[sdiy] super-nice LED interface ..

[Harry Bissell Jr]

Hmmm if you do the 40KHz trich you'd need
bandpass amplifiers. (maybe only one). The big trouble
will be that direct sunlight (or similar) source would
saturate the detector.

Looking for shadows would be crude, you can't count on
the direction of the external light source

H^) harry

--- The Old Crow <oldcrow at oldcrows.net> wrote:

>   My guess is the 8x8 dot-matrix LED block is
> scanned in rows (see the 
> start-up "lamp test" at the very beginning of the
> video) and uses eight 
> sense amplifiers via a simple switch array that
> keeps the active row 
> from saturating the sense amps.  So, a single
> instance of the sense 
> action would be, light up a row, then "scan down"
> the adjacent unlit row 
> or rows by sampling the sense amps with an 8-channel
> A/D (probably in a 
> PIC or AVR part or some other uC).  Then store the
> values, change to the 
> next row, sample...and so on.
> 
>   For noise immunity (ambient light), perhaps the
> lighted row is pulsed 
> at some carrier rate, like..oh, 40KHz (like IR
> remotes) and the sampled 
> signals are sifted for the carrier.  Some other
> bit-frobbery ensues, and 
> the pretty LCD display of the repsonse is the
> result.
> 
> Crow
> /**/
> 
> Ian Fritz wrote:
> 
> > 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.
> 
> 
>