Re: Private baby GPS

Another problem would be the gain changes required to receive
the pulse at distances from 1 to 30 meters.

I suspect limiting the range to something like 5 or 10 meters per
receive station would be cheaper under the score than making them
30 m capable, this may be pretty demanding. But then again, this
just my first feeling, I have not really worked on the idea.

However, using ultrasonic ranging over some tens of meters, you would
have to cope with ranging errors due to wind velocity. Sound velocity
in air is about 320m/second. Wind velocities could easily change
the velocity by 2 to 5%.

Yep, that's one of the problems one will have to deal with.

Another one I thought of is Doppler effect related - what if the kid
is very very naughty and runs lightning fast.... :-) :-) :-) (Sorry for
not
resisting that, I just pictured it and got carried away :-).

Dimiter

------------------------------------------------------
Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------

Mark Borgerson wrote:
In article <1162172555.289481.41090@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
giorgis.3erolas@xxxxxxxxx says...

Didi wrote:
Giorgis wrote:
I would like to be able to setup a private GPS like settup.
Lets say I have a garden. I would like to setup 4-5 transmitters on a
post at it's corners.

Then I would like to have a box that would indicate it's position with
relative high accuracy
with respect to the transmitters.

Any ideas ?

Regards
Giorgis

RF based devices will cover a larger area at a not so high accuracy.
If the garden is not that large - or at the cost of more receiver
stations - you can use a modulated ultrasonic transmitter to attach
to the naughty kid and detect its position very precisely (at least
until the kid does not get naughty enough to get rid of the tag... :-)

Dimiter


Hmmm ... intersting application ;-) I'd like to be able to use it
indoors.
I am hoping to get half meter accuracy or better. The hints are a start
...

Any other takers ? :-)

What type of accuracy can be expected with ultrasonic ?


I would expect that range measurements with an ultrasonic device
would be on the order of a few centimeters.

However, using ultrasonic ranging over some tens of meters, you would
have to cope with ranging errors due to wind velocity. Sound velocity
in air is about 320m/second. Wind velocities could easily change
the velocity by 2 to 5%.

Another problem would be the gain changes required to receive
the pulse at distances from 1 to 30 meters. For an isotropic
source, the energy received is going to vary ~ as the cube
of the distance.

Mark Borgerson

.

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