The analog IO 0 (zero) provides a pure analog outgoing. Does it range from 0 to 5 or just from 0 to 3.3?
Does this MC support attachinterrupt?
Operating voltage of this board is 3.3V based on the following page. So GPIO pins are also running on 3.3V.
https://www.arduino.cc/en/Main.ArduinoBoardMKRFox1200