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

[Jerry Gray-Eskue]

-----Original Message-----
From: Jerry Gray-Eskue [mailto:jerryge at cableone.net]
Sent: Wednesday, February 03, 2010 7:27 PM
To: cheater cheater
Subject: RE: [sdiy] Pots vs Encoders, was Re: [sdiy] dave smith
*instruments*


This type technique is sometimes called dithering in graphics.
Basically you use interpolation or vector math to determine the illumination
level of each pixel, LED in this case.
The illumination level is proportional to the tangent (I think that is the
correct term) of the vectors distance to each led with the total light
output a constant sum of the levels.
With the total light output constant and the eye interprets the point source
as between the LEDs.
See the Relative Luminous Intensity vs. Forward Current chart in a Vishay
Semiconductors LED data sheet for an example of the drive levels to light
output function.
The higher the resolution (number of LEDS) and closer the spacing of the
LEDs the better the illusion works.
With the light levels properly controlled the motion will appear steady.

- Jerry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of cheater cheater
Sent: Wednesday, February 03, 2010 6:32 PM
To: Tom Wiltshire
Cc: Synth DIY
Subject: Re: [sdiy] Pots vs Encoders, was Re: [sdiy] dave smith
*instruments*


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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>>> Synth-diy at dropmix.xs4all.nl
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>>
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>

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