Python & CircuitPython

It's easy to use the MLX90640 sensor with Python and CircuitPython, and the Adafruit CircuitPython MLX90640 module. This module allows you to easily write Python code that reads temperature using the thermal camera.

You can use this sensor with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.

CircuitPython Microcontroller Wiring

First wire up a MLX90640 to your board for an I2C connection, exactly  as shown below.  Here's an example of wiring a Feather M4 to the sensor with I2C:

  • Board 3V to sensor VIN (red wire)
  • Board GND to sensor GND (black wire)
  • Board SCL to sensor SCL (yellow wire)
  • Board SDA to sensor SDA (blue wire)

Python Computer Wiring

Since there are dozens of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported

Here's the Raspberry Pi wired with I2C:

  • Pi 3V to sensor VCC (red wire)
  • Pi GND to sensor GND (black wire)
  • Pi SCL to sensor SCL (yellow wire)
  • Pi SDA to sensor SDA (blue wire)

CircuitPython Installation of MLX90640 Library

You'll need to install the Adafruit CircuitPython MLX90640 library on your CircuitPython board.

First make sure you are running the latest version of Adafruit CircuitPython for your board.

Next you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle.  Our CircuitPython starter guide has a great page on how to install the library bundle.

You'll need to manually install the necessary libraries from the bundle:

  • adafruit_mlx90640.mpy
  • adafruit_bus_device

Before continuing, make sure your board's lib folder has the adafruit_mlx90640.mpy, and adafruit_bus_device files and folders copied over.

Python Installation of MLX90640 Library

You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!

Once that's done, from your command line run the following command:

  • sudo pip3 install adafruit-circuitpython-mlx90640

If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!

CircuitPython & Python Usage

To demonstrate the usage of the sensor we'll run the mlx90640_simpletest.py program which prints the temperatures or shows them as ASCII. As this example is too complicated to run from the REPL, you'll save the following code to your board as code.py and connect to the serial console to see the output.

import time
import board
import busio
import adafruit_mlx90640

PRINT_TEMPERATURES = False
PRINT_ASCIIART = True

i2c = busio.I2C(board.SCL, board.SDA, frequency=800000)

mlx = adafruit_mlx90640.MLX90640(i2c)
print("MLX addr detected on I2C")
print([hex(i) for i in mlx.serial_number])

mlx.refresh_rate = adafruit_mlx90640.RefreshRate.REFRESH_2_HZ

frame = [0] * 768
while True:
    stamp = time.monotonic()
    try:
        mlx.getFrame(frame)
    except ValueError:
        # these happen, no biggie - retry
        continue
    print("Read 2 frames in %0.2f s" % (time.monotonic() - stamp))
    for h in range(24):
        for w in range(32):
            t = frame[h * 32 + w]
            if PRINT_TEMPERATURES:
                print("%0.1f, " % t, end="")
            if PRINT_ASCIIART:
                c = "&"
                # pylint: disable=multiple-statements
                if t < 20:
                    c = " "
                elif t < 23:
                    c = "."
                elif t < 25:
                    c = "-"
                elif t < 27:
                    c = "*"
                elif t < 29:
                    c = "+"
                elif t < 31:
                    c = "x"
                elif t < 33:
                    c = "%"
                elif t < 35:
                    c = "#"
                elif t < 37:
                    c = "X"
                # pylint: enable=multiple-statements
                print(c, end="")
        print()
    print()

If you change the values for the variables at the top of the program, you can switch from printing out an ASCII image to printing out the temperatures in a grid. Change PRINT_TEMPERATURES to True and PRINT_ASCIIART to False, so that the two lines are as follows:

Download: file
PRINT_TEMPERATURES = True
PRINT_ASCIIART = False

Connect to the serial console to see the temperatures printed out in a grid. Fitting them all in a proper grid involved making my terminal window significantly larger than the default size.

That's all there is to using the MLX90640 with CircuitPython!

This guide was first published on Jan 29, 2020. It was last updated on Jan 29, 2020. This page (Python & CircuitPython) was last updated on May 31, 2020.