Tabs are actually quite simple:
- If it's named
<something>.inoit will get merged with the main tab. It's just like working in one big file and you don't need to do anything special. - If it's named
<something>.cppor<something>.cit's a completely separate translation unit and has to be manually "enroled" into the Arduino system by including theArduino.hheader.
So it's simplest to just name them as INO files not CPP files and you don't have to do anything special.:

