Re: [linux-audio-dev] off topic, optical protocols

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Subject: Re: [linux-audio-dev] off topic, optical protocols
From: D. Stimits (stimits_AT_idcomm.com)
Date: Tue Mar 05 2002 - 07:14:06 EET


Taybin Rutkin wrote:
>
> On Mon, 4 Mar 2002, D. Stimits wrote:
>
> > schemes can be used such that center and center drift does not care
> > about some of the component wear. Add to this that eliminating any D/A
> > or A/D controller and using direct optical means is a guaranteed 100%
> > linear signal, no temperature drive ever. No noise, no drift, no wear,
> > no A/D, no D/A.
>
> Well, you'll have to have an A/D converter somewhere in the line. If the
> optical cable is digital, then the A/D converter would live in the
> microphone. But there isn't any way to remove the A/D conversion. You
> wouldn't need a D/A converter unless you wanted to playback.

Not true. I can produce binary coded output based on optical reflections
against something similar to a carefully constructed geometric shape.
The light will activate one of many optical sensors that are in a binary
on-or-off-only mode, the displacement of the sound impact will be
directly coded to digital values. There is no analog component, aside
from the spring qualities of the sound absorbing surface, but that is
totally mechanical, not electrical (something ordinary microphones also
suffer from). Aside from a physical movement, there is no need for even
the slightest amount of analog path within the input path.

Imagine for a moment you have a laser diode aiming horizontally, and it
is aimed at a reflective sphere, that the reflection path is onto an
array of optical sensors, and that the geometry provides a unique sensor
to be activated for each physical position of the sphere (or a disco
ball with many small facets, pardon my ascii art not looking like a
sphere or disco ball):

        |
 ------> \
       | \_
       |
 ..............

Each dot "." above represents an optical sensor, and fine motions up or
down of the sphere change the angle at which the light reflects off of
it. This can be expanded to 2D or even a 3D scheme. Variations on the
geometry can have other desirable effects, such as isolating for motion
in only one axis and being immune to motion in others. If ordinary
optical protocols of an audio card could use this, it would be useful to
me. If it required producing a PCI card as well, forget it.

>
> Digital versus analog is orthagonal to electrical versus optical.

The control surfaces involved have zero analog component. None. Only
mechanical. The question isn't whether I can directly produce a digital
value without an analog to digital converter, the question is whether,
once produced, I can use an ordinary sound card optical in with it. That
question is in turn divided into two categories, one being what effort
is required to produce hardware that takes a binary value for a sound
amplitude, and modulates the optical line properly for a sound card to
read it. The second part of the question is whether such a signal could
be used for non-sound uses, is it possible to use a sound card optical
input and read those values, and use them as something like a joystick
driver. Is the hardware too isolated to directly sample the digital
optical values without going through the D/A converter?

D. Stimits, stimits_AT_idcomm.com

>
> Taybin


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