Driveway Motion Sensor

the

cracked

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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

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

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

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

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

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

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