Archived question

Why won't my bar code scan? It looks fine to me.
This is almost always a printing issue. Most likely your problem is one of the following:

Over printing
Thermal and thermal transfer printers have adjustable burn times and temperature settings. People are always cranking these up, thinking the blacker the image, the better. The best way to spot over printing is to look at a narrow space between two wide bars. If your printer is putting down too much ink, the wide bars will expand, shrinking the narrow space. The narrow space should be the same width as the narrow bars; adjust your printer until they are the same.

Missing Start or Stop Code
All bar codes have unique start/stop patterns. Code 128 complicates this by having three different start patterns, but only one stop pattern. Take a look at the Code 39 character set for the start/stop (which are the same) code, the 128 spec, the Interleaved 2 of 5 spec, and the UPC spec. This is often caused by improperly using a font to generate a bar code. This is a problem where a verifier can't help, you'll have to figure it out for yourself.

Insufficient White Space
Bar codes must have white space on each side of the symbol. The spec is usually 1/10 of an inch or ten times the narrow bar, which ever is lesser. Note that some manufacturer's scanners are more sensitive to white space issues than others.

Inaccurate printing
Some printers, especially dot matrix printers, can print inconsistent bars and spaces. The bars and spaces within a symbol should not vary. This issue can also be seen with laser printers when cutting and pasting bar code, due to resolution matching problems. If your bars and spaces vary a lot, the scanner won't be able to read them.

Good luck.

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