Option Explicit

Private Const LOWER_BOUND As Integer = 48
Private Const UPPER_BOUND As Integer = 90

Private Sub Timer1_Timer()
Text1.Text = Text1.Text & CreateRandomChar
End Sub

Private Function CreateRandomChar() As String
Dim intAscii As Integer

Do
intAscii = Int((UPPER_BOUND - LOWER_BOUND 1) * Rnd LOWER_BOUND)
Loop While (IsAlphaNumeric(intAscii))

CreateRandomChar = Chr(intAscii)

End Function

Private Function IsAlphaNumeric(ByRef intAsc) As Boolean

If (intAsc > 47 And intAsc < 58) Or (intAsc > 64 And intAsc < 91) Then
IsAlphaNumeric = False
Else
IsAlphaNumeric = True
End If

dim num as integer
dim letter as integer