Random string function... not random

[BrinX]

hey
i am using the below function to generate a random string of x amount of charactors:

Function RandomString(ByVal mask As String) As String
    Dim i As Integer
    Dim acode As Integer
    Dim options As String
    Dim char As String
    
    ' initialize result with proper lenght
    RandomString = mask
    
    For i = 1 To Len(mask)
        ' get the character
        char = Mid$(mask, i, 1)
        Select Case char
            Case "?"
                char = Chr$(1 + Rnd * 127)
                options = ""
            Case "#"
                options = "0123456789"
            Case "A"
                options = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
            Case "N"
                options = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0" _
                    & "123456789"
            Case "H"
                options = "0123456789ABCDEF"
            Case Else
                
                options = ""
        End Select
    
        
        If Len(options) Then
            
            char = Mid$(options & Right$(options, 1), 1 + Int(Rnd * Len(options) _
                ), 1)
        End If
               
        Mid(RandomString, i, 1) = char
    Next

End Function

problem is every time i call the function it produce the same output each time.. not random at all