Calculating with flow variables in function node

General
1

strong textHi, wanna request help as a beginner.
couldn’t `t find a solution for the topic anywhere by my self.

Issue: get two values from dashboard number node (store them in two flow variables as “t” & “n” ) and one from a sensor with msg.topic = sensor (data import is ok).

now i want to calculate (percentage) with this 3 values in a function node, here is the lack of knowledge.

tried this:

var "f" = { (Number.flow.get("t")   -  Number.flow.get("n")) / Number.msg.topic.sensor};
msg.payload = ["f" +”%”];
return msg;

would be glad for any hint :wink:

í`m also insecure for best practice to store the dashboard values in flow.
direct at the number node or with a extra change node after the number node.

is msg.topic the tight “position” to give the live sensor data in the function node or would it be better anywhere else?

yes - more lack then knowledge

at all it should bring me a sensor calibration flow, based at min-, max-, present-value , cause i couldn`t find a flow about this - if there is a existing one - please let me know.

thanks for your help!
km

2

a) Normally sensor data would have the sensor identification in msg.topic and the sensor reading in msg.payload.

b) The dashboard number input node will surely create a numeric value rather than a string.
If you save that to context flow.set("t", msg.payload) then it is stored as a number and you don't need to convert it in your calculation.
Similarly the sensor reading may well be a number not a string.

c) When you declare a variable you don't need to wrap it in quotes.
You don't need the quotes when you use it either :
var f=42
msg.payload = f +"%"
Note that you do need quotes - single or double - round the name of a context variable to indicate that the name is a string, not the name of some other variable.

d) wrapping [f + "%"] in square brackets makes the payload an array (with just one element).
Is that what you intended?

3

Also Number is a function, so it would be
Number(flow.get("t"))

4

Thank you for your help and quick reply!

read/set of variable and calculation is solved.

Can you please let me know where is the correct place to store a value (min - max calibration values) so this are always available at start of the flow without active input? In a “value” File or is it possible to write form Numeric dashboard input to the default value of a variable?

There is another issue with dashboard:

  • no sidebar available at dashboard (sure settings to show are enabled)
  • dashboard node is updated (node-red-dashboard and no other one installed)
  • dashboard node removed / install with restart etc. no effort
    Someone any hint?
5

How many dashboard tabs have you got?
The sidebar is only shown if you have widgets enabled on more than one tabs.

6

thx jbudd had only one active :roll_eyes:

7

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