The author has done some good work ensuring good design practices; trace separation, fuses, etc. but I don't see any extra I/O brought out on this particularl switch. You would have to carefully solder to the chip itself, and modify the code a bit.
You could use magnetic switches. Put a magnet on the blinds and the switch in window sill.
The author notes that this is not an Arduino, but uses the same chip that the Arduino uses. The author doesn't explain how the chip is programmed. This method could have been used.
It may be just as easy to use an RF Nano with a little power supply. This suggestion is not nearly as robust as the author's. For example, these power supplies have gotten bad reviews mainly because the mains power traces are too close together. I justify using them because in all likelihood a failure will pop the power supply and probably the Nano, too, noting that these are cheaper than the fuses you would put in to protect them. I am fully aware of the risks involved in doing this, and you should be, too (eg. burning down your house).
-OSD
I liked domoticz (was very easy to set up and use). Together with dzVents scripting wasn't that difficult either. But I also had some problem with it lately, so I was actually thinking about switching to openhab (2).
I see a lot of "!TSF" and "NACK" which seems to be radio communication problems.
That's MySensors related and can be related to many things, from soldering problem to power / capacitor issues.
In MY_DEBUG mode you should see your temp/hum printed on serial every ~15s so there is something wrong there, either wiring or a code issue.
Ty with the example included with the library "i2c_SI7021.h", without any MySensors related stuff, to see if your sensor is detected. You should see temp/hum on the serial.
@tlustoch
The node is a very simple one. So I never considered boot loaders, as the node would not need changing sketches during it's lifetime. I have boot loading functionality on my other designs, this one is a minimal board. Any extra chip would beat the purpose of the word "minimal".
It's a dumb node for a reason