>>>>An optical "window" with width affected by position would probably be
>>easy enough. read light level shining through "window" to get
>>position.
>
> Dammit Russel.. this is too simple and effective to be true!!
>
> What do you neozelandeses eat? A lot of Omega-3 fish I guess. I gotta
> eat more too. :-)
>
> Thanks, I'll invent something along the lines of a single light source
> getting proportionally dimmed by something displacement related. Easy
> and effective, and probably much more precision than I'll ever need.

Glad you like it.
Certainly not original - probably done since earliest of  valve days.
Use of 2 detectors allows compensation as light source ages.

Can be a tapering shadow mask if source and/or detector diffuse.

Can probably use a balanced detector pair so level shifts with
position so detector "slides" across range differentially with
position. May be able to use this to make effectively independent of
source brightness. Just possibly two photo transistors and little else
:-).

If really lucky maybe a dual photo interrupter with a suitably shaped
mask sliding through the interrupter pair.



          Russell.
--=20
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