Arduino Infrared Temperature Sensor: Complete Tutorial with MLX90614

Introduction

Building an Arduino infrared temperature sensor enables non-contact temperature measurement for health monitoring, industrial automation, and IoT projects. This complete tutorial uses the MLX90614 infrared thermometer sensor with Arduino Uno to create a contactless temperature measurement system, covering hardware connections, Arduino code, calibration, and practical applications with real-world examples.

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Components Required

Essential Parts

Component	Quantity	Purpose
Arduino Uno/Nano	1	Microcontroller
MLX90614 IR Sensor	1	Temperature measurement
I2C LCD Display (16×2)	1	Temperature display (optional)
Jumper Wires	4-8	Connections
Breadboard	1	Prototyping
USB Cable	1	Arduino programming

About MLX90614 Sensor

Key Features:

• Non-contact measurement: 0-5cm to 10cm range
• Temperature range: -40°C to +125°C (object), -40°C to +85°C (ambient)
• Accuracy: ±0.5°C (typical)
• Interface: I²C digital output
• Supply voltage: 3.3V or 5V compatible
• Package: TO-39 (4-pin metal can)

How It Works:

• Infrared thermopile detects IR radiation
• Internal ADC converts to digital temperature
• Factory-calibrated for ±0.5°C accuracy
• Two temperature readings: object and ambient

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Hardware Setup

Wiring Diagram

MLX90614 to Arduino Connection:

MLX90614 Pin   →   Arduino Pin
────────────────────────────────
VIN (Pin 1)    →   5V
GND (Pin 2)    →   GND
SCL (Pin 3)    →   A5 (SCL)
SDA (Pin 4)    →   A4 (SDA)

Note: Some modules include built-in pull-up resistors.
If not, add 4.7kΩ pull-ups on SCL/SDA to 5V.

Circuit Diagram:

        Arduino Uno
         ┌─────┐
     5V  │     │  A5 (SCL) ────── SCL  ┐
    GND  │     │  A4 (SDA) ────── SDA  │  MLX90614
         └─────┘                       │  IR Sensor
                              VIN  ────┘
                              GND  ────── GND

Optional: Adding LCD Display

I2C LCD (16×2) Connection:

LCD I2C Module  →  Arduino
─────────────────────────
VCC             →  5V
GND             →  GND
SDA             →  A4 (shared with MLX90614)
SCL             →  A5 (shared with MLX90614)

Note: MLX90614 and LCD can share I2C bus
(different I2C addresses: MLX90614=0x5A, LCD=0x27)

Physical Setup Tips

1. Sensor positioning: Point MLX90614 at target object (5-10cm distance optimal)
2. Field of view: ~90° cone; closer distance = smaller measurement area
3. Avoid reflective surfaces: May cause inaccurate readings
4. Stable mounting: Use tape or bracket for consistent measurements

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Arduino Code

Basic Temperature Reading

Install Library First:

• Open Arduino IDE → Tools → Manage Libraries
• Search "Adafruit MLX90614" → Install

Simple Code Example:

#include <Wire.h>
#include <Adafruit_MLX90614.h>

Adafruit_MLX90614 mlx = Adafruit_MLX90614();

void setup() {
  Serial.begin(9600);
  
  if (!mlx.begin()) {
    Serial.println("Error: MLX90614 not found!");
    while (1);
  }
  
  Serial.println("MLX90614 IR Temperature Sensor");
}

void loop() {
  // Read temperatures
  float ambientTemp = mlx.readAmbientTempC();
  float objectTemp = mlx.readObjectTempC();
  
  // Print to Serial Monitor
  Serial.print("Ambient: ");
  Serial.print(ambientTemp);
  Serial.print("°C | Object: ");
  Serial.print(objectTemp);
  Serial.println("°C");
  
  delay(1000); // Update every 1 second
}

Output (Serial Monitor):

MLX90614 IR Temperature Sensor
Ambient: 25.3°C | Object: 36.8°C
Ambient: 25.3°C | Object: 36.7°C

Advanced: With LCD Display

Install LCD Library:

• Search "LiquidCrystal I2C" → Install

Complete Code with LCD:

#include <Wire.h>
#include <Adafruit_MLX90614.h>
#include <LiquidCrystal_I2C.h>

Adafruit_MLX90614 mlx = Adafruit_MLX90614();
LiquidCrystal_I2C lcd(0x27, 16, 2); // Address 0x27, 16 columns, 2 rows

void setup() {
  Serial.begin(9600);
  
  // Initialize MLX90614
  if (!mlx.begin()) {
    Serial.println("MLX90614 error!");
    while (1);
  }
  
  // Initialize LCD
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("IR Thermometer");
  delay(2000);
  lcd.clear();
}

void loop() {
  float objectTemp = mlx.readObjectTempC();
  float ambientTemp = mlx.readAmbientTempC();
  
  // Display on LCD
  lcd.setCursor(0, 0);
  lcd.print("Object: ");
  lcd.print(objectTemp, 1);
  lcd.print("C");
  
  lcd.setCursor(0, 1);
  lcd.print("Ambient: ");
  lcd.print(ambientTemp, 1);
  lcd.print("C");
  
  // Also print to Serial
  Serial.print(objectTemp);
  Serial.print(",");
  Serial.println(ambientTemp);
  
  delay(500);
}

Temperature Unit Conversion

Fahrenheit Conversion:

float tempF = (tempC * 9.0 / 5.0) + 32.0;

// Example usage
float objectTempC = mlx.readObjectTempC();
float objectTempF = (objectTempC * 9.0 / 5.0) + 32.0;

Serial.print("Temperature: ");
Serial.print(objectTempC);
Serial.print("°C / ");
Serial.print(objectTempF);
Serial.println("°F");

Adding Temperature Alarm

Trigger Buzzer/LED at Threshold:

#define BUZZER_PIN 8
#define LED_PIN 13
#define TEMP_THRESHOLD 38.0 // Fever threshold (°C)

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  // ... other setup code
}

void loop() {
  float objectTemp = mlx.readObjectTempC();
  
  if (objectTemp > TEMP_THRESHOLD) {
    digitalWrite(LED_PIN, HIGH);
    tone(BUZZER_PIN, 1000); // 1kHz beep
    lcd.setCursor(0, 1);
    lcd.print("HIGH TEMP!  ");
  } else {
    digitalWrite(LED_PIN, LOW);
    noTone(BUZZER_PIN);
  }
  
  delay(500);
}

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Applications

1. Health Monitoring

Contactless Forehead Thermometer:

• Mount sensor in handheld enclosure
• Point at forehead (5cm distance)
• Display temperature on LCD
• Alarm for fever detection (>38°C)

Arduino + MLX90614 + LCD + Battery = Portable thermometer

2. Industrial Automation

Machine Temperature Monitoring:

• Monitor motor/bearing temperature
• Non-contact prevents interference
• Data logging to SD card
• Predictive maintenance alerts

3. IoT Temperature Logger

ESP8266/ESP32 Integration:

// Send to cloud (ThingSpeak, Blynk)
WiFiClient client;
String apiKey = "YOUR_API_KEY";
client.print("GET /update?api_key=");
client.print(apiKey);
client.print("&field1=");
client.println(objectTemp);

4. HVAC Control

Smart Thermostat:

• Measure room temperature (ambient)
• Measure object temperature (occupancy detection)
• Control relay for heater/AC
• Energy-efficient heating

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Troubleshooting

Sensor Not Found Error

Problem: Error: MLX90614 not found!

Solutions:

• Check I2C connections (SDA→A4, SCL→A5)
• Verify power supply (5V, GND)
• Test I2C scanner code (detect address 0x5A)
• Add 4.7kΩ pull-up resistors if missing

Inaccurate Readings

Problem: Temperature readings fluctuate or incorrect

Solutions:

• Ensure 5-10cm distance to object
• Avoid reflective/shiny surfaces
• Wait 5 seconds for sensor stabilization
• Check for heat sources nearby (sun, lamps)
• Verify emissivity setting (default 0.95 for skin)

LCD Not Displaying

Problem: LCD backlight on but no text

Solutions:

• Check LCD I2C address (0x27 or 0x3F)
• Adjust contrast potentiometer on LCD module
• Verify shared I2C bus wiring
• Test LCD separately with example code

Conclusion

Building an Arduino infrared temperature sensor with MLX90614 provides accurate contactless temperature measurement (±0.5°C) through simple I2C interface, supporting health monitoring, industrial automation, and IoT applications with minimal wiring and straightforward Arduino code, making it ideal for makers, students, and engineers creating non-contact temperature measurement systems.

Project Summary:

✅ Easy Setup: 4-wire connection (VCC, GND, SDA, SCL)
✅ Accurate: ±0.5°C factory-calibrated
✅ Non-Contact: 5-10cm optimal measurement distance
✅ Arduino Library: Adafruit MLX90614 simplifies coding
✅ Expandable: Add LCD, WiFi, alarms, data logging
✅ Affordable: ~$10-15 sensor cost
✅ Versatile: Medical, industrial, HVAC, IoT applications

Building Arduino projects? Visit AiChipLink.com for Arduino components, sensors, and maker project consultation.

 

 

 

 

 

Written by Jack Elliott from AIChipLink.

 

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