 | | Barcodes & error detection —Brian Davis
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| | | Some of you at BrickFest may have seen Gus, a small robotic forklift that was one of my GBC modules. Gus had two problems at BrickFest. First, while the codereading task was 98% accurate, that still means on average once every 16 circuits of the (...) (19 years ago, 7-Sep-05, to lugnet.robotics)
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| | | | | Re: Barcodes & error detection —
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| | | | | (...) One suggestion that may improve your reliability is to use colour transitions rather than just colours. This would mean, however, that you would need more strips. For example, if you currently represent B=0 and W=1 your barcode for 0110 would (...) (19 years ago, 7-Sep-05, to lugnet.robotics)
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| | | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | | | (...) I actually started out this way, before getting lost in the number of combinations. After you suggested it, I may actually reconsider, because: (...) Perhaps less; right now the reflective strips don't really encode information, they just (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | Re: Barcodes & error detection —Kevin L. Clague
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| | | | | (...) Right off hand I don't know any checking mechanism that works best with false readings of one polarity. Do you know anything about Error Correction Codes? ECC is used to detect and correct single bit errors, it can also detect double bit (...) (19 years ago, 7-Sep-05, to lugnet.robotics)
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| | | | | Re: Barcodes & error detection —Rob Roschewsk
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| | | | | Thanks, you actually made me pull out one of my old comp sci texts :-) I remembered studying this stuff many moons ago .... Error detecting requires a "distance" between codes of at least TWO ... what this means is to detect a single bit error each (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | Re: Barcodes & error detection —Steve Baker
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| | | | | (...) Well, there is a sharp distinction between error DETECTION and error CORRECTION. It's also important to characterize the errors you are getting. Are you getting single bit errors or multi-bit errors? You will certainly need to use more bits in (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | | | (...) Agreed, and, for this application, the bit overhead to allow on-board correction is probably just not worth it. After all, if an error is detected, the forklift can always back up and try to read the barcode again. (...) Almost exclusively (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | Re: Barcodes & error detection —Philippe Hurbain
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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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| | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | (...) Absolutely, but in any real world application there is almost always some error rate. (...) 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 (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | | 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)
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| | | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | | | (...) Gus uses two ight sensors, one to follow the (left edge) of a black line on a white background, and a seperate light sensor on an "outrigger" to read the barcodes. There is no light brick, but instead both use the light sensor itself to supply (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | | Re: Barcodes & error detection —Geoffrey Hyde
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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)
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| | | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | | | (...) I'll have to take some small photos and post them to my Brickshelf account, and I should really include seom response curves from the various lightsensors so you can "see" what the sensor is seeing during a barcode read. (...) Hmmm. I'm not (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | | | | Re: Barcodes & error detection —Anders Isaksson
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| | | | | | (...) Maybe by having every barcode begin and end with the same 'prefix' and 'suffix' sequence (prefix <> suffix)? It takes more bits, but if you manage to read the prefix and the suffix correctly (as you know what they should be) you could be (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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| | | | | | Re: Barcodes & error detection —Philippe Hurbain
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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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| | | | | | Re: Barcodes & error detection —Brian Davis
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| | | | (...) Oh. I'd not thought of that at all. At those angles, the shroud design and the size of the "window" the light sensor can see through get to be tougher problems. (...) It may be because a good retroreflector won't work in this situation - the (...) (19 years ago, 8-Sep-05, to lugnet.robotics)
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