Arduino for Beginners] 6. Thermistor|Hands-on introductory course for beginners


Table of Contents
0:00 About thermistors and analog inputs
0:53 What we will make this time
1:01 Preparation of materials to be used
1:19 Schematic
2:10 Assembling the circuit
2:22 Programming
3:41 Write on the Board
4:00 Summary.

Codes used

This is the code used in the video. Please feel free to use it.

const int analogPin = 0; //A0を使用

const float B = 3950.0; //サーミスタのB定数
const float R0 = 10000.0; //サーミスタの25度での抵抗値(カタログ値)
const float Rd = 10000.0; //検知抵抗の抵抗値
const float Tk = 273.15; //0度=273.15ケルビン

void setup()
void loop()
  float readValue = analogRead(analogPin);
  float Rt = Rd * readValue / (1023 - readValue);
  float Tbar = 1/B * log(Rt/R0) + 1/(Tk + 25);
  float T = 1/Tbar;
  float Tdeg = T - Tk;

6. Thermistor

I'm stuck on the analog read function and the four arithmetic operations.

In this course, we will learn about the analog read function and the four arithmetic operations together!
What you will learn in this lesson
  • analog Read function
  • basic arithmetic operations
  • Data type: float
  • How to use the data monitor

Here we will use the thermistor to learn about the analogRead function, the four arithmetic operations, and the data type float.

About Thermistors and Analog Inputs

A thermistor is a type of temperature sensor that has the characteristic of changing resistance when the temperature changes.

By using this characteristic in reverse, temperature can be measured from the change in resistance.

However, it is difficult to measure resistance directly, so it is generally read by converting it to voltage by setting up a circuit like the following.

The detection resistor Rd is a general resistance, and if Rd does not change its resistance value regardless of temperature, the voltage at point A will vary with the resistance value of Rt.

The amount of change in resistance is determined from the amount of change in this voltage!

The following equation can then be used to convert it to the final temperature.

The B constant is a constant that indicates the characteristics of the thermistor and shows the slope of how much the resistance value changes in response to changes in temperature.

In most cases, the value is found in the thermistor's data sheet, so use that value.

What we will make this time

This is the circuit we created this time, and you can see that the temperature changes when you touch it like this or turn up the heat with a hair dryer.

Now let's make this circuit!

Preparation of materials to be used

The materials used for this project are an Arduino Uno, a breadboard, three male and three female jumper wires, a thermistor, and a 10kΩ resistor.

There are two types of thermistors: the NTC type , whose resistance decreases as heat increases, and the PTC type , whose resistance increases.

Be careful not to make a mistake, as it is mainly the NTC type that is used for temperature sensors!


The following figure shows the circuit diagram to be created for this project.

The analog input terminal of the Arduino has a 10-bit AD converter that can convert analog-like voltages in the range of 0 to 5 V into digital data in the range of 0 to 1023.

The voltage per memory is called the resolution, and in this case, 5V is divided by 1024, so one memory is roughly 5mV.

There are a total of six analog input terminals, and the A0 terminal is used in this case.

A little care must be taken in choosing the resistance value of the Rd!

If Rd is too small or too large, the voltage at point A will swing very little, making it difficult to accurately calculate the resistance.

In reality, fine adjustments are necessary depending on the temperature range you wish to measure, but for the time being, I think it is best to use a value equivalent to the resistance of the thermistor at room temperature.

In the case of this thermistor, since it is 10kΩ, Rd is also 10kΩ.

construct a circuit

The breadboard diagram below follows the schematic diagram.

If we follow this diagram and build a circuit, it will look like this.


Now we will proceed with the coding.

Start the Arduino IDE, click "File→New File" and enter the program shown on this screen.

Lines 5-8 are constants used to calculate resistance.

In this case, since a decimal point is generated by using division, etc., a data type called float is used, which can handle a decimal point.

In this case, we will use a function called serial monitor to see how the values change.

This is a function that allows the Arduino and PC to exchange data via serial communication, allowing you to verify operation while viewing values in real time.

This function can be used by using the function Serial.begin in the setup function.

In the loop function, the analogRead function first reads the voltage value.

Next, determine the current resistance.

The idea of the formula is easy to understand when you think in terms of ratios like this.

The Arduino can perform a variety of calculations, from general calculations called four arithmetic operations to slightly more complex ones such as log and root.

Next, use the formula written here to find T.

This is a well-known formula for calculating thermistor temperature, so if you want some background, check out the following site!

Note that the unit of measurement at this point is Kelvin, which represents absolute temperature.

Finally, after converting to Celsius, throw the value to Serial.println to complete the temperature observation.

The waiting time, i.e., how often the value is updated, can be any number of seconds, but for the time being, it is set to 0.2 seconds.

Write on board

Finally, save the file and press the "Write to microcontroller board" button on the toolbar to write the file.

When writing is complete, press the "Serial Monitor" button in the upper right corner.

Thus, the value would be updated every 0.2 seconds.

First, measure the room temperature to see if the calculation is correct, and see if it roughly matches your senses.


So this is what we have learned in this issue.

What I learned from this lesson
  • analog Read function
  • basic arithmetic operations
  • Data type: float
  • How to use the data monitor
Let's do it!
Check that the temperature changes by touching or warming it up with your hand. Check that the temperature changes by touching it with your hand or by warming it up.

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