diff --git a/docs/wasp.rst b/docs/wasp.rst
index 18c0803..8026a51 100644
--- a/docs/wasp.rst
+++ b/docs/wasp.rst
@@ -3,6 +3,9 @@
 WASP Reference Manual
 =====================
 
+.. contents::
+    :local:
+
 System management
 -----------------
 
@@ -47,7 +50,6 @@ Device drivers
 
 .. automodule:: drivers.signal
    :members:
-   :undoc-members:
 
 .. automodule:: drivers.st7789
    :members:
diff --git a/wasp/drivers/signal.py b/wasp/drivers/signal.py
index 974adb5..b72a218 100644
--- a/wasp/drivers/signal.py
+++ b/wasp/drivers/signal.py
@@ -1,26 +1,46 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 # Copyright (C) 2020 Daniel Thompson
 
-class Signal(object):
-    '''Simplified Signal class
+"""Inverting pin wrapper
+~~~~~~~~~~~~~~~~~~~~~~~~
+"""
 
-    Note: The normal C implementation isn't working for the NRF port
-    '''
+class Signal(object):
+    """Simplified Signal class
+
+    .. note::
+
+        The normal C implementation of the Signal class used by MicroPython
+        doesn't work on the nRF family. This class provides a temporary
+        workaround until that can be addressed.
+
+    .. automethod:: __init__
+    """
 
     def __init__(self, pin, invert=False):
+        """Create a Signal object by wrapping a pin."""
         self.pin = pin
         self.invert = invert
 
     def __call__(self, v=None):
+        """Shortcut for :py:meth:`.value`"""
         return self.value(v)
 
     def value(self, v=None):
+        """Get or set the state of the signal.
+
+        :param v: Value to set, defaults to None (which means get the signal
+                  state instead.
+        :returns: The state of the signal if v is None, otherwise None.
+        """
         if v == None:
             return self.invert ^ self.pin.value()
         self.pin.value(self.invert ^ bool(v))
 
     def on(self):
+        """Activate the signal."""
         self.value(1)
 
     def off(self):
+        """Deactivate the signal."""
         self.value(0)