Monday, February 28, 2011

Barcode Check Digit Validation

Boxes we send out to the Annex need to be barcoded before we can send them. I like to have that barcode linked to the box data in our Collections Management Database, aka KIDB. However, we have only one barcode scanner and sometimes must key in barcodes manually. I needed to validate the barcodes.

On our Box Inventory form there is an Add Barcode button which brings up an input box for the barcode. Here is the code behind that button:

Private Sub cmdBarcode_Click()

     Dim strBar As String           'Variable for the barcode
     Dim strCheck As String       'Variable to hold the output of CheckDigit()

     'Pick up barcode from input box.
     strBar = InputBox("Enter Barcode", "Barcode")

     If strBar = "" Then
          Exit Sub
          strCheck = CheckDigit(strBar)
          'Debug.Print dblBar
          'Test the calculated check digit against the check digit enter with the barcode.
          If strCheck = "Barcode Valid" Then
               MsgBox (strCheck)
               'Code here to do whatever it is you want with the valid barcode.
               MsgBox (strCheck)
               'Reopen barcode input box.
               Call cmdBarcode_Click
          End If
     End If

End Sub

You will note that this doesn’t appear to do much. The real action is in the function CheckDigit(). You could put the code from CheckDigit() into the button’s OnClick event, but I prefer to put it in a module so that I can easily import it into other databases. In fact I tend to park any functions I might use elsewhere in a module I call BasicFunctionsRDM. You can place this code in any module you like.

Public Function CheckDigit(strBar As String)
'Copyright 2009 Cornell University Library.
'This code was originally written by Randall Miles, Technical Services Archivist.
'Kheel Center for Labor-Management Documentation and Archives.
'227 Ives Hall
'Cornell University
'Ithaca, NY 14853-3901
'Phone: 607-255-3183
'Fax: 607-255-9641
'You are free to use this code for any non-commercial purpose 
'provided this copyright notice is left unchanged.
'To use this code for a commercial purposes contact 
'Cornell University Library to obtain permission.
'This function verifies that the Codabar type barcode, 
'the type commonly used in libraries, is correct.

     Dim int01 As Integer       'Variable for first digit in barcode.
     Dim int02 As Integer       'Second digit.
     Dim int03 As Integer       'And so on.
     Dim int04 As Integer
     Dim int05 As Integer
     Dim int06 As Integer
     Dim int07 As Integer
     Dim int08 As Integer
     Dim int09 As Integer
     Dim int10 As Integer
     Dim int11 As Integer
     Dim int12 As Integer
     Dim int13 As Integer
     Dim int14 As Integer        'Variable for the check digit in the barcode.
     Dim dblSum As Double    'Variable used to calculate the check digit.

     'Parse out the individual digits of the barcode.
     'Digits in the odd places (1, 2, 5, 7, 11, 13) are multiplied by 2.
     'Digits in the even places are not multiplied.
     'If any multiplied digit is greater than 9 subtract 9 from it.
     int01 = 2 * Mid(strBar, 1, 1)
     If int01 > 9 Then
          int01 = int01 - 9
          int01 = int01
     End If
     int02 = Mid(strBar, 2, 1)
     int03 = 2 * Mid(strBar, 3, 1)
     If int03 > 9 Then
          int03 = int03 - 9
          int03 = int03
     End If
     int04 = Mid(strBar, 4, 1)
     int05 = 2 * Mid(strBar, 5, 1)
     If int05 > 9 Then
          int05 = int05 - 9
          int05 = int05
     End If
     int06 = Mid(strBar, 6, 1)
     int07 = 2 * Mid(strBar, 7, 1)
     If int07 > 9 Then
          int07 = int07 - 9
          int07 = int07
     End If
     int08 = Mid(strBar, 8, 1)
     int09 = 2 * Mid(strBar, 9, 1)
     If int09 > 9 Then
          int09 = int09 - 9
         int09 = int09
     End If
     int10 = Mid(strBar, 10, 1)
     int11 = 2 * Mid(strBar, 11, 1)
     If int11 > 9 Then
          int11 = int11 - 9
          int11 = int11
     End If
     int12 = Mid(strBar, 12, 1)
     int13 = 2 * Mid(strBar, 13, 1)
     If int13 > 9 Then
         int13 = int13 - 9
         int13 = int13
    End If
    int14 = Mid(strBar, 14, 1)

     'Add digits 1 through 13 together.
     dblSum = int01 + int02 + int03 + int04 + int05 + int06 + int07 + int08 
     dblSum = dblSum + int09 + int10 + int11 + int12 + int13
     'Debug.Print dblSum
     'If the sum is evenly divisible by 10 then the check digit equals 0.
     'Otherwise take the remainder from the division add 
     'subtract it from 10 to get the check digit.
     If Right(dblSum, 1) = 0 Then
         dblSum = 0
          dblSum = Right(dblSum / 10, 1)
          dblSum = 10 - dblSum
     End If
     'Debug.Print dblSum

     If dblSum = int14 Then
          CheckDigit = "Barcode Valid"
          CheckDigit = "Invalid Barcode"
     End If

End Function

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