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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi all. Despite going through this thing with a fine toothcomb, I can't find any PIR sensor. All that seems to be there is a blob chip, a couple of discretes and what looks like a CdS light sensor with a black cover. So can someone please tell me how it can possibly detect anything except light changes? I can trigger this thing reliably from 8 feet away just by walking past.
(they also have PIR "cameras" too that move when you walk past!)
regards, -A
"Bother" said Pooh, as someone dropped a paint scraper in the sub's reactor room...
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Some cheap devices that actually do trigger on abrupt light changes as people walk past.
There are many pyroelectric materials that gives a voltage when they are heated or cooled. Adding a filter in front that absorbs anything but deep IR will make them generate a small voltage when you walk past. Cheap detectors usually have thin film sensors that are cheap to make.
It is possible to do this with a peltier element by adding a high gain amplifier. IR temperature sensors are often specially designed peltier elements with a temperature sensor at the back. Then the voltage generated gives the temperature on the incoming radiation, assuming that the radiation spectrum is fairly average.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
The common sensors usually look similar to this:
The ones available from local supply have a square sensor chip in a metal can. The detection speed is somewhat limited, but more accurate than traditional sensors.
Registered Member #1394
Joined: Sun Mar 16 2008, 06:18PM
Location:
Posts: 111
If you looking for a PIR motion sensor you can get than at parallax or sparkfun, then you can get pic's and program them to sense when motion is detected.
In simplest terms my method requires programming.
If you don't want to program you can buy a motion detector like they use at stores that beep when you walk in to let them know that someone is there. I guess that you could modify one and hook it up to the speakers. These are not cheap tho, i $20 + they are a rip off when you could get a PIR motion sensor for $9.99 that can detect a person moving 20 feet away.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
hmm.. i had some success with a 12F675 here, however the main headache is the signal resolution which is inadequate even using the A-D at maximum resolution.
I can get some sort of faint reading (single bit changes) but not reliably. However a simple idea to increase the gain would be to derive a high voltage (15V or so) output via diode multiplier that is used to drive the sensor. Output then fed through a small tantalum capacitor to the PIC to filter out high frequency noise.
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Pound World "PIR" sensors??!!!
