Commit bc0bc764 authored by Damien George's avatar Damien George
Browse files

docs: Add debounce tutorial; order Pin methods; add pull resistor info.

parent 183ac71d
......@@ -55,6 +55,9 @@ an ordinal pin number:
You can set ``pyb.Pin.debug(True)`` to get some debug information about
how a particular object gets mapped to a pin.
When a pin has the ``Pin.PULL_UP`` or ``Pin.PULL_DOWN`` pull-mode enabled,
that pin has an effective 40k Ohm resistor pulling it to 3V3 or GND
respectively (except pin Y5 which has 11k Ohm resistors).
Constructors
------------
......@@ -62,7 +65,7 @@ Constructors
.. class:: pyb.Pin(id, ...)
Create a new Pin object associated with the id. If additional arguments are given,
they are used to initialise the pin. See ``init``.
they are used to initialise the pin. See :meth:`pin.init`.
Class methods
......@@ -88,24 +91,6 @@ Class methods
Methods
-------
.. method:: pin.__str__()
Return a string describing the pin object.
.. method:: pin.af()
Returns the currently configured alternate-function of the pin. The
integer returned will match one of the allowed constants for the af
argument to the init function.
.. method:: pin.gpio()
Returns the base address of the GPIO block associated with this pin.
.. method:: pin.high()
Set the pin to a high logic level.
.. method:: pin.init(mode, pull=Pin.PULL_NONE, af=-1)
Initialise the pin:
......@@ -126,10 +111,37 @@ Methods
Returns: ``None``.
.. method:: pin.high()
Set the pin to a high logic level.
.. method:: pin.low()
Set the pin to a low logic level.
.. method:: pin.value([value])
Get or set the digital logic level of the pin:
- With no argument, return 0 or 1 depending on the logic level of the pin.
- With ``value`` given, set the logic level of the pin. ``value`` can be
anything that converts to a boolean. If it converts to ``True``, the pin
is set high, otherwise it is set low.
.. method:: pin.__str__()
Return a string describing the pin object.
.. method:: pin.af()
Returns the currently configured alternate-function of the pin. The
integer returned will match one of the allowed constants for the af
argument to the init function.
.. method:: pin.gpio()
Returns the base address of the GPIO block associated with this pin.
.. method:: pin.mode()
Returns the currently configured mode of the pin. The integer returned
......@@ -158,15 +170,6 @@ Methods
will match one of the allowed constants for the pull argument to the init
function.
.. method:: pin.value([value])
Get or set the digital logic level of the pin:
- With no argument, return 0 or 1 depending on the logic level of the pin.
- With ``value`` given, set the logic level of the pin. ``value`` can be
anything that converts to a boolean. If it converts to ``True``, the pin
is set high, otherwise it is set low.
Constants
---------
......
Debouncing a pin input
======================
A pin used as input from a switch or other mechanical device can have a lot
of noise on it, rapidly changing from low to high when the switch is first
pressed or released. This noise can be eliminated using a capacitor (a
debouncing circuit). It can also be eliminated using a simple function that
makes sure the value on the pin is stable.
The following function does just this. It gets the current value of the given
pin, and then waits for the value to change. The new pin value must be stable
for a continuous 20ms for it to register the change. You can adjust this time
(to say 50ms) if you still have noise. ::
import pyb
def wait_pin_change(pin):
# wait for pin to change value
# it needs to be stable for a continuous 20ms
cur_value = pin.value()
active = 0
while active < 20:
if pin.value() != cur_value:
active += 1
else:
active = 0
pyb.delay(1)
Use it something like this::
import pyb
pin_x1 = pyb.Pin('X1', pyb.Pin.IN, pyb.Pin.PULL_DOWN)
while True:
wait_pin_change(pin_x1)
pyb.LED(4).toggle()
......@@ -43,4 +43,5 @@ Tips, tricks and useful things to know
:maxdepth: 1
:numbered:
debounce.rst
pass_through.rst
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