[sdiy] Pot linearity towards extremes

[Neil Johnson]

Rutger Vlek wrote:
> I'm working on what's basically a continuous pot turned into a 16-position switch. It's a circuit that uses a simple free-running ADC to convert a 0 to 5V output from a potentiometer digital outputs that control switching of a 16-way CMOS switch and a 16-way LED driver. The led driver lights a LED in a ring of 16 around the pot to indicate the selected position. However, in the prototype the LED being lit doesn't line up with the position of the pot. The pot is a 10K linear one, but from my measurements it seems it is non-linear towards the extremes. The angle of physical rotation doesn't line up so well with the angle over which the resistance changes

If you look at the datasheet of the pots you are using you should find
a curve showing the pot resistance as a percentage of travel.  You may
also find out the mechanical rotation and the electrical rotation,
where the electrical rotation is less than the mechanical rotation.
In other words at each end of the mechanical rotation you have a
region of non-linear behaviour.

This is normal for non-precision pots and is (should be) documented in
the datasheets.  For example both Alps and Bourns document the track
curves.

Neil
-- 
http://www.njohnson.co.uk