Subject:
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Re: how does a bar code reader work?
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Newsgroups:
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lugnet.robotics, lugnet.trains
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Date:
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Thu, 30 Dec 1999 14:06:14 GMT
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Viewed:
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958 times
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In lugnet.robotics, Guido Heunen writes:
> Hi,
>
> Can someone explain me how the bar code reader of the codepilot works.
> I figured out the basics, but I can not get to the clocking stuff. You can
> move either slow or fast over the bar codes to program the codepilot.
>
> I want to use the rcx to detect different trains by fixing a bar code under
> the engine and wagon chasis. With this, I hope to redirect trains to another
> track, stopping at stations, changing train composition etc...
Well I don't have the code pilot but at my previous job I worked on Warehouse
Control systems that were Bar Code intensive.
As I am sure you know a bar code is just a simple representation of letters
and/or numbers that are readable by a scanner. I have to mention this first
because you would not believe the number of people I ran into that thought a
bar code included information like prices, case quantity, item description,
etc.
We all know the common UPC symbol because it is on almost anything we buy now.
There are lot's of other types of barcode symbolizations out there including a
3D barcode that you have probably seen on UPS packages that looks kind of like
a bullseye with dots radiating out from the center.
Anyway to make a long story short every barcode includes some sort of start and
stop "bit" or charater so the scanner knows what the begining of the data is
and were the end is. Everything in between is data usually in the form of
numbers but in some cases can be letters.
Depending on the reader you need to be aware of a couple of things.
1. Pen reader. (From the pictures I think this is what the code pilot is)
you must scan the barcode from left to right perpendicular to the lines of the
barcode. I find these a bit tricky and unreliable at times because it is to
dependant on a human using the device properly. Although in theory speed does
not matter scanning extremely fast or very slow will not get allways get a good
scan.
2. Wide area beam. These usually have to be used at close range and are
fairly reliable. You will see these in lots of retail stores. They usually
detach from a mount so the clerk can hold the scanner right up to the barcode.
3. Scan Gun. These emit a wide beem of light that has to cover the barcode
completely from left to right to get a good read. These are great at long
range and depending on the quality of the gun they are very consistant. You
may have also seen these in retail stores. (Often Home Depot or Lowes has
these).
I hope this is what you wanted. If the Code Pilot does actually work like a
Pen reader I would not suggest it for your project because they usually have to
be in contact with the barcode and they are not 100% reliable for getting a
good scan the first time.
If you can find a way to incorporate a Wide area beam to your train that might
be the way to go because you don't need to be in contact with the barcode but I
assume the reader will be in close proximity to the barcode and these again are
pretty forgiving and reliable.
Eric K.
PS - Just got my first RCX for Christmas from my wife so I will probably be
joining some of the discusion here more in the near future.
The New England LEGO Users Group
http://www.nelug.org/
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Message has 1 Reply:
Message is in Reply To:
 | | how does a bar code reader work?
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| Hi, Can someone explain me how the bar code reader of the codepilot works. I figured out the basics, but I can not get to the clocking stuff. You can move either slow or fast over the bar codes to program the codepilot. I want to use the rcx to (...) (24 years ago, 30-Dec-99, to lugnet.robotics, lugnet.trains)
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