Quad Encoder Problem

[RossWaddell]

Quite possibly it was using an earlier rotary encoder. I switched to a CUI ACZ11 (datasheet) one because I needed the button. Perhaps the Grayhill one I was using before (datasheet) showed the single-increment-per-detent. The CUI datasheet doesn't explicitly state it goes through a full quadrature cycle but one of the diagrams seems to infer that.

Again, thanks for your patience, Henrik. Your explanation makes sense to me now (I hadn't realized that different mechanical encoders behave differently. Should have checked that, of course).

EDIT: I just replaced the CUI encoder with the Grayhill one on my breadboard and guess what - it increments by 1. Mystery solved. Sadly, there doesn't seem to be a cheap Grayhill encoder with a push button so I'll just have to add comments in case I ever switch encoders again to do this test (or read the data sheet more carefully).