Implement Threshold feature

[DavyLandman]

We have 3 levels of Warnings we want to give:

• Level 1: CO2 is above a certain threshold (for example 1000) but (already) decreasing
• Level 2: CO2 is above a certain threshold (for example 1000) and not decreasing
• Level 3: CO2 is above a second threshold (for example 1500)

Open questions:

1. which color should the led be for the different levels (taking into account that the case is most likely the logo with the led for an eye)
2. Should the led always pulse at same intensity?
3. how to detect decreasing trend?
4. how to avoid hysteresis?

This is an example CO2 curve:

and a detail shot of a peak:

Progress:

• [x] implement threshold detection of the 3 levels
• [ ] change color scheme of led.

[DavyLandman]

Color options from: https://personal.sron.nl/~pault/

or one of these without the reds:

[DavyLandman]

To detect a decreasing trend I compare the current (1 minute wide rolling mean) CO2 value, and compare that to the max value the past half hour. I consider it decreasing if it's closer than 50% of the threshold.

I suspect that we'll need to tweak this logic in the future, as when you get closer to the threshold, the sensitivity between level 1 and 2 changes.

[DavyLandman]

First version is done, for now it works, later we might need to update it with a better way to detect the downwards trend