[sdiy] RE: Modified potentiometer response curves?

[Mattias Rickardsson]

Hi Paul & Kevin,
thanks for the recommended documents (even though I've already seen them;)

2008/5/8 Paul Perry <pfperry at melbpc.org.au>:
>
>  I strongly suspect that a centre tapped linear pot would be the best
>  starting point for your x^3.

Definitely true. But since centre-tapped pots are not readily
available among my preferred pot makers, I'm afraid it's out of the
question.

>  Generation of control voltages of various transformations is a well-explored
>  field. I even have a book dealing solely with this

I'd say that voltage transformation is a very different thing from pot
curve modification, where the input voltage should pass with only a
change in amplitude and where it is the _pot_ value that is actually
subject to a transformation.

The "S"-curved responses obtained by shunting a linear pot's wiper
with resistors to its both ends are definitely useful, but with the
inclusion of an OP-amp and some clever feedback I'm sure that many
even more interesting responses could be achieved. I'm especially
thinking of obtaining a zero-derivative like in the middle of an x^3
curve, and also having the mid position guaranteed to be zero (even
without external trimming), instead of "half the range".


/mr