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spicierModbus2mqtt

Written and (C) 2018 Max Brueggemann [email protected]

Contains code from modbus2mqtt, written and (C) 2015 Oliver Wagner [email protected]

Provided under the terms of the MIT license.

Overview

spicierModbus2mqtt 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.

Changelog

  • version 0.72, 12. of November 2023: add loop break option again due to user request, reconnect on modbus tcp connection loss and serial device not found
  • version 0.68, 31. of October 2023: use asyncio with pymodbus, add option to use function code 16 when writing single registers, remove loop break option
  • version 0.66, 29. of November 2022: print Modbus exceptions generated by devices
  • version 0.65, 25. of November 2022: fixed incompatibility with newer version of pymodbus, readjusted the Dockerfile
  • version 0.64, 16. of October 2022: Adjustment of the Dockerfile (enforcing pymodbus 2.5.3, otherwise it tries to use 3.0 and this failes); typo fixed; main-/poller-loop log entry
  • version 0.63, 04. of October 2022: added reading and writing of int32 values, fix regarding negative floats
  • version 0.62, 6. of February 2022: major refactoring, project is now python module available via pip
  • version 0.5, 21. of September 2019: print error messages in case of badly configured pollers
  • version 0.4, 25. of May 2019: When writing to a device, updated states are now published immediately, if writing was successful.

Spicier?

Main improvements over modbus2mqtt by Oliver Wagner:

  • more abstraction when writing to coils/registers using mqtt. Writing is now possible without having to know slave id, reference, function code etc.
  • specific coils/registers can be made read only
  • multiple slave devices on one bus are now fully supported
  • polling speed has been increased significantly. With modbus RTU @ 38400 baud more than 80 transactions per second have been achieved.
  • switched over to pymodbus which is in active development.
  • Improved error handling, the software will continuously retry when the network or device goes down.

Feel free to contribute!

Installation

run sudo pip3 install modbus2mqtt

Without installation

Requirements:

Installation of requirements:

  • 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)
  • run pip3 install pymodbus
  • run pip3 install paho-mqtt

Usage

If you've installed using pip:

  • example for rtu and mqtt broker on localhost: modbus2mqtt --rtu /dev/ttyS0 --rtu-baud 38400 --rtu-parity none --mqtt-host localhost --config testing.csv
  • example for tcp slave and mqtt broker on localhost: modbus2mqtt --tcp localhost --config testing.csv remotely: modbus2mqtt --tcp 192.168.1.7 --config example.csv --mqtt-host mqtt.eclipseprojects.io

If you haven't installed modbus2mqtt you can run modbus2mqtt.py from the root directory of this repo directly:

  • example for rtu and mqtt broker on localhost: python3 modbus2mqtt.py --rtu /dev/ttyS0 --rtu-baud 38400 --rtu-parity none --mqtt-host localhost --config testing.csv
  • example for tcp slave and mqtt broker on localhost: python3 modbus2mqtt.py --tcp localhost --config testing.csv remotely: python3 modbus2mqtt.py --tcp 192.168.1.7 --config example.csv --mqtt-host mqtt.eclipseprojects.io

For docker support see below.

Configuration file

THE FIRST LINE OF THE CONFIG FILE HAS TO BE:

"type","topic","col2","col3","col4","col5","col6"

The Modbus data which is to be polled is defined in a CSV file. There are two types of rows, each with different columns; a "Poller" object and a "Reference" object. In the "Poller" object we define the type of the modbus data and how the request to the device should look like (which modbus references are to be read, for example: holding registers at references 0 to 10). With the reference object we define (among other things) to which topic the data of a certain data point (registers, coil..) is going to be published. Modbus references are as transmitted on the wire. In the traditional numbering scheme these would have been called offsets. E. g. to read 400020 you would use reference 20. Refer to the example.csv for more details.

  • Use "coils", for modbus functioncode 1
  • Use "input status", for modbus functioncode 2
  • Use "holding registers", for modbus functioncode 3
  • Use "input registers", for modbus functioncode 4

Reference objects link to the modbus reference address and define specific details about that register or bit. Pollers and references are used together like this:

poll,kitchen,7,0,5,coil,1.0
ref,light0,0,rw
ref,light1,1,rw
ref,light2,2,rw
ref,light3,3,rw
ref,light4,4,rw

This will poll from Modbus slave id 7, starting at coil offset 0, for 5 coils, 1.0 times a second.

The first coil 0 will then be sent as an MQTT message with topic modbus/kitchen/state/light0.

The second coil 1 will then be sent as an MQTT message with topic modbus/kitchen/state/light1 and so on.

Note that the reference addresses are absolute addresses and are NOT related to the start address of the poller! If you define a reference that is not within the pollers range you will get an error message. So another example:

poll,someTopic,1,2,11,coil,1.0
ref,light9,9,rw

This will poll states of 11 coils from slave device 1 once a second, starting at coil 2. The state of coil 9 will be published to mqtt with the topic modbus/someTopic/state/light0 if column 3 contains an 'r'.

If you publish a value (in case of a coil: True or False) to modbus/someTopic/set/light0 and column 3 contains a 'w', the new state will be written to coil 9 of the slave device.

Some other "interpretations" of register contents are also supported:

poll,garage,1,0,10,holding_register,2
ref,counter1,0,rw,float32BE 
ref,counter2,2,rw,uint16
ref,somestring,3,rw,string6

This will poll 10 consecutive registers from Modbus slave id 1, starting at holding register 0.

The last row now contains the data format. Supported values: float32BE, float32LE, uint32BE, uint32LE, uint16 (default), stringXXX with XXX being the string length in bytes.

Note that a float32BE will of course span over two registers (0 and 1 in the above example) and that you can still define another reference object occupying the same registers. This might come in handy if you want to modify a small part of a string separately.

Topics

Values are published as strings to topic:

"prefix/poller topic/state/reference topic"

A value will only be published if it's raw data has changed, e.g. before any formatting has been applied. The published MQTT messages have the retain flag set.

A special topic "prefix/connected" is maintained. It states whether the module is currently running and connected to the broker (1) and to the Modbus interface (2).

We also maintain a "connected"-Topic for each poller (prefix/poller_topic/connected). This is useful when using Modbus RTU with multiple slave devices because a non-responsive device can be detected.

For diagnostic purposes (mainly for Modbus via serial) the topics prefix/poller_topic/state/diagnostics_errors_percent and prefix/poller_topic/state/diagnostics_errors_total are available. This feature can be enabled by passing the argument "--diagnostics-rate X" with x being the amount of seconds between each recalculation and publishing of the error rate in percent and the amount of errors within the time frame X. Set X to something like 600 to get diagnostic messages every 10 minutes.

Writing to Modbus coils and registers

spiciermodbus2mqtt subscribes to:

"prefix/poller topic/set/reference topic"

If you want to write to a coil:

mosquitto_pub -h -t modbus/somePoller/set/someReference -m "True"

to a register:

mosquitto_pub -h -t modbus/somePoller/set/someReference -m "12346"

Scripts addToHomeAssistant.py and create-openhab-conf.py

These scripts are not really part of this project, but I decided to include them anyway. They were written because I grew more and more frustrated with the Modbus capabilities of OpenHAB and Home Assistant.

So what exactly do they do? Completely different things actually.

  • addToHomeAssistant.py can only be run within modbus2mqtt.py. It can be invoked by passing --add-to-homeassistant when running modbus2mqtt.py. It uses MQTT messages to add all the stuff from the .csv file to home assistant automatically. Just try it. I recommend using a non productive instance of Home Assistant for testing :-)

  • create-openhab-conf.py can be used independently. It parses the .csv file and creates configuration files (.things and .items) for OpenHAB (version 2+ only). This is of course not necessary for using spicierModbus2mqtt whit OpenHab but it removes a lot of hassle from it. I use it to create a basic working structure and then rename and rearrange the items by hand.

Docker

spicierModbus2mqtt 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.csv. For example:

docker build -t modbus2mqtt . && docker run -v $(pwd)/example.csv:/app/conf/modbus2mqtt.csv modbus2mqtt --tcp <modbus-tcp-host> --mqtt-host <mqtt-host>