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.. _2.2.2_js_pi5_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_extension_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/2.2.2_Thermistor_bb.png


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

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/raphael-kit/nodejs/

**Step 3:** Run the code.

.. raw:: html

   <run></run>

.. code-block:: 

    sudo node thermistor-2.js

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

**Code**

.. code-block:: js

    const mcpadc = require('mcp-spi-adc');

    // Open MCP3008 channel 0 (CH0), analog input from thermistor voltage divider
    const adc = mcpadc.openMcp3008(0, { speedHz: 1350000 }, (err) => {
      if (err) {
        console.error('Failed to open MCP3008 channel:', err);
        process.exit(1);
      }

      console.log('MCP3008 thermistor channel opened.');

      setInterval(() => {
        adc.read((err, reading) => {
          if (err) {
            console.error('ADC read error:', err);
            return;
          }

          const adcValue = reading.value; // Float: 0.0–1.0
          const raw = Math.round(adcValue * 1023); // 10-bit integer value

          const Vr = 3.3 * raw / 1023; // Convert to voltage (assuming 3.3V Vref)
          const R0 = 10000;            // Fixed resistor: 10k
          const B = 3950;              // B constant
          const Rt = R0 * Vr / (3.3 - Vr); // Thermistor resistance

          const tempK = 1 / ((Math.log(Rt / R0) / B) + (1 / (273.15 + 25))); // Kelvin
          const tempC = tempK - 273.15; // Celsius
          const tempF = tempC * 1.8 + 32; // Fahrenheit

          console.log(`Celsius: ${tempC.toFixed(2)} °C  |  Fahrenheit: ${tempF.toFixed(2)} °F`);
        });
      }, 1000);
    });


**Code Explanation**

.. code-block:: js

    setInterval(() => {
      adc.read((err, reading) => {
        ...
      });
    }, 1000);

Sets up a loop to read from MCP3008 channel 0 every 1000 milliseconds (1 second). The `read` function returns an analog value between 0.0 and 1.0.

.. code-block:: js

    const raw = Math.round(reading.value * 1023);

Converts the normalized float ADC value into a raw 10-bit integer (range 0–1023).

.. code-block:: js

    const Vr = 3.3 * raw / 1023;

Calculates the voltage at the thermistor (``Vr``) using the ADC reading. Assumes MCP3008 reference voltage is 3.3V.

.. code-block:: js

    const Rt = R0 * Vr / (3.3 - Vr);

Uses the voltage divider formula to calculate the thermistor resistance ``Rt``, where ``R0`` is a fixed resistor (10kΩ) in series.

.. code-block:: js

    const tempK = 1 / ((Math.log(Rt / R0) / B) + (1 / (273.15 + 25)));

This applies the **B-parameter equation** (a simplified form of the Steinhart-Hart equation) to estimate the temperature in Kelvin.

.. code-block:: js

    const tempC = tempK - 273.15;
    const tempF = tempC * 1.8 + 32;

These convert the Kelvin temperature to Celsius and then Fahrenheit.

.. code-block:: js

    console.log(`Celsius: ${tempC.toFixed(2)} °C  |  Fahrenheit: ${tempF.toFixed(2)} °F`);

Prints both the Celsius and Fahrenheit temperature values with two decimal points of precision to the console.


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

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