From: firstname.lastname@example.org (Glenn Gundlach)
Subject: Re: steppermotor as encoder -> presto, moterized pot.
Date: 5 Oct 2002 22:21:03 -0700
References: <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: 6 Oct 2002 05:21:04 GMT
email@example.com (Richard Steven Walz) wrote in message news:<firstname.lastname@example.org>...
> In article <email@example.com>,
> Frank Bemelman wrote:
> >Just had an idea, and I'm not planning to actually build
> >something, but liked to share the idea - if it is an idea.
> >What we want is a moterized pot for a homemade amplifier,
> >so that it can be controlled both manually and by remotecontrol.
> >Since we lack mechanical skills (not me of course) we want it to
> >be mechanically simple. For cosmetic reasons we want the volume
> >knob to turn as well, when using the remote.
> >Okay. We use a size 17 steppermotor from an old 5.25 floppy
> >drive. Some circuit to convert to logic levels, a PIC
> >to decode etc. Now we have a signal to control a digital
> >volume control. Easy.
> >PIC also controls 4 outputs (steppers from floppydrives are
> >often unipolar) if the remote wants to move the 'pot'. In this
> >case, the software ignores the inputs, and simply increases
> >or decreases the control of the *digital* pot, and stepping
> >the motor with knob accordingly.
> >Frank Bemelman
> Silly, use a digital pot! An up-dn counter with a clock which dials in a
> resistive network tap to set a value, which goes to an op-amp in the
> feedback loop.
> If you just really want the knob to move mysteriously, use a stepper.
> Okay for a tuner or such, but for a pot that's silly!
Actually, it isn't silly at all. There are serious limitations on
digital pots in terms of resolution, bandwidth, noise, voltage levels
and such that would be handled better by a good old pot.
My 2 cents.