Movement/Vibration Detection

ceebee

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Jan 7, 2009, 9:11:27 PM1/7/09

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I am looking for a way to detect movement/vibration around a specific
area, using some type of sensor(s) that are buried under the ground.
I would like this sensor to activate an alarm when there is vibration
around it - such as digging, or vehicles driving, etc.

I have heard of sensors for house alarms that are buried in the ground
surrounding the house - could that be applicable? I thought about
seismographic equipment, but that might used for too big of a scale.

If anyone has information regarding this, or could point me in the
right direction, it would be appreciated.

Thanks.

Jasen Betts

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Jan 8, 2009, 2:51:08 AM1/8/09

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bury a multimode optic fibre. shine a laser in one end, put a video camera,
(or wiimote light-source sensor) at the output end look for changes.

Leon

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Jan 8, 2009, 5:50:38 AM1/8/09

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Geophones aren't very expensive, and will do what you want.

Leon

PeterD

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Jan 8, 2009, 9:48:52 AM1/8/09

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Since the OP is gmail and therefore blocked...

Is it important to reject false positives from sources outside the
perimeter you are protecting? Do you need to detect non-metallic as
well as metallic 'signals'.

If only metallic then there are lot's of wire loop detectors
available.

If non-metallic perimeter detection is necessary, then a double fluid
tube system would work, however such systems are more complex and
frequently require maintenance.

If you are only interested in area detection, and not perimeter
protection, then a geophone system would work just fine.

MooseFET

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Jan 8, 2009, 10:04:03 AM1/8/09

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Yes. I would suggest more than one geophone. A micro controller with
a multichannel ADC can digitize the signal from, lets say, three
geophones. The software can then do some simple processing to reduce
the response to things like earthquakes and increase the response to
activity within the area of interest.

The easiest system to think about is one with horizontal motion
sensing geophones in a row. These won't see much motion from a source
directly below. The speed of sound through the ground is close enough
to constant that you can exclude shock-waves that appear to be going
past the line of geophones. Sources within the area of interest will
get to the middle geophone before the ones on either end.

>
> Leon

RFI-EMI-GUY

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Jan 8, 2009, 11:40:13 PM1/8/09

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Hmm; Maybe I should put some in my backyard! With a bit of tweaking, you
could design a circuit to triangulate the location of the intruder and
direct a mini-gun equipped robot to dispatch him!

Simple detector circuit here:
http://www.discovercircuits.com/DJ-Circuits/geophone3.htm

Geophones are available surplus at a relatively low cost.

"Use only Genuine Interocitor Parts" Tom Servo ;-P

Herman

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Jan 9, 2009, 8:40:06 AM1/9/09

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"RFI-EMI-GUY" <Rhyo...@NETTALLY.COM> wrote in message
news:4966d52a$0$4894$9a6e...@unlimited.newshosting.com...

I have solved this problem with an ultrasonic receiver from a transmitter
receiver pair. With a simple amplifier I was able to detect a dog walking
on the lawn from 40 feet. This was developed to follow a flow of water to a
blockage in a sewer line.

MooseFET

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Jan 9, 2009, 9:16:30 AM1/9/09

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Others have used humans armed with side arms to do this sort of
thing. You need more geophones so that you get the location
information. The software involved uses an FFT of several thousand
points. A modest DSP is needed.