Using Node-Red to graph scale data

Having used Node-Red briefly about two years ago, i decided to load it again onto the Raspberry Pi which listens for my BS440 scale. Just to dig into Node-Red and see where it got.

Installing Node-Red is a breeze although it takes a coffee and a beer or two before it is installed. But it’s more than worth the wait! A newly added set of nodes is the “dashboard” which can be added through the palette manager once Node-Red is up and running.

My idea was that i could graph the BS440 scale data which is stored into a CSV file (if the CSV plugin is enabled). I was shocked to find out i had made a fully operational webpage showing the data within one hour of coding (or drawing to be more precise)! And that included getting  familiar with Node-Red.

The result is a fancy looking page which shows nicely on my SmartPhone and is lightning fast. It offers a drop down selection for the type of data and two buttons to select the user. Ain’t that cool!

So how is this done? Without giving a lecture on Node-Red (i’ll leave it up to you to explore this piece of magic) this is what the flow looks like:


The core is reading the CSV file. The filename is set by selecting a user. Once the file is read it is converted to a node-js object. Type selects which data we want to graph. The selected type of data is read from the object and fed into the graph node.

The selecting thing might need some explanation as it uses JSONata (just watch the video). It is included in Node-Red and enables you to make a query from a bunch of JSON formatted data in just a single statement. As an example. If you want to craft an array of “vet” values from all data and change the unix timestamp to show milliseconds on the fly the JSONata for that is just:

[ { “key”: “vet”, “values”: msg.payload.[tijd*1000, vet] } ]

and the node “Select vet”  then looks like (note the J: selection)


The rest of the nodes just show the dropdown list and store and show the current user.

The project is made available on my Github

On to the next project. Lets have fun!

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