This is only indirectly related, but I remember reading an article
*several* years ago about a technique that was being used to spy on people.
IIRC they used a photosensor and extensive optics (telescope) and measured
the reflected light output of a monitor/tv. With enough processing they
could reconstruct the image displayed on the screen (well enough to read
text), even without a direct view of the CRT, and at large distances (1/2
mile?). Something about the refresh rate and the v-sync pulses to
synchronize off, and just an ambient light level correlating to a pixel
intensity.

If they can do that, surely you can transfer a few bytes.

-Denny


> Hi Folks,
>
> I'm designing a little PIC-based gadget that will have 8-10 variable
paramaters that I'll store on-board the PIC.
> I'd like people to be able to configure this gadget by means of a PC
program. The program will have the nice interface and do the
> necessary calculations, but ultimately the 8-10 8-bit variables that will
result need to be delivered to the PIC. I want to keep
> cost and weight down, so my idea is to use a phototransistor on the PC
board to watch a "flashing box" on the monitor that sends
> serial data from the PC program. The user would hold the board up to the
monitor, hit a key, and the data would be transferred.
>
> Has anyone done anything like this before? I think it would be relatively
straight forward, but I'm not sure how to filter and
> massage the input from the phototransistor. Any help would be
appreciated.
>
> Thanks,
>
> Jeff
>
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