control any channel via a direct GPIO pin. Switch pumps, lights, heaters, and fans from any Automato sensor node.
Mains switching for your grow
The Relay Board gives any Automato sensor node the ability to switch mains-voltage loads — pumps, lights, heaters, fans, solenoids. Four independent SPDT channels, each rated 10 A / 250 VAC.
The onboard Hi-Link PSU powers the board directly from mains — no separate supply needed. Optoisolated control keeps your microcontroller safely isolated from line voltage.
Two ways to control it
- USB-C — connect directly to the Sensor Board via USB-C cable for plug-and-play control (planned addition — not in current schematic)
- GPIO pin — wire any Automato node directly via the 3-pin screw terminal (SPI to 74HC595)
Safety note: This board connects to mains voltage. Follow all local electrical codes. If in doubt, consult a licensed electrician.
Safety defaults: All relays default to OFF at boot, on power loss, and on connectivity loss. This is by design and cannot be changed.
Pairing with the Brain Board? Connect via Qwiic to the SparkFun Qwiic GPIO (TCA9534, I2C 0x20) for relay control without consuming GPIO pins on the microcontroller.
| Relay channels | 4× Omron G5LE-14 DC3 — SPDT, rated 10 A / 250 VAC |
| Relay driver | Toshiba 74HC595D shift register — SPI-controlled, daisy-chainable |
| MOSFET drivers | Diodes Inc. DMG3418L (N-ch) — one per relay coil |
| Freewheeling diodes | SMC 1N4007 (per relay), BAS16LT1G (signal path) |
| AC/DC power supply | Hi-Link HLK-PM03 — 100–240 VAC input, 3.3 V / 3 W output |
| Mains protection | Littelfuse TMOV14RP140E metal-oxide varistor (MOV) |
| Mains connectors | TE Connectivity 3-213598-4 (live, neutral, earth) and 5-pin screw terminal |
| Low-voltage connector | Phoenix Contact 1935789 (3-pin, for GPIO control signal + 5V + GND) |
| Host control — Option 1 | USB-C connector from Sensor Board (not in current schematic — planned addition) |
| Host control — Option 2 | Direct GPIO pin from any Automato sensor node via 3-pin screw terminal |
| Status LEDs | 4× Würth green LED — one per relay channel |
| Decoupling | Kemet 47 nF (×4 relay), 220 µF bulk, 100 nF and 10 µF supply caps |
| License | MIT (hardware) |
| Pin / Label | GPIO | Function |
|---|---|---|
| Relay OUT 1–4 | — | SPDT switched contacts — NO, COM, NC per channel |
| AC LINE IN | — | Live, neutral, earth mains input |
| USB-C (host) | — | Control connection from Sensor Board via USB-C cable (planned — not in current schematic) |
| GPIO CTRL | SPI (74HC595) | Direct GPIO control from sensor node — SER, SRCLK, RCLK via 3-pin screw terminal |
| VCC | — | 5 V logic supply from host or USB hub |
| GND | — | Common ground (low-voltage side, isolated from mains) |
Relay wiring & safety guide
Mains wiring, best practices, safety checklist
First relay automation
Quick start — control a pump from sensor data
Hardware files on GitHub
KiCad schematics, BOM, PCB layout
Relay control API
HTTP endpoints and automation rules
Pair with the Brain Board
Qwiic GPIO expansion for relay control
Pair with the Sensor Board
LoRa + relay for distributed setups