[sdiy] Digital Pots

[Harry Bissell Jr]

--- Roman <modular at go2.pl> wrote:

> what IC you mean, Harry?

I did not see the AD5290 (which did not exist last
time
I looked... its got a data of 8/5/2005 and no pricing
yet.

I mistook the 7376 for part of the D/A line
apparently.

since Roman has spanked me :^) I invite tose
interested to look at the number of Analog Devices
offerings in
5V or less (BIG number) to the +/-15V (small number).

(last time I looked it was only one... now two :^)

I do not know how well these work (do they make much
noise when you change value) ?

Still... with a 256 position pot we are getting close
to a 'perfect' part for hacking old gear.  Limited
values and finite end resistance might still be an
issue, as might be distortion (if any)

HAS to be better than a Vactrol...

H^) harry



> There are:
> AD7376 +/-15V digital pot 128 pos., 10, 50, 100k, 1M
> AD5290 +/-15V digital pot, 256 pos., 10, 50, 100k
> all 3 leads of the digipot can be at any voltage
> between -15 and +15V.
> In some cases most if not all current output DACs
> with external reference input can be used as digipot
> too, offering higher resoulution than typical
> 128-256 steps of a digipot. But then we get
> something like a resistive divider with one end
> connected to GND.
> 
> Roman
> 
> ---- Wiadomo¶æ Oryginalna ----
> Od: Harry Bissell Jr <harrybissell at prodigy.net>
> Do: Jeff Farr <moogah at gmail.com>,
> synth-diy at dropmix.xs4all.nl
> Data: Thu, 4 Aug 2005 10:49:35 -0700 (PDT)
> Temat: Re: [sdiy] Digital Pots
> 
> > Check the voltage levels they can be used at. MOST
> > are 5V supply (or less).
> > 
> > The one that Analog Devices lists as +/-15V is
> more
> > properly called a multiplying DAC
> > 
> > Putting a resistor in parallel will change the
> > 'taper' of the pot. It will not be linear anymore.
> > This could be a 'bug' or a 'feature' depending on
> if
> > you like the effect.
> > 
> > H^) harry
> > 
> > --- Jeff Farr <moogah at gmail.com> wrote:
> > 
> > > SO, while scouring the net for a way to connect
> a
> > > MIDIBox SEQ to a 808
> > > clone so that all the parameters are digitally
> > > controlled I've come
> > > across a series of IC's at analog devices and
> > > maxim-ic called digital
> > > potentiometers.  There is a large variety of
> them in
> > > many different
> > > resolutions, of specific interest are the ones
> with
> > > 127 possible
> > > values.  Has anybody tried to use these as an in
> > > between from encoders
> > > + digital interface to regular VC circuits? 
> Some of
> > > them are 2
> > > terminal and are listed as , but others have
> three
> > > which would seem
> > > ideal.
> > > 
> > > Quote from site:
> > > "The AD5247 provides a compact 2 mm x 2.1 mm
> > > packaged solution for 128
> > > position adjustment applications.
> > > 
> > > This device performs the same electronic
> adjustment
> > > function as a
> > > mechanical potentiometer or a variable resistor.
> The
> > > low temperature
> > > coefficient makes this device ideal for high
> > > accuracy and stability
> > > variable resistance adjustments. "
> > > 
> > >
> >
>
http://www.analog.com/en/subCat/0,2879,761%255F797%255F0%255F%255F0%255F,00.html
> > > 
> > >
> >
>
http://www.analog.com/en/prod/0,,761_797_AD7376%2C00.html
> > > 
> > > Seems with such a selection there should be at
> least
> > > one that will
> > > work.  There aren't alot of available resistance
> > > values, but if I'm
> > > not mistaken I can place it in parallel with a
> > > regular resistor to
> > > achieve the desired range through 1/Rt = 1/R1 +
> 1/R2
> > > etc.
> > > 
> > > 
> > 
> > 
> 
> 
>