How to Use MLX90621: Examples, Pinouts, and Specs

The MLX90621 is a compact, low-cost infrared thermal sensor designed for non-contact temperature measurement. It features a 16x4 pixel array, enabling the detection of temperature variations across a surface. This makes it ideal for applications such as thermal imaging, human body temperature monitoring, industrial process control, and home automation.

• Thermal imaging cameras
• Non-contact temperature measurement
• HVAC (Heating, Ventilation, and Air Conditioning) systems
• Industrial process monitoring
• Medical diagnostics and fever detection
• Smart home devices

The MLX90621 is a highly versatile sensor with the following key technical details:

The MLX90621 is typically available in a TO-39 package with the following pinout:

The MLX90621 is straightforward to use in a circuit, especially with microcontrollers like the Arduino UNO. Below are the steps and best practices for integrating the sensor:

1. Power Supply: Connect the VDD pin to the 3.3V output of the Arduino and the VSS pin to the GND.
2. I²C Communication: Connect the SDA pin to the Arduino's A4 pin and the SCL pin to the A5 pin (for older Arduino boards) or the dedicated SDA/SCL pins on newer boards.
3. Pull-Up Resistors: Use 4.7kΩ pull-up resistors on the SDA and SCL lines to ensure proper I²C communication.

The following code demonstrates how to read temperature data from the MLX90621 using the Arduino IDE. This example uses the Adafruit MLX90621 library.

#include <Wire.h>
#include <Adafruit_MLX90621.h>

// Create an instance of the MLX90621 object
Adafruit_MLX90621 mlx = Adafruit_MLX90621();

void setup() {
  Serial.begin(9600); // Initialize serial communication for debugging
  Serial.println("Initializing MLX90621...");

  // Initialize the MLX90621 sensor
  if (!mlx.begin()) {
    Serial.println("Failed to initialize MLX90621. Check connections!");
    while (1); // Halt execution if initialization fails
  }
  Serial.println("MLX90621 initialized successfully!");
}

void loop() {
  float temperatures[64]; // Array to store temperature readings

  // Read temperature data from the sensor
  mlx.readPixels(temperatures);

  // Print the temperature data to the Serial Monitor
  for (int i = 0; i < 64; i++) {
    Serial.print("Pixel ");
    Serial.print(i);
    Serial.print(": ");
    Serial.print(temperatures[i]);
    Serial.println(" °C");
  }

  delay(1000); // Wait 1 second before the next reading
}

• Ensure the sensor is not exposed to direct sunlight or strong infrared sources, as this may affect accuracy.
• Use a stable 3.3V power supply to avoid fluctuations in readings.
• Keep the I²C lines as short as possible to minimize noise and interference.
• Calibrate the sensor if precise temperature measurements are required for your application.

1. Sensor Not Detected on I²C Bus:

   • Cause: Incorrect wiring or missing pull-up resistors.
   • Solution: Double-check the connections and ensure 4.7kΩ pull-up resistors are present on the SDA and SCL lines.

2. Inaccurate Temperature Readings:

   • Cause: Environmental interference or improper calibration.
   • Solution: Avoid placing the sensor near heat sources or reflective surfaces. Perform a calibration if necessary.

3. Arduino Freezes During Operation:

   • Cause: I²C communication issues or insufficient power supply.
   • Solution: Verify the power supply voltage and ensure proper pull-up resistor values.

Q: Can the MLX90621 measure the temperature of multiple objects simultaneously?
A: Yes, the 16x4 pixel array allows the sensor to measure the temperature of multiple objects within its field of view.

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

Q: Is the MLX90621 compatible with 5V microcontrollers?
A: The MLX90621 operates at 3.3V. If using a 5V microcontroller, level shifters are required for the I²C lines to prevent damage to the sensor.

By following this documentation, you can effectively integrate and use the MLX90621 in your projects.