Analog input module DomBus21

digitalModbusRS-485

Overview
The Creasol DomBus21 is a low‑consumption latching relay module for automated control of loads and monitoring. It provides three SPST latching relays, one optoisolated AC input for voltage presence/zero‑cross detection and four configurable low‑voltage inputs (analog or digital). The compact module is suitable for switchboxes and junction boxes and connects over an industrial RS485 bus.

Key functions

• 3 latching SPST relays, 15 A each, enabling/disabling loads or generators (up to 3 kW per relay, 250 Vac rating).
• 1 optoisolated AC input (100–250 V) for voltage presence and zero‑cross detection.
• 4 configurable low‑voltage inputs: analog (NTC 10k), digital (pushbutton, twinbutton), alarm sensor (balanced) or pulse counter/meter.
• Very low standby consumption (~15 mW) due to latching relay coils active only during transitions.
• Firmware options: DomBus (multi‑master, DCMD events) or Modbus RTU (standard master/slave).
• RS485 industrial bus (115200 bps) for long runs; compact dimensions 59 × 42 × 21 mm.

Typical applications / examples

• Control heat pumps or boilers to eliminate standby power draw.
• Switch gate or garage power to prevent theft when alarmed.
• Disconnect small photovoltaic inverters at night or during storms.
• Control outdoor lighting and long‑duration loads with near‑zero standby consumption.

Features

• 3× 15 A SPST latching relays: coil driven only during state change (no continuous coil current).
• 1× AC optoisolated input (100–250 V) for zero‑cross and presence detection.
• 4× configurable low‑voltage inputs: IN1..IN4 support analog, digital, twinbutton, counter, SENSOR_ALARM, NTC.
• ≈15 mW power consumption even with relays in ON state.
• Firmware: DomBus (works with Domoticz and via DomBusGateway with MQTT for Home Assistant, Node‑RED, OpenHAB, ioBroker) or Modbus RTU.
• RS485 bus: industrial grade, 115200 bps, recommended up to ~500 m with alarm cable.
• Compact: 59 × 42 × 21 mm, fits standard switchboxes and junction boxes.

DomBus21 ports capabilities (DomBus firmware)
Default address: 0xff21
Port 1 - RL1: OUT_DIGITAL. SPST 15 A latching relay; coil active only during transitions. INAC should be connected to AC mains for zero‑cross handling.
Port 2 - RL2: OUT_DIGITAL. Same as RL1.
Port 3 - RL3: OUT_DIGITAL. Same as RL1.
Port 4 - INAC: IN_AC, IN_COUNTER. Optoisolated AC input (100–250 V) for presence and zero‑cross detection; can monitor breaker feedback, PIR with 230 V output, appliance ON detection.
Port 5 - IN1: IN_DIGITAL, IN_DIGITAL_PULLDOWN, IN_ANALOG, IN_TWINBUTTON, IN_COUNTER, SENSOR_ALARM. Analog/digital input with 10k pull‑up to 3.3 V; use common GND.
Port 6 - IN2: Same capabilities as IN1.
Port 7 - IN3: IN_DIGITAL, IN_DIGITAL_PULLDOWN, IN_ANALOG, IN_COUNTER. Configurable pull‑up/pull‑down; common GND.
Port 8 - IN4: Same as IN3.

DomBus21 Modbus RTU capabilities (Modbus firmware)
On power‑up the module signals Modbus address (reg 8192), baudrate (8193) and parity (8194) via LED. Default Modbus slave address: 33 (0x21).
Registers example: Addr 0..2 control RL1..RL3 (0=OFF, 1 or 65280=ON, other values = timed ON). Addr 3 = INAC (0=OFF, 1=ON). Addr 4..7 = IN1..IN4 (0=OFF, 1=ON or analog ranges if configured). Detailed registers cover port options, inversion, timing, serial speed and firmware revision.

DCMD / automation features (DomBus firmware)
Ports accept DCMD commands and generate events (OFF, ON, PULSE, PULSE1/2/4, VALUE ranges). DCMD enables local module‑to‑module automations that operate even if the central controller is offline (e.g. pulse‑based toggles, value thresholds for thermostatic control).

Application notes & installation highlights

• Use INAC zero‑cross detection to reduce in‑rush current on capacitive loads and limit overvoltage on inductive loads when disabling.
• RS485 wiring: prefer linear bus with 100–150 Ω termination resistors at both ends; shield to GND on one side; common GND between devices.
• Provide a stable 12 V supply with UPS/backup if controller/modules must remain operational during outages.

Safety and installation notes
DomBus21 handles up to 15 A per relay (rated 250 Vac). Ensure correct wiring, appropriate fusing and wire gauge. Verify terminal heating under load (e.g. IR camera) and follow local electrical codes.

Technical specifications

• Model: Creasol DomBus21
• Relays: 3 × SPST latching relays, 15 A, 250 Vac (up to ~3 kW per relay)
• AC input: 1 × INAC optoisolated input, 100–250 Vac (zero‑cross & presence detection)
• Low‑voltage inputs: 4 configurable inputs (analog/digital/twinbutton/counter/SENSOR_ALARM/NTC)
• Power consumption: ~15 mW (even with relays ON)
• Bus: RS485 industrial grade, 115200 bps (DomBus); recommended up to ~500 m with alarm cable
• Protocols: DomBus (multi‑master) or Modbus RTU
• Dimensions: 59 × 42 × 21 mm
• Default addresses: DomBus 0xff21; Modbus default slave: 33 (0x21)