Subject:
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Re: IR for bots
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 28 Mar 1997 06:01:19 GMT
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Original-From:
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Keith the wonder wookie <kas219@psu.edu{IHateSpam}>
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Viewed:
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1552 times
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At 08:19 PM 3/27/97 -0800, you wrote:
> > Or is it necessary to inject another frequency on the 40 Khz that can be
> > decoded? Then the output of the decoder (like a 567) is read by the HB.
> > I understand that tone encoding allows for multiple tasks on one
> > carrier, But my main interest here is for object avoidance.
>
> Our robot worked well with a dual 555 timer. 38KHz for the IR and
> combined with a 500 Hz square wave. When the square wave was high, 38K
> was on, making it a 50% duty cycle transmission. As I understand the
> receiver circuitry, it was tuned to 38K. Worked fine for us, but I
> don't know the correct answers to why 50%? Why modulate? Why not just
> straight 38K?
>
>
If you don't modulate the signal you run the risk of having another 40kHz
signal (a.k.a. remoth control) trigger the reciever. If you modulate it
and look only for you modulation code, then the chances of a stray signal
are minimal. I have been using a wall detection system that does not
modulate the signal simply for simplicity of design and I have not had any
major problems that would cause me to change my design. Godd luck.
Keith
Keith Soldavin
kas219@email.psu.edu
http://www.personal.psu.edu/users/k/a/kas219/
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Message is in Reply To:
 | | IR for bots
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| Hello everyone, My thinking (albeit limited), has been that simply driving an IR LED with ac (ie:40Khz) as opposed to static dc, is enough to discriminate it from other frequencies like 60 Hz. or whatever. Then, when the detector picks up sufficient (...) (28 years ago, 20-Mar-97, to lugnet.robotics.handyboard)
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