oh, also very important: i ended up with six magnets around the wheel, iirc.
note that the diameter of the wheel was rather small, so you may be able to place even more before detection zones start to overlap. in any case, more magnets = more resolution and faster response.
to give you an example: for speed calculations, you need to know how much time passed between two pulses, so you need to have detected two magnets to even start calculations. starting from a standstill, and using only one magnet, that means at least one full revolution and then some to see that same magnet twice. with 6 magnets, that is reduced to a movement of only 60 degrees.
