'Argumentos:
'Numero = Valor que deseamos convertir en texto
'Estilo = Formato de salida
'           1 = MAYUSCULAS
'           2 = minusculas
'           3 = Tipo Titulo
'Los valores negativos los convierte a positivos
'El valor minimo en 0, el valor maximo es  9,999,999,999,999.99

Public Function NumLetras(ByVal Numero As Double, ByVal Estilo As Integer) As String
  Dim NumTmp As String
  Dim c01 As Integer
  Dim c02 As Integer
  Dim pos As Integer
  Dim dig As Integer
  Dim cen As Integer
  Dim dec As Integer
  Dim uni As Integer
  Dim letra1 As String
  Dim letra2 As String
  Dim letra3 As String
  Dim Leyenda As String
  Dim Leyenda1 As String
  Dim TFNumero As String
        
  If Numero < 0 Then Numero = Abs(Numero)

  NumTmp = Format(Numero, "000000000000000.00")        'Le da un formato fijo
  c01 = 1
  pos = 1
  TFNumero = ""
  'Para extraer tres digitos cada vez
  Do While c01 <= 5
    c02 = 1
    Do While c02 <= 3
      'Extrae un digito cada vez de izquierda a derecha
      dig = Val(Mid(NumTmp, pos, 1))
      Select Case c02
        Case 1: cen = dig
        Case 2: dec = dig
        Case 3: uni = dig
      End Select
      c02 = c02 + 1
      pos = pos + 1
    Loop
    letra3 = Centena(uni, dec, cen)
    letra2 = Decena(uni, dec)
    letra1 = Unidad(uni, dec)
            
    Select Case c01
      Case 1
        If cen + dec + uni = 1 Then
          Leyenda = "Billon "
        ElseIf cen + dec + uni > 1 Then
          Leyenda = "Billones "
        End If
      Case 2
        If cen + dec + uni >= 1 And Val(Mid(NumTmp, 7, 3)) = 0 Then
          Leyenda = "Mil Millones "
        ElseIf cen + dec + uni >= 1 Then
          Leyenda = "Mil "
        End If
      Case 3
        If cen + dec = 0 And uni = 1 Then
          Leyenda = "Millon "
        ElseIf cen > 0 Or dec > 0 Or uni > 1 Then
          Leyenda = "Millones "
        End If
      Case 4
        If cen + dec + uni >= 1 Then
          Leyenda = "Mil "
        End If
      Case 5
        If cen + dec + uni >= 1 Then
          Leyenda = ""
        End If
      End Select
            
      c01 = c01 + 1
      TFNumero = TFNumero + letra3 + letra2 + letra1 + Leyenda
      
      Leyenda = ""
      letra1 = ""
      letra2 = ""
      letra3 = ""
  Loop
       
  If Val(NumTmp) = 0 Or Val(NumTmp) < 1 Then
    Leyenda1 = "Cero Pesos "
  ElseIf Val(NumTmp) = 1 Or Val(NumTmp) < 2 Then
    Leyenda1 = "Peso "
  ElseIf Val(Mid(NumTmp, 4, 12)) = 0 Or Val(Mid(NumTmp, 10, 6)) = 0 Then
    Leyenda1 = "de Pesos "
  Else
    Leyenda1 = "Pesos "
  End If
  
'  '***************************************************************
'  'Nota: la funcion StrConv solo funciona en Excel2000 en adelante
'  'si es tu caso, usa el siguiente codigo
'  TFNumero = TFNumero & Leyenda1
'  Select Case Estilo
'    Case 1
'      TFNumero = UCase(TFNumero)
'    Case 2
'      TFNumero = LCase(TFNumero)
'    Case Else
'      TFNumero = Application.WorksheetFunction.Proper(TFNumero)
'  End Select
  
  TFNumero = TFNumero & Leyenda1
  Select Case Estilo
    Case 1
      TFNumero = StrConv(TFNumero, vbUpperCase)
    Case 2
      TFNumero = StrConv(TFNumero, vbLowerCase)
    Case Else
      TFNumero = StrConv(TFNumero, vbProperCase)
  End Select
  
  TFNumero = "(" & TFNumero & Mid(NumTmp, 17) & "/100 M.N.)"
            
  NumLetras = TFNumero
    
End Function

Private Function Centena(ByVal uni As Integer, ByVal dec As Integer, _
                         ByVal cen As Integer) As String
Dim cTexto As String

  Select Case cen
    Case 1
      If dec + uni = 0 Then
        cTexto = "cien "
      Else
        cTexto = "ciento "
      End If
    Case 2: cTexto = "doscientos "
    Case 3: cTexto = "trescientos "
    Case 4: cTexto = "cuatrocientos "
    Case 5: cTexto = "quinientos "
    Case 6: cTexto = "seiscientos "
    Case 7: cTexto = "setecientos "
    Case 8: cTexto = "ochocientos "
    Case 9: cTexto = "novecientos "
    Case Else: cTexto = ""
  End Select
  Centena = cTexto
    
End Function

Private Function Decena(ByVal uni As Integer, ByVal dec As Integer) As String
Dim cTexto As String
  
  Select Case dec
    Case 1:
      Select Case uni
        Case 0: cTexto = "diez "
        Case 1: cTexto = "once "
        Case 2: cTexto = "doce "
        Case 3: cTexto = "trece "
        Case 4: cTexto = "catorce "
        Case 5: cTexto = "quince "
        Case 6 To 9: cTexto = "dieci"
      End Select
    Case 2:
      If uni = 0 Then
        cTexto = "veinte "
      ElseIf uni > 0 Then
        cTexto = "veinti"
      End If
    Case 3: cTexto = "treinta "
    Case 4: cTexto = "cuarenta "
    Case 5: cTexto = "cincuenta "
    Case 6: cTexto = "sesenta "
    Case 7: cTexto = "setenta "
    Case 8: cTexto = "ochenta "
    Case 9: cTexto = "noventa "
    Case Else: cTexto = ""
  End Select
  
  If uni > 0 And dec > 2 Then cTexto = cTexto + "y "
    
  Decena = cTexto
  
End Function

Private Function Unidad(ByVal uni As Integer, ByVal dec As Integer) As String
Dim cTexto As String
  
  If dec <> 1 Then
    Select Case uni
      Case 1: cTexto = "un "
      Case 2: cTexto = "dos "
      Case 3: cTexto = "tres "
      Case 4: cTexto = "cuatro "
      Case 5: cTexto = "cinco "
    End Select
  End If
  Select Case uni
    Case 6: cTexto = "seis "
    Case 7: cTexto = "siete "
    Case 8: cTexto = "ocho "
    Case 9: cTexto = "nueve "
  End Select
  
  Unidad = cTexto

End Function