USB barcode scanner?
palcibiades-first at yahoo.co.uk
Sun Nov 30 11:07:26 EST 2008
They are LED or Laser. The difference is range and fragility. The LED ones
have to be used much closer up to the code, like 6 inches, but they are very
robust. The Laser ones can be used quite a distance away, but don't drop
them. I prefer LED. They will get dropped.
As others say, the 'wedge' ones act like a keyboard, and need no drivers.
But, and it may not matter in your application, bear in mind that they send
the characters they read followed by either return or enter but not both.
This has a couple of consequences. If you allow keyboard entry of codes as
well, obviously you have to handle both enter and return. Also I had some
timing problems. I made caps D send mouseup to a Discount button. The user
wanted for the cashier to be able to either do discounts by just using the
reader, or alternatively, just using the mouse. Problem was that it sent
mouseup to the Discount button and then sometimes but not always then sent
return when the user was expected to first enter the amount of the
discount.... I fixed this by the brute force method of sending to an
invisible dummy button, waiting a fraction of a second, and then sending
mouseup on, so absorbing the enter.
Sarah's little stack was very useful in decoding what exactly the reader was
sending. If you want to handle some keypresses, this means that you know
exactly what is being sent and so you can harmonize the keyboard and the
kbarcode, if you can run Linux apps, is a great free package for generating
bar codes and printing bar code labels. Bear in mind that if you generate
labels in a word processor, like for a cash register laminated sheet, and
there are quite a few free bar code fonts out there that can be used for
this, you have to use start/stop characters, and these differ from Windows
to Linux, and I assume the Mac will be different as well. Its * for Linux,
and if I recall correctly its ! in Windows. You can find yourself staring at
the thing in frustration wondering why the shop label codes work perfectly,
but the ones you have just made up do not. This is probably why.
I found the really hard issue to be not so much this stuff, as the tradeoffs
you end up considering between convenience and security. Very hard to
strike the balance. You have to spend some time thinking like a thief and
craftily installing logs, and whatever you do you'll miss something.
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