MobiFlight is an open source project that allows you to create your own home cockpit for your favorite flight simulator in a flexible, affordable and extremely user-friendly way.
Since it pops up mentioned on Discord from time to time, until it eventually finds a way in more "official" documentation, it may be useful to post it here too:
Key Matrix with MF.pdf
Make it Possible to use a Matrix Keypad for the MCDU etc.
https://playground.arduino.cc/Code/Keypad
[Issue created by Bastischen: 2017-08-13] [Last updated on bitbucket: 2018-02-11]