Summary

Encoder wheel for a simple 1-channel, or quadrature shaft encoder. STL files for 5 mm and 8 mm diameter shafts, OpenSCAD file for any custom size. For a detector, I used two 0603 LED-phototransistor pairs with 0.200" spacing for a quadrature output. The detector was fiddly to make, and this has only 32 counts per turn. It is useful to play with, but if you just want something practical, complete encoder modules with 600 counts/turn now start around $15 on ebay. Search for "photoelectric rotary encoder", for example LPA3806-600BM