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.. _2.2.2_c_mcp3008:

2.2.2 Thermistor(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
------------

Just like photoresistor can sense light, thermistor is a temperature
sensitive electronic device that can be used for realizing functions of
temperature control, such as making a heat alarm.

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

In this project, we need the following components. 

.. image:: ../img/list2_2.2.2_thermistor.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_thermistor`
        - |link_thermistor_buy|
    *   - :ref:`cpn_mcp3008`
        - \-

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


.. image:: ../img/schematic_2.2.2_thermistor_mcp3008.png


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

**Step 1:** Build the circuit.

.. image:: ../img/july24_2.2.2_thermistor_mcp3008.png

**Step 2:** Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/c/2.2.2-2/

**Step 3:** Compile the code.

.. raw:: html

   <run></run>

.. code-block::

    gcc 2.2.2_Thermistor.c -o Thermistor -lwiringPi -lm

.. note::
    -lm is to load the library math. Do not omit, or you will make
    an error.

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

.. raw:: html

   <run></run>

.. code-block::

    ./Thermistor

With the code run, the thermistor detects ambient temperature which will
be printed on the screen once it finishes the program calculation.

.. 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`.

**Code**

.. code-block:: c

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

    #define SPI_CHANNEL 0  // CE0
    #define SPI_SPEED   1000000  // 1MHz

    int read_ADC(int channel) {
        if (channel < 0 || channel > 7) return -1;

        unsigned char buffer[3];
        buffer[0] = 1;  // Start bit
        buffer[1] = (8 + channel) << 4;  // Single-ended mode + channel
        buffer[2] = 0;

        wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

        int value = ((buffer[1] & 3) << 8) | buffer[2];
        return value;
    }

    int main(void) {
        int analogVal;
        double Vr, Rt, temp, cel, Fah;

        if (wiringPiSetup() == -1) {
            printf("setup wiringPi failed!\n");
            return 1;
        }

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

        while (1) {
            analogVal = read_ADC(0);  // Read from CH0

            // MCP3008 is 10-bit ADC (0–1023)
            Vr = 3.3 * analogVal / 1023.0;  // Assume Vref = 3.3V
            Rt = 10000.0 * Vr / (3.3 - Vr); // Voltage divider, 10k resistor
            temp = 1 / ((log(Rt / 10000.0) / 3950.0) + (1 / (273.15 + 25.0)));
            cel = temp - 273.15;
            Fah = cel * 1.8 + 32;

            printf("Celsius: %.2f C  Fahrenheit: %.2f F\n", cel, Fah);
            delay(1000);
        }

        return 0;
    }


Code Explanation
---------------------------

.. code-block:: c

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

These header files include libraries for GPIO control (``wiringPi.h``), SPI communication (``wiringPiSPI.h``), standard I/O operations (``stdio.h``), and math functions (``math.h``) in C.

.. code-block:: c

    #define SPI_CHANNEL 0
    #define SPI_SPEED   1000000

Define constants for the SPI channel and SPI communication speed. Here, SPI channel 0 (CE0) and a clock speed of 1 MHz are used.

.. code-block:: c

    int read_ADC(int channel)

This function reads analog data from a specified channel of the MCP3008 ADC.

.. code-block:: c

    buffer[0] = 1;
    buffer[1] = (8 + channel) << 4;
    buffer[2] = 0;

These lines format the SPI command according to the MCP3008 protocol: a start bit, configuration for single-ended mode, and the channel number.

.. code-block:: c

    wiringPiSPIDataRW(SPI_CHANNEL, buffer, 3);

Transfer the SPI command and receive the 10-bit ADC data from MCP3008.

.. code-block:: c

    int value = ((buffer[1] & 3) << 8) | buffer[2];

Extract and combine the 10-bit ADC result from the returned SPI buffer.

.. code-block:: c

    if (wiringPiSetup() == -1) { ... }
    if (wiringPiSPISetup(SPI_CHANNEL, SPI_SPEED) == -1) { ... }

These lines initialize WiringPi and configure SPI. If initialization fails, the program exits.

.. code-block:: c

    analogVal = read_ADC(0);

Reads the analog signal from MCP3008 channel 0, where the thermistor voltage divider is connected.

.. code-block:: c

    Vr = 3.3 * analogVal / 1023.0;

Convert the digital ADC value into an analog voltage. The ADC range is 0–1023 with 3.3V reference voltage.

.. code-block:: c

    Rt = 10000.0 * Vr / (3.3 - Vr);

Calculate the resistance of the thermistor using the voltage divider formula. A 10kΩ resistor is assumed in series with the thermistor.

.. code-block:: c

    temp = 1 / ((log(Rt / 10000.0) / 3950.0) + (1 / (273.15 + 25.0)));

Use the B-parameter equation to convert the thermistor resistance to temperature in Kelvin. 
 
**T(K) = 1 / [ln(Rt/R₀)/B + 1/T₀]**, where  
- R₀ = 10kΩ  
- B = 3950  
- T₀ = 25°C = 298.15K

.. code-block:: c

    cel = temp - 273.15;

Convert the temperature from Kelvin to degrees Celsius.

.. code-block:: c

    Fah = cel * 1.8 + 32;

Convert the Celsius temperature to Fahrenheit.

.. code-block:: c

    printf("Celsius: %.2f C  Fahrenheit: %.2f F\n", cel, Fah);

Display the temperature in both Celsius and Fahrenheit on the terminal with 2 decimal places of precision.


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

.. .. image:: ../img/image203.jpeg