[sdiy] Pots vs Encoders, was Re: [sdiy] dave smith *instruments*

[cheater cheater]

Tom,
hmm!

This is a simple way of doing this:
Say you have 16 leds and your knob scans to 128 values. Say you are at
value = 0. Then, only the first led is turned on. For value = 1, the
first led is at 7/8 and the second led is at 1/8. Then at value = 8,
only the second led is lit. For value = 9, the second led is 7/8 lit
and the third led is 1/8 lit.

If you do that, as you are moving the knob, the point will seem to
accelerate and slow down. This is because our algorithm of
interpolation does not really correspond to the physical nature of the
medium we are displaying on. I wonder if there is a best worked out
way of doing this. I am sure this is a pretty basic technique in 2d
graphics.

Of course one way would be to scan the knob at a much higher
resolution. Then you could correct the position of the virtual point
by using a specific, 1-1 function. The question of what this function
should look like is quite interesting, but I'm pretty sure it has been
worked out already. Perhaps the specific form of the medium in
question could require a much more general approach than is common
with 2d computer graphics, which usually deal with raster graphics.
Has anyone got experience with 2d graphics here?

I will need to look into some weird new books to figure this out :-)

D.

On Thu, Feb 4, 2010 at 01:13, Tom Wiltshire <tom at electricdruid.net> wrote:
> If you used PWM to control the brightness of the LEDs, the 'extra'
> resolution would be the resolution of the PWM - 8 or 10 bit is easily
> possible.
>
> You wouldn't be able to tell much beyond 16 or 32 levels though, I'd have
> thought. The effect would just get smoother looking. Still, it's a good
> idea.
>
> T.
>
>
> On 3 Feb 2010, at 23:39, cheater cheater wrote:
>
>> I wonder what is actually the maximum bit depth available with this
>> sort of approach. Anyone know what the accuracy improvement with this
>> sort of... hmm.. how do we call this? Anti-aliasing? Interpolation?
>>
>> D.
>>
>> On Wed, Feb 3, 2010 at 21:26, Ingo Debus <igg.debus at t-online.de> wrote:
>>>
>>> Am 02.02.2010 um 15:22 schrieb Tom Wiltshire:
>>>
>>>>  you typically get 15 or 31 LEDs around the ring, which is 5-bit
>>>> accuracy
>>>> at best
>>>
>>> Only if you allow only one LED lit at a time. If you allow one or two lit
>>> (one = spot on, two = value is in between) you get almost twice the
>>> resolution. If you can control the LEDs' brightness you can get even
>>> more.
>>>
>>> Ingo
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