[sdiy] super-nice LED interface ..

[Ian Fritz]

At 10:39 AM 10/13/05, Paul Perry wrote:

>----- 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.

Oh I see, it's a scanner?  Not quite clear on exactly how that thing 
works.  If your finger was between two devices then there would be strong 
coupling when one is an emitter and the other a detector.  But if you move 
away towards one of the devices wouldn't the coupling get weaker?

At any rate the cartoon shows a whole set of alternating devices emitting, 
so the scanning aspect isn't very clear to me.


>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.


Well, we like our flashy lights, don't we.  :-)

   Ian