Optical Encoder:
Pros: can be cheap, accurate, less parts to break
Cons: can be expensive, absolute position not know in basic setup

Basics

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Quadrature encoding

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How to use

res, quadrature, device issues, eqs...

How to build a rotory optical encoder

Make/buy shafts of some sort. Probably want something you can put a pretty knob on. Next get some codewheels. An inexpensive codewheel can be made by printing one on a transparency. Make sure your printer has a high enough resolution and that the transparency material doesn't distort the image too much. Some simple parameter changing in this PostScript is a good start: optencbars.ps. Make sure it works with your sensing device. Mount the rotor somewhere. Put the codewheel on it. Mount the sensor in the right spot. Wire up and use.

How to build a linear optical encoder

similar to the rotory model but use a codestrip instead of a wheel. Setup a slier that has the sensor that moves along strip. Absolute position on this device is a more tricky problem... it really has physical limits.

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