Re: Controlling pots digitally
- From: Bill Sloman <bill.sloman@xxxxxxxx>
- Date: Mon, 24 Aug 2009 20:19:31 -0700 (PDT)
On Aug 24, 8:53 pm, Barry <magnus.morab...@xxxxxxxxx> wrote:
Hi,
We have a pair of speakers which we need to control from a pc. The
functionality we wish to control is currently controlable via a set of
knobs on the speakers. Each knob controls a pot.
From a non invasive perspective, could I turn the pot using a motor or
some similar mechanism? Could you perhaps direct me toward more info
on this subject.
From an invasive perspective, would replacing the pot with a digital
equivalent be a workable option? Might it introduce noise into the
circuit?
Digital potentiometers would be the preferred option. They can
introduce noise if you don't think about what you are doing.
What ever the solution we choose, it should not introduce noise into
the cicuit. I would also be desirable also if the mechanism itself was
noise free since we work in a music environment.
The catch with digital potentiometers is that people tend to drive
them directly from a digital processor, which links to ground of your
music electronics to the (noisy) ground of your digital processor.
The nervous designer will galvanically isolate the digital
potentiometer from the processor that drives it, usually with an opto-
isolator, though there are other options. Analog Devices has devised a
chip-scale isolating transformer
http://www.analog.com/library/analogDialogue/archives/39-10/iCoupler.pdf
and Texas Instruments have a capacitatively coupled range of parts
like the ISO15 that thye got when they took over Burr-Brown.
You could also use a balun as a common-mode choke to keep the worst of
the noise on the digital ground out of the ground wiring of the music
electronics, but that does involve having a pretty good idea of what
you are doing.
--
Bill Sloman, Nijmegen
.
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