DIN Relay Module

Overview

The DIN Relay Module is the primary output device in the Domoriks ecosystem. It provides 8 individually controllable relay channels on a compact DIN-rail PCB that fits neatly inside a standard electrical cabinet.

Each channel is controlled via Modbus RTU commands over the RS-485 bus. The module acts as a Modbus RTU slave and holds its relay states independently of the bus master — if Home Assistant restarts, your lights stay as they were.

ℹ Pcb images

Placeholder — add your own KiCad 3D render or physical PCB photo here.

Specifications

Parameter	Value
Form factor	4 DIN units (72mm wide)
Supply voltage	24V DC
Relay channels	8 × SPDT
Max relay load	10A @ 250V AC
Communication	RS-485, Modbus RTU
Baud rate	9600 / 19200 / 38400 (configurable)
Modbus address	1–247 (DIP switch)
MCU	STM32G0 series
Protection	Reverse polarity, TVS on RS-485

Hardware design files

All design files are open source under MIT:

Schematic — hardware/din-relay-module/schematic.pdf
PCB layout — KiCad .kicad_pcb + Gerber export
BOM — hardware/din-relay-module/bom.csv
3D model — STEP file for cabinet planning

din-relay-module/
├── din-relay-module.kicad_pro
├── din-relay-module.kicad_sch
├── din-relay-module.kicad_pcb
├── bom.csv
├── gerbers/
│   ├── din-relay-module-F_Cu.gbr
│   ├── din-relay-module-B_Cu.gbr
│   └── ...
└── docs/
    ├── schematic.pdf
    └── assembly.pdf

Modbus register map

Register	Type	Description
0x0001	Coil	Relay 1 (0 = off, 1 = on)
0x0002	Coil	Relay 2
…	…	…
0x0008	Coil	Relay 8
0x0100	Holding	Module firmware version
0x0101	Holding	Modbus address (read)

Wiring

Power and RS-485 bus enter via a 4-pin screw terminal:

Terminal 1: +24V DC
Terminal 2: GND
Terminal 3: RS-485 A (non-inverting)
Terminal 4: RS-485 B (inverting)

Each relay output has its own 3-pin screw terminal (COM / NO / NC).

⚠ Mains wiring

Relay outputs switch mains voltages. All mains wiring must be performed by a qualified electrician in accordance with local regulations.

Firmware

The relay module firmware is written in C and targets the STM32G0. See the Firmware docs for build and flash instructions.

Fabrication

You can order PCBs from any standard PCB fab using the Gerber files in the repository. See PCB Fabrication for recommended fabs and tips on component sourcing.