Compact Switch Module

Hardware reference for the Domoriks 8-input DIN-rail switch and button interface board.

Overview

The Compact Switch Module reads 8 dry-contact switch or push-button inputs and reports their state over the RS-485 Modbus RTU bus. It is designed to integrate your existing wall switches and momentary push buttons into the Domoriks system without any changes to the switch wiring.

ℹ Module images

Add your KiCad 3D render or module photo here.

Specifications

Parameter Value
DIN rail width 2 units (36 mm)
PCB dimensions 36 × 90 mm
Supply voltage 24V DC
Supply current ~50 mA
Input channels 8×
Input type Potential-free dry contact (NO or NC)
Input voltage 0V (closed) / floating (open) — internally pulled up
Optical isolation Yes — inputs are galvanically isolated from MCU
Debounce 20 ms default (configurable in firmware)
MCU STM32G030F6P6
RS-485 transceiver SN65HVD3082E
Communication RS-485, Modbus RTU
Default baud rate 9600 8N1
Modbus address range 1–247
Address selection 8-position DIP switch
Connectors 4-pin screw terminal (power + bus); 2-pin per input
Operating temperature −10 to +55 °C

Terminal layout

Power and bus (J1)

Pin 1  +24V DC
Pin 2  GND
Pin 3  RS-485 A
Pin 4  RS-485 B

Switch inputs (J2–J9, one per channel)

Pin 1  IN  — connect one side of switch/button
Pin 2  GND — connect other side of switch/button

Inputs are active-low. A closed contact (Pin 1 connected to GND) reads as 1 (closed/pressed) in Modbus.

💡 Nc switches

If your switch is normally closed (NC), it will read as 1 at rest and 0 when pressed. You can invert the logic in HA automations or set the debounce register for NC operation in firmware.

Wiring wall switches

Standard single-pole toggle switches are wired with two wires:

Switch terminal 1 → Module IN  (e.g. terminal 5 for input 1)
Switch terminal 2 → Module GND (e.g. terminal 2)

The existing 230V circuit on the switch is not disconnected. The switch continues to function as a local control for the load, while also sending its state to the RS-485 bus.

⚠ Low-voltage only

The switch module input terminals carry 3.3V signal levels. Never connect mains voltage to an input terminal. The switch input wires must be a separate low-voltage run from the switch, NOT shared with the mains switch loop.

Modbus register map

Discrete inputs (FC02 read)

Register Description
0x0001 Input 1 state (0 = open, 1 = closed)
0x0002 Input 2 state
… …
0x0008 Input 8 state

Holding registers (FC03 read, FC06 write)

Register R/W Description
0x0100 R Firmware version
0x0101 R Modbus address
0x0102 R/W Baud rate
0x0110 R/W Input 1 debounce (ms, default 20)
0x0111 R/W Input 2 debounce (ms)
… … …
0x0117 R/W Input 8 debounce (ms)

Input event types in Home Assistant

The HA integration exposes each switch input as a binary sensor entity. Input events arrive via the polling loop.

For push buttons (momentary contacts), use an HA automation triggered on state change:

trigger:
  - platform: state
    entity_id: binary_sensor.doorbell_button
    to: "on"
action:
  - service: notify.mobile_app
    data:
      message: "Someone at the door"

DIP switch addressing

Same scheme as the relay module. See the DIN Relay Module docs for the full address table. Ensure switch and relay modules have different addresses on the same bus.

Design files

Available in the GitHub repository:

  • KiCad project files
  • Gerber files
  • BOM with LCSC part numbers
  • Schematic PDF
← DIN Relay Module Wiring Guide →