While thinking about some better and cheaper way to make a good and high resolution encoder for my EQ6, among many similar components and products I found this one, from US Digital:
http://usdigital.com/products/aedr/
This contact-less, optical reflective sensor requires just a printed stripe pattern on a white background (could be done by laser printer on paper) in a form of tape (that can be wrapped around shaft) or round circle, and I can have a cheap encoder with very high resolution, that can be used with Ek box or equivalent.
For example, 75 lpi (lowest resolution sensor) is ~3 l/mm, this is easily printable with moderate laser or ink jet printer.
10cm (33mm dia) will have 90 strips per rev, this is 360 tics/rev with Ek's box!
Of course, there is no limit to this: thicker the shaft (or wider wheel around which the paper tape is wrapped), higher the resolution. The higher resolution configuration chip (212 lpi) will have ~1000 tics/rev.
For 10,000 t/r we need a wheel 30cm in dia, quite reasonable for any dobson mount.
There is really no need to spend k$ for off the shelf encoders, when something like this is available for couple of bucks.
I will try to get samples and build a prototype, and I will report results here when I am finished.
The expected cost for any resolution encoder with this sensor is around $10 each.. (Because paper tape with printed pattern costs nothing).
Food for thought for astro equipment manufactures
