herosdevices.hardware.raspberrypi.max318xx.max31865
===================================================

.. py:module:: herosdevices.hardware.raspberrypi.max318xx.max31865

.. autoapi-nested-parse::

   MAX31865 Resistance to Digital Converter.

   This module implements an interface for the MAX31865 resistance temperature detector (RTD) converter.
   The chip communicates over SPI. This implementation uses GPIO bit-banging on a Raspberry Pi.
   Using spidev would be more efficient, but initial attempts with spidev were unsuccessful.

   This code is based on the work of steve71: https://github.com/steve71/MAX31865

   Classes:
   - MAX31865: Provides methods to read resistance and temperature from PT100/PT1000 sensors.
     - Initialization allows configuration of SPI pins, reference resistance, and wiring type.
     - Methods to fetch resistance, convert resistance to temperature, and handle errors.

   Usage:
   - Instantiate multiple sensor objects for different chip select pins.
   - Loop to read and print temperature readings.
   - Gracefully handle interruption and clean GPIO resources.

   Notes:
   - Proper wiring and pull-down resistors are essential.
   - Optimized for use with a Raspberry Pi and RPi.GPIO.









Module Contents
---------------

.. py:data:: A
   :value: 0.003908


.. py:data:: B
   :value: -5.775e-07


.. py:data:: C
   :value: -4.183e-12


.. py:function:: c_v_d(r: float, r_0: float) -> float

   Calculate temperature using Callendar-Van Dusen equation.

   This function converts resistance to temperature based on the Calendar-Van Dusen
   equation, which relates resistance in Ohms to temperature in Celsius. It uses numpy
   for polynomial root solving.

   :param r: Resistance in Ohms.
   :type r: float
   :param r_0: Resistance at 0°C in Ohms.
   :type r_0: float

   :returns: Estimated temperature in degrees Celsius.
   :rtype: float

   :raises ImportError: If numpy is not installed.
   :raises ValueError: If the polynomial root calculation encounters issues (e.g., negative discriminant).


.. py:function:: c_v_d_quad(r: float, r_0: float) -> float

   Approximate temperature using a quadratic form of the Callendar-Van Dusen equation.

   This method offers a fast and reasonably accurate way to estimate temperature
   from resistance, suitable for class A PT100 sensors with about 0.2°C accuracy.

   :param r: Resistance in Ohms.
   :type r: float
   :param r_0: Resistance at 0°C in Ohms.
   :type r_0: float

   :returns: Estimated temperature in degrees Celsius.
   :rtype: float

   :raises ValueError: If the discriminant in the quadratic formula is negative.


.. py:class:: MAX31865(cs_pin: int = 8, miso_pin: int = 9, mosi_pin: int = 10, clk_pin: int = 11, r_0: float = 1000.0, r_ref: float = 400.0, three_wire: bool = False)

   Bases: :py:obj:`herosdevices.hardware.raspberrypi.max318xx.max318xx.MAX318xx`


   Interface class for MAX31865 resistance temperature sensor.

   :param cs_pin: Chip select GPIO pin (default: 8).
   :type cs_pin: int
   :param miso_pin: MISO GPIO pin (default: 9).
   :type miso_pin: int
   :param mosi_pin: MOSI GPIO pin (default: 10).
   :type mosi_pin: int
   :param clk_pin: Clock GPIO pin (default: 11).
   :type clk_pin: int
   :param r_0: Resistance at 0°C, in Ohms (default: 1000 for PT1000).
   :type r_0: float
   :param r_ref: Reference resistor resistance, in Ohms (default: 400).
   :type r_ref: float
   :param three_wire: Use 3-wire configuration (default: False).
   :type three_wire: bool
   :param log: Optional logger for debug messages.
   :type log: logging.Logger


   .. py:attribute:: r_ref
      :value: 400.0



   .. py:attribute:: r_0
      :value: 1000.0



   .. py:attribute:: config
      :value: 162



   .. py:method:: read_resistance(cs_pin: int) -> float

      Initiate resistance measurement and return resistance value.

      :returns: Resistance in Ohms.
      :rtype: float



   .. py:method:: read_temp(convert: collections.abc.Callable[[float, float], float] = c_v_d_quad) -> dict

      Read resistance and convert to temperature.

      :param convert: Function to convert resistance to temperature.
                      Defaults to c_v_d_quad.
      :type convert: function

      :returns: Temperature in Celsius.
      :rtype: float



   .. py:attribute:: cs_pins


   .. py:attribute:: miso_pin
      :value: 9



   .. py:attribute:: mosi_pin
      :value: 10



   .. py:attribute:: clk_pin
      :value: 11



   .. py:method:: write_register(reg_num: int, data_byte: int) -> None

      Write a byte to a specified register.

      :param regNum: Register number to write to.
      :type regNum: int
      :param dataByte: Data byte to write.
      :type dataByte: int



   .. py:method:: read_register(cs_pin: int, num_registers: int, reg_num_start: int | None = None) -> list[int]

      Read one or more bytes starting from a specified register.

      :param cs_pin: Chip select GPIO pin number.
      :type cs_pin: int
      :param numRegisters: Number of bytes to read.
      :type numRegisters: int
      :param regNumStart: Starting register number for the read operation.
      :type regNumStart: int, optional

      :returns: List of bytes read from the device.
      :rtype: list



   .. py:method:: send_byte(byte: int) -> None

      Send a byte via SPI by bit-banging.

      :param byte: Byte value to send.
      :type byte: int



   .. py:method:: recv_byte() -> int

      Receive a byte via SPI by bit-banging.

      :returns: Byte received.
      :rtype: int



   .. py:method:: create_dict(values: list[float], observable: str, unit: str) -> dict

      Build dictionary of observables to be returned by the sensor.