[sdiy] digital control of CV

jure zitnik kokoon at gmail.com
Tue Sep 4 12:55:39 CEST 2007

i don't think any variable acceleration would feel ok, if i were you
i'd try setting two fixed step values, one for "slow" rotation
(step=1) and one for "fast" rotation (eg step=10). then try to set the
rotational velocity that limits "slow" and  "fast" so the whole thing
feels comfortable. i can't imagine it would work with a continuous
variable step.

also - if i remember correctly thorsten klose implemented something
like that in midibox, try to look there (the code is available, there
is also a forum)


On 9/4/07, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 4 Sep 2007, at 08:26, jure zitnik wrote:
> >
> > david: encoders have *low* resolution. a few tens of values per
> > revolution. while they're useful for some things, they feel quite
> > lousy for let's say cutoff control, try to imagine. 24 values per turn
> > mean that either you'll have terrible stepping (if you want to cover
> > the entire range in one turn) or that you'll have to spin the knob
> > like crazy to get to the other end. i know some implement
> > "intelligent" acceleration, that is if you turn the encoder faster,
> > the steps will be bigger (i'm talking about software of course)... but
> > it just doesn't feel as good as a pot.
> After a previous thread and discussion with Edward King, I got an
> alphanumeric LCD display, a pot, a rotary encoder, and a PIC
> processor together to do some experiments.
> With a pot connected to an A2D input, I was able to pick an exact
> value at 10-bit resolution. Eg: "I want 500!" twiddle, twiddle,
> nudge, nudge. You can get to any value in a few movements. 12-bit
> resolution was a bit too much, both because of increased AD jitter,
> and the difficulty of moving a pot with such accuracy. It is hard to
> set a pot at this resolution, and I wasn't able to reliably get to a
> particular value.
> The rotary encoder was a 24-detent affair, like Jure mentions.
> Obviously single stepping through over a thousand values is possible
> but very slow. So then I started experimenting with measuring the
> time between detents, the rotational velocity, and incrementing the
> count proportionally (as suggested above). This was a disaster.
> Whilst the count goes up a lot if you turn fast, and slowly if you
> turn slowly, getting to any particular value is more or less
> impossible. I found I couldn't control or judge accurately how fast I
> had to turn to get a given increment. For example, if I want a value
> of 500, and the current value is 400, I need to turn at a speed that
> gives me an increment in the tens, say. How fast is that? I had no idea.
> Obviously having the increment directly proportional to velocity
> wasn't getting me anywhere, so then I added a velocity curve table
> between the encoder and the increment, and experimented with various
> curves to try and improve the response. Again, no real success.
> Getting this software right is crucial, but difficult , it seems.
> I'm sure this has to be possible, but I really didn't get any
> encouraging results. Does anyone know any nice commercial examples or
> has anyone tried this sort of experiment?
> Regards,
> Tom

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