How to Use MLX90640: Examples, Pinouts, and Specs

The MLX90640 is a 32x24 pixel thermal imaging sensor designed for non-contact temperature measurement. It operates in the infrared spectrum, allowing it to detect temperature variations across a surface or environment. With a wide temperature detection range of -40°C to 300°C, the MLX90640 is ideal for applications such as thermal monitoring, HVAC systems, robotics, and even human body temperature detection. Its compact size and high accuracy make it a versatile choice for both industrial and consumer applications.

• Resolution: 32x24 pixels
• Temperature Range: -40°C to 300°C
• Field of View (FoV): Available in 55°x35° or 110°x75° models
• Accuracy: ±1°C (typical, for ambient temperatures of 0°C to 50°C)
• Interface: I²C (Inter-Integrated Circuit)
• Supply Voltage: 3.3V to 3.6V
• Current Consumption: ~23mA (typical)
• Refresh Rate: Configurable, 0.5Hz to 64Hz
• Operating Temperature: -40°C to 85°C
• Dimensions: 11mm x 12mm x 5.5mm (approx.)

The MLX90640 typically comes in a breakout board format. Below is the pin configuration:

1. Power Supply: Connect the VDD pin to a 3.3V power source and the GND pin to ground.
2. I²C Communication: Connect the SDA and SCL pins to the corresponding I²C pins on your microcontroller (e.g., Arduino UNO).
3. Pull-Up Resistors: Ensure that the SDA and SCL lines have pull-up resistors (typically 4.7kΩ) to maintain proper I²C communication.
4. I²C Address: Use the ADDR pin to set the I²C address if multiple MLX90640 sensors are used on the same bus.
5. Interrupt Pin: The INT pin is optional and can be used for advanced configurations, such as triggering specific events.

• Thermal Isolation: Avoid placing the sensor near heat sources or reflective surfaces to prevent inaccurate readings.
• Refresh Rate: Choose an appropriate refresh rate based on your application. Higher refresh rates consume more power.
• Calibration: The MLX90640 is factory-calibrated, but additional calibration may be required for specific use cases.
• I²C Pull-Up Resistors: Ensure proper pull-up resistors are in place for reliable I²C communication.
• Field of View: Select the appropriate FoV model (55°x35° or 110°x75°) based on the area you want to monitor.

Below is an example of how to interface the MLX90640 with an Arduino UNO:

#include <Wire.h>
#include <Adafruit_MLX90640.h>

// Create an MLX90640 object
Adafruit_MLX90640 mlx;

// Define the refresh rate (e.g., 8Hz)
#define REFRESH_RATE MLX90640_REFRESH_8_HZ

// Create a buffer to store temperature data
float frame[32 * 24];

void setup() {
  Serial.begin(115200);
  Wire.begin();

  // Initialize the MLX90640 sensor
  if (!mlx.begin()) {
    Serial.println("Failed to find MLX90640 sensor. Check connections!");
    while (1);
  }

  // Set the refresh rate
  mlx.setMode(REFRESH_RATE);
  Serial.println("MLX90640 initialized successfully!");
}

void loop() {
  // Read temperature data into the frame buffer
  if (mlx.getFrame(frame)) {
    Serial.println("Temperature data:");
    for (int i = 0; i < 32 * 24; i++) {
      Serial.print(frame[i]);
      Serial.print(" ");
      if ((i + 1) % 32 == 0) {
        Serial.println(); // Print a new line after every 32 values
      }
    }
    delay(1000); // Delay to match the refresh rate
  } else {
    Serial.println("Failed to read frame data!");
  }
}

• Install the Adafruit MLX90640 library in the Arduino IDE before running the code.
• Ensure the I²C pull-up resistors are properly connected for stable communication.

1. Sensor Not Detected:

   • Cause: Incorrect wiring or I²C address mismatch.
   • Solution: Double-check the connections and ensure the correct I²C address is used.

2. Inaccurate Temperature Readings:

   • Cause: Sensor exposed to heat sources or reflective surfaces.
   • Solution: Isolate the sensor from direct heat sources and avoid reflective surfaces.

3. I²C Communication Errors:

   • Cause: Missing or incorrect pull-up resistors on SDA/SCL lines.
   • Solution: Add 4.7kΩ pull-up resistors to the SDA and SCL lines.

4. Slow Refresh Rate:

   • Cause: Refresh rate set too low.
   • Solution: Increase the refresh rate in the code, but be mindful of power consumption.

1. Can the MLX90640 detect human body temperature?

   • Yes, the MLX90640 can detect human body temperature, but ensure proper calibration for accurate results.

2. What is the maximum distance for accurate temperature measurement?

   • The effective distance depends on the Field of View (FoV) and the size of the object. For small objects, closer distances yield better accuracy.

3. Can I use multiple MLX90640 sensors on the same I²C bus?

   • Yes, you can use multiple sensors by configuring different I²C addresses using the ADDR pin.

4. Is the MLX90640 suitable for outdoor use?

   • The sensor can operate in outdoor environments, but it should be protected from direct sunlight, rain, and extreme conditions for reliable performance.