[sdiy] Two parameter mechanical controller thoughts....

[rburnett at richieburnett.co.uk]

Might be too far towards the expensive end of the scale, but also check 
out "LVDT" for accurate absolute linear non-contact position sensing.

-Richie,

On 2019-06-10 03:06, Pete Hartman wrote:
> On Sun, Jun 9, 2019 at 6:22 PM <rsdio at audiobanshee.com> wrote:
> 
>> Have you ever used a set of digital calipers? They have a pattern
>> that is read optically, so the system knows where the slider is
>> positioned at any time. 0-calibration is usually necessary on the
>> affordable ones. I believe that the pattern is basically the same as
>> the quadrature in a rotary encoder, except that it’s straight -
>> not circular. I’m not sure how easy it would be to build something
>> like this, but if possible then it would be a lot less problematic
>> than something with long rubber bands.
> 
> Google gets me lots of hits for "linear optical encoder" that involves
> transmissive sensors, i.e. it's clear with stripes and you have an LED
> on one side and a sensor on the other.
> 
> Not having as much luck yet finding anything where both the light
> source and the sensor are on the same side, but still digging through
> various links.  This really seems like a good way to go, aside from
> the whole question of absolute positioning -- when I power on, where
> is it at?  It can be saved in non-volatile space but I honestly don't
> trust that very far, in terms of long term tracking.
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