A low jitter, low cost optical chopper

An optical chopper is described that has comparable performance to commercially available units. The new chopper is built within the frame of a hard disk drive, and uses the existing motor and its disk for operation. The rotation speed is measured using a photo-interrupter and is adjusted with a microcontroller. Chopping frequencies from 150 Hz to 1650 Hz with phase jitter less than 0.38 degrees per revolution have been demonstrated. The hardware design and control algorithm are described, and results showing the phase jitter characteristics are presented. The performance of this new design is comparable to that of commercial optical choppers, and can be built for a fraction of their cost.