RGB and Tunable White LED Controller for Home Assistant — RGB-621-R1, DIN Rail, Modbus RTU

Tech Specs

Note: Relay outputs are not internally fused. Use external overcurrent protection per applicable standards and installation requirements.

Installation, Environmental & Mechanical

Home Assistant / Modbus / Web Config Integration

The RGB-621-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 24 V DC.
2. Connect USB-C – Connect USB-C cable to the module.
3. Open WebConfig – Open WebConfig page in Chrome or Edge browser.
4. Connect Device – Click Connect and select the device.
5. Configure – Set Modbus address and baud rate.
6. Test I/O – Test LED channels, relay, and digital inputs.
7. Save & Disconnect – Save settings and disconnect USB-C.

Features:

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

WebConfig v0.2.0 — gesture engine, hold-to-dim, scenes, 12-bit gamma, and relay FOLLOW (USB-C; settings stored 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:
  rgb1:
    url: https://github.com/isystemsautomation/homemaster-dev
    ref: main
    files:
      - path: RGB-621-R1/Firmware/v0.2.0/default_rgb_621_r1_plc/default_rgb_621_r1_plc.yaml
        vars:
          rgb_prefix: "RGB#1"
          rgb_id: rgb_1
          rgb_address: 3
    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.

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: how many relay channels you need and what should switch the load and wiring a new house before the walls close.

Frequently asked questions

Which LED strips does it work with?

Constant-voltage, common-anode strip at 12 or 24 V DC — RGB, RGB plus cool and warm white, or tunable white alone using just the CW and WW channels. The five outputs are low-side MOSFET sinks: the strip's positive rail goes to the LED supply, each colour's negative to a channel terminal. Addressable strip such as WS2812 or SK6812 is a different technology and is not what this module drives.

How does it get into 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 light then appears in Home Assistant over the native ESPHome API. No MQTT broker, no hand-written Modbus register map.

Will the strip make an audible whine?

It can. PWM runs at a fixed frequency of about 1 kHz, which is inside the audible range, and some strips and power supplies react to that with a faint tone at certain brightness levels — this is a property of the strip and its driver as much as of the controller. If it matters in a bedroom, test the specific strip and supply before committing to them. We would rather say this here than have you find out after installation.

Why 12-bit if Home Assistant only sends 0–255?

Because the low end is where dimming falls apart. Eight bits gives 255 steps spread linearly across a response the eye reads logarithmically, so the last few percent arrive in visible jumps. Twelve bits with gamma correction puts far more steps where perception is most sensitive. The module publishes both scales on Modbus — 0–255 and 0–4095 — so an integration can use whichever it supports.

How much LED load can it take?

The module path is fused at 10 A, from an external 12–24 V LED supply that is separate from the module's own 24 V DC power. That 10 A is a shared budget: one channel may take the full 10 A, or the current may be split across however many channels you use. Terminal blocks and board heat dissipation sit above the fuse; size the external LED PSU for strip length and W/m.

Can it control colour temperature without RGB?

Yes. Use the CW and WW channels alone for a tunable-white fixture and leave the R, G and B channels unconnected. The relay and the digital inputs work the same way in that configuration.

Do I have to use HomeMaster controllers?

No. The module is a standard Modbus RTU slave on RS-485, address 1–247 (default 3) and baud 9600–115200 (default 19200). Any Modbus master reaches it: a third-party PLC, a SCADA system, or your own ESP32 with an RS-485 transceiver.

Is the RS-485 port isolated?

No. The digital inputs use an ISO1212 IEC 61131-2 front end, which conditions the input but is not galvanic isolation, and the RS-485 transceiver shares the device's logic ground. What is present is transient protection — TVS diodes, resettable PTC fuses and fail-safe biasing. Run COM to every node on the bus, and fit an external RS-485 isolator where the bus crosses into a separate electrical installation.

Cabling and Wirings

Power Supply

Module power (V+ / 0V): The RGB-621-R1 logic and communication operate from 24 V DC SELV/PELV only. Connect +24 V and 0 V (GND) to the terminals marked V+ and 0V (top block).

LED power (+ / −): The LED supply terminals (LED PS or + / − on the top block) accept 12 V or 24 V DC. Use a separate supply for the LED strip; supported LED strips are 12/24 V DC common-anode.

Connect + to V+ and − to 0V.

Terminal Block Layout

Top row (LED PS | 24Vdc | RELAY | DI 24Vdc)

Bottom row (LED | RS-485)

Ports & service interfaces

Housing notes

• Relay is SPST-NO. There is no NC terminal - this is not an SPDT equivalent.
• LED channels are labelled R G B CW WW, not CH1..CH5.
• Common anode: one + terminal shared by all five channels.
• The LED strip needs its own PSU on LED PS. The module supply cannot power it.

Top block: LED + / − (12 or 24 V DC LED supply), V+ / 0V (24 V DC module supply), Relay NO/C, I1 / GND / I2 (digital inputs). Bottom block: R, G, B, CW, WW (low-side PWM), COM (LED + common, 12/24 V), A, B, COM (RS-485).

Front view: power, relay, inputs (top); PWM and RS-485 (bottom).

LED Output Wiring

LED channels (R, G, B, CW, WW) are low-side PWM sinks (AP9990GH-HF). Connect the LED strip + to COM (positive from your 12 or 24 V LED supply) and each color cathode to its channel. Supported LED strips: 12/24 V DC common-anode. LED PS accepts 12 or 24 V DC, fused at 10 A per module (shared across channels). Size the external LED PSU for strip length and W/m. Do not share with module logic supply.

LED Strip Connections

RGB Connection

• Connect the LED strip common positive (12/24 V) to the COM terminal.
• Connect individual channels: R → Red, G → Green, B → Blue.
• All outputs are low-side switching (sinking), meaning the module controls the negative side of each LED channel.

RGB + CW Connection

• Same as RGB, with an additional CW → Cool White channel.
• Used for tunable white + RGB applications.

RGB + CW + WW (RGBCCT)

• Full 5-channel configuration: R, G, B, CW, WW.
• LED strip must be common-anode (shared positive via COM).
• This is the native operating mode of the module.

CWWW (Dual White)

• Only CW and WW channels are used.
• Allows color temperature control (CCT) without RGB.

RGB (4-wire) LED strip connection.

RGB + CW (5-wire) LED strip connection.

CCT / Tunable White (CW + WW) connection.

Full RGBCCT (6-wire) LED strip connection.

Relay Wiring

Dry-contact relay output (C / NO). Rated load (system limit): 3 A @ 250 V AC (resistive); max 750 VA @ 250 V AC, 90 W @ 30 V DC. For inductive loads, add an external flyback diode or RC snubber. Keep relay conductors away from signal wiring.

⚠️ External protection required: The relay output MUST be protected by an external fuse or circuit breaker sized for the load and wiring. Relay output circuits are not internally fused. External overcurrent protection is mandatory for safe operation.

⚠️ Hazardous voltage: Relay terminals may carry mains AC or high-voltage DC depending on the connected load. Installation and servicing must be performed by qualified personnel in accordance with local electrical codes.

Relay normally open (NO) and common (C) connection to load.

Digital Input Wiring

Inputs use an ISO1212 IEC 61131-2 digital-input front-end (not galvanic isolation). Connect potential-free (dry) contacts — wall switches, push buttons, or relay / open-collector / transistor outputs that simply close I1/I2 to GND. 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). Each input has a PTC fuse, TVS, and reverse protection.

Dry-contact wiring to I1 and I2 (common GND).

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 COM-A-B. 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.

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; external 120 Ω at both bus ends.

Cable Recommendations & Shield Grounding

General Routing Rules

• Route low-level signal cables (RS-485, DI) separately from power and LED wiring.
• If crossing power cables is unavoidable, cross at 90°.
• Keep cable runs as short as practical; avoid parallel runs with high-current conductors.

RS-485 (Modbus) Cable

• Twisted pair recommended (120 Ω characteristic impedance).
• Shielded cable recommended in industrial environments.
• Use one twisted pair for A/B and a third conductor for COM. COM must be run to every node.
• Examples: J-Y(ST)Y 2×2×0.5 mm² or LI2YCY PiMF 2×2×0.50.

Shield Grounding

• Bond cable shield(s) to cabinet PE/EMC ground at one end (PLC side recommended).
• Do not connect shields directly to signal terminals (A/B/COM).

System Architecture & Pinout

System block diagram.

RP2350A MCU pinout.

Field board layout.

MCU board layout.

Safety and Installation Notes

• Module logic: use only SELV/PELV 24 V DC on V+ / 0V. LED supply (+ / −) can be 12 or 24 V DC.
• Install inside control cabinet; protect wiring terminals from accidental contact.
• Each module must have its own 24 V DC supply for V+ / 0V; do not bridge GND_FUSED and logic GND externally.
• Never connect mains voltage to any terminal.
• Use upstream fusing and snubbers for inductive loads on the relay.
• Size LED supply and wiring for the strip load (length × W/m), within the LED PS ceiling of 10 A per module (shared across channels in use).
• Installation and servicing by qualified personnel only.

Compliance & Certifications

The RGB-621-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)

Licensing. Hardware design files — schematics, PCB layouts and bills of materials — are published under CERN-OHL-W v2. Firmware and the ESPHome integration packages are published under the MIT licence. Full terms are in the LICENSE files in the HOMEMASTER repository.