A position detector for determining the angular position of a rotatable element, the detector having a single light source for directing a uniform wide angle field of light in a direction generally along the longitudinal axis of the rotatable element, multiple sector-shaped light detectors aligned...http://www.google.ca/patents/US5844673?utm_source=gb-gplus-sharePatent US5844673 - Axial led position detector for determining the angular position of a rotatable element 
