Python & CircuitPython

It's easy to use the MAX31865 sensor with Python or CircuitPython, and the Adafruit CircuitPython MAX31865 module.  This module allows you to easily write Python code that reads the range from the sensor.

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 MAX31865 to your board exactly as shown on the previous pages for Arduino.   Here's an example of wiring a Feather M0 to the sensor with a SPI connection:

  • Board 3V to sensor VIN
  • Board GND to sensor GND
  • Board SCK to sensor CLK
  • Board MOSI to sensor SDI
  • Board MISO to sensor SDO
  • Board D5 to sensor CS (or any other digital I/O pin)

Python Computer Wiring

Since there's 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 SPI:

  • Pi 3V3 to sensor VIN
  • Pi GND to sensor GND
  • Pi MOSI to sensor SDI
  • Pi MISO to sensor SDO
  • Pi SCLK to sensor CLK
  • Pi GPIO5 to sensor CS (or use any other free GPIO pin)

CircuitPython Installation of MAX31865 Library

Next you'll need to install the Adafruit CircuitPython MAX31865 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.  For example the Circuit Playground Express guide has a great page on how to install the library bundle for both express and non-express boards.

Remember for non-express boards like the Trinket M0, Gemma M0, and Feather/Metro M0 basic you'll need to manually install the necessary libraries from the bundle:

  • adafruit_max31865.mpy
  • adafruit_bus_device

Before continuing make sure your board's lib folder or root filesystem has the adafruit_max31865.mpy, and adafruit_bus_device files and folders copied over.

Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.

Python Installation of MAX31865 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-max31865

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 initialize it and read the range and more from the board's Python REPL.

Run the following code to import the necessary modules and initialize the SPI connection with the sensor:

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import board
import busio
import digitalio
import adafruit_max31865
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
cs = digitalio.DigitalInOut(board.D5)  # Chip select of the MAX31865 board.
sensor = adafruit_max31865.MAX31865(spi, cs)

Notice you need to explicitly define the chip select digital I/O pin--be sure to use the same pin as your wiring (D5 if following this example exactly).

By default the MAX31865 class assumes a 2 wire sensor, however you can change this by setting the wires keyword argument in the initializer.  Set this to the number of wires in your sensor (2, 3, or 4).  For example to create a 3 wire sensor:

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import board
import busio
import digitalio
import adafruit_max31865
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
cs = digitalio.DigitalInOut(board.D5)  # Chip select of the MAX31865 board.
sensor = adafruit_max31865.MAX31865(spi, cs, wires=3)

Be sure to set wires to the appropriate value for your sensor!

In addition you can specify the nominal resistance and reference resistance of the RTD with these optional keyword arguments of the initializer:

  • rtd_nominal - This is the resistance value in Ohms of the RTD at a nominal value (typically 0 degrees Celsius).  This defaults to 100 for a PT100 sensor.  For a PT1000 change it to 1000 Ohms.
  • ref_resistor - The reference resistor value in Ohms.  The default is 430 Ohms which matches the PT100 version of the breakout.  For a PT1000 breakout change this to 4300 Ohms.

For example here's how to create a 2-wire PT1000 sensor instance with 1000 Ohm nominal resistance and 4300 Ohm reference resistance:

Download: file
import board
import busio
import digitalio
import adafruit_max31865
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
cs = digitalio.DigitalInOut(board.D5)  # Chip select of the MAX31865 board.
sensor = adafruit_max31865.MAX31865(spi, cs, rtd_nominal=1000.0, ref_resistor=4300.0)

Now you're ready to read values from the sensor using any of these properties:

  • temperature - The temperature measured by the sensor in degrees Celsius.
  • resistance - The resistance of the RTD in Ohms.
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print('Temperature: {0:0.3f}C'.format(sensor.temperature))
print('Resistance: {0:0.3f} Ohms'.format(sensor.resistance))

See the simpletest.py example for a complete demo of printing the range every second.  Save this as code.py on the board and examine the REPL output to see the temperature printed every second.

That's all there is to using the MAX31865 with CircuitPython!

Full Example Code

# Simple demo of the MAX31865 thermocouple amplifier.
# Will print the temperature every second.
import time

import board
import busio
import digitalio

import adafruit_max31865


# Initialize SPI bus and sensor.
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
cs = digitalio.DigitalInOut(board.D5)  # Chip select of the MAX31865 board.
sensor = adafruit_max31865.MAX31865(spi, cs)
# Note you can optionally provide the thermocouple RTD nominal, the reference
# resistance, and the number of wires for the sensor (2 the default, 3, or 4)
# with keyword args:
#sensor = adafruit_max31865.MAX31865(spi, cs, rtd_nominal=100, ref_resistor=430.0, wires=2)

# Main loop to print the temperature every second.
while True:
    # Read temperature.
    temp = sensor.temperature
    # Print the value.
    print('Temperature: {0:0.3f}C'.format(temp))
    # Delay for a second.
    time.sleep(1.0)
This guide was first published on Nov 15, 2016. It was last updated on Nov 15, 2016. This page (Python & CircuitPython) was last updated on Dec 05, 2019.