herosdevices.hardware.raspberrypi.max318xx.max318xx

Implements the MAX31865 resistance-to-digital converter interface.

The MAX31865 chip communicates via SPI, and in this implementation, SPI communication is carried out through bit-banging using the RPi.GPIO library. For better performance, using an SPI library such as spidev is recommended, but this code is a first approach.

Note: numpy is only required if implementing the full Calendar-Van Dusen equations.

This code is adapted from steve71’s work: https://github.com/steve71/MAX31865

Module Contents

exception herosdevices.hardware.raspberrypi.max318xx.max318xx.FaultError

Bases: Exception

Exception class for handling faults detected in the RTD or wiring.

class herosdevices.hardware.raspberrypi.max318xx.max318xx.MAX318xx(cs_pins: dict, miso_pin: int = 9, mosi_pin: int | None = 10, clk_pin: int = 11)

Base class for MAX318xx series resistance-to-digital converters.

Handles SPI communication via bit-banging using GPIO pins.

cs_pin

{“description”: “Chip select GPIO pin number”}.

Type:

dict

miso_pin

Master In Slave Out GPIO pin number.

Type:

int

mosi_pin

Master Out Slave In GPIO pin number.

Type:

int

clk_pin

Clock GPIO pin number.

Type:

int

cs_pins

miso_pin = 9

mosi_pin = 10

clk_pin = 11

write_register(reg_num: int, data_byte: int) → None

Write a byte to a specified register.

Parameters:

• regNum (int) – Register number to write to.

• dataByte (int) – Data byte to write.

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.

Parameters:

• cs_pin (int) – Chip select GPIO pin number.

• numRegisters (int) – Number of bytes to read.

• regNumStart (int, optional) – Starting register number for the read operation.

Returns:

List of bytes read from the device.

Return type:

list

send_byte(byte: int) → None

Send a byte via SPI by bit-banging.

Parameters:

byte (int) – Byte value to send.

recv_byte() → int

Receive a byte via SPI by bit-banging.

Returns:

Byte received.

Return type:

int

create_dict(values: list[float], observable: str, unit: str) → dict

Build dictionary of observables to be returned by the sensor.