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
Driveway Motion Sensor
Apr 04, 2007
6 Replies
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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 |
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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
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