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.. _2.1.9_py_mcp3008:

2.1.9 Joystick(MCP3008)
=========================

Introduction
------------

In this project, We're going to learn how joystick works. We manipulate
the Joystick and display the results on the screen.

Required Components
------------------------------

In this project, we need the following components. 

.. image:: ../img/image317 - Copy.png

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_joystick`
        - \-
    *   - :ref:`cpn_mcp3008`
        - \-

Schematic Diagram
------------------

When the data of joystick is read, there are some differents between
axis: data of X and Y axis is analog, which need to use MCP3008 to
convert the analog value to digital value. Data of Z axis is digital, so
you can directly use the GPIO to read, or you can also use ADC to read.

.. .. image:: ../img/2.1.9_joystick_schematic_1.png

    *   - T-Board Name
        - physical
        - WiringPi
        - BCM

    *   - SPICE0
        - pin24
        - 10
        - 8
    *   - SPIMOSI
        - pin19
        - 12
        - 10
    *   - SPIMISO
        - pin21
        - 13
        - 9
    *   - SPISCLK
        - pin23
        - 14
        - 11
    *   - GPIO22
        - pin15
        - 3
        - 22


.. image:: ../img/schematic_2.1.9_joystick_mcp3008.png


Experimental Procedures
--------------------------

**Step 1:** Build the circuit.

.. image:: ../img/july24_2.1.9_joystick_mcp3008.png

**Step 2:** Set up the SPI interface and install the ``spidev`` library (see :ref:`spi_configuration` for detailed instructions). If you have already completed these steps, you can skip this.

**Step 3:** Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/python

**Step 4:** Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 2.1.9-2_Joystick.py

After the code runs, turn the Joystick, then the corresponding values of
x, y, Btn are displayed on screen.

.. warning::

    If there is an error prompt  ``RuntimeError: Cannot determine SOC peripheral base address``, please refer to :ref:`faq_soc` 

**Code**

.. note::

    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``raphael-kit/python``. After modifying the code, you can run it directly to see the effect.


.. raw:: html

    <run></run>

.. code-block:: python

    #!/usr/bin/env python3

    import RPi.GPIO as GPIO
    import spidev
    import time

    # Define GPIO pin for joystick button (SW pin)
    BTN_PIN = 22

    # Set up GPIO mode
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(BTN_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)  # Use internal pull-up

    # Initialize SPI communication with MCP3008
    spi = spidev.SpiDev()
    spi.open(0, 0)  # SPI bus 0, CE0
    spi.max_speed_hz = 1000000  # 1 MHz

    def read_adc(channel):
        """
        Reads analog value from the specified MCP3008 channel (0–7)
        :param channel: ADC channel number (0–7)
        :return: 10-bit integer value (0–1023)
        """
        if channel < 0 or channel > 7:
            return -1
        adc = spi.xfer2([1, (8 + channel) << 4, 0])
        value = ((adc[1] & 0x03) << 8) | adc[2]
        return value

    try:
        # Main loop to read and print joystick values and button state
        while True:
            # Read X and Y values from MCP3008 channels 1 and 2
            x_val = read_adc(1)  # Joystick VRX connected to CH1
            y_val = read_adc(2)  # Joystick VRY connected to CH2

            # Read the state of the joystick button (SW)
            Btn_val = GPIO.input(BTN_PIN)  # 0 = pressed, 1 = released

            # Print the read values
            print('X: %d  Y: %d  Btn: %d' % (x_val, y_val, Btn_val))

            time.sleep(0.2)

    except KeyboardInterrupt:
        pass

    finally:
        spi.close()
        GPIO.cleanup()


**Code Explanation**

.. code-block:: python

    #!/usr/bin/env python3

    import RPi.GPIO as GPIO
    import spidev
    import time

This section imports the required libraries:

- ``RPi.GPIO`` is used to handle GPIO input (joystick button).
- ``spidev`` is used to communicate with the MCP3008 ADC chip via SPI.
- ``time`` is used to introduce delays between readings.

.. code-block:: python

    # Define GPIO pin for joystick button (SW pin)
    BTN_PIN = 22

    # Set up GPIO mode
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(BTN_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)

    # Initialize SPI communication with MCP3008
    spi = spidev.SpiDev()
    spi.open(0, 0)  # SPI bus 0, CE0
    spi.max_speed_hz = 1000000

This block sets the GPIO mode to ``BCM``, initializes the joystick button input on GPIO22 with a pull-up resistor, and configures the SPI interface with MCP3008 using bus 0 and chip enable 0 (CE0) at 1 MHz.

.. code-block:: python

    def read_adc(channel):
        """
        Reads analog value from the specified MCP3008 channel (0–7)
        :param channel: ADC channel number (0–7)
        :return: 10-bit integer value (0–1023)
        """
        if channel < 0 or channel > 7:
            return -1
        adc = spi.xfer2([1, (8 + channel) << 4, 0])
        value = ((adc[1] & 0x03) << 8) | adc[2]
        return value

Defines the ``read_adc()`` function to read analog data from a specific MCP3008 channel. It sends three bytes over SPI and interprets the response to return a 10-bit value from 0 to 1023.

.. code-block:: python

    try:
        # Main loop to read and print joystick values and button state
        while True:
            # Read X and Y values from MCP3008 channels 0 and 1
            x_val = read_adc(0)  # Joystick VRX connected to CH0
            y_val = read_adc(1)  # Joystick VRY connected to CH1

            # Read the state of the joystick button (SW)
            Btn_val = GPIO.input(BTN_PIN)  # 0 = pressed, 1 = released

            # Print the read values
            print('X: %d  Y: %d  Btn: %d' % (x_val, y_val, Btn_val))

            time.sleep(0.2)

    except KeyboardInterrupt:
        pass

    finally:
        spi.close()
        GPIO.cleanup()

This main loop reads and prints the X/Y analog positions from the joystick and its button state every 200ms. If the script is interrupted via keyboard (Ctrl+C), SPI and GPIO are properly cleaned up.