How to Use mlx90614: Examples, Pinouts, and Specs

The MLX90614 is a non-contact infrared temperature sensor designed to measure the temperature of objects without requiring direct physical contact. Manufactured by Melexis, this sensor utilizes infrared thermopile technology and integrates a low-noise amplifier, 17-bit ADC, and a powerful DSP for accurate temperature readings. It communicates via the I2C protocol, making it easy to interface with microcontrollers and other digital systems.

• Non-contact temperature measurement in industrial and medical applications
• Thermal imaging systems
• HVAC (Heating, Ventilation, and Air Conditioning) monitoring
• Consumer electronics, such as smart thermostats
• Automotive climate control systems

The MLX90614 is available in various models, but the following specifications are common across most variants:

The MLX90614 is typically available in a 4-pin TO-39 package. Below is the pinout description:

1. Power Supply: Connect the VDD pin to a 3.6V to 5.5V power source and the VSS pin to ground.
2. I2C Communication: Connect the SDA and SCL pins to the corresponding I2C pins on your microcontroller. Use pull-up resistors (typically 4.7kΩ) on both SDA and SCL lines if not already present on your board.
3. Bypass Capacitor: Place a 0.1µF ceramic capacitor between VDD and VSS for noise filtering.

The MLX90614 can be easily interfaced with an Arduino UNO using the Wire library. Below is an example code to read the object temperature:

#include <Wire.h>

// MLX90614 default I2C address
#define MLX90614_I2C_ADDR 0x5A

// MLX90614 register for object temperature
#define MLX90614_TOBJ1 0x07

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Start serial communication for debugging
  Serial.println("MLX90614 Temperature Sensor Test");
}

void loop() {
  float objectTemp = readTemperature(MLX90614_TOBJ1); // Read object temperature
  Serial.print("Object Temperature: ");
  Serial.print(objectTemp);
  Serial.println(" °C");
  delay(1000); // Wait 1 second before the next reading
}

// Function to read temperature from the MLX90614
float readTemperature(uint8_t reg) {
  Wire.beginTransmission(MLX90614_I2C_ADDR); // Start communication with sensor
  Wire.write(reg); // Request data from the specified register
  Wire.endTransmission(false); // Send repeated start condition
  Wire.requestFrom(MLX90614_I2C_ADDR, (uint8_t)3); // Request 3 bytes of data

  if (Wire.available() < 3) {
    return NAN; // Return NaN if data is not available
  }

  uint16_t data = Wire.read(); // Read low byte
  data |= Wire.read() << 8; // Read high byte and combine
  uint8_t pec = Wire.read(); // Read PEC (Packet Error Code, not used here)

  // Convert raw data to temperature in Celsius
  return (data * 0.02) - 273.15;
}

• Ensure proper pull-up resistors are used on the I2C lines.
• Avoid placing the sensor in direct sunlight or near heat sources, as this may affect accuracy.
• The sensor's field of view (FOV) should be considered when positioning it to ensure accurate readings.
• Use a stable power supply to minimize noise and improve measurement accuracy.

1. No Data from Sensor:

   • Ensure the I2C connections (SDA, SCL) are correct and secure.
   • Verify that the pull-up resistors are properly connected.
   • Check the sensor's power supply voltage (3.6V to 5.5V).

2. Inaccurate Temperature Readings:

   • Ensure the sensor is not exposed to reflective surfaces or direct sunlight.
   • Verify that the sensor is within its specified operating temperature range.

3. I2C Communication Errors:

   • Confirm the I2C address (default: 0x5A) matches the one in your code.
   • Check for conflicting devices on the I2C bus.

Q: Can the MLX90614 measure the temperature of liquids?
A: Yes, but the sensor must have a clear line of sight to the liquid's surface. Ensure the liquid is not reflective to avoid inaccurate readings.

Q: How can I reduce noise in the temperature readings?
A: Use a stable power supply, add a bypass capacitor (0.1µF) near the sensor, and average multiple readings in your code.

Q: Can I change the I2C address of the MLX90614?
A: Yes, the I2C address can be changed by writing to the sensor's EEPROM. Refer to the manufacturer's datasheet for detailed instructions.

Q: What is the maximum distance for accurate temperature measurement?
A: The effective range depends on the size and emissivity of the target object. For small objects, the sensor should be placed closer to ensure accurate readings.