[sdiy] programmable pots

[Jay Schwichtenberg]

There are a number of issues when using some of these so check the specs
carefully.

Some have either voltage and/or current limits on their inputs. For example
a number are ran off 5V because they are controlled by digital circuits. In
some this limits the inputs to them to 0-5V. Not good for us analog jocks.
Check into the interface also. Some are slow and harder to interface to.
Also check the 'taper'. There are log and linear ones.

Also look into multiplying DACs. They take a reference voltage and attenuate
that relative to the digital input. Sometimes these are easier to use than
digital pots and have more resolution.

Jay

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of john mahoney
> Sent: Friday, August 15, 2003 1:28 PM
> To: Cornutt, David K; synth-diy at dropmix.xs4all.nl; Glen
> Subject: [sdiy] programmable pots
>
>
> > >The current versions are only availabe with (at most)
> > >100 taps, so quantizing would be a problem...
> >
> > As a work-around, could you use more than one, to get more resolution?
>
> Here they are, called "digitally programmable potentiometers." Add DPP to
> your acronym list, folks.
>     http://www.mouser.com/catalog/615/202.pdf
> They are non-volatile, which is quite handy. You can use them as digitally
> controllable trimpots, for example.
>
> There are 256-tap units; all those are 28K Ohms.
> The 32- and 100-tap models are available in 10K, 50K and 100K.
> Precision is not specified. <assumption> Presumably it is is
> pretty tight. A
> 100-tap unit needs greater than 1% precision, otherwise why have 100 taps?
> </ass.>
>
> The math (or "maths" in British):
>     32-tap 100K resolves to 3.125K Ohms per step
>     100-tap 100K resolves to 1K Ohms
>     100-tap 10K resolves to 100 Ohms
>     256-tap 28K resolves to 109 Ohms
>
> You could combine a 100K/32 and a 10K/100 to get the equivalent of 1000
> steps of 100 Ohms each, approx. 10-bit resolution. This wastes some
> resolution (only using 1K of the 10K unit) but requires no special tricks.
>
> Maybe the PhDs can figure out a way to use 2 of them, one at full strength
> and the other through a divider to lower its effective resistance. Is this
> possible? Approx. 13- or 14-bit resolution would then be achievable, like
> so:
>
> Primary: 100-tap 100K provides 100 steps of 1K
> Secondary: 100-tap 10K divided by 10 (to yield 1K) provides 100
> steps of 10
> Ohms each. Total of 10,000 increments.
>     or 256-tap 28K divided by 28 (again, to yield 1K) provides
> 256 steps of
> 4 Ohms each. Total of 25,600 increments.
>
> Again, I dunno about this divide by 10 or 28 stuff. :-)
> --
> john
>
>
> ----- Original Message -----
> From: "Glen" <mclilith at charter.net>
> To: "Cornutt, David K" <david.k.cornutt at boeing.com>;
> <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, August 15, 2003 3:36 PM
> Subject: RE: [sdiy] tubes, MOVs, etc.
>
>
> > At 03:21 PM 8/15/03 , Cornutt, David K wrote:
> >
> > >The current versions are only availabe with (at most)
> > >100 taps, so quantizing would be a problem...
> >
> > As a work-around, could you use more than one, to get more resolution?
> >
> > later,
> > Glen Berry
> >
>