Good morning hitmeifu,
I was having troubles as well but I ended up modifying the arduino code to set the idle time to longer and it looks like it works. Using just the regular code, I found out that when the ship would load on the launch pad I was getting data for a very short amount of time (like 20 seconds in total) by expanding the idle time numbers I havent lost connection between the board and KSP. Also, are you using the most updated code? I know in the OP it has KSPdemo12, but here's the link to the most recent one
https://sites.google.com/site/zitronfiles/KSPIODemo13.zip
Safe flying!