DIM-420-R1 Dual-Channel AC Dimmer Module (MOSFET-Based)

🚧 Project Status: Under Active Development & Testing

Important Notice: This documentation, hardware designs, and firmware are for the pre-release version of the HomeMaster system. All information is preliminary and may contain errors or be subject to change.

• Hardware: Modules are currently in the prototyping and testing phase. Final production versions may differ.
• Firmware: Firmware is under active development and is considered beta. Features, configurations, and stability are being refined.

Please use this information for evaluation and development purposes only.

1. Introduction

1.1 Overview of the DIM-420-R1 Module ✨

The DIM‑420‑R1 is a modular dimmer I/O device for dual‑channel phase‑cut AC dimming in the HomeMaster MicroPLC / MiniPLC ecosystem. It exposes 2 dimming channels, 4 isolated digital inputs, 4 configurable user buttons, 4 user LEDs, and an RS‑485 Modbus RTU interface. Setup and diagnostics are performed in‑browser via WebConfig over USB‑C (Web Serial)—no special software required.

It integrates seamlessly with MiniPLC / MicroPLC controllers, third‑party Modbus masters, ESPHome / Home Assistant, and SCADA/PLC systems. Typical use: connect wall switches to the DIs, pick Leading/Trailing edge per load, set Lower/Upper thresholds, and control scenes from a PLC or locally with press‑logic.

Quick use case:
Wire DI1–DI4 to wall switches → select Momentary or Latching with Short/Long/Double logic → choose Cut Mode and Load Type per channel → map LEDs/Buttons → connect RS‑485 A/B → control and monitor via PLC / ESPHome.

1.2 Features & Architecture

Core Capabilities

1.3 System Role & Communication 🔌

The DIM‑420‑R1 is a standalone Modbus RTU slave on an RS‑485 multi‑drop trunk. It executes local input press‑logic and dimming behavior, mirrors state to discrete inputs/holding registers, and accepts control via coils/holding writes from a master (PLC/SCADA/ESPHome). A live JSON snapshot and event log stream over Web Serial for commissioning and diagnostics.

⚠️ Note: If multiple DIM‑420‑R1 modules share the same RS‑485 line, assign unique Modbus IDs in WebConfig and verify termination/bias.

2. Use Cases

Scene Control with Wall Switches

Control dimmed lighting scenes using standard wall switches wired to the digital inputs.

• Short press toggles CH1 to preset.
• Long press ramps CH1 up or down.
• Double press sets CH2 to max.

Setup Instructions:

• Wire DI1–DI4 to wall pushbuttons.
• In WebConfig → set DI1: Momentary.
• Map actions:
  • Short → Toggle CH1
  • Long → Increase CH1
  • DoubleShort → Go Max CH2
• Set CH1 preset = 180 and CH2 upper threshold = 255.
• Save configuration and test with physical input.

3. Safety Information

These guidelines apply to the DIM‑420‑R1 dimmer module. Ignoring them may result in equipment damage, electric shock, or fire.

⚠️ Mixed‑voltage device — The module contains both SELV/PELV control electronics and hazardous AC mains on the dimmer channels (Lx_IN/Lx_OUT, Nx_IN/Nx_OUT). The logic side is galvanically isolated (opto + isolated 5 V rails), but mains is present on the power section and output terminals. Handle as a mains device.

3.1 General Requirements

3.2 Installation Practices

3.3 I/O & Interface Warnings

Power

Inputs (SELV)

Dimming Channels (MAINS)

Communication & USB (SELV)

✅ Pre‑Power Checklist

• All AC and SELV cables are routed separately with strain relief.
• No bridges between logic GND and GND_ISO1/2; isolation gaps unobstructed.
• RS‑485 polarity/termination verified; DI wiring and logic mode match configuration.
• Cut Mode and Lower/Upper thresholds set per lamp/driver datasheet; start with light loads.
• Upstream MCB/RCD sized for the load; enclosure closed before applying mains.

4. Installation & Quick Start

The DIM‑420‑R1 is a smart dual-channel dimmer with Modbus RTU and onboard USB‑C WebConfig. Setup has two main stages:

1. Wiring & power (24 V + RS‑485 + AC load)
2. Digital configuration (WebConfig → Modbus ID, Cut Mode, etc.)

4.1 What You Need

💡 Quick path mount: wire 24 VDC, RS‑485 (A/B/COM), and DI → connect USB‑C → open WebConfig → set Modbus & cut mode → tune thresholds → map DIs/LEDs → save → disconnect USB → go live.

4.2 Power

The DIM‑420‑R1 uses 24 VDC SELV for logic, UI, RS‑485, and Web Serial.
AC power is handled separately by the dimming channels (see §4.4).

🔌 Supply Details

⚡ Current

• ~50 mA idle (logic + UI only)
• Add budget if using all 4 LEDs, buttons, and rapid RS‑485 comms.
• AC loads pull from separate mains lines — never through the 24 V rail.

4.3 Networking & Communication

DIM‑420‑R1 supports RS‑485 Modbus RTU for runtime control and USB‑C WebConfig for setup.

4.3.1 RS‑485 (Modbus RTU)

🧷 Terminals

A B COM

Located bottom-left on module:

Use shielded twisted pair, terminate at both ends (~120 Ω), and bias if required.

🔁 Protocol

4.3.2 USB‑C (WebConfig)

For setup/diagnostics via Chromium:

🖥 Steps

1. Connect USB‑C to PC
2. Open ConfigToolPage.html (local or hosted)
3. Click Connect (Web Serial)
4. Set:
   • Modbus Address & Baud
   • Channel Cut Mode (Leading/Trailing)
   • Lower/Upper thresholds
   • Input mode: Momentary/Latching
   • Map LEDs / Buttons
5. Click Save
6. Disconnect USB → RS‑485 master takes over

🔐 If Connect is disabled, ensure you're using Chromium + USB permission is granted. On macOS/Linux, close any app that may be holding the port (e.g., serial monitor).

Let me know if you'd like the follow-up section 4.4 Wiring Examples or 5 Controller Integration.

4.4 Installation & Wiring

The DIM‑420‑R1 separates low‑voltage logic (24 VDC, RS‑485, USB‑C, DIs) from mains‑side dimmer outputs (L/N IN/OUT). Use the visuals below when wiring.

🔌 24 VDC Logic Power

Connect regulated 24 VDC (SELV) to the top‑left POWER terminals V+ and 0V.
This powers the MCU, LEDs, USB‑C (setup), and RS‑485 interface.

🔘 Digital Inputs (DI1–DI4)

Wire dry‑contact switches to the opto‑isolated inputs.
Each input has its own paired Gnd and must be wired independently.
Input mode (Momentary/Latching), debounce, invert, and press‑logic are set in WebConfig.

Tip: keep DI wiring separate from mains cabling and provide strain relief.

🧷 RS‑485 (Modbus RTU)

Bottom‑left terminals are labeled B A COM (as on the front panel).

• B / A → RS‑485 differential pair (use shielded twisted pair)
• COM → optional reference ground to the controller
• Terminate the bus at both ends (~120 Ω) if not already present
• Defaults: Slave ID 3, 19200 baud, 8N1 (change in WebConfig)

🧰 USB‑C Port (Front)

For setup/diagnostics only:

• In‑browser WebConfig over Web Serial (Chromium‑based browsers)
• Firmware updates via UF2 bootloader

Disconnect USB‑C after commissioning; use RS‑485 for runtime control.

4.5 Software & UI Configuration

You can configure the DIM‑420‑R1 entirely from a Chromium browser using Web Serial. No drivers or apps required.

🔗 Online WebConfig:
https://www.home-master.eu/configtool-dim-420-r1

🖥 Browser & Cable

• Use a Chromium‑based browser (Chrome / Edge / Brave).
• Connect a USB‑C cable to the module.
• Power the module with 24 VDC (USB only provides data).

🔗 Modbus Connection

1. Open the WebConfig tool from the link above.
2. Select the current Modbus Address and Baud Rate.
3. Click Connect and allow Serial access.
4. The Active Modbus Configuration banner shows detected values.

Default: Slave ID = 3, Baud = 19200, 8N1.

A live Serial Log keeps the last 5 messages for quick feedback.

🎚 Dimming Channels (CH1 & CH2)

Each dimmer channel can be configured for its intended load and behavior:

• AC Presence / Frequency badges confirm input signal quality.
• Load Type: Lamp (log), Heater (linear), or Key (non‑dimmable).
• Cutoff Mode: Leading (RL) or Trailing (RC).
• Lower/Upper Thresholds: Clamp range for reliable dimming.
• Preset Level: Value used when toggle/on events occur.
• Percent Slider: Sends live target; UI reflects actual level (0–255).

Changes apply instantly and persist to flash ~1.5s after the last edit.

🟢 Digital Inputs (DI1–DI4)

Configure press logic, target channels, and press actions:

• Input mode: Momentary or Latching
• Mappable press types: Short, Long, Double, Short‑then‑Long
• Actions: Turn on/off, Toggle, Ramp, Go to MAX, Ping‑pong

Each DI has its own mapping per event and an optional invert.

🔘 Buttons & LEDs

Configure onboard pushbuttons and indicator LEDs:

• Buttons: Trigger actions like Toggle CH1, Ramp up/down, MAX preset.
• LEDs: Mode (Steady / Blink) and Source (Channel or None).

Button presses are de‑bounced and detected in firmware. LED states are updated live.

💾 Save & Restore

• Config is stored automatically in flash after changes.
• Settings persist through power loss and reset.

If Connect is greyed out: check USB cable, browser support (Chrome/Edge), and Serial permissions.

5. DIM‑420‑R1 — Technical Specification

5.1 Diagrams & Pinouts

System Block Diagram	MCU Pinout

Field Board Layout	MCU Board Layout

5.2 I/O Summary

5.3 Electrical Specifications

⚠ Installer note: Fuse 24 VDC input externally; protect AC loads per local code.

5.4 Terminal Map

All terminals are 5.08 mm pitch, 300 V / 20 A rated, 26–12 AWG.

5.5 Absolute Electrical Specifications

5.6 Protection Features

• 24 V Input

  • Diode reversed path
  • TVS: SMBJ33A
  • High-side P-MOS + fuse (F1206HI8000V024TM)

• DI Channels

  • ISO1212 opto-isolated front end
  • PTC: 1206L016WR
  • TVS: SMBJ26CA

• Dimmer Stage

  • Power switches: WMM36N65C4, 650 V
  • Isolation: SFH6156‑3T optocouplers
  • Input bridge: MB6S
  • Zero-cross & snubber integrated

• RS‑485

  • Transceiver: MAX485
  • TVS: SMAJ6.8CA
  • Pull-up/down: 4.7 kΩ bias
  • Termination pads included

• USB-C

  • USB-UART: RP2350
  • ESD Clamp: PRTR5V0U2X
  • Data-line resistors: 27 Ω

5.7 Mechanical

5.8 Environmental & Compliance

6. Modbus RTU Communication

The DIM‑420‑R1 communicates via Modbus RTU over RS‑485 as a slave device, polled by a PLC, SCADA, or ESPHome-based controller. It exposes discrete inputs, coils, and holding registers for full control and monitoring of the module.

6.1 Default Communication Settings

6.2 Address Map

The following Modbus function codes are used:

• FC01 / FC05 — Coils (write-triggered actions)
• FC02 — Discrete Inputs (status flags)
• FC03 / FC06 / FC16 — Holding Registers (configuration + real-time control)

6.3 Discrete Inputs (FC02)

6.4 Coils (FC01 / FC05)

Coils are momentary triggers. Write 1 to trigger; auto-resets to 0.

6.5 Holding Registers (FC03 / FC06 / FC16)

Writing Percent×10 immediately recalculates and applies Level based on LoadType, Lower/Upper limits.

6.6 Register Usage Examples

6.7 Polling Recommendations

• Interval: 500–1000 ms recommended for discrete input/holding register polling
• Write timing: Momentary coils are safe to write every 1–2 seconds max
• Avoid flooding: Do not poll coils or write continuously at high speed
• Sync strategy: Read current Level before changing Percent to avoid flicker

6.8 Additional Notes

• All config/state is mirrored over Modbus and Web Serial snapshot
• Modbus address and baud rate are editable via USB-C (WebConfig)
• Disabling a DI via coil makes its press events inert until re-enabled

7. ESPHome Integration Guide

The DIM‑420‑R1 integrates natively with ESPHome and Home Assistant via Modbus RTU using a plug-and-play YAML package.
No local logic is required — all channel control, DI events, LEDs, and feedback are exposed as entities.

7.1 Installation via packages: Block

Add the DIM‑420‑R1 using the official GitHub YAML:

packages:
  dim1:
    url: https://github.com/isystemsautomation/HOMEMASTER
    ref: main
    files:
      - path: DIM-420-R1/Firmware/default_dim_420_r1_plc/default_dim_420_r1_plc.yaml
        vars:
          dim_prefix: "DIM#1"
          dim_id: dim_1
          dim_address: 5
    refresh: 1d

Replace dim_address with the actual Modbus ID of your device.
dim_prefix controls the name of entities in Home Assistant (e.g., DIM#1 CH1 Level).

7.2 Required UART/Modbus Setup

Add this to your configuration.yaml if not using a package:

uart:
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200

modbus:
  id: modbus_bus

The DIM‑420‑R1 supports 9600–115200 baud. Defaults to 19200/8N1/ID 3.

7.3 Exposed Entities (Per Package)

Example:

• DIM#1 CH1 On (switch) → writes coil 200
• DIM#1 CH1 Percent (number) → writes register 440
• DIM#1 DI1 (binary_sensor) → maps discrete input 1
• DIM#1 LED1 (binary_sensor) → LED status from Modbus

7.4 Override & Acknowledge Actions

The included YAML handles:

• Ramp via button: components (step up/down)
• Preset recall via switch: (CH ON)
• DI disable/enable via modbus write
• Button logic via controller or mapped automation

Use the on_turn_on: + delay: + switch.turn_off: pattern for all momentary actions (e.g., toggles).

7.5 Home Assistant Tips

• Device classification is already embedded in the package
• Add device_class: light to numeric outputs if desired
• Use ESPHome's delta filters to prevent value flooding
• Use entity_id: contains "DIM#1" for dashboard grouping
• All sensors/entities are safe to publish with on_value: logic

8. Programming & Customization

8.1 Supported Languages

• Arduino / PlatformIO
• C++ (direct RP2040 SDK)
• (MicroPython partially supported, but not recommended for precise dimming)

8.2 Flashing the Module

The DIM‑420‑R1 includes a USB‑C interface for:

• WebConfig diagnostics
• Firmware updates via UF2
• Serial flashing via Arduino IDE / PlatformIO

🔌 UF2 Drag-and-Drop Method

1. Hold Button 1 + Button 2
2. Connect USB-C
3. A drive named RPI-RP2 will appear
4. Drag your firmware.uf2 into it
5. Device reboots into normal mode

🔧 Flash via Arduino or PlatformIO

1. Connect USB-C
2. Optional: press Reset (or hold U3+U4 for hard reset)
3. Upload via selected COM port

Button Mapping (Front Panel)

8.3 Arduino / PlatformIO Notes

🔌 Required Libraries

#include
#include
#include
#include
#include
#include
#include
#include "pico/time.h" // time_us_64(), add_alarm_in_us(), alarm_id_t

9. Maintenance & Troubleshooting

🟢 LED Status

🧰 Common Issues

10. Open Source & Licensing

• Hardware: CERN-OHL-W v2.0
• Firmware: GNU GPLv3

All repositories are publicly available at:

🔗 https://github.com/isystemsautomation/HOMEMASTER/tree/main/DIM-420-R1

11. Downloads

12. Support

Need help using, wiring, or flashing the DIM‑420‑R1? Try these:

• 💼 Official Support Portal
• 🔧 WebConfig Tool
• 🎥 YouTube Tutorials
• 💬 Reddit Community
• 🧪 Hackster Projects
• 📷 Instagram

Or open an issue on GitHub if you're a developer or tester.