maybe some cheap microphone?
use it to sense only very low frequencies (I would say under 100 Hz? or =

even lower...)

   Bruno L. Albrecht
   Eng. da Computa=E7=E3o/06
   Falker Automa=E7=E3o Agr=EDcola Ltda.
   http://www.falker.com.br


Em 15/05/2010 23:54, jim escreveu:
> 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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