Just a note that I have some new boards in stock now, I’ve also renamed it into "“Doorbell modernizr” 
Because soldering was taking a bit too much of my time and was too error prone, I now got some professionally assembled. This doesn’t however make it cheaper unfortunately (you would need to go to pretty high batch sizes for that).
All code and designs are still open source:
The device now also works with Domoticz and OpenHAB out of the box by the way 