Introduction

DomBus are modules designed for industrial and home automation systems that are available with 2 different protocols:

• DomBus protocol, that is supported by Domoticz home automation controller, is a reliable protocol that permits to manage dozens of modules and get status from modules as soon as they changes. Also it includes the so-called DCMD commands that, similarly to KNX, are transmitted between DomBus modules in the same bus to activate outputs in case of events (switch or pushbutton pressed, temperature value, power value, ....) without needing for the intervention or the home automation controller, useful solution to get a home automation system that works even in case of domotic controller fault. The Creasol DomBus plugin have to be installed in Domoticz, using the Python Plugin Manager or downloading the software from GitHub (see the section below).
• Modbus RTU protocol, widely used in industrial and home automation systems, is supported by almost any domotic controller like Home Assistant, OpenHAB, IObroker, Node-RED, ...
  Modbus is a master-slave protocol that permits to activate and deactivate a single relay, all relays or a group of relays by a single command. Also, it's possible to specify, for each relay, the ON time from 31.5ms to 1500 days, so the relay automatically switches OFF after the selected time.

The Modbus RTU version can be used by Node-RED system to realize flows including relay outputs, digital and analog inputs, temperature, humidity, energy sensors, electric vehicle charging station, and more.

Configuration

First, the modbus palette should be enabled: if not already enabled, type the command

npm install node-red-contrib-modbus

then restart Node-RED.

The above flow shows how to use the 8 relays module DomBus31 with Node-RED: drag  Modbus-Write to the flow, and configure it as shown in the picture.

To have complete information about DomBus modules, check https://www.creasol.it/domotics

Below some information about the 8 relay module DomBus31

DomBus31 module Modbus RTU capabilities

The following specifications refers the Modbus version: DomBus31 is available with 2 firmware, DomBus protocol and Modbus protocol, so the latter firmware should be chosen in this case.

Default slave address: 49 (0x31)

It's possible to activate one or more outputs for a certain amount of time (monostable/timer output) as indicated in the table. The parameter corresponding to the needed time can be computed using the following rules:

From 0 to 60s => 31.25ms resolution 1=31.25ms, 1920=60s => value=time_in_milliseconds/32
From 1m to 1h with 1s resolution 1921=61s, 3540+1920=5460=1h => value=(time_in_seconds-60)+1920
From 1h to 1d with 1m resolution 5461=1h+1m, 1380+5460=6840=24h => value=(time_in_minutes-60)+5460
From 1d to 1500 days with 1h resolution 6841=25h, 6842=26h, and so on => value=(time_in_hours-24)+6840

The following tables show some Modbus commands examples.