Thanks for that link. Looking at the patterns, I came up with an idea of using just 2 LEDs/rings, yet being able to fix an absolute position within 1/8 of a turn. In the pic below, the inner lines measure relative angular change. The outer lines encode 8 markers around the ring (like hours on a clock). They are numbers 0-7 but in binary (using 4 spots). A "gray" space in the inner ring marks the beginning (or the end) of the binary marker in the outer ring (depending on the direction). I used gray lines in "blank" spots, so it's more clear. One can speed up the acquisition of an absolute angle with more binary markers around the ring (more spots per marker). With 5 spots per marker (numbers 0-15), you could fix an abs. position within 1/16 of a turn. The angle accuracy depends on the number of spots in the inner ring. In this case it's 360/184=~2 deg
