Hi,
this use of leds as sensor remember to me an Application related to Leds used as Optical Sensors (instead of a Photodiode) directly connected to a PIC.

See this:   www.merl.com/papers/docs/TR2003-150.pdf 

Some months ago I made a little circuit similar to this (on a 12F629 instead of 16F876) for use as an inexpensive photometer. Interesting results, if "cheap" is the first focus.


regards
Marco

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>From      : piclist-bounces@mit.edu
To          : "PIC List" PICLIST@mit.edu
Cc          : 
Date      : Thu, 13 Apr 2006 11:44:35 +1200
Subject : [EE] Multi-Touch Sensing through LED Matrix Displays







> File this idea away for future reference.
> Use of a multi-LED display as a touch sensor simultaneously with its 
> use as a display.
> Off LEDs are used as sensors of adjacent on LEDs with light paths 
> being interrupted by fingers interrupting the light paths.
> 
> Interestingly, cites a 1977 Forrest Mims comment.
> 
>         http://mrl.nyu.edu/~jhan/ledtouch/index.html
> 
> Presumably this could be done as part of multiplexing a display with 
> no visual effect on displayed information.
> Cries out for interactive display.
> Analog sensing possible.
> Use of IR LEDS (perhaps mixed with visible ones) could allow visually 
> dark sensor.
> 
> ____________
> 
> 
> Upper level is a personal research page from Jeff Han at NYU.
> Some interesting material.
> 
>         http://mrl.nyu.edu/~jhan/
> 
> 
> 
> 
> 
> Ref: Matthew McMahon
> 
> 
>  
> 
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