Subject:
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Re: Barcodes & error detection
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 8 Sep 2005 12:39:48 GMT
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Viewed:
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1159 times
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In lugnet.robotics, Philippe Hurbain wrote:
> Error correction is good, but no error
> is probably better...
Absolutely, but in any real world application there is almost always some
error rate.
> > a '1' (black)... read as a '0' (white).
>
> This may be caused by specular reflexion on a
> too shiny black stripe. We had that problem...
> solved by tilting the light sensor...
John Barnes also suggested that to me after I posted, and I'm embarassed to
admit that the thought hadn't occured to me. I need to test (again), but there
are at least two reasons why I'm not overly optimistic on this being the
solution. First, there is slight variation in the barcodes themselves that may
negate this (light sensor inclined 2 degrees to the west will still be
perpendicular if a section of the barcode is inclined 2 degrees to the west;
rare, yes, but the error rate is already only 3%). Second and more critically,
to distinguish all three "colors" (white, black, and highly reflective) the
reflective "shiny" tape needs to give as bright as return as possible -
essentially that same shiny, specular reflection that needs to be avoided at
other times.
Using retroreflective white tape or reflective but slightly diffusive tape
(an aluminum duct tape slightly crinkled and flattened again; I tried it as flat
as possible as well) would seem to work, but actual tests show that it often
can't be distinguished from white.
--
Brian Davis
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Message has 3 Replies:
 | | Re: Barcodes & error detection
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| (...) Are you lighting the area with a light brick, or relying on ambient illumination? I find the Lego light sensor extremely finicky in "real work" situation, and try to always shield the area from ambient and provide my own illumination. -Rob A> (19 years ago, 8-Sep-05, to lugnet.robotics)
| | | Re: Barcodes & error detection
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| "Brian Davis" <brdavis@iusb.edu> wrote in message news:IMI0IC.z2M@lugnet.com... (...) I'm just curious, but how much development did you do making the area where the light sensors themselves are mounted as black and light-proofed as possible to (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
| | | Re: Barcodes & error detection
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| (...) I had in mind a steeper angle - let's say 20-30°. Light sensor optics is very primitive!!! (...) Serious objection... From my laser sensor experience, I tend to think that retroreflective tape would work well, but maybe not enough to separate (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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Message is in Reply To:
| | Re: Barcodes & error detection
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| Hello Brian, Error correction is good, but no error is probably better... (...) This may be caused by specular reflexion on a too shiny black stripe. We had that problem during the Billund AFOL mindstorms competition, it was solved by tilting the (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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