On Tue, Nov 18, 2003 at 10:29:20AM -0800, H.C. Croon enlightened us
thusly
> Declan wrote:
>
> > Can someone point me at decent reading about infared? I am looking
> > at a project involving infared detection, sunlight, and people.
> > Suffice it to say this is someone else's idea about which I am
> > instructed not to be specific.
> >
> > In this application, I ideally want to sense people with complete
> > sunlight rejection using infared. The 2 standard techniques -
> > Emitter Pulsing, and movement detection as used in home alarm PIR
> > detectors are unsuitable for various reasons. False positives are
> > basically unavoidable, and I can cope with that. I want to minimize
> > it, however. I don't want false negatives, however.
> >
> > Let me be more clear: I am not worried about the orb of the sun
> > creating a false positive. I AM worried about not picking up
> > something (i.e. a false negative) at 30 degrees right or left of it.
>
> Hi Declan,
>
> Although you gave a lot of details, something is still missing. When
> you detect the subject emitting IR, can it be that the sun is seen in
> allmost the same direction, so causing a blinding effect?
Yes. In that case I would expect to take the sun as the false positive
and am able to proceed. There's a limit to how many suns I'm likely to
encounter in 360 degrees ;-). My query only reveals a little of what's
going on.
>
> Is the subject, you want to detect, something technical, on which you
> can choose a modulation frequency (perhaps you want not to answer this
> question, which I will understand very well).
As I said, people, or large parts of them. I am scouring the place
without success for a sensible treatment of the general frequencies.
>
> Can the space angle which is covered by the subject be a
> discriminating feature?
Not realistically. I don't need distance information from IR. We're
thinking small/inexpensive with cpu, not large/technically complicated
>
> Can distance be a dicriminating feature? When you use 2 detectors, you
> have 3-dim information.
This gets complex, Harry. I'm not sighting on someone, you know. This is
safety, not military. I routinely turn down work for gambling and the
military.
>
> All these questions depend havily on what it is supposed to cost.
What I am looking for is reading to check the feasability. I need the
freauencies that everything emits. We all enjoy discussing the design
strategy, but I haven't given out enough info to get much help on that.
Where I need the help is a treatment of what frequencies things emit
(Particularly people and the sun).
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
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