Issue with Real-Time Data Reading from MQTT Node - Unable to Display Graph

Dashboard
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Hello,

I'm facing a challenge while trying to display a real-time graph based on data retrieved from an MQTT node in Node-RED. My approach involves reading data from the MQTT node and transforming it into the appropriate format. However, despite my efforts, I'm unable to visualize a functional graph. It seems that I might be missing something in my approach.

Here's a snippet of the code I'm currently using in the function node:

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Feed the mqtt node into a debug node and show us what you see in the debug pane.

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For real time data you only need to send the y value and maybe a topic to the chart, it will use the current time as x.

eg msg.payload = 42

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I'm trying to display both time and measurement data from an MQTT node.

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So it's not real time then?

Regardless of that, the format you are trying to assemble with series, data and labels arrays is for stored data and I believe that when you send data in that form, the chart node will redraw with a clean sheet. If there's only one data point you don't get any lines on the chart.

Sorry, multiple edits to adjust what my phone thinks I should be saying.

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Experiencing timestamp inaccuracies on Node-RED charts due to a time difference between microcontroller data and the clock of the Raspberry Pi running Node-RED.

My issue revolves around the challenge of displaying the data I receive from an MQTT node at specific time intervals on a chart.

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Show us an example set of data points, and what you want the chart to look like.

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Probably the stored data format is what you need them, but you need to store the data.

Personally I get data from sensors and store it in a database then at intervals run a query to get the most recent couple of hundred records and feed it to the chart.

No doubt it could be done with context storage too

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I provided the dataset above. The data I intend to display consists of timestamps on the X-axis and measurements on the Y-axis. The chart should be a linear graph.

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What units are the timestamps in, and how do you know when to drop samples off the front of the chart?

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The time is measured in milliseconds starting from zero, and the data is sent upon pressing a button in the dashboard.

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Do you mean each sample is sent to MQTT when the button is pressed? Or is a complete sequence sent when the button is pressed?
If it is a complete sequence then the ideal would be to change the sender so that it sends the whole set as an array instead of a sequence of separate samples.

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After pressing the button, an entire series of data is sent until the process is stopped

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Do you mean pressing the button starts it sending, then it keeps sending, every 125 msec, until the process is stopped?

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Yes, I have two buttons for triggering data transmission and stopping. Is it possible to achieve this without using a database, directly from the data I currently have?

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Do you need the chart to build up as the process runs, or would it be ok to wait till it is all received and then draw it?

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It would be sufficient if the chart was generated after pressing the stop data transmission button.

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I'm not sure what the n in your data is, but if you change the msg (the complete msg, not the msg.payload) to be like

{topic:"myseries", payload:0.135, timestamp:250}

Then it should accept the data and timestamp

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I don't quite understand how to do it. Could you elaborate further on how to build the function node?