Hi All, I am building an application to publish and subscribe to MQTT topic, Though I am able to publish to the topic, I cannot subscribe and display the response receive in a particular topic. Below is my code: import dash import dash_html_components as html import dash_core_components as dcc impo…

Hi @Anup1 You have a function: def on_message(client, userdata, msg): I can’t find where is the line that call that function an pass the 3 variables defined. :thinking: The error message is saying that this 3 variables content are missing. :woozy_face:

Hi @Eduardo , You are right, basically the function should be called like this: def display_Output(clicked): if clicked: def on_message(client, userdata, msg): global p r= msg.topic p= msg.payload return p mqttc.on_message = o…

But where is the data to be used in the function? I do not see this variables in any other part of the code. Sorry, I don’t understand how this function works? :thinking:

“on_message” is a call back function from the Paho.Mqtt ( Ref link ). I am sorry for not explaining the problem clearly, consider the below script which works fine in publishing and subscribing the message from MQTT topics. import paho.mqtt.client as mqtt import json # Define Variables Regisration_…

Hey @Anup1 In this example you are using the line: mqttc.on_message = on_message That line executes the function on_message, but in the Dash callback there is no such line. Then you are returning a function that has never been called :thinking:

@Eduardo Exactly you are right, I had written the function wrong, but I have updated it now. Below is code: def display_Output(clicked): MQTT_HOST = "172.17.0.2" #MQTT_HOST = "localhost" MQTT_PORT = 1883 MQTT_KEEPALIVE_INTERVAL = 45 MQTT_TOPIC_Registration_Response = "gw/D4…

Sorry, I have no experience in using MQTT :woozy_face: Don’t you need to add a loop (do while) function that is triggered width mqttc.loop_start() :thinking:

@Eduardo Thank you very much for the support :slight_smile: , Upon adding the same question in Stackoverflow I got to know that on_message does not return anything and MQTT call back functions should be handled by using websockets. So handling MQTT in Plotly Dash isnt straight forward as writing …

How fast do you need updates? If delay of ~1s is acceptable, you could just make an on_message handler that writes the mqtt message(s) to a file on disk, and then read this file from a callback triggered by an interval component. If you need faster updates though, I agree that a websocket would be…

@Emil Oh the accepted latency is in milliseconds so, I am trying to build the application using websockets.

Subscribe and Display MQTT in Dash

Dash Python

Sylvos July 19, 2021, 8:24am 13

aegis1980/dash-mqtt: MQTT with Dash Plotly (github.com)

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Subscribe and Display MQTT in Dash

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