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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

Step 4: Run the executable file

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 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. 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
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

1. 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)

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

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

   # 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
   

3. 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).

   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
   

4. 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.

   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)
   

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

   except KeyboardInterrupt:
       pass
   
   finally:
       spi.close()
       GPIO.cleanup()