[Fwd: Re: [sdiy] super-nice LED interface ..]

[Harry Bissell Jr]

Somehow, "Gordon Nanosecond" just doesn't
have the same ring... :^P

H^) harry

--- John L Marshall <j.l.marshall at comcast.net> wrote:

> A nanosecond is about a "Lightfoot".
> 
> Thank you Gordon.
> 
> Take care,
> John
> 
> www.sound-photo.com
> 47-30-39.02 N, 122-09-51.75 W, elev 440'
> ----- Original Message ----- 
> From: "Sumanth Peddamatham" <peddamat at gmail.com>
> To: <synth-diy at dropmix.xs4all.nl>
> Sent: Thursday, October 13, 2005 12:41 PM
> Subject: Re: [Fwd: Re: [sdiy] super-nice LED
> interface ..]
> 
> 
> > Here's a quick experiment you can do.  Grab and
> led, hook it up to a
> > DMM, shine a light on the led, and watch the
> voltage fluctuate.  I
> > don't remember what the animation on Jeff's site
> demonstrates, but
> > with a microprocessor, you could have each led in
> the matrix on for a
> > tiny fraction of a second, and measure the voltage
> on the adjacent
> > leds.  It would take a bit of tweaking, but it
> shouldn't be too hard.
> >
> > As for the Jason's question, no, it's not
> *currently* possible to turn
> > on the led and have it measure it's own
> reflection.  I don't have time
> > right now to hammer out the math, but at the
> distances that we're
> > working with, the roundtrip time for the light
> waves is way too short.
> >
> >
> > Sumanth Peddamatham
> >
> > On 10/13/05, Joe Grisso <jgrisso at det3.net> wrote:
> >> It seems the light is reflected to adjacent
> cells, and then an average
> >> intensity is taken. I also found a quick online
> resource summarizing the
> >> photodiode effect with LEDs:
> >>
> >>
>
http://archive.chipcenter.com/eexpert/akruger/akruger042.html
> >>
> >> One thing I think most people missed was that the
> video was taken in the
> >> dark. If we were to do it in normal or bright
> ambient light conditions,
> >> would the representative wavelengths in the
> ambient light overload the
> >> photodiode effect and make what little
> information you get off of the
> >> adjacent LEDs indistinguishable from the noise in
> the surrounding light?
> >>
> >> Of course this can be corrected by using a
> polarizer or a light filter of
> >> some kind, but why? The more cost effective way
> is to use either a
> >> resistive or capacitive material, a-la touchpads.
> >>
> >> Best Regards,
> >>
> >> Joe Grisso
> >> Detachment 3 Media, Ltd.
> >>
> >> > ----- Original Message -----
> >> >> but .. all LED's are on in that demo, so does
> this mean that the array
> >> has LED's that are 'off', but still being used as
> a detector, or does
> >> it mean that LED's can be used as detectors even
> when lit?
> >> >>
> >> > No, as you can see from the diagram on the
> page, the leds alternate in
> >> such a way that ones adjacent to the point being
> examined are on, and
> >> the light diffuses through the finger (or
> possibly reflects from it) to
> >> the middle one, which is at the same time in
> receive mode. I'm not
> >> personally impressed by this, I think  capacitive
> sensors are more
> >> practical. You are going to need a certain amount
> of processing to try
> >> to work out what is going on.
> >> >
> >> > paul perry melbourne australia
> >>
> >>
> >>
> >>
> >>
> > 
> 
>