diff --git a/circuitpython_mocks/board.py b/circuitpython_mocks/board.py
index 61bc016..e4285d2 100644
--- a/circuitpython_mocks/board.py
+++ b/circuitpython_mocks/board.py
@@ -1,4 +1,8 @@
-"""A module that hosts mock pins."""
+"""A module that hosts mock pins and default :py:class:`~busio.SPI`,
+:py:class:`~busio.I2C`, and :py:class:`~busio.UART` data buses."""
+
+#: A dummy identifier to allow detection when using this mock library.
+board_id = "CIRCUITPYTHON_MOCK"
 
 
 class Pin:
@@ -7,6 +11,33 @@ class Pin:
     pass
 
 
+A0 = Pin()
+A1 = Pin()
+A2 = Pin()
+A3 = Pin()
+A4 = Pin()
+A5 = Pin()
+A6 = Pin()
+A7 = Pin()
+A8 = Pin()
+A9 = Pin()
+A10 = Pin()
+A11 = Pin()
+A12 = Pin()
+A13 = Pin()
+A14 = Pin()
+A15 = Pin()
+A16 = Pin()
+A17 = Pin()
+A18 = Pin()
+A19 = Pin()
+A20 = Pin()
+A21 = Pin()
+A22 = Pin()
+A23 = Pin()
+A24 = Pin()
+A25 = Pin()
+
 D0 = Pin()
 D1 = Pin()
 D2 = Pin()
@@ -110,6 +141,8 @@ class Pin:
 
 SDA = Pin()
 SCL = Pin()
+SDA1 = Pin()
+SCL1 = Pin()
 
 CE1 = Pin()
 CE0 = Pin()
@@ -121,7 +154,6 @@ class Pin:
 TXD = Pin()
 RXD = Pin()
 
-# create alias for most of the examples
 TX = Pin()
 RX = Pin()
 
@@ -129,3 +161,39 @@ class Pin:
 MOSI_1 = Pin()
 SCLK_1 = Pin()
 SCK_1 = Pin()
+CS = Pin()
+
+WS = Pin()
+SD = Pin()
+
+LED = Pin()
+NEOPIXEL = Pin()
+DOTSTAR = Pin()
+
+
+def SPI():
+    """Creates a default instance (singleton) of :py:class:`~busio.SPI`"""
+    from circuitpython_mocks.busio import SPI as ImplSPI
+
+    return ImplSPI(SCK, MOSI, MISO)
+
+
+def I2C():
+    """Creates a default instance (singleton) of :py:class:`~busio.I2C`"""
+    from circuitpython_mocks.busio import I2C as ImplI2C
+
+    return ImplI2C(SCL, SDA)
+
+
+def STEMMA_I2C():
+    """Creates a default instance (singleton) of :py:class:`~busio.I2C`"""
+    from circuitpython_mocks.busio import I2C as ImplI2C
+
+    return ImplI2C(SCL1, SDA1)
+
+
+def UART():
+    """Creates a default instance (singleton) of :py:class:`~busio.UART`"""
+    from circuitpython_mocks.busio import UART as ImplUART
+
+    return ImplUART(TX, RX)
diff --git a/circuitpython_mocks/busio/__init__.py b/circuitpython_mocks/busio/__init__.py
index c9a0c77..3777ba0 100644
--- a/circuitpython_mocks/busio/__init__.py
+++ b/circuitpython_mocks/busio/__init__.py
@@ -2,7 +2,7 @@
 
 from enum import Enum, auto
 import sys
-from typing import List
+from typing import List, Optional
 
 import circuitpython_typing
 
@@ -17,11 +17,39 @@
     SPITransfer,
 )
 from circuitpython_mocks._mixins import Expecting, Lockable
-from circuitpython_mocks.board import Pin
+from circuitpython_mocks.board import (
+    Pin,
+    SDA,
+    SDA1,
+    SCL,
+    SCL1,
+    SCK,
+    MOSI as PinMOSI,
+    MISO as PinMISO,
+    TX,
+    RX,
+    MISO_1,
+    MOSI_1,
+    SCK_1,
+)
 
 
 class I2C(Expecting, Lockable):
-    """A mock of `busio.I2C` class."""
+    """A mock of :external:py:class:`busio.I2C` class."""
+
+    _primary_singleton: Optional["I2C"] = None
+    _secondary_singleton: Optional["I2C"] = None
+
+    def __new__(cls, scl: Pin, sda: Pin, **kwargs) -> "I2C":
+        if scl == SCL and sda == SDA:
+            if cls._primary_singleton is None:
+                cls._primary_singleton = super().__new__(cls)
+            return cls._primary_singleton
+        if scl == SCL1 and sda == SDA1:
+            if cls._secondary_singleton is None:
+                cls._secondary_singleton = super().__new__(cls)
+            return cls._secondary_singleton
+        return super().__new__(cls)
 
     def __init__(
         self,
@@ -31,6 +59,8 @@ def __init__(
         frequency: int = 100000,
         timeout: int = 255,
     ):
+        if hasattr(self, "expectations"):
+            return
         super().__init__()
 
     def scan(self) -> List[int]:
@@ -99,6 +129,22 @@ def writeto_then_readfrom(
 
 
 class SPI(Expecting, Lockable):
+    """A mock of :external:py:class:`busio.SPI` class."""
+
+    _primary_singleton: Optional["SPI"] = None
+    _secondary_singleton: Optional["SPI"] = None
+
+    def __new__(cls, clock: Pin, MOSI: Pin, MISO: Pin, **kwargs) -> "SPI":
+        if clock == SCK and MOSI == PinMOSI and MISO == PinMISO:
+            if cls._primary_singleton is None:
+                cls._primary_singleton = super().__new__(cls)
+            return cls._primary_singleton
+        if clock == SCK_1 and MOSI == MOSI_1 and MISO == MISO_1:
+            if cls._secondary_singleton is None:
+                cls._secondary_singleton = super().__new__(cls)
+            return cls._secondary_singleton
+        return super().__new__(cls)
+
     def __init__(
         self,
         clock: Pin,
@@ -183,6 +229,15 @@ def write_readinto(
 class UART(Expecting, Lockable):
     """A class that mocks :external:py:class:`busio.UART`."""
 
+    _primary_singleton: Optional["UART"] = None
+
+    def __new__(cls, tx: Pin, rx: Pin, **kwargs) -> "UART":
+        if tx == TX and rx == RX:
+            if cls._primary_singleton is None:
+                cls._primary_singleton = super().__new__(cls)
+            return cls._primary_singleton
+        return super().__new__(cls)
+
     class Parity(Enum):
         ODD = auto()
         EVEN = auto()
@@ -250,3 +305,6 @@ def write(self, buf: circuitpython_typing.ReadableBuffer) -> int | None:
         len_buf = len(op.expected)
         op.assert_expected(buf, 0, len_buf)
         return len(buf) or None
+
+
+_UART = UART(TX, RX)
diff --git a/circuitpython_mocks/digitalio/__init__.py b/circuitpython_mocks/digitalio/__init__.py
index 487c72f..1cd455f 100644
--- a/circuitpython_mocks/digitalio/__init__.py
+++ b/circuitpython_mocks/digitalio/__init__.py
@@ -1,5 +1,5 @@
 from enum import Enum, auto
-
+from typing import Union, Optional
 from circuitpython_mocks._mixins import ContextManaged, Expecting
 from circuitpython_mocks.digitalio.operations import GetState, SetState
 from circuitpython_mocks.board import Pin
@@ -34,13 +34,17 @@ def __init__(self, pin: Pin, **kwargs):
         self._pin = pin
         self.switch_to_input()
 
-    def switch_to_output(self, value=False, drive_mode=DriveMode.PUSH_PULL):
+    def switch_to_output(
+        self,
+        value: Union[bool, int] = False,
+        drive_mode: DriveMode = DriveMode.PUSH_PULL,
+    ):
         """Switch the Digital Pin Mode to Output"""
         self.direction = Direction.OUTPUT
         self.value = value
         self.drive_mode = drive_mode
 
-    def switch_to_input(self, pull=None):
+    def switch_to_input(self, pull: Optional[Pull] = None):
         """Switch the Digital Pin Mode to Input"""
         self.direction = Direction.INPUT
         self.pull = pull
@@ -50,12 +54,12 @@ def deinit(self):
         del self._pin
 
     @property
-    def direction(self):
+    def direction(self) -> Direction:
         """Get or Set the Digital Pin Direction"""
         return self.__direction
 
     @direction.setter
-    def direction(self, value):
+    def direction(self, value: Direction):
         self.__direction = value
         if value == Direction.OUTPUT:
             # self.value = False
@@ -66,7 +70,7 @@ def direction(self, value):
             raise AttributeError("Not a Direction")
 
     @property
-    def value(self):
+    def value(self) -> Union[bool, int]:
         """The Digital Pin Value.
         This property will check against `SetState` and `GetState`
         :py:attr:`~circuitpython_mocks._mixins.Expecting.expectations`."""
@@ -78,7 +82,7 @@ def value(self):
         return op.state
 
     @value.setter
-    def value(self, val):
+    def value(self, val: Union[bool, int]):
         if self.direction != Direction.OUTPUT:
             raise AttributeError("Not an output")
         assert self.expectations, "No expectations found for DigitalInOut.value.setter"
@@ -89,25 +93,25 @@ def value(self, val):
         op.assert_state(val)
 
     @property
-    def pull(self):
+    def pull(self) -> Optional[Pull]:
         """The pin pull direction"""
         if self.direction == Direction.INPUT:
             return self.__pull
         raise AttributeError("Not an input")
 
     @pull.setter
-    def pull(self, pul):
+    def pull(self, pul: Optional[Pull]):
         if self.direction != Direction.INPUT:
             raise AttributeError("Not an input")
         self.__pull = pul
 
     @property
-    def drive_mode(self):
+    def drive_mode(self) -> DriveMode:
         """The Digital Pin Drive Mode"""
         if self.direction != Direction.OUTPUT:
             raise AttributeError("Not an output")
         return self.__drive_mode
 
     @drive_mode.setter
-    def drive_mode(self, mod):
+    def drive_mode(self, mod: DriveMode):
         self.__drive_mode = mod
diff --git a/docs/board.rst b/docs/board.rst
index 63ad627..20c9796 100644
--- a/docs/board.rst
+++ b/docs/board.rst
@@ -3,7 +3,6 @@
 
 .. automodule:: circuitpython_mocks.board
     :members:
-    :undoc-members:
 
 This module includes the following dummy pins for soft-testing:
 
diff --git a/docs/busio.rst b/docs/busio.rst
index 3665683..fae3ad9 100644
--- a/docs/busio.rst
+++ b/docs/busio.rst
@@ -2,7 +2,22 @@
 =================
 
 .. automodule:: circuitpython_mocks.busio
-    :members:
+
+    .. autoclass:: circuitpython_mocks.busio.I2C
+        :members: readfrom_into, writeto, writeto_then_readfrom, scan
+    .. autoclass:: circuitpython_mocks.busio.SPI
+        :members: readinto, write, write_readinto, configure, frequency
+    .. autoclass:: circuitpython_mocks.busio.UART
+        :members: readinto, readline, write
+
+        .. py:class:: circuitpython_mocks.busio.UART.Parity
+
+            A mock enumeration of :external:py:class:`busio.Parity`.
+
+            .. py:attribute:: ODD
+                :type: Parity
+            .. py:attribute:: EVEN
+                :type: Parity
 
 ``busio.operations``
 --------------------
diff --git a/docs/conf.py b/docs/conf.py
index 3b86a1f..07d417c 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -20,9 +20,14 @@
     "sphinx_immaterial",
     "sphinx.ext.autodoc",
     "sphinx.ext.intersphinx",
+    "sphinx.ext.viewcode",
     "sphinx_jinja",
 ]
-autodoc_class_signature = "separated"
+
+# autodoc_class_signature = "separated"
+autodoc_default_options = {
+    "exclude-members": "__new__",
+}
 
 templates_path = ["_templates"]
 exclude_patterns = ["_build", "Thumbs.db", ".DS_Store"]
@@ -32,7 +37,7 @@
         "pins": [
             x
             for x in dir(circuitpython_mocks.board)
-            if not x.startswith("_") and x != "Pin"
+            if not x.startswith("_") and x not in ("Pin", "board_id")
         ]
     }
 }
@@ -63,6 +68,7 @@
     "features": [
         "navigation.top",
         "search.share",
+        "toc.follow",
     ],
     "palette": [
         {
diff --git a/docs/digitalio.rst b/docs/digitalio.rst
index 46f1072..0ae48d7 100644
--- a/docs/digitalio.rst
+++ b/docs/digitalio.rst
@@ -2,10 +2,42 @@
 =================
 
 .. automodule:: circuitpython_mocks.digitalio
-    :members:
+
+    .. autoclass:: circuitpython_mocks.digitalio.DigitalInOut
+        :members: value, deinit, direction, drive_mode, pull, switch_to_input, switch_to_output
+
+    .. py:class:: circuitpython_mocks.digitalio.Direction
+
+        A mock enumeration of :external:py:class:`digitalio.Direction`.
+
+        .. py:attribute:: INPUT
+            :type: Direction
+        .. py:attribute:: OUTPUT
+            :type: Direction
+
+    .. py:class:: circuitpython_mocks.digitalio.DriveMode
+
+        A mock enumeration of :external:py:class:`digitalio.DriveMode`.
+
+        .. py:attribute:: PUSH_PULL
+            :type: DriveMode
+        .. py:attribute:: OPEN_DRAIN
+            :type: DriveMode
+
+    .. py:class:: circuitpython_mocks.digitalio.Pull
+
+        A mock enumeration of :external:py:class:`digitalio.Pull`.
+
+        .. py:attribute:: UP
+            :type: Pull
+        .. py:attribute:: DOWN
+            :type: Pull
+
 
 ``digitalio.operations``
 ------------------------
 
 .. automodule:: circuitpython_mocks.digitalio.operations
-    :members:
+
+    .. autoclass:: circuitpython_mocks.digitalio.operations.SetState
+    .. autoclass:: circuitpython_mocks.digitalio.operations.GetState
diff --git a/docs/index.rst b/docs/index.rst
index 646caef..3a68f06 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -18,6 +18,7 @@ projects (with pytest).
 
             .. literalinclude:: ../tests/test_i2c.py
                 :language: python
+                :end-before: def test_default():
 
             .. code-annotations::
                 #. |pytest-used-import|
@@ -26,6 +27,7 @@ projects (with pytest).
 
             .. literalinclude:: ../tests/test_spi.py
                 :language: python
+                :end-before: def test_default():
 
             .. code-annotations::
                 #. |pytest-used-import|
@@ -34,6 +36,7 @@ projects (with pytest).
 
             .. literalinclude:: ../tests/test_uart.py
                 :language: python
+                :end-before: def test_default():
 
             .. code-annotations::
                 #. |pytest-used-import|
diff --git a/tests/test_i2c.py b/tests/test_i2c.py
index b125b18..152d52d 100644
--- a/tests/test_i2c.py
+++ b/tests/test_i2c.py
@@ -9,7 +9,6 @@
 def test_i2c():
     import board
     from busio import I2C
-
     from adafruit_bus_device.i2c_device import I2CDevice
 
     address = 0x42
@@ -38,3 +37,30 @@ def test_i2c():
             i2c.write(buf, end=1)
         with i2c_dev as i2c:
             i2c.write_then_readinto(buf, buf, out_end=1, in_end=1)
+
+
+def test_default():
+    # here we cannot import from the monkey-patched sys path because
+    # the mock modules use absolute imports.
+    from circuitpython_mocks import board, busio
+    from collections import deque
+
+    i2c = board.I2C()
+    assert hasattr(i2c, "expectations")
+    assert isinstance(i2c.expectations, deque)
+    i2c_dupe = busio.I2C(board.SCL, board.SDA)
+    assert i2c == i2c_dupe
+    i2c.expectations.append(I2CRead(0x42, bytearray(1)))
+    assert i2c_dupe.expectations == i2c.expectations
+    op = i2c_dupe.expectations.popleft()
+    assert not i2c.expectations
+
+    i2c1 = board.STEMMA_I2C()
+    assert hasattr(i2c1, "expectations")
+    assert isinstance(i2c1.expectations, deque)
+    i2c1_dupe = busio.I2C(board.SCL1, board.SDA1)
+    assert i2c1 == i2c1_dupe
+    i2c1.expectations.append(op)
+    assert i2c1_dupe.expectations == i2c1.expectations
+    op = i2c1_dupe.expectations.popleft()
+    assert not i2c1.expectations
diff --git a/tests/test_spi.py b/tests/test_spi.py
index b2c1ffa..de64262 100644
--- a/tests/test_spi.py
+++ b/tests/test_spi.py
@@ -10,9 +10,8 @@
 def test_spi():
     from busio import SPI
     from digitalio import DigitalInOut
-
-    from adafruit_bus_device.spi_device import SPIDevice
     import board
+    from adafruit_bus_device.spi_device import SPIDevice
 
     # do setup
     with SPI(board.SCK, board.MOSI, board.MISO) as spi_bus:
@@ -41,3 +40,30 @@ def test_spi():
             spi.write(buf, end=1)
         with spi_dev as spi:
             spi.write_readinto(buf, buf, out_end=1, in_end=1)
+
+
+def test_default():
+    # here we cannot import from the monkey-patched sys path because
+    # the mock modules use absolute imports.
+    from circuitpython_mocks import board, busio
+    from collections import deque
+
+    spi = board.SPI()
+    assert hasattr(spi, "expectations")
+    assert isinstance(spi.expectations, deque)
+    spi_dupe = busio.SPI(board.SCK, board.MOSI, board.MISO)
+    assert spi == spi_dupe
+    spi.expectations.append(SPIRead(bytearray(1)))
+    assert spi_dupe.expectations == spi.expectations
+    op = spi_dupe.expectations.popleft()
+    assert not spi.expectations
+
+    spi1 = busio.SPI(board.SCK_1, board.MOSI_1, board.MISO_1)
+    assert hasattr(spi1, "expectations")
+    assert isinstance(spi1.expectations, deque)
+    spi1_dupe = busio.SPI(board.SCK_1, board.MOSI_1, board.MISO_1)
+    assert spi1 == spi1_dupe
+    spi1.expectations.append(op)
+    assert spi1_dupe.expectations == spi1.expectations
+    _ = spi1_dupe.expectations.popleft()
+    assert not spi1.expectations
diff --git a/tests/test_uart.py b/tests/test_uart.py
index c333bbc..c4fa92e 100644
--- a/tests/test_uart.py
+++ b/tests/test_uart.py
@@ -27,3 +27,20 @@ def test_uart():
         serial.readinto(buf)
         _result = serial.readline()
         assert serial.write(buf) == 1
+
+
+def test_default():
+    # here we cannot import from the monkey-patched sys path because
+    # the mock modules use absolute imports.
+    from circuitpython_mocks import board, busio
+    from collections import deque
+
+    uart = board.UART()
+    assert hasattr(uart, "expectations")
+    assert isinstance(uart.expectations, deque)
+    uart_dupe = busio.UART(board.TX, board.RX)
+    assert uart == uart_dupe
+    uart.expectations.append(UARTRead(bytearray(1)))
+    assert uart_dupe.expectations == uart.expectations
+    _ = uart_dupe.expectations.popleft()
+    assert not uart.expectations