[sdiy] Pot linearity towards extremes

[Jean-Pierre Desrochers]

Hi Rutger,
For precision pot readings I use plastic type servo motor pots.
Those with 360 degrees rotation used on motor shafts.
These are mostly 2% linearity wise like this one:
http://www.pearlelectronics.in/potentiometer.html#servo-potentiometer-servo-pot


Because of there great mechanical linearity they track
the lines on there front panel layout.
I used them for my Ultra-VCO's:
http://www.arcenson.com/projects/Modular/M103B_UltraVCO/Specifications/M103B_MOTM300_UltraVCO_specs.pdf


http://www.arcenson.com/projects/Modular/M103B_UltraVCO/Module_pictures/M103B_MOTM300_UltraVCO_Precision_pot_details2.jpg


 JP 

Le 2016-12-14 11:03, Rutger Vlek a écrit : 

> Hi list,
> 
> 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 linearly. Is that a common property of pots? I hadn't seen it so clearly before. Any ideas on how to easily overcome it without needing both a gain and offset trimmer in the circuit?
> 
> Regards,
> 
> Rutger
> 
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