Parallax motion detectors

JohnR2010

I have been testing the PIR Mini Sensor (#28033) in a battery powered Propeller project and it works great until I use it outside in the sun. I expected it to get false positives if direct sun is in its path so all is okay I was just testing. My question is do the other IR detectors #28032, #555-28027 work any better? I don't expect them to but I thought I would ask the forum.

This brings us to X-Band Motion Detector for outside usage. From reading the product guide it looks like it not only detects motion but also can report the speed of the device with the "frequency of the high/low signals". Can I tell if a target is approaching or leaving the detector? From reading the description I don't think I can. If not, can I put two of these units back to back pointed in opposite directions? Will the antennas require some type of minimum separation or a wave guide to direct the beam? I'm building a vehicle detector for my driveway and would like to know if a car is coming or going. To have the speed of the car is a huge bonus!!

GordonMcComb

Sunlight can have a modest effect on the sensor, but in any case you may need to point it down and not directly at the sun. Allow to settle 10-15 minutes (at least) before testing. PIR sensors work by comparing the difference in the heat focused onto a pair of side-by-side sensors. For the most reliable readings PIR sensors should be allowed to become acclimated to the temperature of their environment. Wind, thermal heat rising from concrete and asphalt, and swaying trees limbs are typical culprits of false triggering when used outdoors.

Can't answer the question about the X-Band motion detector. While it uses radar, the device didn't appear too hackable to use it for things like speed measurement.

I would think the most effective (reliability, cost) method would be to use loop detectors in the driveway. Old school, yes, but effective because of its simplicity. Two sensors could detect direction; three or more could also give you speed. Of course, this part works works when there's just one vehicle over the detectors.

JohnR2010

Thanks Gordon for the response. I didn't have my motion detector pointed towards the sun during the outside test. It was mounted to a rafter up inside my gazebo and pointed down to the wood floor, no moving branches nothing going in and out but an occasional chicken. I tested it outside for two days and at night no false detections but as soon as the sun reached the floor it started firing randomly about ever 5 minutes. It is now inside the chicken coop and is working like a charm so the detector is good and temperature isn't an issue. I just don't think it is usable out in the sun again I didn't expect to be.

I have a ground loop detector hooked up to my security system now that lets us know if a car is in the driveway. It has limited reach and is about useless during a storm. Any lightning strike within 10 - 20 miles will set it off.

I need a detector at the far end of the driveway about 2,500 feet away, it is going to be ZigBee based and solar powered I have all that covered. Now I'm just looking for the sensor (low current requirements as I'm limited on power). I would be open to interfacing with a ground loop sensor but I'm not interested in constructing one from scratch. If you know of one I can bury and interface easily with the Propeller let know I will take a look at it. Speed isn't a requirement but direction is. If there is a ground loop sensor I can employ I will get two of them and that will give me direction and allow me to filter out the lightening.

Thanks again for your time!

GordonMcComb

JohnR2010 wrote: »

I tested it outside for two days and at night no false detections but as soon as the sun reached the floor it started firing randomly about ever 5 minutes. It is now inside the chicken coop and is working like a charm so the detector is good and temperature isn't an issue. I just don't think it is usable out in the sun again I didn't expect to be.

I imagine it's from the heat radiating back up from the floor, not the light. PIRs are not sensitive to visible light, nor do they trigger from static infrared light. There must be a rapid change of this thermal radiation within its field of view for it to trigger. Sometimes these kinds of false triggers can be resolved by taking successive readings from two sensors, preferably not looking at the same exact spot, but still within the security zone you wish to cover.

I think I'd opt for the larger of the Parallax sensors if you aren't cramped for space. The lens is larger, so it collects more energy, but its field of view is slightly less. Note that unlike the ordinary outdoor PIR sensor on security lights, the Parallax PIR has an omnidirectional lens. Outdoor security lights have a "zoned" Fresnel lens so that the top of the field has a longer view. This way they can trigger more reliably without having to require the intruder to be standing right underneath the light!

You can find install-ready ground loop sensors from any outfit that deals with automatic gates (like that for apartment complexes), that sort of thing. A quick search also showed up a bunch on eBay for around $140-170. Installed properly it should not be susceptible to any but the most severe electrical storm. You will need two to detect direction. Interfacing to a Propeller will requiring looking at the specs to see what the sensor outputs. Some are just dry contact relay points, and others are designed to only interface with certain master systems.

Burying it would be easiest if your driveway is dirt; otherwise you'll need to get a cutter for the concrete or asphalt, then patch. Before doing that I'd strongly advise a reasonable amount of testing elsewhere on your property.