Modbus MQTT and Node-Red

Modbus is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment.-ref Modbus Faqs Because of its popularity there is a growing requirement for reading data and controlling Modbus devices over TCP/IP networks using MQTT.

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Two Way communication Using MQTT and Python

MQTT is a publish and subscribe protocol with no direct connection between clients. However many applications require a client to client type connection. Examples are: Chat Sensor or device control This can be achieved in all versions of MQTT but it has been made easier in MQTTv5 with the introduction of request response in the publish payload. In this tutorial we look at achieving the same in MQTTv3.1.1.

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Using the Node-Red Template Node

There are two template nodes in node-red. They are the HTML template node and the dashboard template node. In this tutorial we will discuss the HTML template node which is a core node, and is located in the function section.

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MQTTv5 Shared Subscriptions

Shared subscriptions provide for client load balancing. With normal subscriptions(non shared subscriptions) if,for example,  4 clients subscribe to a topic and a client published a message on that topic then that message is sent to all  4 subscribing clients. With a shared subscription then the message would only be sent to one of the subscribing clients.

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MQTTv5 Topics and Topic Aliases

MQTTv5 Topics are essentially the same as those in v3.1.1 (See Understanding MQTT topics) ,but two new features have been introduced. They are: Topic aliases Shared Topics In this tutorial we will be covering topic aliases.

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Examining MQTTv5 User Properties

Properties (MQTTv5) are probably one of the most important additions to the MQTT protocol, and are available in most MQTT message types. The property fields are dependent upon message type, so a CONNECT message will have different property fields than a PUBLISH message.

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My Modbus Working Notes

I have developed a few flows for third parties that have mainly involved decoding Modbus data. However I have never used Modbus in a live environment and needed to get familiar with the basics in order to develop and test these flows. Fortunately the people I worked with had a very good understanding of Modbus, but not of node-red, JavaScript and MQTT These are my working notes from my efforts to create these flows and in particular an MQTT to Modbus bridge. If you are new to Modbus you may find them useful.

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Node-Red Initialising Flow Data on Startup

Often you want your flow to start with known conditions. For example you may have a flow that records various sensors and have alarms set when the sensors exceed a given value. As an example you may want to trigger an alarm when the temperature falls below 3 degrees or exceeds 30 degrees Centigrade.

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Using MQTT-Lens- Beginners Guide

MQTT Lens is an add-on for the chrome browser that lets you publish messages to an MQTT broker and subscribe to MQTT topics and receive messages using the chrome web browser. Once installed you access it via the url chrome://apps as shown below:

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