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2.2.2 Thermistor

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
ADC0834	-

Schematic Diagram

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/python-pi5

Step 3: Run the executable file

sudo python3 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.

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 ADC0834
import time
import math

# Initialize the ADC0834 module
ADC0834.setup()

# Run the process in a try-except block
try:
    while True:
        # Read the analog value from the sensor
        analogVal = ADC0834.getResult()

        # Convert the analog value to a voltage
        Vr = 5 * float(analogVal) / 255

        # Calculate the resistance of the thermistor
        Rt = 10000 * Vr / (5 - Vr)

        # Calculate the temperature in Kelvin
        temp = 1 / (((math.log(Rt / 10000)) / 3950) + (1 / (273.15 + 25)))

        # Convert Kelvin to Celsius
        Cel = temp - 273.15

        # Convert Celsius to Fahrenheit
        Fah = Cel * 1.8 + 32

        # Print the temperature in both Celsius and Fahrenheit
        print('Celsius: %.2f C  Fahrenheit: %.2f F' % (Cel, Fah))

        # Wait for 0.2 seconds before the next read
        time.sleep(0.2)

# Handle KeyboardInterrupt for graceful termination
except KeyboardInterrupt:
    # Clean up ADC0834 resources
    ADC0834.destroy()

Code Explanation

1. This section imports the ADC0834 library for analog-to-digital conversion, the time library for implementing delays, and the math library for conducting mathematical operations.

   #!/usr/bin/env python3
   # -*- coding: utf-8 -*-
   
   import ADC0834
   import time
   import math
   

2. Initializes the ADC0834 module to enable reading of analog values.

   # Initialize the ADC0834 module
   ADC0834.setup()
   

3. Implements an infinite loop for continuous data reading. The loop reads the analog value from a thermistor, converts this value to voltage, calculates the thermistor’s resistance, and then translates this resistance into temperature measurements in Kelvin, Celsius, and Fahrenheit. It also outputs the temperature readings in Celsius and Fahrenheit, pausing for 0.2 seconds between each reading.

   # Run the process in a try-except block
   try:
       while True:
           # Read the analog value from the sensor
           analogVal = ADC0834.getResult()
   
           # Convert the analog value to a voltage
           Vr = 5 * float(analogVal) / 255
   
           # Calculate the resistance of the thermistor
           Rt = 10000 * Vr / (5 - Vr)
   
           # Calculate the temperature in Kelvin
           temp = 1 / (((math.log(Rt / 10000)) / 3950) + (1 / (273.15 + 25)))
   
           # Convert Kelvin to Celsius
           Cel = temp - 273.15
   
           # Convert Celsius to Fahrenheit
           Fah = Cel * 1.8 + 32
   
           # Print the temperature in both Celsius and Fahrenheit
           print('Celsius: %.2f C  Fahrenheit: %.2f F' % (Cel, Fah))
   
           # Wait for 0.2 seconds before the next read
           time.sleep(0.2)
   

4. Catches a KeyboardInterrupt exception to gracefully terminate the program and includes clean-up instructions for the ADC0834 resources upon termination.

   # Handle KeyboardInterrupt for graceful termination
   except KeyboardInterrupt:
       # Clean up ADC0834 resources
       ADC0834.destroy()