Detailed PIR information?

Clock Loop

I would like to know what the thermal limitaitons are for your new PIR unit.

It would be nice to know the max/min temps the unit will operate in. Also knowing the humidity limits would help.
Do these have a warrantee of any kind? [noparse]:)[/noparse]

Post Edited By Moderator (Chris Savage (Parallax)) : 1/13/2006 9:04:19 PM GMT

Jon Williams

These are not intended for commercial use -- it sounds like you may want to consider a PIR unit from a security system vendor that can provide you with those details and assurances.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

Clock Loop

Heh, I was just thinking of using some of these units around the outside of my home. It gets up to 100degF max here, and as low as 5 degF wintertime.
The sensors lens would be exposed to the brunt of the temp.

Thats why I was questioning.

Jon Williams

I don't think the temperature is a problem so much as the enclosure -- ours is kind of hobbyist packaging and may not be suited for unprotected environments. If you're app isn't critical, it won't cost much to give it a try.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

LoopyByteloose

I have a few more 'industrial' PIRs that come in a metal can, but they do not have the logic circuitry. You have to add it.
Also, while they can range out to 30 meters, it is done by a special Fresnel Lens that that has foreground, middle ground, and far lenses all in one multiple package.

Operating temperatures -20 degrees Centigrade to +60 degress Centigrade
Storage temperatures -35 to +80

I started to assemble one, and found out that soldering is a bit more tricky.
Since they are heat sensitive devices, they SHOULD NOT be soldered complete flush against the board. They need to stand off about 3/8".
Also when soldering, and appropriate heatsink connected to the lead between the device and the board should be inplace.
Apparently damage may occur.

These can sense actually if the motion originates from either left or right [noparse][[/noparse]if rotated 90 degrees that could be up and down].

Parallax's devices are very handy [noparse][[/noparse]because you don't have to add op amps and digital logic], but seem to be designed for interior motion detection in a room - probablly for use as an automatic light switch and/or occupant present. In pairs, they could give you the direction.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

pjv

Hi Kramer;

With simple minded, that is single sensor element PIR's, the motion detection method is actually very clever...... it's really only possible because of the Fresnell Lens.

If the lens were removed, then the bare slab of heat sensing silicon does just that; sense heat. A person (heat source) standing in front of it, and moving somewhat from one side to the other would not be detectable because the same heat is falling on the sensor. Moving closer or farther away will produce SOME output, but not optimal.

What the lens does with its multi-faceted sections, is it alternately focus the heat onto or off the sensor, depending on your location relative to the field of view of each of the Fresnell lens elements. Then, as there is side-to-side motion of the heat source, this has the effect of turning a relatively steady IR level into a wildly fluctuating AC signal readily amplified by an (easy to build) AC coupled amplifier, and hence detection of side to side motion.

This same effect also greatly enhances the signal when forward/backward motion is detected, because as far as the sensing element behind the lens is concerned, one moment the heat source is there, and the next moment its not. This also makes it nearly impossible (for the better units) to slowly "sneak up" on it to foil detection.

Very simple, yet very clever indeed!

Cheers,

Peter (pjv)

LoopyByteloose

The PIRs have actually two coupled sensors in them and detect a magnitude of motion. Thermopiles are the devices [noparse][[/noparse]which are similar] that detect a magnitude of heat.

Parallax's PIR has a 'single bit output' whereas I can configure a 'two bit or left/right output' Also, the circuitry allows for adjustment of sensitivity. That would require an array of two or more Parallax PIRs that were appropriately aligned.

I bought these 'cheap' at about $3USD each, but I suspect that in the USA they might cost $30-50USD. Here they seem to be an overstock of a surplus item, so they are prices 'to move'.

I presume that you can omit the 'compound' Fresnel Lens and create single lens optics that are taylored to a particular robot's field of vision. Originally someone wanted a robot that would follow their dog. I don't think the Fresnel Lens that I have will really do that well. They appear to be a 'bug's eye' that will detect motion anywhere withing the field. Mine has a single panel of three rows of Fresnel Lens and each has more than one in order to creat a very wide angle of vision.

With the compound Fresnel, it is optimized for triggering on movement, but the movement from left to right or vise versa could start anywhere in the field of vision. A single lens would recognize when an object entered and left the actual field of vision [noparse][[/noparse]more definite information].

Of course if you have more than one object withing the field of vision, the data gets muddled. There are PIR arrays, but then you are talking quite a bit of money and I suspect you might have to justify what you are doing as they might be specific for military use.

[noparse][[/noparse]So much of our modern life style has evloved from products originally for military - ie., air conditioning, the internet, etc.]

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

gibbman

Not to get toooo far off the PIR topic, if you have an interest is some REAL Fresnel lenses, your attention is invited to:
http://www.lighthouseratings.com/Lens/
Have one about 4 miles across the water from me in the Currituck Light.
Jim