[time-nuts] position determination over short distance

[iovane at inwind.it]

Rick Harold wrote:
> All,
>
> I'm planning doing some experiments in distance measurement.  They don't
> deal with atomic time directly but with extreme short periods of time.
>
> I need to determine the position of a instrument with a 1mm accuracy or
> less.
> The instrument is not connected to a mechanical device but is separate &
> independent.
> The surface which the instrument is positioned on is close to the size of a
> 11"x11" square.
>
> I thought of using 1 RF transmitters (not sure of freq) on bottom of the
> device near the surface.
> The surface would have RF receivers on 3 or 4 edges/corners to receive the
> signal.
>
> If each of the receivers positions are known and they then send a signal to
> a central circuit (again known positions) how can I differentiate the time
> of arrival
> at the central location?  Does anybody know of a circuit/chip or system
> which would determine the time 'difference'.
> Obviously this is used to triangulate the position of the instrument.
> Light travels 1 mm in ~3.3 picoseconds so I would suspect the differentiator
> would have to have that or better resolution.
> It could also use some proportional method to extrapolate the position since
> the surface has a fixed size.
>
> Any ideas/thoughts?
>
> Thanks in advance.
>
> Rick Harold
>   

Just yesterday, reading an article on an Italian magazine, I 
got in the know of an interesting device which could be 
suitable to the purpose. It is a micro "camera", 1024 x 768 
pixels, whose output is not a video signal, but numeric values
for X and Y, representing the position of a "hot dot". In the 
original design, the hot dot is a IR LED, a couple of meters 
away. This camera has a two wire output, CLOCK and DATA. It 
outputs continuously X,Y,CRLF,X,Y,CRLF and so on. As I 
understood, if there is more than one hot point, say two, the 
output would be something like X,Y,X,Y,CRLF....
I guess that, if the hot dot takes more than one pixel, one 
will get a stream of XY values before a CRLF.
Unluckily, this device is not available as a part, being a 
component of a Nintendo video game, precisely it is part of 
the Nintendo Wii remote control (remote control is found on 
ebay around 25$). 
The magazine is the italian edition of "Elektor" (12/2008 
issue) which is published in several languages 
(www.elektor.com). I think the article always appeared in 
English on back issues abroad.
Also see the interesting

http://en.wikipedia.org/wiki/Wii_Remote

Hope this could be of interest.

Antonio I8IOV