That is a common way for positioning information for dynamic positioning
systems used for oil rigs and offshore supply boats in the oil fields.  Look
for acoustic positioning systems on Google and you will get some more
information.  Kongsberg is one maker.  Speed of sound is different in the
water of course.

Brian Kraut
Engineering Alternatives, Inc.
www.engalt.com

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of M. Adam Davis
Sent: Thursday, January 10, 2008 1:46 PM
To: Microcontroller discussion list - Public.
Subject: [EE] Audio Positioning System (GPS with sound instead of radio)


I've seen the occasional topic on the piclist with this general idea,
but quick searches on the internet don't show that anyone has
succeeded in creating (or opening their hardware/software/notes)

So I'm thinking about making a simple a positioning system using a few
speakers (sounders) placed about the room with a hand-held receiver
that simply times the reception of each sounder's pulse.

To aid in simplicity, the pulses from the sounders will not contain
any coding, will be within human audio range (so cheap speakers and
mics can be used, as well as being a useful demonstration for
listeners), and the sounders will talk to each other via wire so clock
skew doesn't happen over time.  Pulses will be sent out about once a
second, short enough and with long enough gaps inbetween each that
they will never overlap in the region of interest nor will reflections
be an issue (receiver ignores pulses coming too quickly after the last
pulse).

All the receiver has to do is time the pulse reception relative to
each other of the 3 or 4 sounders, and then perform some simple
trigonometry.  4 sounders would allow the receiver to either recover a
clock, or altitude.  Location of the sounders would be fixed in the
receiver so the firmware has to be changed for a different
configuration (simple, easy to develop, I'll complexify later if
desired)

With tones in the kHz range it seems that a very quick & cheap APS
(audio position system) could be made with gross resolution measured
in feet (at least 10 feet, which isn't much since most demonstration
rooms would be smaller than 40x40, but it would be a start and would
give enough information on where to tweak it.)  Again, complexity
could be added in stages - zero crossing/phase detection, information
encoded in the pulses, etc can improve resolution, accuracy, ease of
deployment, etc.  For now, KISS.

At any rate, I'm no analog guru.  I was planning on amplifying the mic
and filtering it for a particular frequency before doing some sort of
AGC/envelope/ASK sensing scheme.  Perhaps mostly in software (ADC) as
future tweaking would benefit from that.  It's been a long time since
my DSP classes though...

What suggestions/ideas/concepts do you have now that you've read
through this?  Keep in mind I want the first iteration to be as simple
as possible while still getting some positioning information on the
receiver.

-Adam

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