Art,

Geophones can easily put out several hundred millivolts depending on the
strength of the movement.
If you're looking for a sort of annunciator for a property, a geophone is a
good choice because it 
Requires no electrical power to run it.  Only mechanical power, which you
don't have to supply anyway.
The output can be connected to almost anything for use as a signaling
device.  If you were to connected 
It to an oscope for instance, and with a little practice, you can tell what
is coming onto your property.
Like a car, a truck, motorcycle, bicycle, etc.  You probably don't want to
get that sophisticated, but it
Can be done.

Regards,

Jim

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Art
Sent: Saturday, May 15, 2010 11:09 PM
To: Microcontroller discussion list - Public.
Subject: RE: [TECH]low power motor vehicle sensor

Hi Jim,

A large coil with a magnet suspended in it is also called a 
seismometer, single axis. It still needs power to run the 
electronics-which is costly because low power op amps tend to be 
noisy at the lower frequencies.

The seismometers I've seen and read about need amplifiers-is the coil 
on a geophone large enough so that an amplifier is not needed??? If 
so, it must be one wonkin' big mother of a coil!!!! By 'slightly' I 
think you must mean pico amps per volt-which is a bit more than 'slightly'.

I'll google geophone and see what I come up with.

Piezo cable and air filled hoses are not stealthy and are problematic 
in the winter, especially during plowing operations.

Regards,

Art




.
>Art,
>
>If you want a zero power ground tremor sensor, use a geophone.
>These are basically a coil suspended around d a magnet.
>Any movement causes the coil to move, generating a voltage.
>You can amplify the voltage slightly, and go from there.
>
>Jim
>
>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
>Art
>Sent: Saturday, May 15, 2010 9:40 PM
>To: piclist@mit.edu
>Subject: [TECH]low power motor vehicle sensor
>
>Hi All,
>
>I need suggestions for a low power (or zero power) detector for
>automobiles. It is for a rural site that is wooded, so all vehicles
>must pass along a relatively narrow driveway with lots of trees on
>both sides. So, it is relatively easy to conceal detection hardware.
>Since vehicles are relatively large masses of steel, the thought of a
>magnetic sensor came to mind. As a vehicle drives by the sensor, a
>change in the static magnetic flux is detected. I did some tests in
>my own driveway, and I can see a compass on the edge of the driveway
>move slightly as my John Deere lawn mower is driven past.  But, I
>can't figure out how to build something that is practical as anything
>I could build would be relatively high mass and I don't have a clue
>regarding how to get from 'concept' to a practical sensor.
>
>A sensor for detecting ground tremors might work, but I think those
>need more power than I'd prefer to use. If I have to power a sensor,
>I'd probably need it to draw less than 1 ma.
>
>The obvious answer is PIR, but in a wooded area, they false all the
>time and they do use much more power than I'd prefer. I'm not sure if
>the field of view for a PIR can be made narrow enough to minimize
>false alarms or not-but I have some PIR;s that have a 10 degree FOV,
>and it's not nearly narrow enough.
>
>Any suggestions from the group?
>
>Thanks,
>
>Art
>
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