For instance, I'm in PA (sigh, although I love where I live), and there are 3 in-person methods: Optical Scan, DRE (Direct Recording Electronic), and Paper Ballots. I voted by Paper Ballot in my rather small little township.
How is this determined state by state? Would it not make sense if in-person voting used the same method everywhere?
The US constitution grants authority for making election rules to the states, individually. The federal govt. does not have constitutional authority to set, or dictate any election rules beyond the rules stated in the constitution.