.. note::

    Hello, welcome to the SunFounder Raspberry Pi & Arduino & ESP32 Enthusiasts Community on Facebook! Dive deeper into Raspberry Pi, Arduino, and ESP32 with fellow enthusiasts.

    **Why Join?**

    - **Expert Support**: Solve post-sale issues and technical challenges with help from our community and team.
    - **Learn & Share**: Exchange tips and tutorials to enhance your skills.
    - **Exclusive Previews**: Get early access to new product announcements and sneak peeks.
    - **Special Discounts**: Enjoy exclusive discounts on our newest products.
    - **Festive Promotions and Giveaways**: Take part in giveaways and holiday promotions.

    👉 Ready to explore and create with us? Click [|link_sf_facebook|] and join today!

.. _2.2.1_py_mcp3008:

2.2.1 Photoresistor(MCP3008)
===============================

.. note::

   .. image:: ../img/mcp3008_and_adc0834.jpg
      :width: 25%
      :align: left
    

   Depending on your kit version, please identify whether you have **ADC0834** or **MCP3008** and proceed with the matching section.

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

Photoresistor is a commonly used component of ambient light intensity in
life. It helps the controller to recognize day and night and realize
light control functions such as night lamp. This project is very similar
to potentiometer, and you might think it changing the voltage to sensing
light.

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

In this project, we need the following components. 

.. image:: ../img/list2_2.2.1_photoresistor.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_led`
        - |link_led_buy|
    *   - :ref:`cpn_mcp3008`
        - \-
    *   - :ref:`cpn_photoresistor`
        - |link_photoresistor_buy|

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

.. .. image:: ../img/2.2.1_photoresistor_schematic_1.png

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

    *   - 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_2.2.1_photoresistor_mcp3008.png


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

**Step 1:** Build the circuit.

.. image:: ../img/july24_2.2.1_photoresistor_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 the executable file.

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 2.2.1-2_photoresistor.py

When the code is running, the brightness of the LED will change according to the light intensity sensed by the photoresistor.

.. 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

    # GPIO pin for PWM LED
    PWM_PIN = 22

    # Setup GPIO
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(PWM_PIN, GPIO.OUT)

    # Initialize PWM (frequency = 1000Hz)
    pwm = GPIO.PWM(PWM_PIN, 1000)
    pwm.start(0)  # Start with 0% duty cycle

    # Initialize SPI (MCP3008 on Bus 0, CE0)
    spi = spidev.SpiDev()
    spi.open(0, 0)
    spi.max_speed_hz = 1000000  # 1 MHz

    # Function to read MCP3008 ADC value
    def read_adc(channel):
        """
        Read analog value from MCP3008 (channel 0–7)
        Returns: 10-bit value (0–1023)
        """
        if channel < 0 or channel > 7:
            return -1
        r = spi.xfer2([1, (8 + channel) << 4, 0])
        value = ((r[1] & 3) << 8) | r[2]
        return value

    # Main loop to read ADC and set PWM brightness
    try:
        while True:
            analogVal = read_adc(0)
            print(f"value = {analogVal}")

            # Scale ADC value (0–1023) to duty cycle (0–100)
            duty_cycle = analogVal * 100 / 1023
            pwm.ChangeDutyCycle(duty_cycle)

            time.sleep(0.2)

    except KeyboardInterrupt:
        pass

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

**Code Explanation**

#. Import necessary libraries:

   - ``RPi.GPIO`` to control GPIO pins and generate PWM signal.
   - ``spidev`` to interface with the MCP3008 ADC via SPI.
   - ``time`` to handle timing and delays.

   .. code-block:: python

       #!/usr/bin/env python3

       import RPi.GPIO as GPIO
       import spidev
       import time

#. Configure GPIO pin 22 as PWM output using BCM mode. Then, initialize software PWM at 1000 Hz with a starting duty cycle of 0%.

   .. code-block:: python

       # GPIO pin for PWM LED
       PWM_PIN = 22

       # Setup GPIO
       GPIO.setmode(GPIO.BCM)
       GPIO.setup(PWM_PIN, GPIO.OUT)

       # Initialize PWM (frequency = 1000Hz)
       pwm = GPIO.PWM(PWM_PIN, 1000)
       pwm.start(0)  # Start with 0% duty cycle

#. Set up the SPI interface to communicate with MCP3008 on bus 0, chip enable 0 (CE0), and configure SPI speed to 1 MHz.

   .. code-block:: python

       # Initialize SPI (MCP3008 on Bus 0, CE0)
       spi = spidev.SpiDev()
       spi.open(0, 0)
       spi.max_speed_hz = 1000000  # 1 MHz

#. Define a function ``read_adc(channel)`` to read analog values from MCP3008. The function sends three bytes to the chip and reconstructs a 10-bit analog value (0–1023) from the response.

   .. code-block:: python

       # Function to read MCP3008 ADC value
       def read_adc(channel):
           """
           Read analog value from MCP3008 (channel 0–7)
           Returns: 10-bit value (0–1023)
           """
           if channel < 0 or channel > 7:
               return -1
           r = spi.xfer2([1, (8 + channel) << 4, 0])
           value = ((r[1] & 3) << 8) | r[2]
           return value

#. This is the main loop that:
   - Reads analog input from channel 0 of the MCP3008.
   - Converts the value to a PWM duty cycle (0–100%).
   - Adjusts the brightness of the LED using ``pwm.ChangeDutyCycle()``.
   - Repeats every 0.2 seconds.

   .. code-block:: python

       # Main loop to read ADC and set PWM brightness
       try:
           while True:
               analogVal = read_adc(0)
               print(f"value = {analogVal}")

               # Scale ADC value (0–1023) to duty cycle (0–100)
               duty_cycle = analogVal * 100 / 1023
               pwm.ChangeDutyCycle(duty_cycle)

               time.sleep(0.2)

#. When the user interrupts the program with Ctrl+C, the PWM and GPIO are properly cleaned up, and the SPI interface is closed.

   .. code-block:: python

       except KeyboardInterrupt:
           pass

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