Arduino UNO with 10k NTC Thermistor - Detailed Example

This example demonstrates how to measure temperature using a 10k NTC thermistor with a B-parameter of 3950. The thermistor is connected in a voltage divider with a 10kΩ resistor, and the Arduino reads the voltage at the midpoint of the divider. Using the **Steinhart-Hart equation**, the thermistor resistance is converted to a temperature value. The temperature is displayed in all SI units: **Kelvin (K)**, **Celsius (°C)**, and **Fahrenheit (°F)**.

Detailed Steps

Components

Circuit Connection

Arduino Code


/*
 * © 2024 Copyright Peter I. Dunne, all rights reserved.
 * Prepared for educational use.
 * The ADC is 10 bit, this is of relatively low accuracy, use professional test equipment for accuracy.
 * Released under the Mozilla Public License
 * Arduino UNO with 10k NTC Thermistor and B-parameter of 3950
 * Measures temperature and converts it to Kelvin, Celsius, and Fahrenheit.
 */

const int thermistorPin = A0;     // Thermistor connected to A0
const int referenceResistor = 10000;  // 10k reference resistor (Ohms)
const float B_coefficient = 3950; // B-parameter of thermistor
const float nominalTemperature = 298.15; // 25°C in Kelvin
const float nominalResistance = 10000;   // 10k ohms at 25°C
const float VRef = 5.0; // Arduino reference voltage
const int maxADCValue = 1023;    // 10-bit ADC

void setup() {
    Serial.begin(115200);  // Start serial communication
    Serial.println("Arduino NTC temperature measurement, by Peter Ivan Dunne, ©2024, all rights reserved");
    Serial.println("Released under the Mozilla Public License");
    Serial.println("https://jazenga.com/educational");
}

void loop() {
    // Read analog value from the thermistor
    int adcValue = analogRead(thermistorPin);

    // Convert the ADC value to voltage
    float voltage = (adcValue / float(maxADCValue)) * VRef;

    // Calculate resistance of the thermistor
    float thermistorResistance = referenceResistor * ((VRef / voltage) - 1);

    // Steinhart-Hart equation to calculate temperature in Kelvin
    float steinhart;
    steinhart = thermistorResistance / nominalResistance;  // (R/Ro)
    steinhart = log(steinhart);                            // ln(R/Ro)
    steinhart /= B_coefficient;                            // 1/B * ln(R/Ro)
    steinhart += 1.0 / nominalTemperature;                 // + (1/To)
    steinhart = 1.0 / steinhart;                           // Invert to get temperature in Kelvin

    // Convert temperature to Celsius
    float temperatureC = steinhart - 273.15;
    
    // Convert temperature to Fahrenheit
    float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;

    // Output temperature in Kelvin, Celsius, and Fahrenheit
    Serial.print("Temperature: ");
    Serial.print(steinhart, 2);
    Serial.print(" K, ");
    Serial.print(temperatureC, 2);
    Serial.print(" °C, ");
    Serial.print(temperatureF, 2);
    Serial.println(" °F");

    delay(1000);  // Wait 1 second before next reading
}

How It Works