MLX90614 | GUILCOR SENSORS

MLX90614
Temperature sensors

Infrared temperature sensor for non-contact measurement, ideal for medical, industrial, and automation applications with high accuracy.

Maximum precision
+/- 0,2°K

Minimum temperature
-70°C

Maximum temperature
+380°C

Resolution
0,02°C

Power supply voltage

3,0→5,5V

Response time

0,1 à 1 s

Typical current
1,5 mA

Price
High

What is a MLX90614 sensor ?

The MLX90614 is a non-contact infrared (IR) sensor that measures the temperature of an object or surface from a distance.

It converts thermal infrared radiation into absolute temperature using a thermopile and an integrated digital ASIC.

Available in narrow (5°) or wide (35°) field of view versions, it is used for both medical thermometers and industrial monitoring, HVAC systems, or smart devices.

Operating principle

The sensor is based on Planck's law and the principle of IR radiation.

A hot object emits radiation proportional to its absolute temperature; the thermopile of the MLX90614 converts this flux into voltage, which is then linearized, compensated, and digitized.

Simplified formula used in the sensor:

T_objet = ( V_IR / S + T_amb⁴ )^(1/4)

where:

VIR = voltage measured by the thermopile
S = sensitivity factor
Tamb = internal temperature of the sensor

💡 The internal calibration corrects for emissivity effects, thermal noise, and non-linearity.

Example of digital conversion (SMBus bus)

Register (hex)	Description	Resolution
0x06	Object temperature 1	0,02 °C / LSB
0x07	Object temperature 2 (if double optics)	0,02 °C / LSB
0x08	Ambient temperature	0,02 °C / LSB

T(°C) = (value x 0,02) - 273,15

Temperature / Voltage Response Curve IR

Temperature (°C)	Thermopile voltage (µV)
-40	5
0	18
50	42
100	75
200	160
300	250
380	310

💡 The relationship is nonlinear but corrected by the internal DSP.

Principle diagram (SPI/I²C connection)

+3.3V
 │
[MLX90614]
 │ SDA/SI ─────┐
 │ SCL/SCK ────┤── MCU (I²C or SPI depending on version)
 │ PWM / SDA2 ─┘ (temperature signal output)
 │ GND

💡 Some industrial versions (MLX90614ESF-DCC) offer a direct PWM or SPI output.

Application areas

🏥 Non-contact medical thermometers

⚙️ Industrial monitoring and motorization

🚗 Engine / brake / exhaust temperature measurement

🏠 Home automation (HVAC, thermal presence detectors)

🧠 Robotics and intelligent assistance systems

Should I choose a MLX90614 sensor ?

Strengths points

🌡️ Contactless measurement
→ Ideal for inaccessible, dangerous, or moving areas.
🎯 High precision ±0.2 K
→ Internal compensation of ambient temperature and factory calibration.
🧠 Integrated DSP
→ Direct output in °C via SMBus or PWM, with no software processing required.

Weaknesses points

📏 Sensitivity to emissivity
→ Shiny or reflective surfaces can distort measurements without correction.
💨 Tslow response time (~0.5 s)
→ Less suitable for rapid dynamic measurements.
📦 Optical fragility
→ The IR lens requires a clean environment and protection against dust.

Useful information

Here is some useful information regarding the MLX90614 sensors.

Main registers

Adress (hex)	Name	Description
0x03	Ambient temperature	16 bits – in Kelvin ×50
0x04	Emissivity	0xFFFF = 1.0 (adjustable)
0x05	Sensor configuration	SMBus/PWM Mode
0x06–0x07	Object temperature 1 / 2	16 bits
0x2E	I²C Address	Programmable (EEPROM)

Example of reading (pseudo-code)

i2c_start();
i2c_write(0x5A << 1);     // Sensor address
i2c_write(0x07);          // Object temperature
i2c_start();
i2c_write((0x5A << 1) | 1);
LSB = i2c_read_ack();
MSB = i2c_read_nack();
i2c_stop();

raw = (MSB << 8) | LSB;
tempC = (raw * 0.02) - 273.15;

✅ Example:

Gross value = 16450 → Temperature = 55.85 °C

Typical integration diagram

3.3V ───────────┐ │ [MLX90614] │ SDA ───────┐ │ SCL ───────┤── MCU (Arduino, STM32, ESP32…) │ PWM ───────┘ (output temperature) │ GND

💡 A 100 nF capacitor between VCC and GND is recommended.

Example of emissivity calibration