Motion Sensor for moving cars

Discussion in 'The Projects Forum' started by LightAce, Nov 7, 2011.

  1. LightAce

    Thread Starter New Member

    Sep 19, 2010
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    My group and I are trying to figure out which motion sensor would be best capable of detecting a passing car moving at least 15-20mph. We were thinking PIR however it usually takes about 1.8 seconds for it to detect movement which is too long for a car moving at that speed.

    What would be the best motion sensor for this application?
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
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    Uh oh. Are you on the same side as the people behind this other thread, or are you competitors?

    http://forum.allaboutcircuits.com/showthread.php?t=61530

    I'm not too happy with a college design course that becomes a contest in who can get the best advice off Internet discussion groups. And I'd bet the prof wouldn't be either!
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
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    Time for some research. You can still use the internet and arrive at an answer, but you have to use your noggen. Start reading Datasheets!
     
  4. jbord39

    Member

    Mar 31, 2010
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    Since when is asking knowledgable people about a good direction not research? Anyway I am guessing we are the same group or going to different colleges.
     
  5. LightAce

    Thread Starter New Member

    Sep 19, 2010
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    I don't think we go to the same college. I have been looking at ultrasonic sensors like those used in radar guns but not sure if that's the most straightforward way of going about this. I just need help on moving in the right direction
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, radar guns were using KU-band pulse doppler radar; 18GHz range. They used to use X-band (9GHz) back in the 70's and 80's.

    Now there's LIDAR/LADAR, which makes it more difficult for motorists to detect their use.

    Stanley came out with a level that has a built-in laser "tape measure", good to within 1/4" at 100 feet. I can't help but wonder if that could be a candidate for hacking.
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Detecting a passing car, from what perspective? The car being passed, or from a bridge to see if two cars are moving in the same direction, with one moving faster than the other?

    There are some pretty cool designs for driver-less cars out there thanks to DARPAs $1 million reward (detail on wiki).

    Could you explain the full project a little more clearly than "detect a passing car 15-20mph", such as location of sensor, 15-20mph relative to what, what is defined as passing, etc?
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    I have been quite impressed with the performance of a driveway alarm that I purchased and installed a couple of years back. It uses a magnetic pickup along with interface circuit and a simple battery powered wireless transmitter. It does a darn good job of detecting the vehicle traffic that passes my driveway at 20 to 30 mph even though it is easily 10 feet away from the road.

    The device can be seen at www.mightymule.com. It is their driveway alarm product.

    hgmjr

    FIXED my typo in the URL per Sgtwookie's comment....
     
    Last edited: Nov 7, 2011
    SgtWookie likes this.
  9. hgmjr

    Moderator

    Jan 28, 2005
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    Thanks sgtwookie for the correction. Must pay better attention.

    hgmjr
     
  10. John P

    AAC Fanatic!

    Oct 14, 2008
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    Well well, look what's on the Sparkfun site:
    http://www.sparkfun.com/news/726
    Title: "Laser Tape Measure Hacking Challenge", dated 2011.11.07
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Hmm, I had no idea they were having a laser tape hacking challenge.

    Anyway, that laser I mentioned is too expensive for a project like this, and the risk factor is just too high.

    Hgmjr's post jostled my memory a bit; I'd seen a Vehicle Loop Detector earlier this year and had thrown it in a simulation; here's a link to the project description:
    http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm

    And here's the schematic:

    [​IMG]

    As far as the loop, what he's written on the schematic is 4 turns of wire in a 6' diameter loop; that calculates out to roughly 64uH; you'd need just under 76 feet of wire for such a loop. Even if you go to Radio Shack, that much wire will only run you around $7. It doesn't have to be any particular type of wire, either.
     
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