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).
Are talking about optical wavelengths? There are a lot of sites where
you can find solar spectra under different conditions.