PC ISA Bus Quadrature Encoder Card

Keywords: incremental encoder, mouse, hacking, quadrature, infrared emitter, detector, position, rotation, odometry

An incremental optical encoder is nothing more than a slotted disk and infrared (IR) emitter-detector pairs. Disk rotation results in IR pulses which must be handled; pulse counting, timing and quadrature yields the disk's angular position, velocity and direction respectively. The photo on the left illustrates a PC based ISA bus card solution that automatically handles encoder pulses and yields disk measurements.

Motivation and Audience

There are many instances when rotation angle, velocity and direction must be accurately measured. Examples include robot odometry, XYZ (lead screw) table motion measurements, telescope lateral and longitudinal positioning and knob inputs.

PC based solutions are attractive because of event-driving; through software, angle feedback can be used to improve navigation or positioning.

The ISA bus provides you an easy interface to build your PC quadrature card upon. Your card will plug into your PC's motherboard much like a modem or sound card does. Although commercial PC bus based cards cost hundreds of dollars, this tutorial will show you how you can prototype one for less than $50US, in an afternoon.

This tutorial is broken down as follows: