.. 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_c_pi5_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


Principle
---------

A photoresistor or photocell is a light-controlled variable resistor.
The resistance of a photoresistor decreases with increasing incident
light intensity; in other words, it exhibits photo conductivity. A
photoresistor can be applied in light-sensitive detector circuits, and
light- and darkness-activated switching circuits.

.. image:: img/image196.png
    :width: 200
    :align: center


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

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

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/davinci-kit-for-raspberry-pi/c/2.2.1-2/

**Step 3:** Compile the code.

.. raw:: html

   <run></run>

.. code-block:: 

    gcc 2.2.1_Photoresistor.c -o photoresistor -lwiringPi -lm

**Step 4:** Run the executable file.

.. raw:: html

   <run></run>

.. code-block:: 

    ./photoresistor

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

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi_pi5`.

**Code**

.. code-block:: c

    #include <wiringPi.h>
    #include <wiringPiSPI.h>
    #include <stdio.h>
    #include <softPwm.h>

    #define SPI_CHANNEL 0      // Use SPI channel 0 (CE0)
    #define SPI_SPEED   1000000 // 1 MHz SPI speed
    #define LedPin      3       // GPIO3 (WiringPi) for LED PWM

    // Read ADC value from MCP3008, channel 0~7
    int readMCP3008(int channel) {
        if (channel < 0 || channel > 7) return -1;

        unsigned char buffer[3];
        buffer[0] = 1;                          // Start bit
        buffer[1] = (8 + channel) << 4;         // SGL/DIF = 1, D2-D0 = channel
        buffer[2] = 0;

        wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

        // Combine the result
        int result = ((buffer[1] & 3) << 8) | buffer[2];
        return result;
    }

    int main(void) {
        if (wiringPiSetup() == -1) {
            printf("wiringPi init failed!\n");
            return 1;
        }

        if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) {
            printf("SPI setup failed!\n");
            return 1;
        }

        softPwmCreate(LedPin, 0, 100); // Init software PWM

        while (1) {
            int analogVal = readMCP3008(0); // Read from CH0
            printf("ADC Value: %d\n", analogVal);

            // Scale 10-bit ADC value (0–1023) to PWM range (0–100)
            int pwmVal = analogVal * 100 / 1023;
            softPwmWrite(LedPin, pwmVal);

            delay(100);
        }

        return 0;
    }


**Code Explanation**

The codes here are the same as that in 2.1.4 Potentiometer. If you have
any other questions, please check the code explanation of :ref:`2.1.4_c_pi5_mcp3008` for details.

.. Phenomenon Picture
.. ------------------

.. .. image:: ../img/image199.jpeg