I've seen an existance proof which indicates that this is possible.
Back when I was first getting involved with computers (circa 1972),
some digitizer tablets worked by speed-of-sound measurements.
The stylus tip contained a small  spark gap which was energized 
when the stylus pressed on the  tablet. This created a spark, 
and the spark a minuscule roll of  thunder. Microphones situated 
along the edges of the tablet recorded the arrival times of the sound, 
and the location of the stylus calculated within a millimeter or two.

This was a peripheral for a DEC PDP-8E.

This was calculating a position over about 20 cm to a millimeter,
in real time, in 1972. Doing so to a resolution of a centimeter or
two, in 2001, ever several meters sounds feasible.

Peter Trei  

> ----------
> From:         Ray Dillinger[SMTP:[EMAIL PROTECTED]]
> Sent:         Friday, January 12, 2001 4:37 PM
> To:   John Young
> Subject:      Re: NONSTOP Crypto Query
> On Fri, 12 Jan 2001, John Young wrote:
> >Wright also describes the use of supersensitive microphones
> >to pick up the daily setting of rotors on cryptomachines of the 
> >time, in particular the Hagelins made by CryptoAG.
> Hmmm.  That sounds like a trick that could be brought up to 
> date.  If you get two sensitive microphones in a room, you 
> should be able to do interferometry to get the exact locations 
> on a keyboard of keystrokes from the sound of someone typing.  
> I guess three would be better, but with some reasonable 
> assumptions about keys being coplanar or on a surface of known 
> curvature, two would do it.  Interesting possibilities.
>                               Bear
> [A quick contemplation of the wavelength of the sounds in question
> would put an end to that speculation I suspect. --Perry]

Reply via email to