Art, Look at surplus dealers. I've seen them for just a few bucks at some surplus dealers on the web. Try WWW.EBAY.COM. There is a lot of 3 for about $30.00. I may have one or two laying around here. I'm cleaning out my lab, so if I run onto any, I'll set them aside. Regards, Jim -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Art Sent: Sunday, May 16, 2010 12:08 AM To: Microcontroller discussion list - Public. Subject: RE: [TECH]low power motor vehicle sensor 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 > > > >-- > >http://www.piclist.com PIC/SX FAQ & list archive > >View/change your membership options at > >http://mailman.mit.edu/mailman/listinfo/piclist > > > >-- > >http://www.piclist.com PIC/SX FAQ & list archive > >View/change your membership options at > >http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > >Checked by AVG - www.avg.com > >Version: 9.0.819 / Virus Database: 271.1.1/2875 - Release Date: > >05/15/10 02:26:00 > >-- >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist > >-- >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist > > > >Checked by AVG - www.avg.com >Version: 9.0.819 / Virus Database: 271.1.1/2875 - Release Date: >05/15/10 02:26:00 -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist