Saw-tooth to rectangular function / create additional message

General
1

Sorry if this is a beginner question, but I have the following situation:

A KNX message is received everytime a binary switch changes its value, i.e. toggles between on and off. When displaying these on or off status in a dashboard line chart, obviously and correctly a saw-tooth pattern results, with diagonal lines between the 0 and the 1 state.

However, this does not reflect the binary nature and makes it difficult to immediately and intuitively see in which periodes the switch was on or off. What I want is a rectangular shape with a horizontal line at 1 for on and at 0 for off.

My thought was that I would simply need to add an additional data point each time a new state arrives. For example, the state is 0 since quite a time and a 1 is received, I would add a 0, so the line chart represents the old and the new 0 value and immediately after I would give the 1 resulting in the almost-vertical rise to state 1. Perfect representation of the switch values.

But how do I do this in NodeRed? I need a node that can create one additional message and passes on the original message very close after each other (otr maybe it works consecutive at the same time).

2

Assuming you are using the standard dashboard chart then set the Interpolate field in the config to Step.

3

Wow, perfect, they even thought of this. Sorry for the stupid question, I didn't even had the idea that they might have programmed that. Fantastic! Solved.

But, anyway, would there have been a solution like mine? Duplicating message with changed payload?

4

Yes, you could do that in a function node, saving the previous value in the node context then each time a new value comes in send the previous one first. The node red docs page Writing Functions tells you how to use the node context.

5

Hm, I can simply use then inverted state without memorising the previous state, but I cannot figure out how to make one function return two messages.

6

See the docs https://nodered.org/docs/user-guide/writing-functions

7

That is ok, provided you can absolutely guarantee you will only get a message on a state change which may be true in your case. Personally I wouldn't do that though, it is called defensive programming.

8

Yeah, your are right and I agree from a programmer's point of view. However, in this case the KNX actor can be set to send a message only on change.

Anyway, your answer with "interpolate: step" solved then issue in a perfect way, so now I am just curious how I could produce two messages from one incoming message.

9

Have you read the guide Dave linked to?

10

Sorry, got distracted by the "store in context" issue. Yes, I now processed the multiple output options. This solved the issue. I could implement everything I wanted.

Thanks again!

11

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