The 3 of 9 code
 

This code easy to use allows the coding of 43 characters : 10 digits, 26 capital letters, the symbols $ % + -. / and the space. The extend mode makes it possible to code the 128 ASCII characters ; in this mode characters added compared to the "simple" mode are coded with 2 characters.

Let's learn encoding system.

Each 43 character of the simple mode is composed with a fix pattern made up of 5 black bars and 4 white bars (space).
The bars can be fine or thick (the thick ones make 2,2 to 3 times the width of fines)
There are always 3 thick bars among the 9 bars
A fine white bar added to the end allows the separation with the following character.
A special character (Affected to the symbol *) is used as delimitor of beginning and end.
A checksum can be added; it is calculated by adding up the values of each character drawn from the following table, then by taking the remainder of the division of this sum by 43.
In the following table the narrow black bars are symbolized by "1", the thick ones by "111", narrow white bars by "0" and the thick ones by "000".
 

Exemple of checksum for : ZB65732
35 + 11 + 6 +5 +7 +3 +2 = 69
69 / 43 = 1, remainder 26 which corresponds to the letter Q
New code with the checksum : ZB65732Q

The extend mode.

The charaters not forming part of the simple mode are coded with one of the 4 prefix % $ / +  followed by a basic character according to the following table. To literally use the charaters which are used as prefix or the symbol * it will be necessary to use a coding on 2 characters.

Bar code making.

Since we can create the bar code pattern it remains us to draw it on the screen and to print it on a paper sheet. Two approaches are possible :

• The graphic method where each bar is "drawn" as a full rectangle. This method enable to compute the width of each bar with a one pixel precision and so we can work with widths which are perfect multiple of the used device pixel. This give us a good accuracy specially if the device have a low density as it's the case with screens and inkjet printers. This method require special programming routines and does not allow to make bar codes with a current software.
• The special font in which each character is replaced by a bar code. This method allow the use of any software like a text processing or a spreadsheet. (For example OpenOffice, the free clone of MSoffice !) The scale settings according to the selected size can bring away small misshaping of the bar drawing. With a laser printer there's no probs.

All the found 3 of 9 barcodes on the net (Incomplete demonstration font) aren't free, several times expensive, and with uncertain quality; the width module isn't always permanent  in the font definition. I've decided consequently to draw entirely a 3 of 9 font and to propose it for download. I test it on a laser printer with size 11, what gives a small barcode with a width of about 1,6 mm/car, result : reading at 100% ! On a good inkjet printer, we must go up to the size 15 what give a character width of 2,1mm.

The font " code39.ttf "

This font contain the 43 basic charactersand the delimitor under the symbol *. Each character ends with a fin white bar of separation.

Structure of a 3 of 9 barcode

A 3 of 9 barcode will be build up in the following way :

• A start delimitor symbolized by the character *
• As many characters as necessary, the characters of the extend mode will be prefixed.
• An end delimitor

A small program to test basic mode

This test program manages neither the extend mode nor the checksum.

The Code39$ function can be re-used in any other program written with Visual BASIC 6; it can also be copied just as it is in a VBA macro linked to an Excel or Word document.

Public Function Code39$(chaine$)
  'V 1.0.0
  'Parametres : une chaine
  'Parameters : a string
  'Retour : * une chaine qui, affichee avec la police CODE39.TTF, donne le code barre
  '         * une chaine vide si parametre fourni incorrect
  'Return : * a string which give the bar code when it is dispayed with CODE39.TTF font
  '         * an empty string if the supplied parameter is no good
  Dim i%
  Code39$ = ""
  If Len(chaine$) > 0 Then
  'Verifier si caracteres valides
  'Check for valid characters
    For i% = 1 To Len(chaine$)
      Select Case Asc(Mid$(chaine$, i%, 1))
      Case 32, 36, 37, 43, 45 To 57, 65 To 90
      Case Else
        i% = 0
        Exit For
      End Select
    Next
    If i% > 0 Then
      Code39$ = "*" & chaine$ & "*"
    End If
  End If
End Function

Since the first publication of this page, I'd received numbered versions in different languages :