I already have a Arduino UNO card, and would like to use that one.
But MobiFlight seems to only support Mega, not UNO 
I also found this, that looked promising:
But using this I am so far not able to write back to FS, only read values.
(You must have FSUIPC7 running for this SDK to work)
I can program whatever is needed, but I need som āarchitectureā-pictures to show how it all fits togetherā¦
I also looked at fs2link, but that one seems very old.
I have been able to use the Arduino to simulate a joystick, but only for input signals, and not for output from MSFS. (To make an UNO inot a joystick you need to flip the firmware to simulate it as a USB Host)
Currently I uses that for adjusting trim using a potmeter and raising and lowering gears using buttons for each command.
I have added some āstupidā green LEDs that lights up accordingly, but they are currently not connected to FS, only responds on the button being pressed (Due to this, currently the ligths only respond to the buttons, and does not check if the gear is actually up or down)
But it would be great to make MSFS āwrite backā to the Arduino.
Then I could add a radio LCD-etc.
(and I could then also run it in ānormalā COM-mode with the proper firmware which makes things a little easier.)
Any pages/tutorials I should look at?..