Simplest way to communicate Arduino to cRIO?

[tStano]

Would using several sidecar relay slots fed to inputs on the arduino work? You could use x of them to make an x-bit number. If you aren't doing complex calculations between the two, and just doing something like what light routine to run, I think that'd be good.

I suggest the relay slots because of how unlikely it is you're using all of them, but I'm not entirely sure how that signal works. I'm more sure of the DIO, but you're prolly using lots of those for other things already.

You could also use the solenoid breakout and module instead of relay channels on the sidecar, and in the same way, I'm sure that would work.