MLX90614 IR thermometer with Arduino Uno — wiring and accurate readings

The MLX90614 reads temperature from the infrared light an object gives off, so it measures without touching. The GY-906 module (about ₹600) is popular for motor and bearing checks, cooking projects and contactless thermometers.

It is an I2C device at 0x5A. On the Uno it wires to SDA/SCL and, on boards with a regulator, to 5V. It reports two numbers: the object temperature it is looking at, and the ambient temperature of the sensor itself.

The quirks section below matters more than the code here. The sensor sees a wide cone, not a dot, so distance, shiny surfaces and glass all change the reading. The sketch prints both temperatures twice a second.

Wiring

Board quirks

• The board’s I2C pull-ups sit at its 3.3 V rail. The Uno reads 3.3 V as a HIGH, so the GY-906 works directly. Look for the regulator before feeding it 5 V.
• The common BAA version sees a 90° cone: at 5 cm it averages a spot about 10 cm wide. Hold the object close and fill that cone, or the reading mixes in the background.
• Shiny metal reflects IR and reads far too low (a hot steel pan can read like room temperature). Put a strip of black electrical tape on it and measure the tape.
• It isn’t a medical thermometer: skin reads 1–3 °C below body temperature and depends on distance. Fine for “is the motor hot?”, not for fever screening.

Code

// MLX90614 (GY-906) non-contact IR thermometer on an Arduino Uno R3, I2C at 0x5A.
// VIN → 5V (GY-906 has a regulator), GND → GND, SCL → SCL (A5), SDA → SDA (A4).
#include <Wire.h>
#include <Adafruit_MLX90614.h>

Adafruit_MLX90614 mlx;

void setup() {
  Serial.begin(9600);
  if (!mlx.begin()) {
    Serial.println(F("MLX90614 not found at 0x5A - check SDA/SCL and power"));
    for (;;) {}
  }
  Serial.println(F("MLX90614 ready. Hold objects 2-5 cm in front of the sensor."));
}

void loop() {
  Serial.print(F("Object "));
  Serial.print(mlx.readObjectTempC(), 1);
  Serial.print(F(" C   Ambient "));
  Serial.print(mlx.readAmbientTempC(), 1);
  Serial.println(F(" C"));
  delay(500);
}

// MLX90614 (GY-906) non-contact IR thermometer on an Arduino Uno R3, I2C at 0x5A.
// VIN → 5V (GY-906 has a regulator), GND → GND, SCL → SCL (A5), SDA → SDA (A4).
#include <Wire.h>
#include <Adafruit_MLX90614.h>

Adafruit_MLX90614 mlx;

void setup() {
  Serial.begin(9600);
  if (!mlx.begin()) {
    Serial.println(F("MLX90614 not found at 0x5A - check SDA/SCL and power"));
    for (;;) {}
  }
  Serial.println(F("MLX90614 ready. Hold objects 2-5 cm in front of the sensor."));
}

void loop() {
  Serial.print(F("Object "));
  Serial.print(mlx.readObjectTempC(), 1);
  Serial.print(F(" C   Ambient "));
  Serial.print(mlx.readAmbientTempC(), 1);
  Serial.println(F(" C"));
  delay(500);
}

Library: Adafruit MLX90614 Library (Adafruit) — compiled with Adafruit MLX90614 Library 2.1.7.

Expected serial output

MLX90614 ready. Hold objects 2-5 cm in front of the sensor.
Object 29.4 C   Ambient 28.7 C
Object 61.8 C   Ambient 28.8 C

MLX90614 ready. Hold objects 2-5 cm in front of the sensor.
Object 29.4 C   Ambient 28.7 C
Object 61.8 C   Ambient 28.8 C

Common errors