Determining the position of a detented optical encoder

Abstract

Changes in the detent position of a detented control wheel used for the Z-axis in a pointing device are determined in a manner that avoids problems previously experienced. A detented wheel is coupled to an optical encoder that produces a quadrature output signal. A quadrature state table containing entries defining quadrature state change conditions that invoke position change indications is used to determine when transitions between detent positions are reported and includes provision for reporting transitions between detent positions even if quadrature states are missed. Also employed is a physical-to-logical quadrature state conversion scheme that enables the transition point between adjacent detent positions to be correctly determined within a controlled range relative to the adjacent detent positions, regardless of the physical quadrature state while the wheel is in a detent position. The invention also enables the use of unmatched photo-optic sets by combining a duty-cycle encoding scheme and feedback mechanism, and by providing a continuous readjustment throughout of sampling time during use of the pointing device. The duty-cycle encoding scheme is implemented by a microcontroller or logic device that processes the quadrature output signal.