Actually, there is another way to use PIR.

As a result of the Big Bang, in almost every direction there is a
constant but faint
deep red glow. If you purchase very sensitive PIR detectors, you can
detect a person
as he walks between the sky and the sensor (blocking) at several
hundred feet. Even works in daylight. You will need to search for the
most sensitive detector; I think only the Japanese
make them (Hammatsu-sp?).

--Bob

On Wed, Apr 1, 2009 at 9:15 AM, Marco Genovesi <carroz53@gmail.com> wrote:
>
> Olin, thanks for the PIR explanation!
> A bit more words for my question. I'm working on an unusual problem, that=
 is
> discovering airflow exiting
> from small rock cracks on a karst mountain. Caves entrances are often only
> small fissures opened in the rock surface and often
> hidden by soil debris but maybe evidenced due to the internal-external air
> circulation and temperature difference in some seasons
> (typically Summer and Winter). =A0In Summer cave air is generally more co=
ld
> than external and these "blowholes" can be detected
> due to the cold air flux. =A0My actual objective is to survey for these i=
n a
> somewhat large area mountain flank (rough, 0.5 square miles)
> and mapping them with a GPS. I have 2 surveying methods:
>
> 1) observing the area from distance (nearest is 600-800 feet)
> 2) recognizing directly on the terrain
>
> In case (1) I was considering a Thermal IR Camera but price is still
> excessive for me even for low-end models.
> IR Thermometers have a reasonable cost now =A0but from that distance (and
> without a view-finder and a very spot measue area) the results
> seems unreliable.
> Case (2) approach is the reason for which I have asked for the PIR sensor:
> walking with the PIR looking in ahead, and wait it triggers (a led or
> a sound) when sensing a temperature difference. I hope to have explained =
the
> context...
>
> regards,
> Marco
>
>
>
>
>
> ----- Original Message -----
> From: "Olin Lathrop" <olin_piclist@embedinc.com>
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Sent: Wednesday, April 01, 2009 2:35 PM
> Subject: Re: Re:[EE] Temperature detection with a PIR sensor
>
>
>> Jinx wrote:
>>> Think it might be. I tested some PIR circuits a few years ago and
>>> found that cold outside air blowing through the open door into a
>>> warm room was quite apparent on the 'scope and would have
>>> triggered the following logic/micro.
>>
>> Are you sure you were really measuring the air and not hard objects that
>> it
>> cooled down?
>>
>>
>> ********************************************************************
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>> (978) 742-9014. =A0Gold level PIC consultants since 2000.
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