  This paper presents a controlling and positioning approach for an optical
filter disk. In the known applications where Hall-effect sensors and magnets
(radially positioned) are applied, the purpose of the latter is to help
developing a binary code used mainly for filter identification. The number of
sensors is equal to the maximum number of magnets that participate in forming
the filter identity code. Therefore, three sensors and the corresponding number
of magnets radially positioned for each position are required for the
identification of seven filters. The precise position of the filter disk is
reached by counting up the steps of a stepper motor. The presented approach
applies only one Hall-effect sensor. The fore working front of one magnet,
positioned along the disk periphery, is used to precisely mark each filter
position. At a certain distance after the main magnet, a second one is
positioned in order to form an identity code. The paper contains an algorithm
for optical filter disk control and positioning, along with the mathematical
formalism on which it is based.
