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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: steppermotor as encoder -> presto, moterized pot.
References: <email@example.com> <firstname.lastname@example.org>
Date: Sun, 06 Oct 2002 15:56:39 GMT
NNTP-Posting-Date: Sun, 06 Oct 2002 08:56:39 PDT
Tony Williams wrote:
> In article <email@example.com>,
> Frank Bemelman wrote:
> > 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.
> Chuck Simmons is your man for this, but wouldn't
> it be easier to do with a brushless dc-motor?
> One which provides a fixed amplitude rotor position
> signal, no matter how slowly the knob is turned.
Frank sent me an email that I answered. At least part of my thinking
that went into the answer might be appropriate here. Frank's idea boils
down to using the BEMF from the stepper to sense motion whether by the
motor or by turning the knob. Since steppers usually have enormous
torque constants compared to spindle motors, this idea has considerable
merit. I could come up with a long list of problems but I think that
they all could be solved in the application without much cost. It takes
thinking it through and experimenting a bit.
I could take this on. I would use an AVR because I can usually wangle a
free AT90S8515 and the lowest grade seems to run at 10MHz (the specs say
it won't but I do it anyway). Thus the processor power is through the
roof for this application. It looks like a fun project however futile.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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