Alt-BEAM Archive
Message #13464
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Sun, 16 Apr 2000 00:21:02 -0700
Subject: Re: A reply to Zoz ... and a challenge for advanced/bored BEAMers.
Tan wrote:
>
> I found This: http://www5.mediagalaxy.co.jp/smm/tech/b_2_5e.html
> Which is a Pyroelectric Infrared (PIR) Detectors (whatever that is)
> and can detect body heat, so the specs say.
Very nice, Tan. Thanks.
> Would it be useful to detect human/animal/predator, or would any
> IR detector do? (Do IR detectors detect heat anyway?)
Yes, with additional circuitry, that's exactly what these are used for
... typically in outdoor motion detectors.
IR detectors detect Infrared Radiation, and they detect heat indirectly.
The wavelength of the energy radiated by a hot object is an exact
function of its temperature -- the higher the temperature, the brighter
the light. Experienced blacksmiths can tell the temperature of a piece
of metal to within a few degrees by it's colour. At lower temperatures
(e.g. body temp), the colour is down in the infra-red range.
The problem with using an ordinary IR detector is that background
radiation can confuse the detector, which typically measures an average
temperature. The pyroelectric detector you found responds to a sudden
change in radiation / temperature. If you walk in front of one, the
higher temperature of your exposed (or lightly clad) skin moving across
its field of vision will trigger a response.
Now I need to hack a motion detector and figure out the rest of the
circuitry :)
Bruce
13465 Sun, 16 Apr 2000 00:44:10 PDT Re: A reply to Zoz ... and a challenge for advanced/bored BEAMers. beam@sgiblab.sgi.com "leif_ 74" IR stands for Infared. An infared detector uses infared_light_ (invisible to
the human eye) to detect objects. Example:
infared emitter |
| |
0 --------/|-wall
/ |
/ |
0 |
|
infared detector
It bounces infared light off of objects.
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