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2.2.2 Thermistor(MCP3008)

Note

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.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
Thermistor	BUY
MCP3008	-

Schematic Diagram

T-Board Name	physical	WiringPi	BCM
SPICE0	pin24	10	8
SPIMOSI	pin19	12	10
SPIMISO	pin21	13	9
SPISCLK	pin23	14	11

Experimental Procedures

Step 1: Build the circuit.

Step 2: Set up the SPI interface and install the spidev library (see 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.

cd ~/raphael-kit/python-pi5

Step 4: Run the executable file

sudo python3 2.2.2-2_Thermistor_zero.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 If gpiozero doesn’t work.

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-pi5. After modifying the code, you can run it directly to see the effect.

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

import spidev
import time
import math

# 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
    # MCP3008 communication format
    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 (3.3V reference)
        Vr = 3.3 * analogVal / 1023.0

        # Calculate thermistor resistance
        Rt = 10000.0 * Vr / (3.3 - Vr)

        # Calculate temperature in Kelvin using the Steinhart–Hart approximation
        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 temperature
        print('Celsius: %.2f °C  Fahrenheit: %.2f °F' % (Cel, Fah))

        # Wait before next reading
        time.sleep(0.2)

except KeyboardInterrupt:
    spi.close()

Code Explanation

1. This section imports the spidev module for communicating with the MCP3008 ADC via SPI, the time module for delays, and the math module for logarithmic calculations needed in temperature conversion.

   #!/usr/bin/env python3
   # -*- coding: utf-8 -*-
   
   import spidev
   import time
   import math
   

2. Initializes the SPI interface for MCP3008 on bus 0 and device 0 (CE0), setting the maximum SPI clock speed to 1 MHz.

   # 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
   

3. Defines a function to read analog values from a specified MCP3008 channel (0–7). The SPI protocol is used to communicate with the MCP3008, and a 10-bit integer (0–1023) is returned.

   def read_adc(channel):
       """
       Read analog value from MCP3008 channel (0–7)
       """
       if channel < 0 or channel > 7:
           return -1
       # MCP3008 communication format
       adc = spi.xfer2([1, (8 + channel) << 4, 0])
       value = ((adc[1] & 0x03) << 8) | adc[2]
       return value
   

4. Implements a loop to continuously read analog values from a thermistor connected to CH0 of MCP3008. It converts the raw reading into a voltage (based on 3.3V reference), then into resistance, and finally into temperature using the Steinhart–Hart equation. Temperature is output in both Celsius and Fahrenheit. A short delay is inserted between readings.

   try:
       while True:
           # Read analog value from CH0 of MCP3008
           analogVal = read_adc(0)
   
           # Convert to voltage (3.3V reference)
           Vr = 3.3 * analogVal / 1023.0
   
           # Calculate thermistor resistance
           Rt = 10000.0 * Vr / (3.3 - Vr)
   
           # Calculate temperature in Kelvin using the Steinhart–Hart approximation
           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 temperature
           print('Celsius: %.2f °C  Fahrenheit: %.2f °F' % (Cel, Fah))
   
           # Wait before next reading
           time.sleep(0.2)
   

5. Captures a KeyboardInterrupt (Ctrl+C) for graceful program termination. It closes the SPI interface to release the resource.

   except KeyboardInterrupt:
       spi.close()