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Re: Reflected Signal Problem
On Thu, Nov 25, 1999 at 10:13:43PM -0500, Joyce Poon wrote:
> From what I have been reading on the webpage, there are only certain
> frequencies you can modulate your signal to for the sensors to work
> (modulate = "key a certain frequency" in Tim language). IR sensors come
> in kits (an IR emitter + a detector&chip thing). I figure there aren't
Oh dear Joyce. You've been doing research again. :)
The thing about random IR interference, however, is that it's
more-or-less random. I hope... My hope is that it's possible to
partly handle this type of interference detection in the microcontroller,
but I need to know a lot more about the characteristics of the
interference, first... This is where experiment and trial & error
will come in handy...
> Hence, the signal
> frequencies of all the groups may actually be the same. (eg the Sharp
> model -- which seems to be very popular and widely available-- runs at
> 40MHz.) That's why I am slightly concerned about the reflected signal
> problem.
Hmm... I see. My earlier impression had been that we were to devise
this circuitry ourself. Reflected signals do become a more serious
problem if our frequency is the same as our enemy's... I guess first
we need to know what the actual ratio of available-freqences to total-
number-of-groups is.
After that, I can't think of anything better than your "bumper-level
detector" scheme. I'll note two things: 1) they don't really have to
be bumper-level (should be beacon-level), and 2) your suggestion
(see message-id: Pine.SGI.3.96.991124224315.11207809A-100000@skule.ecf)
that we simply decide a surface is reflective after bumping-into it
several times, is extremely unsatisfactory. I can outline the
reasons why, if requested, but you may be able to imagine a few of
the reasons...
What is the cost of an IR detector-emittor pair?
> Secondly, I think "interference" does not refer to intentional
> interference from other groups, but rather from electrical noise/light
Yes, that's my understanding too.
> shielding the motors. I don't think we have to worry about other groups
> deliberately interfering with beacon signals. Apparently, this is very
Yes, this is also what Malone indicated (if you were eavesdropping on
him carefully enough).
> hard to accomplish and I heard Malone said (to another group) that no
> groups had ever succeeded in interfering with beacon signals.
Which I see you were, too. :)
--
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