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modbus2mqtt_2

Yet another Modbus master which publishes via MQTT (and vice versa).
As there are many others, its name is pronounced modbus2mqtt too ;-)

Written and (c) 2024 by Harald Roelle
Provided under the terms of the GPL 3.0 license.

Contains ideas/code/architecture taken from:

  • spicierModbus2mqtt - Modbus master with MQTT publishing
    • Written and (C) 2018 by Max Brueggemann [email protected]
    • Provided under the terms of the MIT license.

Overview

modbus2mqtt_2 is a Modbus master which continuously polls slaves and publishes values via MQTT.

It is intended as a building block in heterogeneous smart home environments where an MQTT message broker is used as the centralized message bus.
Special support is provided for Home Assistant (HASS).

Why _2 ?

Main improvements and changes over spicierModbus2mqtt:

  • Almost complete rewrite
  • Completely async main loop / polling. Very fast, at least with TCP.
  • Improved modularization of code
  • Changed config file format to yaml:
    • All daemon options can (and should) go into the yaml file
    • Command line options still provided for compatibility. Command line overrules config file.
    • Introduced device specification. Hierarchy is now Device -> Poller -> Reference
    • Old CSV format still supported, but not all features are available.
  • Massively improved Home Assistant (HASS) integration
    • Minimal integration almost out of the box, just one option needs to be provided
    • Additional HASS properties can be set for each device and reference in the config file
    • Default option setting possible to reduce config file size
  • Optional printf like MQTT output formatting for references (only via yaml)
  • Optionally, references can have different modbus registers for writing than reading. Especially for supporting Wago devices.
  • Modbus values published without retain flag. This changes the default behavior from spicierModbus2mqtt, but can be switched on by option.
  • Cyclic publishing all values (even unchanged ones, "Publish always") now possible in a configurable interval (not necessarily on every modbus read)
  • Extended diagnostics
  • Extended data types: All data types work for read and write, list data taype for all basic data types

Installation

Requirements:

Installation of requirements:

  1. Install python3 and python3-pip and python3-serial
    On a Debian based system, something like sudo apt install python3 python3-pip python3-serial will likely get you there.
  2. run pip3 install pymodbus
  3. run pip3 install paho-mqtt
  4. run pip3 install pyyaml
  5. run pip3 install jsons

Configuration and usage

modbus2mqtt_2 supports two basic variants of configuration and launching:

  1. Command line + .csv file (legacy and limited)
    python3 modbus2mqtt.py --config path-to-file.csv ... (lots of command line options)
  2. YAML configuration file (new, with all features)
    python3 modbus2mqtt.py --config path-to-file.yaml

Please see Configuration Documentation for details.
Also have a look at the example configurations provided in the config directory

Docker

modbus2mqtt_2 can be run as a docker container, using the included Dockerfile. It allows all usual configuration options, with the expectation that it's configuration is at /app/conf/modbus2mqtt_2.yaml. For example:

To build the image:

docker build -t modbus2mqtt_2 .

To run the image:

docker run -v $(pwd)/config/wago-352-530-430.yaml:/app/conf/modbus2mqtt_2.yaml --name modbus2mqtt_2 --hostname docker-m2m_2 -e TZ=Europe/Berlin modbus2mqtt_2

Tested Modbus devices and feedback

  • Power meter Eastron SDM72D-M-2-MID via Waveshare RS485 TO ETH (B)
  • Decentralized I/O from WAGO:
    • Ethernet head unit model 750-352
    • Digital output model 750-530
    • Digital input model 750-430
  • Waveshare 8-ch Ethernet Relay Module, Modbus TCP

All testing has been done only via Modbus TCP. Please provide any experience with other devices via the Github Issue Tracker, especially when connected with Modbus RTU!

MQTT

Value publishing

Values are published as strings to topic:

mqtt-topic / device-name / state / reference-topic

  • The prefix of all MQTT topics can be specified by option mqtt-topic
  • The device-name is specified by option name in the "Devices" section
  • the reference-topic is specified by option topic in the "References" section of a device

A value will be calculated from the raw Modbus value by:

  1. Applying a transformation according to the option data-type.
  2. Optionally, multiplying it by a scaling factor given by option scaling
  3. Optionally, formatting according to option format-str. This is a printf-like format string.
    For example, to publish a float32 as a voltage value with one decimal place and the unit included: format-str: "%.1fV"

A value will be published if:

  • It's formatted/calculated data has changed (This changed from spicierModbus2mqtt)
  • Optionally, in a configurable regular interval, no matter if data has changed (option publish-seconds)

The published value messages do not have the MQTT retain flag set, but it can be turned on by the option retain-values (different to spicierModbus2mqtt).

Availability / liveness publishing

To indicate if modbus2mqtt_2 is alive, the following topic is maintained:
mqtt-topic / mqtt-client-name / connected
mqtt-client-name is derived from the hostname or set by mqtt-clientid. Publishing is done as MQTT last-will-and-testament (LWT). Therefore, the status shall be correct even if modbus2mqtt_2 dies unexpectedly.

To indicate the liveness of certain device, the following topic is set accordingly:
mqtt-topic / device-name / connected
As this value is handled by modbus2mqtt_2 alone, this value might be wrong when modbus2mqtt_2 died unexpectedly.

Diagnostics

For diagnostic purposes (mainly for Modbus via serial) the topic path
mqtt-topic / device-name / diagnostics / ...
is available. This feature can be enabled by passing the option diagnostics-rate with the number of seconds between each recalculation and publishing the diagnostic infos.

Writing to Modbus coils and registers

For writeable references (option writeable) modbus2mqtt_2 subscribes to
mqtt-topic / device-name / set / reference-topic
On receiving a message from MQTT, the inverse transformation for data-type will be applied and the data is written to the Modbus device.

Data types

For rendering the raw Modbus data, the following data-type values are supported

  • bool
  • int16
  • uint16
  • int32LE
  • int32BE
  • uint32LE
  • uint32BE
  • float32LE
  • float32BE
  • stringLEx with x being an even number of characters
  • stringBEx with x being an even number of characters
  • list-dType-x Generic list type: dType is one of the above data-types, x is the number of elements in the list. Example: list-float32LE-5

References

This work is the result of personally not being satisfied with existing solutions (and me being in the mood to get my hands dirty :-)
Nevertheless there are at some other projects that might suit your needs better (in no particular order, list is incomplete for sure):