Arduino: How to use KY-001 Temperature Sensor Module

Arduino Basics: KY-001 Temperature Sensor Module

Abstract

Learn how to use the KY-001 Temperature Sensor Module with Arduino. This module typically contains a DS18B20 digital temperature sensor or a simple thermistor (like the 10k NTC thermistor). This tutorial will focus on the more common thermistor implementation often found on the KY-001, which requires reading an Analog Input voltage and converting it to a temperature using the Steinhart-Hart equation (simplified).

1. Introduction

The KY-001, in its simplified form, functions as an analog temperature sensor using a Negative Temperature Coefficient (NTC) thermistor in a voltage divider circuit.

NTC Thermistor: Its resistance decreases as its temperature increases.
Voltage Divider: The changing resistance of the thermistor causes a proportional change in the voltage read by the Arduino’s Analog Input Pin.

In this article you’ll learn:

The relationship between resistance and temperature in an NTC thermistor.
How to read the thermistor’s voltage using analogRead().
The steps required to convert the raw Analog-to-Digital Converter (ADC) reading into a physical resistance.
How to use a simplified conversion formula to calculate temperature in Celsius (C) and Fahrenheit (F).

This project introduces a complex nonlinear analog conversion essential for environmental monitoring.

2. Prerequisites and Hardware Setup

Make sure you have:

An Arduino Nano or compatible board.
One KY-001 Temperature Sensor Module (assuming the thermistor version).
Jumper Wires.
Arduino IDE

3. Wiring and Setup for Arduino

The KY-001 module requires an analog input pin.

Step 1 – Identify Pins

The module typically has three pins: Signal (S or OUT), VCC (+), and GND (− or GND).

Step 2 – Connect the Module

Wire the module to the Arduino as follows. The signal pin must be connected to one of the Analog Input Pins (A0-A5).

Connect the GND pin of the KY-001 to the GND pin on the Arduino.
Connect the VCC pin of the KY-001 to the 5V pin on the Arduino.
Connect the S / Signal pin of the KY-001 to Arduino Analog Pin A0.

This image was created with Fritzing

Step 3 – Understanding Key Constants

To convert the resistance to temperature, we need constants specific to the thermistor (assuming a standard 10kΩ NTC with a B-parameter of 3950):

- R0=10000 (Resistance at nominal temperature, 10kΩ)
- T0=298.15 (Nominal temperature in Kelvin, 25∘C)
- B=3950 (The B-parameter, characteristic of the material)
- Rseries=10000 (The fixed resistor in the module’s voltage divider circuit)

4. Writing Temperature Conversion Code

The code requires two main calculations:

ADC Reading to Resistance (R): Uses the voltage divider formula.
Resistance to Temperature (T): Uses the Steinhart-Hart equation (simplified B-parameter model).

Open main.ino and implement the following code.

				
					// 1. Hardware Pin
const int THERMISTOR_PIN = A0;

// 2. Thermistor Constants (Standard 10k NTC with 10k series resistor)
const float R_SERIES = 10000.0; // The fixed resistor value in the voltage divider
const float R_NOMINAL = 10000.0; // Resistance at 25C
const float T_NOMINAL = 298.15; // Temperature in Kelvin at 25C (25 + 273.15)
const float B_COEFFICIENT = 3950.0; // The Beta coefficient of the thermistor material

void setup() {
  Serial.begin(9600);
  Serial.println("KY-001 Thermistor Temperature Sensor Ready!");
}

void loop() {
  // --- A. Read and Convert ADC to Resistance ---
  int rawADC = analogRead(THERMISTOR_PIN);
 
  // Calculate resistance R from voltage divider formula:
  // R = R_SERIES / (1023 / ADC - 1)
  float resistance = R_SERIES / ((1023.0 / rawADC) - 1.0);

  // --- B. Convert Resistance to Temperature (Kelvin) ---
  // Steinhart-Hart simplified B-parameter equation:
  // 1/T = 1/T0 + (1/B) * ln(R/R0)
  float steinhart;
  steinhart = resistance / R_NOMINAL;        // (R / R0)
  steinhart = log(steinhart);                // ln(R / R0)
  steinhart /= B_COEFFICIENT;                // (1/B) * ln(R / R0)
  steinhart += 1.0 / T_NOMINAL;              // 1/T0 + (1/B) * ln(R / R0)
  steinhart = 1.0 / steinhart;               // T (Temperature in Kelvin)

  // --- C. Final Conversion to Celsius and Fahrenheit ---
  float tempC = steinhart - 273.15;          // Convert Kelvin to Celsius
  float tempF = (tempC * 9.0) / 5.0 + 32.0;  // Convert Celsius to Fahrenheit
 
  // --- D. Print Results ---
  Serial.print("Raw ADC: ");
  Serial.print(rawADC);
  Serial.print(" | Temp C: ");
  Serial.print(tempC, 2); // Print with 2 decimal places
  Serial.print(" | Temp F: ");
  Serial.println(tempF, 2);

  delay(1000);
}

Code Explanation

Voltage Divider: The formula R = R_SERIES / (1023 / ADC – 1) calculates the thermistor’s resistance based on the ADC reading and the fixed 10kΩ series resistor.
Steinhart-Hart Model: This is a non-linear equation used to accurately model the resistance-to-temperature relationship of a thermistor. It is done in a step-by-step manner to find the temperature in Kelvin first.
Temperature Change: If you heat the sensor (e.g., with your finger), the resistance decreases, the ADC reading increases, and the calculated temperature rises.

OPTIONAL

If your KY-001 has the DS18B20, which has the single-bus digital temperature sensor, consider using any digital pin instead and the following code:

				
					#include <OneWire.h>
#include <DallasTemperature.h>

// Data wire is plugged into pin 2 on the Arduino
#define ONE_WIRE_BUS 2

// Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
OneWire oneWire(ONE_WIRE_BUS);
// Pass our oneWire reference to Dallas Temperature.
DallasTemperature sensors(&oneWire);

void setup(void)
{
  // start serial port
  Serial.begin(9600);
  Serial.println("Dallas Temperature IC Control Library Demo");
  // Start up the library
  sensors.begin(); // IC Default 9 bit. If you have troubles consider upping it 12. Ups the delay giving the IC more time to process the temperature measurement
}

void loop(void)
{
  // call sensors.requestTemperatures() to issue a global temperature
  // request to all devices on the bus
  Serial.print("\r\nRequesting temperatures...");
  sensors.requestTemperatures(); // Send the command to get temperatures
  Serial.println("DONE");

  Serial.print("Temperature for Device 1 is: ");
  Serial.print(sensors.getTempCByIndex(0)); // Why "byIndex"? You can have more than one IC on the same bus. 0 refers to the first IC on the wire
  delay(1000);
}

5. Uploading and Running the Project

Step 1 – Build & Upload

Complete the standard build and upload process.

Step 2 – Test

Open the Serial Monitor (Tools > Serial Monitor).
Observe the initial reading (should be close to room temperature, ≈20-25∘C).
Hold the sensor firmly between your fingers. The ADC reading should increase, and the calculated temperature (C and F) should rise towards body temperature (≈37∘C).

6. Hands-On Lab Recap

You’ve learned:

The function of an NTC thermistor within a voltage divider.
The two-step process to convert a raw ADC reading into a physical temperature.
How to apply the Steinhart-Hart (B-parameter) model for non-linear temperature sensing.

This concludes the comprehensive series on fundamental KY-series modules, providing you with a complete toolkit for basic electronic projects.

7. Common Issues & Fixes

Issue	Cause	Solution
ADC is fixed at 0 or 1023.	Wiring error or VCC/GND issue	Check that VCC is 5V and GND is secure. Ensure the signal pin is on an Analog pin.
Temperature reading is consistent but incorrect.	Incorrect constants (Rseries or B) used in the code.	Measure the actual series resistor on your module. If the B-coefficient is wrong, the conversion will drift at extreme temperatures.
Code doesn't compile (error on log).	Missing Math Library.	Ensure you are using floating-point variables (float) for all math operations and that log() is recognized.