Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!sun-barr!cs.utexas.edu!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: How can I fool the motion sensors connected to our lights?
Summary: Infrared (IR) versus near infrared (NIR)
Message-ID: <3297@kitty.UUCP>
Date: 19 Jul 89 02:04:01 GMT
References: <1110.AA1110@americ> <163@swituc.UUCP>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 33

In article <163@swituc.UUCP>, root@swituc.UUCP (Admin) writes:
> > >I have just started work somewhere where the lights are controlled by a
> > >system of motion sensors-if nothing moves in a pre-determined amount of
> > > time the lights go off. I find this system most annoying as I am often
> 
> If the motion sensor is an infrared detector, which it probably is, try
> using a 755-type timer IC firing an IR LED once every few minutes, seconds,
> etc.  You can pick up all the parts at Radio Shack for under $10. including
> a small enclosure and battery to power it with.
> 
> I leave it up to the reader to design the (trivial) circuitry.

	While the circuit design is rather trivial, it is unlikely that the
circuit will work for the intended purpose.

	IR LED's of the variety you mention are near infrared (NIR) devices,
and typically have an emission wavelength ranging from 810 nm to 980 nm,
depending upon the particular LED specification.

	Passive infrared detectors (PIR) for use in security and energy
management systems detect MUCH longer wavelength IR, with typical spectral
sensitivity in the range of 2 to 12 microns (2,000 to 12,000 nm).  The
actual characteristics of these sensors depend upon the sensor manufacturer
and the bandpass of the protective cover.  The cover will, for example,
typically NOT pass any energy below 2 microns so as to preclude interference
from ambient light.  After all, the function of a PIR is to detect body heat,
and NOT be influenced by the effects of ambient light.  NIR is too close
to ambient light to be detected.

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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