New on the forum. Sorry if this is a repost, but I could not find anything by searching.
I have bought a Vader costume and want a good voice/sound generator that could somehow be integrated.
Should be able to both generate realistic breathing sounds and voice. Should also have some way to control the fading between breathing and talking in a smooth way if possible.
Electronics and ucontroller is not a problem if some Arduino project or similar exists.

I would guess that the best option if I want a voice converter is some sort of small wireless microphone in the helmet and the electronics + speaker integrated in the chest box.
Another option is to only have a breading sound generator. Either custom made or a phone + bluetooth speaker solution.

Does anyone else here have a good Vader sound system that actually sounds realistic?

Welcome to the forum and good luck with your search. I sadly don't know what are the best options for making you sound like Vader, but you can get clean dialogue and breathing clips from the movies on Starwars.com. At least you could several years ago. I think I saved the breathing file as it was the best I've heard. Don't think I saved the dialogue, though.