Barcode end charactor

Barcodes are not a "fixed length" - there are several different types which encode a different number of digits (in fact, some can contain a whole load more than just digits: EAN128 can contain heaps of information if needed) and five digits is a "valid" barcode number (ish, it's supposed to be leading zero padded to a minimum of 8 digits, plus a checksum digit at the end)

I'm assuming that you are using a "standard" barcode scanner instead of making your own hardware? In which case, the data is almost certainly arriving as if it was entered from a keyboard, and that means that the TextChanged event will occur repeatedly as digits arrive - they don't all appear at once as if by magic, any more than they would if you actually typed the article number!

What I would do is check the documentation on your scanner (or talk to the manufacturer) and find out how to add "lead in" and "tail out" codes to the barcode data it sends - that way you can positively check the incoming data and identify where a barcode starts and stops using the KeyPress event, instead of relying on TextChanged to detect something.