Hi Jim,

I just got back from a google search and got quite an education in a 
short time.

My guess is that a motor vehicle passing within 5 to 8 feet of one 
would be easily detectable and that I might just need a peak detector 
to trip an alarm transmitter.

What I haven't found yet is someone selling them for a reasonable cost.

 From my brief google tour, I think I need a relatively high 
frequency unit, in the 5 to 20 Hz range which is better suited for 
detecting more 'local' disturbances.

I'll keep looking.

Regards,

Art


>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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