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