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.. _2.2.2_py_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
-----------------

.. .. image:: ../img/2.2.2_thermistor_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

.. 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:** 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 2.2.2-2_thermistor.py

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

.. 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
    # -*- coding: utf-8 -*-

    import spidev
    import time
    import math
    import RPi.GPIO as GPIO

    # Set GPIO mode
    GPIO.setmode(GPIO.BCM)

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

    def read_adc(channel):
        """
        Read analog value from MCP3008 channel (0–7)
        """
        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:
        while True:
            # Read analog value from CH0 of MCP3008
            analogVal = read_adc(0)

            # Convert to voltage (assuming 3.3V reference)
            Vr = 3.3 * analogVal / 1023.0

            # Calculate thermistor resistance (R2 in voltage divider is 10kΩ)
            Rt = 10000.0 * Vr / (3.3 - Vr)

            # Steinhart–Hart calculation
            tempK = 1.0 / (((math.log(Rt / 10000.0)) / 3950.0) + (1.0 / (273.15 + 25.0)))

            # Convert to Celsius and Fahrenheit
            Cel = tempK - 273.15
            Fah = Cel * 1.8 + 32

            # Print the result
            print('Celsius: %.2f °C  Fahrenheit: %.2f °F' % (Cel, Fah))

            time.sleep(0.2)

    except KeyboardInterrupt:
        pass

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

**Code Explanation**

#. This section imports required libraries:

   - ``spidev`` for SPI communication with MCP3008
   - ``time`` for delay functionality
   - ``math`` for logarithmic operations in the Steinhart–Hart temperature formula
   - ``RPi.GPIO`` for initializing and cleaning up GPIO (included for structural completeness)

   .. code-block:: python

       #!/usr/bin/env python3
       # -*- coding: utf-8 -*-

       import spidev
       import time
       import math
       import RPi.GPIO as GPIO

#. Initializes the GPIO mode as BCM and configures the SPI interface on bus 0 and device 0 (CE0), with a speed of 1 MHz.

   .. code-block:: python

       # Set GPIO mode
       GPIO.setmode(GPIO.BCM)

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

#. Defines a function ``read_adc(channel)`` to read analog values from a specified MCP3008 channel (0–7). It sends a 3-byte SPI command and receives a 10-bit analog result (0–1023).

   .. code-block:: python

       def read_adc(channel):
           """
           Read analog value from MCP3008 channel (0–7)
           """
           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

#. Main loop: Reads analog voltage from a thermistor on channel 0, converts it to resistance, then uses the Steinhart–Hart equation to estimate temperature in Celsius and Fahrenheit. Updates are printed every 0.2 seconds.

   .. code-block:: python

       try:
           while True:
               # Read analog value from CH0 of MCP3008
               analogVal = read_adc(0)

               # Convert to voltage (assuming 3.3V reference)
               Vr = 3.3 * analogVal / 1023.0

               # Calculate thermistor resistance (R2 in voltage divider is 10kΩ)
               Rt = 10000.0 * Vr / (3.3 - Vr)

               # Steinhart–Hart calculation
               tempK = 1.0 / (((math.log(Rt / 10000.0)) / 3950.0) + (1.0 / (273.15 + 25.0)))

               # Convert to Celsius and Fahrenheit
               Cel = tempK - 273.15
               Fah = Cel * 1.8 + 32

               # Print the result
               print('Celsius: %.2f °C  Fahrenheit: %.2f °F' % (Cel, Fah))

               time.sleep(0.2)

#. The ``finally`` block ensures graceful shutdown. It closes the SPI interface and performs GPIO cleanup to release all hardware resources.

   .. code-block:: python

       except KeyboardInterrupt:
           pass

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