MAX31856

CircuitPython module for the MAX31856 Universal Thermocouple Amplifier. See examples/simpletest.py for an example of the usage.

  • Author(s): Bryan Siepert

Implementation Notes

Hardware:

Software and Dependencies:

class adafruit_max31856.MAX31856(spi: SPI, cs: DigitalInOut, thermocouple_type: int = 3)

Driver for the MAX31856 Universal Thermocouple Amplifier

Parameters:

  • spi (SPI) – The SPI bus the MAX31856 is connected to.

  • cs (Pin) – The pin used for the CS signal.

  • thermocouple_type (ThermocoupleType) – The type of thermocouple. Default is Type K.

  • sampling (~int) – Number of samples to be averaged [1,2,4,8,16]

  • filter_50hz (~bool) – Filter 50Hz mains frequency instead of 60Hz

Quickstart: Importing and using the MAX31856

Here is an example of using the MAX31856 class. First you will need to import the libraries to use the sensor

import board
from digitalio import DigitalInOut, Direction
import adafruit_max31856

Once this is done you can define your board.SPI object and define your sensor object

spi = board.SPI()
cs = digitalio.DigitalInOut(board.D5)  # Chip select of the MAX31856 board.
sensor = adafruit_max31856.MAX31856(spi, cs)

Now you have access to the temperature attribute

temperature = sensor.temperature
property averaging: int

Number of samples averaged together in each result. Must be 1, 2, 4, 8, or 16. Default is 1 (no averaging).

property fault: Dict[str, bool]

A dictionary with the status of each fault type where the key is the fault type and the value is a bool if the fault is currently active

Key

Fault type

“cj_range”

Cold junction range fault

“tc_range”

Thermocouple range fault

“cj_high”

Cold junction high threshold fault

“cj_low”

Cold junction low threshold fault

“tc_high”

Thermocouple high threshold fault

“tc_low”

Thermocouple low threshold fault

“voltage”

Over/under voltage fault

“open_tc”

Thermocouple open circuit fault
initiate_one_shot_measurement() → None

Starts a one-shot measurement and returns immediately. A measurement takes approximately 160ms. Check the status of the measurement with oneshot_pending; when it is false, the measurement is complete and the value can be read with unpack_temperature.

property noise_rejection: Literal[50, 60]

The frequency (Hz) to be used by the noise rejection filter. Must be 50 or 60. Default is 60.

property oneshot_pending: bool

A boolean indicating the status of the one-shot flag. A True value means the measurement is still ongoing. A False value means measurement is complete.

property reference_temperature: float

Wait to retrieve temperature of the cold junction in degrees Celsius. (read-only)

property reference_temperature_thresholds: Tuple[float, float]

The cold junction’s low and high temperature thresholds as a (low_temp, high_temp) tuple

property temperature: float

Measure the temperature of the sensor and wait for the result. Return value is in degrees Celsius. (read-only)

property temperature_thresholds: Tuple[float, float]

The thermocouple’s low and high temperature thresholds as a (low_temp, high_temp) tuple

unpack_reference_temperature() → float

Reads the reference temperature from the register

unpack_temperature() → float

Reads the probe temperature from the register

class adafruit_max31856.ThermocoupleType

An enum-like class representing the different types of thermocouples that the MAX31856 can use. The values can be referenced like ThermocoupleType.K or ThermocoupleType.S Possible values are

  • ThermocoupleType.B

  • ThermocoupleType.E

  • ThermocoupleType.J

  • ThermocoupleType.K

  • ThermocoupleType.N

  • ThermocoupleType.R

  • ThermocoupleType.S

  • ThermocoupleType.T