diff --git a/pyad2/ad2.py b/pyad2/ad2.py
index 865ad38..e7569be 100644
--- a/pyad2/ad2.py
+++ b/pyad2/ad2.py
@@ -65,7 +65,7 @@ class AD2Factory(object):
             device = cls.__devices[0]
 
         vendor, product, sernum, ifcount, description = device
-        device = USBDevice((sernum, ifcount - 1))
+        device = USBDevice(interface=sernum)
 
         return AD2(device)
 
diff --git a/pyad2/devices.py b/pyad2/devices.py
index d00ba5e..2ef56a0 100644
--- a/pyad2/devices.py
+++ b/pyad2/devices.py
@@ -167,18 +167,21 @@ class USBDevice(Device):
 
         :returns: the interface used to connect to the device.
         """
-        return (self._serial_number, self._endpoint)
+        return self._interface
 
     @interface.setter
     def interface(self, value):
         """
         Sets the interface used to connect to the device.
 
-        :param value: Tuple containing the serial number and endpoint number to use.
-        :type value: tuple
+        :param value: May specify either the serial number or the device index.
+        :type value: str or int
         """
-        self._serial_number = value[0]
-        self._endpoint = value[1]
+        self._interface = value
+        if isinstance(value, int):
+            self._device_number = value
+        else:
+            self._serial_number = value
 
     @property
     def serial_number(self):
@@ -219,21 +222,23 @@ class USBDevice(Device):
         """
         self._description = value
 
-    def __init__(self, interface=(None, 0)):
+    def __init__(self, interface=0):
         """
         Constructor
 
-        :param interface: Tuple containing the serial number and endpoint number to use.
-        :type interface: tuple
+        :param interface: May specify either the serial number or the device index.
+        :type interface: str or int
         """
         Device.__init__(self)
 
         self._device = Ftdi()
-        self._serial_number = interface[0]
-        self._endpoint = interface[1]
+
+        self._device_number = 0
+        self._serial_number = None
+        self.interface = interface
         self._vendor_id = USBDevice.FTDI_VENDOR_ID
         self._product_id = USBDevice.FTDI_PRODUCT_ID
-        self._device_number = None
+        self._endpoint = 0
         self._description = None
 
     def open(self, baudrate=BAUDRATE, no_reader_thread=False):
diff --git a/pyad2/tests/test_ad2.py b/pyad2/tests/test_ad2.py
index 0737a00..7715a7e 100644
--- a/pyad2/tests/test_ad2.py
+++ b/pyad2/tests/test_ad2.py
@@ -36,15 +36,15 @@ class TestAD2Factory(TestCase):
         with patch.object(USBDevice, 'find_all', return_value=[(0, 0, 'AD2', 1, 'AD2')]):
             device = AD2Factory.create()
 
-            self.assertEquals(device._device.interface, ('AD2', 0))
+            self.assertEquals(device._device.interface, 'AD2')
 
     def test_create_with_param(self):
         with patch.object(USBDevice, 'find_all', return_value=[(0, 0, 'AD2-1', 1, 'AD2'), (0, 0, 'AD2-2', 1, 'AD2')]):
             device = AD2Factory.create((0, 0, 'AD2-1', 1, 'AD2'))
-            self.assertEquals(device._device.interface, ('AD2-1', 0))
+            self.assertEquals(device._device.interface, 'AD2-1')
 
             device = AD2Factory.create((0, 0, 'AD2-2', 1, 'AD2'))
-            self.assertEquals(device._device.interface, ('AD2-2', 0))
+            self.assertEquals(device._device.interface, 'AD2-2')
 
     def test_events(self):
         self.assertEquals(self._attached, False)
diff --git a/pyad2/tests/test_devices.py b/pyad2/tests/test_devices.py
index cfcf21d..7e7c42f 100644
--- a/pyad2/tests/test_devices.py
+++ b/pyad2/tests/test_devices.py
@@ -34,8 +34,22 @@ class TestUSBDevice(TestCase):
             with self.assertRaises(CommError):
                 devices = USBDevice.find_all()
 
+    def test_interface_serial_number(self):
+        self._device.interface = 'AD2USB'
+
+        self.assertEquals(self._device.interface, 'AD2USB')
+        self.assertEquals(self._device.serial_number, 'AD2USB')
+        self.assertEquals(self._device._device_number, 0)
+
+    def test_interface_index(self):
+        self._device.interface = 1
+
+        self.assertEquals(self._device.interface, 1)
+        self.assertEquals(self._device.serial_number, None)
+        self.assertEquals(self._device._device_number, 1)
+
     def test_open(self):
-        self._device.interface = ('AD2USB', 0)
+        self._device.interface = 'AD2USB'
 
         with patch.object(self._device._device, 'open') as mock:
             self._device.open(no_reader_thread=True)
@@ -43,7 +57,7 @@ class TestUSBDevice(TestCase):
             mock.assert_any_calls()
 
     def test_open_failed(self):
-        self._device.interface = ('AD2USB', 0)
+        self._device.interface = 'AD2USB'
 
         with patch.object(self._device._device, 'open', side_effect=[USBError('testing'), FtdiError]):
             with self.assertRaises(NoDeviceError):
@@ -53,7 +67,7 @@ class TestUSBDevice(TestCase):
                 self._device.open(no_reader_thread=True)
 
     def test_write(self):
-        self._device.interface = ('AD2USB', 0)
+        self._device.interface = 'AD2USB'
         self._device.open(no_reader_thread=True)
 
         with patch.object(self._device._device, 'write_data') as mock:
@@ -67,7 +81,7 @@ class TestUSBDevice(TestCase):
                 self._device.write('test')
 
     def test_read(self):
-        self._device.interface = ('AD2USB', 0)
+        self._device.interface = 'AD2USB'
         self._device.open(no_reader_thread=True)
 
         with patch.object(self._device._device, 'read_data') as mock: