Just an update regarding the Renovent Climate system:
I created the following cheat sheet:
To be able to read the 'filter' value I converted the default RJ11 to RJ12.
Now it should be able to warn me that I need to change the filter.
As I use the EasyPCB and already used all available pins on the prototype board, I had to solder an extra wire to pin 8.
Q: How do I access A2, A3 and D8? A: They are not accesses through the PCB, so you need to directly solder to the pro mini.
As this Pin 8 is not used with pull up resistor (I thought it was dangerous to do that because adding 3v of the Renovent would kill the input.) I needed to build some sort of pull-down resistor from keeping the input pin from floating. And hell yes it was floating like hell (resulting in a lot of messages, that even the debouncer was unable to deal with).
Normally when the filter is 'clean' there is a 0v on P8. If the filter needs to be cleaned there is a +/- 3v on P8
This how it was solved: