How do I connect the the second Arduino and do I need to upload a program for them to communicate to each other?

Hello and I think i already answered this in an email earlier, but will put it on here so others will also have the answer.

Only Mobiflight software is needed. I currently use between 27 and 34 Ardunio Megas in my sim. This all seems to depend on your computer hub capabilites. However, 8 arduinos or less is never going to be an issue.

You only need to slect the arduino you want to use in mF device list and then the pin. Simples.

If your are still struggling or need more info, drop me a line.

Kind regards, karl