HomeMaster DIM-420-R1 — Modbus AC Dimmer, 2-Channel MOSFET

Tech Specs

Note: For absolute maximum ratings, detailed dimming load characteristics, and safety margins, always refer to the official DIM‑420‑R1 datasheet. Datasheet values are the authoritative reference.

Installation, Environmental & Mechanical

Home Assistant / Modbus / Web Config Integration

The DIM‑420‑R1 is a Modbus RTU slave on RS‑485 and can be controlled by:

• HomeMaster MicroPLC and MiniPLC controllers
• SCADA/PLC systems with Modbus RTU support
• Home Assistant using ESPHome Modbus integration package
• Any third‑party Modbus RTU master controller

Local behaviour (press logic, cut mode, thresholds, LED mapping) is configured using a browser‑based WebConfig tool over USB‑C (Web Serial). All parameters are stored in onboard flash and restored at power‑up.

Quick Setup Process (USB‑C WebConfig)

1. Mount & Power – Mount the module on a DIN rail and connect 24 V DC logic power.
2. Connect USB‑C – Connect a USB‑C cable from the module to a PC.
3. Open WebConfig – Open configtool-dim-420-r1 in a Chromium‑based browser.
4. Connect Device – Click Connect and grant serial permissions.
5. Configure – Set Modbus address and baud, choose cut mode (Leading/Trailing) and load type per channel, adjust lower/upper thresholds, and map DI/Button/LED behaviour.
6. Save & Disconnect – Confirm that configuration is saved to flash, then disconnect USB‑C.

What WebConfig is and how it works: WebConfig is a browser-based configuration UI that runs entirely in your Chromium browser using the Web Serial API. Once connected, it continuously exchanges JSON messages with the DIM‑420‑R1 to read the current configuration (Modbus address, baud rate, cut mode, thresholds, DI/LED/button mapping) and apply any changes you make in the forms. Channel tiles show live AC presence and frequency badges, sliders let you test dimming levels in real time, and per‑input / per‑button tables control how wall switches and front buttons drive CH1/CH2. All edits are applied immediately and written to the module’s flash a short time after the last change, so your settings persist across power cycles.

Features:

• Driverless, browser‑based setup using Web Serial
• Live preview of mains frequency and channel status
• Per‑channel cut mode, preset, and threshold tuning
• Configurable DI press logic and LED sources
• Persistent flash storage and JSON diagnostics stream

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

packages:
  dim1:
    url: https://github.com/isystemsautomation/homemaster-dev
    ref: main
    files:
      - path: DIM-420-R1/Firmware/v0.1.0/default_dim_420_r1_plc/default_dim_420_r1_plc.yaml
        vars:
          dim_prefix: "DIM#1"
          dim_id: dim_1
          dim_address: 5  # Modbus address set in WebConfig for this DIM
    refresh: 1d

Cabling and Wirings

24 V DC Logic Power

Connect regulated 24 V DC SELV to the POWER terminals V+ and 0V. This powers the MCU, LEDs, RS‑485 interface, and USB‑C logic.

Connect + to V+ and − to 0V. Use a SELV 24 V DC supply with upstream protection.

Logic Power Checklist

• Use a regulated 24 V DC SELV power supply
• Install an external fuse or breaker (typ. 0.5 A) upstream of V+
• Observe polarity V+ / 0V
• Route 24 V DC wiring separately from mains AC dimmer outputs

Digital Inputs (DI1–DI4)

Wire dry‑contact wall switches or isolated low‑voltage contacts to DI1–DI4 with their corresponding DIx_GND returns. Input mode (Momentary/Latching), debounce, invert, and press actions are configured in WebConfig.

Each input has its own DIx / DIx_GND pair. Use dry contacts only; do not apply mains to DI terminals.

• Keep DI wiring separate from AC dimmer wiring and other high‑current conductors.
• Use twisted pairs per DI channel where possible.
• Configure press logic (Short / Long / Double / Short‑then‑Long) and mapping in WebConfig.
• Inputs share 24 V‑derived isolated rails through ISO1212 devices; see field board schematic for details.

RS‑485 (Modbus RTU) Wiring

The bottom‑left terminals labelled A / B / COM connect the DIM‑420‑R1 to the RS‑485 Modbus trunk.

Connect A, B, and (optionally) COM to the RS‑485 bus. Terminate at the two physical ends only.

• Use shielded twisted pair for A/B; use the second pair for COM or spare.
• Terminate the bus with ≈120 Ω resistors at the two physical ends only.
• Keep stubs short and avoid star wiring.
• Use a common 0 V reference (COM) between controller and modules unless galvanic isolation requires otherwise.

AC Load Wiring (Dimming Channels)

The dimming channels use mains domain terminals Lx_IN / Lx_OUT / Nx_IN / Nx_OUT (for CH1 and CH2). These carry hazardous voltage. Follow the wiring diagrams and load ratings in the official datasheet and field board schematic.

Typical CH1/CH2 connection using Lx_IN / Lx_OUT / Nx_IN / Nx_OUT terminals. Always follow the official datasheet wiring diagrams.

⚠️ Hazardous voltage: Lx/Nx terminals are on the mains side. Installation and wiring must be performed by qualified personnel only, with power isolated and in accordance with local electrical codes and the DIM‑420‑R1 datasheet.

Cable Recommendations & Shield Grounding

These recommendations apply to digital inputs, RS‑485, and mixed‑voltage installations where the DIM‑420‑R1 shares a cabinet with mains wiring and other control hardware. Detailed limits and examples are described in the DIM‑420‑R1 README and datasheet.

General Routing Rules

• Route low‑voltage signal wiring (24 V, DI, RS‑485, USB) separately from mains‑side dimmer wiring and other high‑current cables.
• Avoid long parallel runs between SELV wiring and mains bundles; cross at 90 ° where necessary.
• Use cable ducts and strain reliefs to prevent mechanical stress on terminals.
• Keep all conductors within their rated temperature and current limits as per the datasheet.

Digital Inputs (DI) Cable

• Use a twisted pair per DI channel (DIx + DIx_GND) for improved noise immunity.
• Recommended wire size: 0.2–0.75 mm² (AWG 24–18), compatible with 5.08 mm terminals.
• In noisy environments or long runs, use shielded twisted pair and follow shield grounding rules below.
• Keep DI runs physically separated from mains dimmer wiring and relay contact wiring.

RS‑485 (Modbus) Cable

• Use a twisted pair for A/B with characteristic impedance ≈120 Ω.
• Prefer shielded twisted pair in industrial or high‑EMI environments.
• Use a daisy‑chain bus (no star topology, minimal stubs).
• Route COM/0 V reference with the bus, using the second pair where available.

Shield Grounding

• Bond cable shields to the cabinet PE/EMC ground at the controller/module end using 360 ° EMC clamps where possible.
• By default, terminate shields at one end only to avoid ground loops; only bond at both ends if both cabinets share a reliable equipotential earth.
• Do not connect shields directly to signal terminals (DI, A/B/COM, V+/0V).
• Keep shield tails short and use dedicated grounding bars or clamps.

System Architecture & Pinout

System block diagram: RP2350A MCU, dimmer power stages, isolated rails, DI front‑end, RS‑485, and USB‑C.

MCU and connector pin assignments for DIM‑420‑R1; see README and schematics for detailed mapping.

Safety and Installation Notes

• The DIM‑420‑R1 is a mixed‑voltage device: it contains SELV 24 V control electronics and hazardous mains AC on dimmer channels.
• Installation, wiring, and maintenance must be performed by qualified personnel familiar with panel building and mains safety.
• Always isolate both 24 V DC and mains AC supplies before working on the device or its wiring.
• Mount inside a dry, clean, ventilated enclosure; protect all terminals against accidental contact.
• Respect isolation barriers between logic GND and mains‑side isolated rails; never bridge logic GND with GND_ISO rails.
• Follow the load type and cut‑mode recommendations in the datasheet to avoid flicker or damage to lamps/drivers.
• Provide appropriate upstream over‑current and residual current protection in accordance with local electrical codes.

Compliance & Certifications

The DIM-420-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)