Here’s a how to on making an optical encoder that can be used for an autonomous robot – Piotr writes – “An optical encoder measures how far something has moved, optically. It does this by looking at a pattern of alternating black-and-white, and counting number of transitions…” Link.
Editor at large - Make magazine. Creative director - Adafruit Industries, contributing editor - Popular Science. Previously: Founded - Hack-a-Day, how-to editor - Engadget, Director of product development - Fallon Worldwide, Technology Director - Braincraft.
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I made an extension for Inkscape which can create optical encoders discs, its really easy to use. I made a post about it on my website: http://www.dgkelectronics.com/inkscape-extension-for-creating-optical-rotary-encoder-discs/