>  I have thought on a LPS (that is, a Local Positionning System as
>  opposed to GPS). More specifically I am thinking on using three
>  ultrasound (or high freq. sound) beacons, all of them emitting
>  simultanously and periodically  a given signal and compute the
>  position and orientation of my rover by using the delay of the
>  signals when reaching two onboard microphones separated a known
>  distance (1 millisecond <=> 30 cms).
>
>  Do you think that this is feasable ? Has someone tried this before ?
>  Is it too late and I should go to sleep ?

Some Piclisters have told me off-line that they thought that this was
feasible.
OK. I will trust them. Now, to start building a prototype I have only an
electret microphone, a 8 Ohm loudspeaker, a 555 and a 567 pll (and, of
course,
plenty of PICs !).

Somebody knows the typical (?) cutoff frequency of the microphone and the
loudspeaker ? This one does not seem to have mobile parts. Is it
piezoelectric ?
I am ashamed to admit that I bought both of them two weeks ago and I
don't know what I got for my money :-(. Anyway I think that perhaps the
easiest
thing to do is to emit differenet frequencies with the loudspeaker, get them
with
the micro and make some kind of Bode diagram of the set....

Somebody has done some kind of tone decoder with a 567 ? How long does it
take to
catch a given frequency ? Is this time always the same ? If it is not the
same,
the idea of sending a sound burst and computing distance through sound delay
won't be feasible...

As you can see, I have plenty of questions. If anybody could give me some
clue,
I would be grateful forever !

Cheers

Joan

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