Merge pull request #28 from diegosolano/main

Added SPI baudrate argument, high res temperature reading, and autoconvert function

adafruit_max31856.py

@@ -124,8 +124,7 @@ class MAX31856:
     :param ~microcontroller.Pin cs: The pin used for the CS signal.
     :param ~adafruit_max31856.ThermocoupleType thermocouple_type: The type of thermocouple.\
       Default is Type K.
-    :param ~int sampling: Number of samples to be averaged [1,2,4,8,16]
-    :param ~bool filter_50hz: Filter 50Hz mains frequency instead of 60Hz
+    :param ~int baudrate: The SPI baudrate. Default is 500000.
 
     **Quickstart: Importing and using the MAX31856**
 
@@ -164,8 +163,9 @@ 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 +253,35 @@ def unpack_temperature(self) -> float:
 
         return temp_float
 
+    def read_high_res_temp(self) -> float:
+        """Reads 19-bit temperature data from the sensor and returns it in degrees Celsius.
+
+        Reading must have already been initiated via:
+        `initiate_one_shot_measurement` or `start_autoconverting`.
+
+        Returns:
+            float: temperature in degrees Celsius
+        """
+        # 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 +392,21 @@ 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 +430,19 @@ 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) -> bytearray:
+        """
+        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: