Every other temperature sensor we've covered needs to physically touch what it's measuring; the MLX90614 breaks that rule entirely, reading an object's temperature from a distance using infrared radiation alone.
What it measures
The MLX90614 estimates an object surface temperature from infrared radiation while measuring its own die temperature for compensation. The familiar ±0.5°C figure applies only over specified ranges, not the full operating span. Field of view, target emissivity, and thermal equilibrium all affect the result, and a general breakout is not a certified medical thermometer.
Wiring it up
The MLX90614 communicates over I2C, needing just two data pins — A4 (SDA) and A5 (SCL) on an Arduino Uno — alongside power and ground. Because I2C devices each carry a unique address, a 16x2 LCD display (itself running through its own I2C adapter) can share that same two-wire bus alongside the sensor without any conflict.
Programming it
Two libraries do the work: the Adafruit MLX90614 library handles reading both temperature values from the sensor, while LiquidCrystal_I2C drives the display. The sketch reads the ambient and object temperatures once a second, printing both to the Serial Monitor and to the LCD simultaneously.
If the display or sensor doesn't respond
Every I2C device ships with a default address, but conflicts or slight manufacturing variation occasionally mean a module doesn't answer at its expected address. Running a simple I2C scanner sketch first — a small program that checks every possible address for a response — confirms the correct one before troubleshooting anything else.
What it's used for
Because it never touches what it's measuring, the MLX90614 fits naturally into fever-screening devices, motion and presence detection based on a person's body heat, and automotive applications like checking engine or brake temperatures without direct contact.
You can find MLX90614 sensors and I2C LCD displays at Juthour Tech.
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