Hi, thanks for the hints 
Unfortunately pin 9 on the old arduino mega board I'm using is broken, so I cannot use the B port.
Edit: sry I mixed up the pin layout.
Pin 15 is broken, Port B only has 6 pins and Port D has pins that shouldn't be set to output, so I guess my best bet is using the pins 22 and higher?
I found this image, does that mean that port A consists of pins 22 to 29?
