DIN-Rail Relay Module for Home Assistant — DIO-430-R1, Modbus RTU, 3 Relays + 4 Inputs

Tech Specs

Installation, Environmental & Mechanical

Home Assistant / Modbus / Web Config Integration

The DIO-430-R1 supports flexible integration with:

• HomeMaster MicroPLC and MiniPLC controllers
• PLC and SCADA systems via Modbus RTU
• Home Assistant using ESPHome or Modbus integration
• Direct USB-C configuration using browser-based WebConfig tool

Configuration parameters are stored persistently in onboard flash and automatically restored at power-up.

Quick Setup Process (USB-C WebConfig)

1. Mount & Power – Mount the module on a DIN rail and connect power.
2. Connect USB-C – Connect USB-C cable to the module.
3. Open WebConfig – Open WebConfig page in any Chromium-based browser (Chrome, Edge, Opera, Brave, Vivaldi).
4. Connect Device – Click Connect and select the device.
5. Configure – Configure Modbus address and baud rate.
6. Map I/O – Configure input-to-relay mapping and LED behavior.
7. Save & Disconnect – Save settings and disconnect USB-C.

Firefox: experimental only (Nightly with the Web Serial flag); Safari and stable Firefox not supported.

Features:

• Driverless browser-based configuration
• Live configuration updates
• Persistent flash storage
• No external software required

WebConfig Configuration Options

• Modbus address (1–247) and baud rate (9600–115200)
• Relay: enable / invert / power-on / auto-off
• Interlock: relay pair with dead-time pause
• Timing: long-press, multi-click gap, debounce, link timeout
• Buttons: short/long-press actions and targets
• LEDs: steady/blink and source mapping
• Persistent save to flash and restore on boot

WebConfig provides I/O mapping and configuration settings (stored persistently in flash).

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200
  parity: NONE
  stop_bits: 1

modbus:
  id: modbus_bus
  uart_id: uart_modbus
  turnaround_time: 100ms
  send_wait_time: 250ms

packages:
  dio1:
    url: https://github.com/isystemsautomation/homemaster-dev
    ref: main
    files:
      - path: DIO-430-R1/Firmware/v0.2.0/default_dio_430_r1_plc/default_dio_430_r1_plc.yaml
        vars:
          dio_prefix: "DIO#1" # shown in Home Assistant entity names
          dio_id: dio_1 # internal unique id
          dio_address: 4 # Modbus address set in WebConfig for this DIO
    refresh: 1d

The module needs a Modbus master on the bus. In a HomeMaster system that is the MiniPLC or the MicroPLC — both run ESPHome and connect to Home Assistant over the native API. To work out how many modules a panel needs and how wide it comes out, use the System Builder.

Circulation pumps, zone valves and boiler interlocks wire to the relay contacts and digital inputs you would use for any other load — the module does not prescribe a particular actuator or thermostat model.

New to this kind of system? Two guides cover the ground: building a Home Assistant automation system and a wired ESPHome smart home.

Going deeper on this module: relay channels and loads in a DIN panel, wired roller shutters and where the interlock belongs and what still works when Home Assistant is down. Related modules: STR-3221-R1, AIO-422-R1 and the OpenTherm Gateway.

Power Supply

The DIO-430-R1 is powered from a regulated 24 V DC supply.

Power Input Specifications

Power input includes:

• Reverse polarity protection
• Surge protection
• TVS suppression
• EMI filtering
• Internal fuse protection

Protection circuits including TVS and fuse components are shown in the schematic.

24 V DC Input (V+ / 0V)

Connect + to V+ and − to 0V.

Installation checklist

• Use a regulated 24 V DC supply
• Install 0.5 A fuse/breaker upstream of V+
• Observe polarity: V+ / 0V
• Route power wiring away from low-level signal wiring

Inputs & Outputs

Digital Inputs (4 channels)

Connect potential-free (dry) contacts — wall switches, push buttons, or relay / open-collector / transistor outputs that simply close INx to GNDx. The module supplies the wetting current from its own 24 V rail; do not feed external voltage into the input. Three-wire sensors must be powered from your own supply, with their switching output wired to the input (the module provides no sensor-supply rail).

Features:

• IEC 61131-2 digital-input front-end using ISO1212 receivers; PTC fuse, TVS surge and reverse-polarity protection per channel
• Dry contact inputs only (voltage-free contact closure). Do not apply external voltage.
• TVS and fuse protection per channel
• Noise-protected inputs

Confirmed in field board schematic.

Wiring example: dry contact wiring to DI inputs.

Do not apply external voltage to INx/GNDx; use voltage-free contacts only.

Relay Outputs

The DIO-430-R1 provides 3 SPDT mechanical relays (HF115F-005-1ZS3) for switching AC or DC loads. Each relay provides SPDT switching contacts (NO / NC / COM) available on the relay output terminals and is driven via optocoupler-isolated control circuitry.

Rating: 3 A MAX continuous per output (board/system limit) is the only usable output rating. Loads above 3 A must use an external contactor or power relay. The relay component may be rated higher, but this does not change the 3 A system limit.

⚠️ External protection required: Every relay output MUST be protected by an external fuse or circuit breaker (≤ 3 A per channel). Relay output circuits are not internally fused. External overcurrent protection is mandatory for safe operation.

Relay Specifications

Relay Specifications

Channel	Contacts	Type	Rating	Description
Relay 1	NO / NC / COM	SPDT	3 A MAX per output (system rating) Relay contact rating higher (component only)	General purpose relay output 1 (NO/NC/COM)
Relay 2	NO / NC / COM	SPDT	3 A MAX per output (system rating) Relay contact rating higher (component only)	General purpose relay output 2 (NO/NC/COM)
Relay 3	NO / NC / COM	SPDT	3 A MAX per output (system rating) Relay contact rating higher (component only)	General purpose relay output 3 (NO/NC/COM)

Relay Wiring Examples

Example wiring using Normally Open (NO) and Normally Closed (NC) relay contacts.

• Each relay has COM / NO / NC terminals
• Use NO for default OFF loads
• Use NC for default ON loads
• ⚡ Loads may carry hazardous voltage
• Supports AC and DC switching (DC and inductive loads require derating)

⚠️ Common protection warning: If a single common fuse or circuit breaker is used to protect multiple relay outputs, the protective device shall NOT be sized by summing relay outputs. The rating of the common protective device shall not exceed 3 A MAX per output (board/system limit).

For inductive or DC loads (contactors, solenoids, motors), use appropriate suppression (RC snubbers, MOVs, or flyback diodes). Loads exceeding the recommended PCB current limit shall be switched using external contactors or wiring methods that bypass PCB copper paths.

User Interface

Communication & Protocols

• Modbus RTU (RS-485) – UART-based communication for expansion modules and field devices

RS-485 / Modbus RTU

Terminal order differs across the HomeMaster range. Always read the silkscreen - do not wire by habit from another module. On this module the order is B-A-COM. Swapping A and B damages nothing but the node will not communicate. COM is required on every node.

All HomeMaster controllers and modules share the same RS-485 front end.

RS-485 Front End

Item	Value
Transceiver	MAX485CSA+T, half-duplex
Galvanic isolation	None — the transceiver shares the device's logic ground
Common-mode range	−7 V … +12 V referred to the device's own ground (MAX485 limit)
Terminals	A / B / COM
Surge protection	3 × SMAJ6.8CA TVS (A–COM, B–COM, A–B)
Overcurrent	2 × resettable PTC, 1.5 A hold, in series with A and B
EMI filtering	Common-mode choke on the A/B pair; COM referenced through 1 MΩ ∥ 4.7 nF
Idle state	Fail-safe biasing on board — do not add external bias resistors
Termination	120 Ω at the two physical ends of the bus only

Bus wiring rules — apply to every device on the bus:

• One twisted pair for A/B, 120 Ω characteristic impedance.
• Run COM to every node. Required, not optional: the ports are not isolated, and COM is what bounds the common-mode voltage the transceivers see.
• Prefer one power supply for the whole bus, distributed in star topology. With separate supplies, additionally tie the 0 V references together at a single point.
• Bond the cable shield to cabinet PE at one end only. Never land a shield on A, B or COM.
• Where the bus crosses into a different electrical installation with its own earthing reference — a utility or billing meter, another building, another cabinet's PE system — fit an external galvanic RS-485 isolator at that boundary. The on-board components are transient protection, not isolation, and will not survive a sustained ground-potential difference.

Connect A, B, and COM to the bus.

Connectors & terminal map

Top row (24Vdc | RELAY OUTPUT)

Bottom row (RS-485 | DI 24Vdc)

Ports & service interfaces

Housing notes

• GND precedes the signal on every DI pair. DIM prints the opposite order - do not wire by habit.
• Power reads 0V then V+. Most other modules read V+ first.
• Relays are SPDT. System limit 3 A @ 250 VAC regardless of the relay component rating.

System Architecture & Pinout

System block diagram showing internal architecture and interfaces.

Complete GPIO and connector pin assignments.

Safety and Installation Notes

• Use only SELV 24 V DC power supply
• Install inside control cabinet
• Protect wiring terminals from accidental contact
• Follow 3 A MAX per output system rating; use an external contactor/power relay for loads above 3 A.
• Use snubbers for inductive loads
• Install proper upstream fuse protection

Compliance & Certifications

The DIO-430-R1 module is CE marked. ISYSTEMS AUTOMATION S.R.L. (HomeMaster® brand) maintains the technical documentation and a signed EU Declaration of Conformity (DoC) available for download in the Documents and Resources section above.

• EMC Directive 2014/30/EU — EN 55032:2015 (Class B emissions), EN 55035:2017 (immunity), tested by Idvorsky Laboratories Ltd. (Job #1648)
• Low Voltage Directive 2014/35/EU — EN 62368-1:2020 + A11:2020, in-house dielectric and isolation testing by ISYSTEMS AUTOMATION compliance laboratory
• RoHS Directive 2011/65/EU — EN IEC 63000 technical documentation
• HomeMaster® — registered EU trademark (EUTM No. 019082911, EUIPO, registered 15 January 2025)

Frequently asked questions

How does it connect to Home Assistant?

Through a Modbus master on the RS-485 bus. In a HomeMaster system that is the MiniPLC or the MicroPLC running ESPHome; the relays and inputs then appear in Home Assistant over the native ESPHome API. No MQTT broker, no Modbus register mapping written by hand — a ready-made ESPHome package is published for the module.

I need 16 relays. Can this do that?

Not in one module — this one has three. Channel count is built up on the bus instead: several DIO-430-R1 modules share the same RS-485 pair, each with its own Modbus address. Where the requirement is many inputs rather than many outputs, the ALM-173-R1 carries 17 opto-isolated inputs. The System Builder works out how many modules a given number of circuits comes to, and what that costs in DIN width and bus load.

Will the relays keep working if Home Assistant goes down?

The input-to-relay mapping you configure lives in the module's flash and is executed by the module, so a local button keeps switching its relay with the server offline. Two things to know: the relays hold their last state while the controller is unreachable, and after a power cycle of the module itself all relays come up open.

What can the digital inputs be connected to?

Dry contacts — wall buttons, door and window contacts, float switches, auxiliary contacts of a contactor. The inputs are module-wetted 24 V and IEC 61131-2 compliant, with an ISO1212 front end. Press logic is configured in WebConfig, so one button can carry several functions by press pattern.

Do I have to use HomeMaster controllers?

No. The module is a standard Modbus RTU slave. Any Modbus master reaches it — a third-party PLC, a SCADA system, or your own ESP32 with an RS-485 transceiver. That is the point of using a standard bus rather than a proprietary one: the module is not locked to the controller it was bought with.

How is it configured?

Over USB-C from a browser using WebConfig — Web Serial, no driver and no vendor application. Modbus address (1–247, default 3) and baud rate (9600–115200, default 19200), input mapping, press logic, LED sources and the output interlock are set there and stored in on-device flash (LittleFS).

Is the RS-485 port isolated?

No. It has transient protection — TVS diodes, resettable PTC fuses, a common-mode choke and fail-safe biasing — but that is surge protection, not galvanic isolation. Run COM to every node on the bus. Where the bus crosses into a separate electrical installation with its own earthing reference, fit an external galvanic RS-485 isolator at that boundary.

Is it open source?

The hardware is published under CERN-OHL-W v2, the firmware and ESPHome packages under MIT. Schematics, board data and the EU Declaration of Conformity are in the Documentation section above.