Codabar is an unusual code because when assigning static values to the character patterns, some of the characters are wider than others. There are 2 element widths defined, and each character contains 4 bars and 3 spaces. Each character is followed by a single narrow space to separate it from the next character. Each pattern begins and ends with one of 4 start/stop characters A-D.

Traditional Codabar defines different element widths for each of the characters in an effort to make all the characters have the same width. Rationalized Codabar uses the same patterns, but assigns only 2 element widths for wide and narrow. It is rationalized Codabar that is implemented here.

Codabar is commonly used in libraries and blood banks. Blood banks use the D stop character to indicate that the next barcode beginning with a D should be concatenated with the current barcode.

Here is the character pattern table. Wide & Narrow bars are denoted with W & N respectively, and similarly, wide and narrow spaces are denoted with w & n.

0: NnNnNwW -: NnNwWnN
1: NnNnWwN $: NnWwNnN
2: NnNwNnW :: WnNnWnW
3: WwNnNnN /: WnWnNnW
4: NnWnNwN .: WnWnWnN
5: WnNnNwN +: NnWnWnW
6: NwNnNnW A: NnWwNwN
7: NwNnWnN B: NwNwNnW
8: nwWnNnN C: NnNwNwW
9: WnNwNnN D: NnNwWwN


You can make a Rationalized Codabar barcode here. You can use your own start/stop letters, or omit them and the program will use A & B for you.

Codabar	Code 2 of 5	Code 3 of 9	Interleaved 2 of 5
Postnet	UPC	Code 128	Code 16k