Added high resolution temp reading

Author: diegosolano

adafruit_max31856.py

@@ -164,8 +164,9 @@ def __init__(
  spi: SPI,
  cs: DigitalInOut, # pylint: disable=invalid-name
  thermocouple_type: int = ThermocoupleType.K,
+ baudrate: int = 500000,
  ) -> None:
- self._device = SPIDevice(spi, cs, baudrate=500000, polarity=0, phase=1)
+ self._device = SPIDevice(spi, cs, baudrate=baudrate, polarity=0, phase=1)
 
  # assert on any fault
  self._write_u8(_MAX31856_MASK_REG, 0x0)
@@ -253,6 +254,27 @@ def unpack_temperature(self) -> float:
 
  return temp_float
 
+ def read_high_res_temp_degC(self) -> float:
+ # Per datasheet, temperature resolution in °C per LSB
+ resolution = 0.0078125
+
+ # Read the temperature registers
+ raw_bytes = self._read_sequential_registers(_MAX31856_LTCBH_REG, 3)
+ # Extract individual bytes from the byte array
+ high_byte = raw_bytes[0] # First byte
+ mid_byte = raw_bytes[1] # Second byte
+ low_byte = raw_bytes[2] # Third byte
+
+ # Combine the bytes into a single 19-bit value
+ combined = (high_byte << 11) | (mid_byte << 3) | (low_byte >> 5)
+
+ # Adjust for two's complement (sign extension for negative values)
+ if combined & 0x40000: # Check if 19th bit is set (negative temperature)
+ combined = combined - 0x80000
+
+ # Convert to temperature using the resolution
+ return combined * resolution
+
  @property
  def reference_temperature(self) -> float:
  """Wait to retrieve temperature of the cold junction in degrees Celsius. (read-only)"""
@@ -363,6 +385,21 @@ def initiate_one_shot_measurement(self) -> None:
  # write it back with the new values, prompting the sensor to perform a measurement
  self._write_u8(_MAX31856_CR0_REG, conf_reg_0)
 
+ def start_autoconverting(self) -> None: # pylint: disable=no-self-use
+ """Starts autoconverting temperature measurements.
+ The sensor will perform a measurement every ~100ms.
+ """
+ # read the current value of the first config register
+ conf_reg_0 = self._read_register(_MAX31856_CR0_REG, 1)[0]
+
+ # and the complement to guarantee the oneshot bit is unset
+ conf_reg_0 &= ~_MAX31856_CR0_1SHOT
+ # or the autoconvert bit to ensure it is set
+ conf_reg_0 |= _MAX31856_CR0_AUTOCONVERT
+
+ # write it back with the new values, prompting the sensor to perform a measurement
+ self._write_u8(_MAX31856_CR0_REG, conf_reg_0)
+
  @property
  def oneshot_pending(self) -> bool:
  """A boolean indicating the status of the one-shot flag.
@@ -386,6 +423,19 @@ def _read_register(self, address: int, length: int) -> bytearray:
  device.readinto(self._BUFFER, end=length)
  return self._BUFFER[:length]
 
+ def _read_sequential_registers(self, start_addr, num_registers=3):
+ """
+ Read a sequence of `num_registers` registers, starting from `start_addr`.
+ """
+ assert num_registers >= 1, "Number of registers to read must be at least 1"
+ buf = bytearray(num_registers)
+ with self._device as device:
+ # Send read command and start address
+ device.write(bytearray([start_addr & 0x7F]))
+ # Read the specified number of registers into the buffer
+ device.readinto(buf)
+ return buf
+
  def _write_u8(self, address: int, val: int) -> None:
  # Write an 8-bit unsigned value to the specified 8-bit address.
  with self._device as device: