[Tinyos-help] Sounder detector

Rene Desgagnes rene.desgagnes at gmail.com
Mon Sep 26 07:52:50 PDT 2005


Hello everyone,

                    I'm trying to do some ranging with four(4) Mica 2.
 I'm using the time of flight to estimate the distance between 2
motes.  To compute this distance, I use this equation :
Speed of Sound  *   time of flight  = distance between 2 motes.  To
evaluate the time of flight, I  take the sounder on mote #1 and the
microphone on mote #2.  I start an accurate timer on mote #1 and
immediately start the sounder.  When, on the mote #2, the
readToneDetector() function equals 0, I send a message to mote #1 then
I compute the time of flight with the timer.

My problem is that the readToneDetector() detects not only the
Sounder's sound but detects noise which has components at 4.3 KHz as
well.  Is there any way to filter the incoming sound from the
microphone to be sure that the mote hears the Sounder 4.3 KHz and not
noise ?

The best would be to sample the incoming sound from the Sounder but to
do that, I must sample at 2 * 4.3 KHz = 8.6 KHz to satisfy Nyquist's
Law.  Even if the mote is able to sample at this rate (I have only
seen post on the forum talking about 8Khz to be the max sampling
rate), the mica 2 doesn't possess enough memory space to store all
that data.

Thank you for your reply,

René Desgagnés



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