Brendan and Dale,

The pot with the centered wiper, end terminals connected to STIFF
sources (like Vcc and GND), is a Thevenin equivalent to Rpot/4 from (in
the case of this example) a source voltage of Vcc/2.

This offers you some interesting possibilities for de-linearizing a
pot.  In one motion control application we needed a pot to control a
(large) servo so that with the pot centered we got no (very little)
motion.  With the pot turned half way from centered to either side (1/4
and 3/4) we got 10% velocity and at the extremes we got full velocity.
Using a 5k pot with the end terminals connected to + and -10V with a 232
ohm de-linearizing resistor from the wiper to ground we got exactly the
curve we were hoping for.  Not much response near center ... lots of
response at the ends.

Regards,
Dave

Brendan Moran wrote:
>
> Isn't that only how it works under AC cnditions, where both DC sources are
> considered the same?
>
> Brendan
>
> ----- Original Message -----
> From: "Dale Botkin" <dale@BOTKIN.ORG>
> To: <PICLIST@mitvma.mit.edu>
> Sent: Tuesday, June 11, 2002 11:53 AM
> Subject: Re: [PIC]:strange analog in problem
>
> > Hrmm...  not sure I'm with you on that one.  With the wiper centered, your
> > input would still see 20K Ohms to either source.  Maybe I'm just slow or
> > theory-challenged, but I don't see how two resistors to two different
> > sources would qualify as "parallel".  I could be wrong though, here I am
> > posting from work again, which results in my being wrong about 3 out of 4
> > times it seems.
> >
> > Dale
> > --
> > "Curiosity is the very basis of education and if you tell me that
> > curiosity killed the cat, I say only the cat died nobly."
> >           - Arnold Edinborough
> >
>
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