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Driveway Motion Sensor

Discussion in 'Electronic Design' started by Phil, Apr 4, 2007.

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  1. Phil

    Phil Guest

    Hello
    I purchased a unit a short time ago that is used to detect cars coming
    into my driveway , I think it works on IR motion sensing , it does let me
    know if a car or person comes down my driveway , the bad part is that the
    thing gives me so many false alarms , seems to be the most problem after the
    sun comes out very bright , I guess my question is in two parts , I cracked
    the detection unit open and found the detector , am wondering exactly how it
    does it thing and could I locate it in another container that is shielded
    better , also wonder if anyone has built or used one of the magnetic
    detectors that appear to be based on the metal detector principal , I hate
    to dig up and put a 6 ft. diameter loop in my driveway , as an old HAM
    operator , I have built a lot of IC projects and at $200.00 for commercial
    unit , I might just try , any comments would be appreciated.
    Phil Lohiser
     
  2. Wim Ton

    Wim Ton Guest

    Maybe one of these small magnetic field sensors(Philips, Honeywell). They
    are sensitive enough for a compass, so they will detect 1.5 tons of steel
    from a meter distance as well.

    Wim
     
  3. John

    John Guest

    Hi, Phil -

    I had one of those. They are PIR (Pyro Infra Red) sensors which are
    sensitive to IR emitted by warm-bodied critters. It is sensitive to the
    *movement* of the warm bodies. Deer, armadillos, rabbits, raccoons, dogs,
    cats, mice, and other creatures can set them off. Unfortunately, so will
    trees and their shadows when the former is swaying in the breeze. I think it
    is the moving contrast between heat (light) and no heat (shadow) that
    triggers it.

    Conversely, mine occasionally missed triggering on a car when the day was
    cold and overcast. I think it was because the skin temperature of the car
    was about the temperature of the surroundings.

    Try to aim it away from objects that move with the wind. Try to aim it
    higher than a critter. You may still get a trigger from a deer.

    Cheers,
    John
     
  4. John

    John Guest

    Hi, Phil -

    I had one of those. They are PIR (Pyro Infra Red) sensors which are
    sensitive to IR emitted by warm-bodied critters. It is sensitive to the
    *movement* of the warm bodies. Deer, armadillos, rabbits, raccoons, dogs,
    cats, mice, and other creatures can set them off. Unfortunately, so will
    trees and their shadows when the former is swaying in the breeze. I think it
    is the moving contrast between heat (light) and no heat (shadow) that
    triggers it.

    Conversely, mine occasionally missed triggering on a car when the day was
    cold and overcast. I think it was because the skin temperature of the car
    was about the temperature of the surroundings.

    Try to aim it away from objects that move with the wind. Try to aim it
    higher than a critter. You may still get a trigger from a deer.

    Cheers,
    John
     
  5. Jim Thompson

    Jim Thompson Guest

    Why not get one of those X-band door opener units.

    I can also imagine using some 40KHz ceramic resonators, one
    transmitting, one receiving... angle shot off the windshield ??

    ...Jim Thompson
     
  6. mpm

    mpm Guest

    Actually, it stands for "Passive Infrared".
    Yes, this technology is affected by direct sunlight.
    Outdoor units are available with special filters and/or software to
    overcome the problems associated with outdoor use. For example, the
    Optex VR-402 series.

    Those of us "old enough" to remember when gas stations used to pump
    the gas for you:

    They had a pneumatic bell setup which seemed to be low-tech, and quite
    reliable.
    You could emulate this with some hose stretched across the driveway.
    For the sensor, (instead of a bell), you could use a World Magnetics
    pressure switch (available from Digikey).

    Might look ugly (though, not to me at least), and would be much less
    headache than digging up the driveway.

    The magnetic loop sensors by the way, are suseptible to lightning
    damage if you live in such as area. Keep that in mind.

    -mpm
     
  7. Luhan

    Luhan Guest

    Hi,

    You could just buy one of those self-contained IR units used in half
    the small businesses in America. It runs on 110 volts and aims at a
    bicycle reflector. Just put it on posts across your driveway about 4
    feet off the ground.

    Luhan
    http://mondo-technology.com
     
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