MLX90614 Contactless IR Temperature Sensor Interfacing with Arduino

The MLX90614 is a contactless IR Temperature sensor which can measure temperature without even touching the object. This exceptional sensor introduced by Melexis uses IR technology that uses the IR radiations to measure temperature and provides a digital output signal through I2C port. Contactless temperature sensors played a major contribution during COVID-19 days to check temperature. In this tutorial, we will discuss pinout details, pin configurations, specifications, features interfacing with Arduino, and applications of an MLX90614 temperature sensor.

MLX90614 Non-Contact IR Temperature Sensor

Table of Contents

MLX90614 Temperature Sensor Introduction

MLX90614 is IR based contactless temperature sensor that can measure the temperature of a particular object between -70°C – 382.2°C and an ambient temperature of -40°C – 125°C without even making physical contact with an object under observation. It is embedded with an I2C port to communicate temperature reading to microcontrollers over an I2C bus. On top of that, it is provided with ESD protection to avoid malfunctioning of the sensor.

The tiny device is highly accurate and precise due to its powerful ADC. A 17-bit ADC is embedded in the module to output the values with 0.14 ˚C of resolution. Melexis has introduced different versions of this sensor based on input voltage requirements i.e., 3 Volts or 5volts and resolving power for different project requirements. But MLX90614 is a sensitive temperature sensor that has a long list of applications, especially in home automation

MLX90614 Pinout

This temperature sensor module comes with a 3.3 voltage regulator, I2C Bus with internal pullup resistors to define a default state and a capacitor for noise filtering. The pinout of the non-contact MLX90614 IR Temperature Sensor module is as shown:

MLX90614 Non-Contact IR Temperature Sensor pinout diagram

Pin Configuration

MLX90614 has two versions and is available in the TO-39 package. The pin configuration details are listed in a table below:

Pin Name	Function
VCC	Positive power supply pin
GND	Reference potential pin
SCL	Open drain Serial Clock pin. An I2C line clock pulses pin for data synchronization.
SDA	Open drain Serial Data pin. An I2C line to communicate data to the host MCU.

Features & Specifications

Operating Voltage: 3.6 Volts – 5.5 Volts
Ambient Temperature Range: -40°C – 125°C
Object Temperature Range: -70°C – 380°C
Measurement resolution: 0.02°C
ESD Sensitivity: 2kV
Sink/Source Current: 25mA
ADC Resolution: 17 bits
IR sensor is integrated with an optical filter, a DSP, and a low noise amplifier for fine output digital signals.
Adaptable for 8-16 Volts applications and can be integrated easily.
Supports power-saving mode and is available in single and dual versions
It is a power-efficient and highly sensitive sensor.

Take a look at the datasheet to see further technicals of different versions of this IR sensor.

IR Sensor working principle

MLX90614 is a contactless IR temperature sensor that works on the Stefan Boltzmann principle. It states that everybody radiates IR radiation proportional to its temperature. This radiation is then measured through the sensor converted to a digital signal and is communicated through the I2C bus to the microcontroller.

The IR sensor module consists of an IR thermopile detector and a signal ASSP processing unit. Thermopile serves the function of collecting the radiation in its field view which varies from version to version. The processing units convert these analog signals to filtered amplified signals.

Block Diagram

The functional diagram of MLX90614 IR Temperature Sensor for conceiving the knowledge of the internal connections of the module is provided below:

MLX90614 Interfacing with Arduino

This section explains the interfacing of the Arduino UNO and MLX90614 contactless IR Temperature sensor. But you can use any Arduino board or microcontroller which have an I2C port. Because the MLX90614 sensor provides temperature output on the I2C bus.

Connection Diagram

The following figure shows the connection diagram between MLX90614 temperature sensor and Arduino.

Connect the power supply pin (Vin) of the temperature sensor to the 5V pin of Arduino and the GND pin of MLX90614 to the GND pin Arduino UNO.
Connect the SDA and SCL pins of the mentioned IR sensor to the A4 and A5 pins of the Arduino UNO for transferring data serially. A4 and A5 pins of Arduino also share alternate function of SDA and SCL pins of I2C port of Arduino Uno.

MLX90614 Non-Contact IR Temperature Sensor interfacing with Arduino

Arduino UNO	MLX90614 IR Sensor
5V	VCC
GND	GND
SDA	A4
SCL	A5

Installing the Adafruit MLX90614 Arduino Library

Before going to the programming section, First, download the Adafruit MLX90614 Arduino library and install it on the Arduino IDE software. It is very convenient to use the prewritten library specifically for the module and add it to the sketches to perform the commands. Download the Adafruit MLX90614 Arduino Library from this link:

Arduino library

After that, follow these steps to install the library: Sketch >Include Library> Add .ZIP Library. Moreover, you can check this video to know how to install new library in Arduino IDE:

After installation, restart the Arduino IDE and it is ready to use.

Arduino Code

The Arduino code for MLX90614 IR Temperature Sensor is provided below:

#include <Wire.h>
#include <Adafruit_MLX_Sensor90614.h>
char *Object_Type[]={"Object","Ambient"};

Adafruit_MLX_Sensor90614 MLX_Sensor = Adafruit_MLX_Sensor90614();

void setup() {
  Serial.begin(9600);
  Serial.println("MLX90614 Sensor MicroLab");  
  MLX_Sensor.begin();  
}

void loop() {

  Display_Temperature('A'); //Get Object temperature in Celsius
  Display_Temperature('B'); //Get Ambient temperature in Celsius
  
  Display_Temperature('C'); //Get Object temperature in Keliven
  Display_Temperature('D'); //Get Ambient temperature in Keliven

  
  Display_Temperature('E'); //Get Object temperature in Fahrenheit
  Display_Temperature('F'); //Get Ambient temperature in Fahrenheit
  Serial.println("########");

  delay(2000);

  
}


float Get_Temperature_Sample(char type)
{
    float temp_value;
    float Object_Temperature = MLX_Sensor.readObjectTempC();
    float Ambient_Temperature = MLX_Sensor.readAmbientTempC();
   if(type =='E')
   {
    temp_value = MLX_Sensor.readObjectTempF(); //Fah. Object
   }else if(type =='F')
   {
    temp_value = MLX_Sensor.readAmbientTempF();//Fah Ambient
   }else if(type =='C')
   {
    temp_value = Object_Temperature + 273.15;// Object Kelvin
   }else if(type =='D')
   {
    temp_value = Ambient_Temperature + 273.15;//Ambient Kelvin
   }else if(type =='A')
   {
    temp_value = Object_Temperature;
   }else if(type =='B')
   {
    temp_value = Ambient_Temperature;
   }
   return temp_value;
 
}

void Display_Temperature(char type)
{
  float temp_data =Get_Temperature_Sample(type);

  if(type =='A')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");    
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("C");
  }else if(type =='B')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("C");
  }else if(type =='C')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("F");
  }else if(type =='D')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("F");
  }

  else if(type =='E')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");     
    Serial.print(temp_data);  
    Serial.print("°");       
    Serial.println(" K");
  }  
  else if(type =='F')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);  
    Serial.print("°");       
    Serial.println(" K");
  }

}

How does the code work?

Include libraries

The first step is to include the required libraries i.e. “Adafruit_MLX90614.h” for temperature sensor, “Wire.h” for I2C protocol. An instance of char type ( *Object_Type) to hold an array of characters is introduced. Also, an object “MLX_Sensor” is created to access the MLX90614 library functions.

#include <Wire.h>
#include <Adafruit_MLX_Sensor90614.h>
char *Object_Type[]={"Object","Ambient"};
Adafruit_MLX_Sensor90614 MLX_Sensor = Adafruit_MLX_Sensor90614();

Inside Setup Function

The void setup performs two things. It initializes the serial monitor with 9600 bps and also initializes the MLX_Sensor object which initialized the IR sensor library to begin taking temperature samples.

void setup() {
  Serial.begin(9600);
  Serial.println("MLX90614 Sensor MicroLab");  
  MLX_Sensor.begin();  
}

Inside Loop Function

Inside the void loop function, we use the function “Display_Temperature” to get temperature measurements in Celcius, Kelvin, and Fahrenheit and display them on Arduino serial monitor. With the help of this function, it displays the ambient temperature plus object temperature in Centigrade, Fahrenheit, and Kelvin. The updated values of temperature will be displayed after a delay of 2000 milliseconds on serial monitor.

void loop() {

  Display_Temperature('A'); //Get Object temperature in Celsius
  Display_Temperature('B'); //Get Ambient temperature in Celsius
  
  Display_Temperature('C'); //Get Object temperature in Keliven
  Display_Temperature('D'); //Get Ambient temperature in Keliven

  
  Display_Temperature('E'); //Get Object temperature in Fahrenheit
  Display_Temperature('F'); //Get Ambient temperature in Fahrenheit
  Serial.println("########");

  delay(2000);


}

We can use an if condition and make code applicable for a practical application like turning off the heater or air conditioner if the temperature exceeds a specific value or is less than a specific value.

Get_Temperature_Sample Function

The “Get_Temperature_Sample()” function is created to receive the temperature values based on the user’s instruction. Three float variables “temp_value, Object_Temperature, and Ambient_Temperature” are created to store the temperature values.

float Get_Temperature_Sample(char type)
{
    float temp_value;
    float Object_Temperature = MLX_Sensor.readObjectTempC();
    float Ambient_Temperature = MLX_Sensor.readAmbientTempC();
   if(type =='E')
   {
    temp_value = MLX_Sensor.readObjectTempF(); //Fah. Object
   }else if(type =='F')
   {
    temp_value = MLX_Sensor.readAmbientTempF();//Fah Ambient
   }else if(type =='C')
   {
    temp_value = Object_Temperature + 273.15;// Object Kelvin
   }else if(type =='D')
   {
    temp_value = Ambient_Temperature + 273.15;//Ambient Kelvin
   }else if(type =='A')
   {
    temp_value = Object_Temperature;
   }else if(type =='B')
   {
    temp_value = Ambient_Temperature;
   }
   return temp_value;
 
}

The object temperature in Celsius is read and stored in Object_Temperature and the ambient temperature in Celsius is read and stored in Ambient_Temperature If the user types a character “E”, the “temp_value” variable receives the temperature of the target object in Fahrenheit through “MLX_Sensor” object and if the user types a character “F”, the “temp_value” variable receives the ambient temperature in Fahrenheit through “MLX_Sensor” object. Similarly, typing the “C” value variable adds 273.15 to the Fahrenheit value present in it and upgrades itself which is the Kelvin temperature of the target object. And “D” will do the same but this time value has the ambient temperature which is upgraded by adding 273.15 to it.

On typing “A” or B”, the “temp_value” variable will get the reading from the Object_Temperature or Ambient_Temperature respectively, and returns it.

A is object temperature in Celsius
B is the ambient temperature in Celsius
C is object temperature in Fahrenheit
D is the ambient temperature in Fahrenheit
E is object temperature in Kelvin
F is the ambient temperature in Kelvin

Display_Temperature() Function

It is another function that will call the Get_Temperature_Sample() function and prints the temperature readings as instructed by the user. For example, if the user types “A”, print functions call the getTemp function, get the reading, and show the readings on Arduino serial monitor. The same goes for all the characters defined.

void Display_Temperature(char type)
{
  float temp_data =Get_Temperature_Sample(type);

  if(type =='A')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");    
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("C");
  }else if(type =='B')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("C");
  }else if(type =='C')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("F");
  }else if(type =='D')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);
    Serial.print("°");      
    Serial.println("F");
  }

  else if(type =='E')
  {
    Serial.print(Object_Type[0]);
    Serial.print(" ");     
    Serial.print(temp_data);  
    Serial.print("°");       
    Serial.println(" K");
  }  
  else if(type =='F')
  {
    Serial.print(Object_Type[1]);
    Serial.print(" ");     
    Serial.print(temp_data);  
    Serial.print("°");       
    Serial.println(" K");
  }

}

Upload the code and observe the readings. The Serial monitor displays the respective readings when specific characters are entered. Note that the MLX90614 IR sensor is a very sensitive device and fluctuates very easily.

Alternate Options

MLX90615
ZTP115
TPIS 1S

Applications

Medical care Systems
Home temperature monitoring
Environment Control
Temperature Gun
DIY Projects
Commercial Applications
Moving object temperature detection

Interface MLX90614 Non-Contact IR Temperature Sensor with Arduino