How I used Node-RED.

Node-RED is a flow-based programming tool. It is used a lot in IoT projects.

I had a requirement to stitch together a number of discrete tasks into a workflow. I felt Node-RED would be a good fit to solve this problem. It makes it very easy to wire together different processes (they are represented as nodes), and pass messages between them, for example a status code or output created by one node can be processed by a different node in the workflow.

Problem Specifics:

I had a requirement to reprocess a file. Files are automatically processed using default parameter values. Sometimes when a file is processed the final output is not optimal, the default parameters used to generate it are not suitable. In this instance I would like to be able to re-run the process repeatedly, tweaking those parameters until such time as I was satisfied with the final set of output results.

There are only 2 python scripts that needed to be run. These are run in sequence, the first script generates a set of files, and the second script converts those files into a set of execution instructions.

I would need a UI to enter the parameter values that are used as the command line arguments to the first script.

Solution Specifics:

Node-RED has a UI component.

There is no coding involved in creating this UI, no UI coding at least.

I only needed 2 fields and 1 button.

The first field was a number in the range from 1 - 8.

The second field contained a list of values drop-down option. To get the values to populate the drop-down did involve a small amount of coding.

This is the complete workflow snippet to populate the drop-down values.

The "Populate LOV" node contains this snippet to generate the list of values, which in this case refer to directory names, these are used as product codes.

ls -lart /home/pi/maker/artmart/out | grep "^d" | sed 's/^.* //' | sed 's/\.*//' | awk NF

The "convert to JSON" node contains this Javascript code to convert the list into a JSON object.

let Arrayobj = [];


msg.payload.split("\n").forEach(
    function(item) {
        node.log(item);
        let nme = item.toString();
        let dir = {[nme] : nme };
        Arrayobj.push(dir);
    }
);


msg.options = Arrayobj;

return msg;

And that is it in terms of the UI.

When the button is pressed it runs the process. The diagram for that is:

The template node collates the 2 input arguments to the node "Process". The Process node calls the bash shell script

. ${ARTMRT}/../bin/reprocess.sh

The reprocess script is very simple, it runs the python scripts in sequence.

export ARTMART=/home/pi/maker/artmart
echo "process product code" $1 " with " $2 " buckets of colour"
rm $ARTMART/out/$1/*.png ||  true
$ARTMART/bin/preprocess.py $2 $1
rm $ARTMART/gcode/$1/*.ng ||  true
$ARTMART/bin/createRecipe.py $1

Conclusion:

The beauty of using a tool in this scenario is it abstracts the detail away from the operation of executing the work. All I have to do is pick a couple of parameter values, and click on a button, then check the outcome.