.. GPIO Zero: a library for controlling the Raspberry Pi's GPIO pins
..
.. Copyright (c) 2015-2021 Dave Jones <dave@waveform.org.uk>
.. Copyright (c) 2016-2020 Ben Nuttall <ben@bennuttall.com>
.. Copyright (c) 2016 Barry Byford <barry_byford@yahoo.co.uk>
.. Copyright (c) 2016 Andrew Scheller <github@loowis.durge.org>
..
.. SPDX-License-Identifier: BSD-3-Clause

=============
Basic Recipes
=============

.. currentmodule:: gpiozero

The following recipes demonstrate some of the capabilities of the GPIO Zero
library. Please note that all recipes are written assuming Python 3. Recipes
*may* work under Python 2, but no guarantees!

Importing GPIO Zero
===================

.. module:: gpiozero

In Python, libraries and functions used in a script must be imported by name
at the top of the file, with the exception of the functions built into Python
by default.

For example, to use the :class:`Button` interface from GPIO Zero, it
should be explicitly imported::

    from gpiozero import Button

Now :class:`~gpiozero.Button` is available directly in your script::

    button = Button(2)

Alternatively, the whole GPIO Zero library can be imported::

    import gpiozero

In this case, all references to items within GPIO Zero must be prefixed::

    button = gpiozero.Button(2)

.. _pin-numbering:

Pin Numbering
=============

This library uses Broadcom (BCM) pin numbering for the GPIO pins, as opposed to
physical (BOARD) numbering. Unlike in the `RPi.GPIO`_ library, this is not
configurable. However, translation from other schemes can be used by providing
prefixes to pin numbers (see below).

Any pin marked "GPIO" in the diagram below can be used as a pin number.  For
example, if an LED was attached to "GPIO17" you would specify the pin number as
17 rather than 11:

.. image:: images/pin_layout.*
    :align: center

If you wish to use physical (BOARD) numbering you can specify the pin number as
"BOARD11". If you are familiar with the `wiringPi`_ pin numbers (another
physical layout) you could use "WPI0" instead. Finally, you can specify pins as
"header:number", e.g. "J8:11" meaning physical pin 11 on header J8 (the GPIO
header on modern Pis). Hence, the following lines are all equivalent:

.. code-block:: pycon

    >>> led = LED(17)
    >>> led = LED("GPIO17")
    >>> led = LED("BCM17")
    >>> led = LED("BOARD11")
    >>> led = LED("WPI0")
    >>> led = LED("J8:11")

Note that these alternate schemes are merely translations. If you request the
state of a device on the command line, the associated pin number will *always*
be reported in the Broadcom (BCM) scheme:

.. code-block:: pycon

    >>> led = LED("BOARD11")
    >>> led
    <gpiozero.LED object on pin GPIO17, active_high=True, is_active=False>

Throughout this manual we will use the default integer pin numbers, in the
Broadcom (BCM) layout shown above.

.. _RPi.GPIO: https://pypi.python.org/pypi/RPi.GPIO
.. _wiringPi: https://projects.drogon.net/raspberry-pi/wiringpi/pins/

LED
===

.. image:: images/led_bb.*

Turn an :class:`LED` on and off repeatedly:

.. literalinclude:: examples/led_1.py

Alternatively:

.. literalinclude:: examples/led_2.py

.. note::

    Reaching the end of a Python script will terminate the process and GPIOs
    may be reset. Keep your script alive with :func:`signal.pause`. See
    :ref:`keep-your-script-running` for more information.

LED with variable brightness
============================

.. image:: images/led_bb.*

Any regular LED can have its brightness value set using PWM
(pulse-width-modulation). In GPIO Zero, this can be achieved using
:class:`PWMLED` using values between 0 and 1:

.. literalinclude:: examples/led_variable_brightness.py

Similarly to blinking on and off continuously, a PWMLED can pulse (fade in and
out continuously):

.. literalinclude:: examples/led_pulse.py

Button
======

.. image:: images/button_bb.*

Check if a :class:`Button` is pressed:

.. literalinclude:: examples/button_1.py

Wait for a button to be pressed before continuing:

.. literalinclude:: examples/button_2.py

Run a function every time the button is pressed:

.. literalinclude:: examples/button_3.py
    :emphasize-lines: 9

.. note::

    Note that the line ``button.when_pressed = say_hello`` does not run the
    function ``say_hello``, rather it creates a reference to the function to be
    called when the button is pressed. Accidental use of ``button.when_pressed
    = say_hello()`` would set the ``when_pressed`` action to :data:`None` (the
    return value of this function) which would mean nothing happens when the
    button is pressed.

Similarly, functions can be attached to button releases:

.. literalinclude:: examples/button_4.py

Button controlled LED
=====================

.. image:: images/led_button_bb.*

Turn on an :class:`LED` when a :class:`Button` is pressed:

.. literalinclude:: examples/button_led_1.py

Alternatively:

.. literalinclude:: examples/button_led_2.py

Button controlled camera
========================

Using the button press to trigger :class:`~picamera.PiCamera` to take a picture
using ``button.when_pressed = camera.capture`` would not work because the
:meth:`~picamera.PiCamera.capture` method requires an ``output`` parameter.
However, this can be achieved using a custom function which requires no
parameters:

.. literalinclude:: examples/button_camera_1.py
    :emphasize-lines: 9-11

Another example could use one button to start and stop the camera preview, and
another to capture:

.. literalinclude:: examples/button_camera_2.py

Shutdown button
===============

The :class:`Button` class also provides the ability to run a function when the
button has been held for a given length of time. This example will shut down
the Raspberry Pi when the button is held for 2 seconds:

.. literalinclude:: examples/button_shutdown.py

LEDBoard
========

.. image:: images/ledboard_bb.*

A collection of LEDs can be accessed using :class:`LEDBoard`:

.. literalinclude:: examples/led_board_1.py

Using :class:`LEDBoard` with ``pwm=True`` allows each LED's brightness to be
controlled:

.. literalinclude:: examples/led_board_2.py

See more :class:`LEDBoard` examples in the :ref:`advanced LEDBoard recipes
<ledboard-advanced>`.

LEDBarGraph
===========

.. image:: images/ledbargraph_bb.*

A collection of LEDs can be treated like a bar graph using
:class:`LEDBarGraph`:

.. literalinclude:: examples/led_bargraph_1.py

Note values are essentially rounded to account for the fact LEDs can only be on
or off when ``pwm=False`` (the default).

However, using :class:`LEDBarGraph` with ``pwm=True`` allows more precise
values using LED brightness:

.. literalinclude:: examples/led_bargraph_2.py

LEDCharDisplay
==============

.. image:: images/led_char_display_bb.*

A common `7-segment display`_ can be used to represent a variety of characters
using :class:`LEDCharDisplay` (which actually supports an arbitrary number of
segments):

.. literalinclude:: examples/led_char_display.py

Alternatively:

.. literalinclude:: examples/led_char_source.py

See a multi-character example in the :ref:`advanced recipes
<multichar-display>` chapter.

Traffic Lights
==============

.. image:: images/traffic_lights_bb.*

A full traffic lights system.

Using a :class:`TrafficLights` kit like Pi-Stop:

.. literalinclude:: examples/traffic_lights_1.py

Alternatively:

.. literalinclude:: examples/traffic_lights_2.py

Using :class:`LED` components:

.. literalinclude:: examples/traffic_lights_3.py

Push button stop motion
=======================

Capture a picture with the camera module every time a button is pressed:

.. literalinclude:: examples/button_stop_motion.py

See `Push Button Stop Motion`_ for a full resource.

Reaction Game
=============

.. image:: images/reaction_game_bb.*

When you see the light come on, the first person to press their button wins!

.. literalinclude:: examples/reaction_game.py

See `Quick Reaction Game`_ for a full resource.

GPIO Music Box
==============

.. image:: images/music_box_bb.*

Each button plays a different sound!

.. literalinclude:: examples/music_box.py

See `GPIO Music Box`_ for a full resource.

All on when pressed
===================

While the button is pressed down, the buzzer and all the lights come on.

:class:`FishDish`:

.. literalinclude:: examples/all_on_1.py

Ryanteck :class:`TrafficHat`:

.. literalinclude:: examples/all_on_2.py

Using :class:`LED`, :class:`Buzzer`, and :class:`Button` components:

.. literalinclude:: examples/all_on_3.py

Full color LED
==============

.. image:: images/rgb_led_bb.*

Making colours with an :class:`RGBLED`:

.. literalinclude:: examples/rgbled.py

Motion sensor
=============

.. image:: images/motion_sensor_bb.*

Light an :class:`LED` when a :class:`MotionSensor` detects motion:

.. literalinclude:: examples/motion_sensor.py

Light sensor
============

.. image:: images/light_sensor_bb.*

Have a :class:`LightSensor` detect light and dark:

.. literalinclude:: examples/light_sensor_1.py

Run a function when the light changes:

.. literalinclude:: examples/light_sensor_2.py

Or make a :class:`PWMLED` change brightness according to the detected light
level:

.. literalinclude:: examples/light_sensor_3.py

Distance sensor
===============

.. image:: images/distance_sensor_bb.*

.. note::

    In the diagram above, the wires leading from the sensor to the breadboard
    can be omitted; simply plug the sensor directly into the breadboard facing
    the edge (unfortunately this is difficult to illustrate in the diagram
    without the sensor's diagram obscuring most of the breadboard!)

Have a :class:`DistanceSensor` detect the distance to the nearest object:

.. literalinclude:: examples/distance_sensor_1.py

Run a function when something gets near the sensor:

.. literalinclude:: examples/distance_sensor_2.py

Rotary encoder
==============

.. image:: images/color_picker_bb.*

.. note::

    In this recipe, I've used a common *anode* RGB LED. Often, Pi projects use
    common *cathode* RGB LEDs because they're slightly easier to think about
    electrically. However, in this case all three components can be found in an
    illuminated rotary encoder which incorporates a common anode RGB LED, and a
    momentary push button. This is also the reason for the button being wired
    active-low, contrary to most other examples in this documentation.

    For the sake of clarity, the diagram shows the three separate components,
    but this same circuit will work equally well with this commonly available
    `illuminated rotary encoder`_ instead.

Have a rotary encoder, an RGB LED, and button act as a color picker.

.. literalinclude:: examples/color_picker.py

Servo
=====

Control a servo between its minimum, mid-point and maximum positions in
sequence:

.. literalinclude:: examples/servo_1.py

Use a button to control the servo between its minimum and maximum positions:

.. literalinclude:: examples/servo_2.py

Automate the servo to continuously slowly sweep:

.. literalinclude:: examples/servo_sweep.py

Use :class:`AngularServo` so you can specify an angle:

.. literalinclude:: examples/angular_servo.py

Motors
======

.. image:: images/motor_bb.*

Spin a :class:`Motor` around forwards and backwards:

.. literalinclude:: examples/motor.py

Robot
=====

.. image:: images/robot_bb.*

Make a :class:`Robot` drive around in (roughly) a square:

.. literalinclude:: examples/robot_1.py

Make a robot with a distance sensor that runs away when things get within
20cm of it:

.. literalinclude:: examples/robot_2.py

Button controlled robot
=======================

.. image:: images/button_robot_bb.*

Use four GPIO buttons as forward/back/left/right controls for a robot:

.. literalinclude:: examples/robot_buttons_1.py

Keyboard controlled robot
=========================

.. image:: images/robot_bb.*

Use up/down/left/right keys to control a robot:

.. literalinclude:: examples/robot_keyboard_1.py

.. note::

    This recipe uses the standard :mod:`curses` module. This module requires
    that Python is running in a terminal in order to work correctly, hence this
    recipe will *not* work in environments like IDLE.

If you prefer a version that works under IDLE, the following recipe should
suffice:

.. literalinclude:: examples/robot_keyboard_2.py

.. note::

    This recipe uses the third-party ``evdev`` module. Install this library
    with ``sudo pip3 install evdev`` first. Be aware that ``evdev`` will only
    work with local input devices; this recipe will *not* work over SSH.

Motion sensor robot
===================

.. image:: images/motion_robot_bb.*

Make a robot drive forward when it detects motion:

.. literalinclude:: examples/robot_motion_1.py

Alternatively:

.. literalinclude:: examples/robot_motion_2.py

Potentiometer
=============

.. image:: images/potentiometer_bb.*

Continually print the value of a potentiometer (values between 0 and 1)
connected to a :class:`MCP3008` analog to digital converter:

.. literalinclude:: examples/pot_1.py

Present the value of a potentiometer on an LED bar graph using PWM to represent
states that won't "fill" an LED:

.. literalinclude:: examples/pot_2.py

Measure temperature with an ADC
===============================

.. IMAGE TBD

Wire a TMP36 temperature sensor to the first channel of an :class:`MCP3008`
analog to digital converter:

.. literalinclude:: examples/thermometer.py

Full color LED controlled by 3 potentiometers
=============================================

.. image:: images/rgbled_pot_bb.*

Wire up three potentiometers (for red, green and blue) and use each of their
values to make up the colour of the LED:

.. literalinclude:: examples/rgbled_pot_1.py

Alternatively, the following example is identical, but uses the
:attr:`~SourceMixin.source` property rather than a :keyword:`while` loop:

.. literalinclude:: examples/rgbled_pot_2.py

Timed heat lamp
===============

If you have a pet (e.g. a tortoise) which requires a heat lamp to be switched
on for a certain amount of time each day, you can use an `Energenie Pi-mote`_
to remotely control the lamp, and the :class:`TimeOfDay` class to control the
timing:

.. literalinclude:: examples/timed_heat_lamp.py

Internet connection status indicator
====================================

You can use a pair of green and red LEDs to indicate whether or not your
internet connection is working. Simply use the :class:`PingServer` class to
identify whether a ping to `google.com` is successful. If successful, the green
LED is lit, and if not, the red LED is lit:

.. literalinclude:: examples/internet_status_indicator.py

CPU Temperature Bar Graph
=========================

You can read the Raspberry Pi's own CPU temperature using the built-in
:class:`CPUTemperature` class, and display this on a "bar graph" of LEDs:

.. literalinclude:: examples/cpu_temperature_bar_graph.py

More recipes
============

Continue to:

* :doc:`recipes_advanced`
* :doc:`recipes_remote_gpio`


.. _Push Button Stop Motion: https://projects.raspberrypi.org/en/projects/push-button-stop-motion
.. _Quick Reaction Game: https://projects.raspberrypi.org/en/projects/python-quick-reaction-game
.. _GPIO Music Box: https://projects.raspberrypi.org/en/projects/gpio-music-box
.. _Energenie Pi-mote: https://energenie4u.co.uk/catalogue/product/ENER002-2PI
.. _illuminated rotary encoder: https://shop.pimoroni.com/products/rotary-encoder-illuminated-rgb
.. _7-segment display: https://en.wikipedia.org/wiki/Seven-segment_display
