> Sergey Dryga wrote:
>
> > Randy Boulter <wrb <at> isp.com> writes:
> >>
> >>I have been tasked with doing a conceptual design for a device that
tracks
> >
> > finger movement using a sensor
> >
> >>device mounted to the finger.  Does anyone have experience with this or
> >
> > something similar?  Or thoughts or
> >
> >>ideas?
> >
> >
> > How about using a (ultra)-sound source at the finger and 3 microphones
to
> > triangulate the position.  Something like this was used for DNA sequence
> > readout from autoradiographs using a pen as pointing device. The
resolution was
> > in sub-mm range (IIRC).
> >
> > Another option is to use 3 sound transducers and microphone on the
finger to
> > find position, similar to GPS, only with ultrasound.

Robert Rolf wrote :

> This method works quite well. We had an old 3-d digitizer that used
> a pen that snapped (electric arc) and 3 mics with about a 0.5 meter
> spacing, and it covered the 1/2 meter cube quite well.
>
> With 4 external sources, (to get better closure on the RMS position
> error), and phase measurements, one could get very good accuracy,
> if a continuos high sample rate was required.
>
> Sounds to me like you're looking to do performance art, so there is
> no budget available to use the optimal technology.
>
> Robert

This sounds like an excellent method, but how far apart would the
microphones have to be if they were placed, say 20 feet away from the sound
source (finger), and still maintain accuracy within a few millimeters?

Randy

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