On Feb 8, 2006, at 3:44 AM, Howard Winter wrote:

>>> How about two phototransistors suction cupped to the monitor
>>> screen and a program to flash two rectangles in the right seuqence ?
>>
>> I had a remarkably similar thought myself, although I was going
>> to use CDS photocells...  We're all sick.
>
> I think CdS cells would be too slow - you really need semiconductor 
> detectors to make it feasible.

Hmm.  I was thinking slower might be better.  We don't want separate
signals at 30khz (horiz scan freq?) on every scan line "near" the
sensor, after all (although that might be easier to filter...)

> Timex made a watch a number of years ago that used this technique

I picked up some of these "PDAs"at christmas, that seem to use
a similar technique:

http://www.geeks.com/details.asp?invtid=AQU-ZTOUCH&cat=PDA

BillW

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