261 lines
9.6 KiB
Python
261 lines
9.6 KiB
Python
# The MIT License (MIT)
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#
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# Copyright (c) 2017 Tony DiCola for Adafruit Industries
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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# THE SOFTWARE.
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"""
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`adafruit_max31865`
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====================================================
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CircuitPython module for the MAX31865 platinum RTD temperature sensor. See
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examples/simpletest.py for an example of the usage.
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* Author(s): Tony DiCola
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Implementation Notes
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--------------------
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**Hardware:**
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* Adafruit `Universal Thermocouple Amplifier MAX31856 Breakout
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<https://www.adafruit.com/product/3263>`_ (Product ID: 3263)
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* Adafruit `PT100 RTD Temperature Sensor Amplifier - MAX31865
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<https://www.adafruit.com/product/3328>`_ (Product ID: 3328)
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* Adafruit `PT1000 RTD Temperature Sensor Amplifier - MAX31865
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<https://www.adafruit.com/product/3648>`_ (Product ID: 3648)
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**Software and Dependencies:**
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* Adafruit CircuitPython firmware for the ESP8622 and M0-based boards:
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https://github.com/adafruit/circuitpython/releases
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* Adafruit's Bus Device library: https://github.com/adafruit/Adafruit_CircuitPython_BusDevice
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"""
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import math
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import time
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from micropython import const
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import adafruit_bus_device.spi_device as spi_device
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__version__ = "0.0.0-auto.0"
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__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_MAX31865.git"
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#pylint: disable=bad-whitespace
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# Register and other constant values:
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_MAX31865_CONFIG_REG = const(0x00)
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_MAX31865_CONFIG_BIAS = const(0x80)
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_MAX31865_CONFIG_MODEAUTO = const(0x40)
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_MAX31865_CONFIG_MODEOFF = const(0x00)
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_MAX31865_CONFIG_1SHOT = const(0x20)
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_MAX31865_CONFIG_3WIRE = const(0x10)
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_MAX31865_CONFIG_24WIRE = const(0x00)
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_MAX31865_CONFIG_FAULTSTAT = const(0x02)
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_MAX31865_CONFIG_FILT50HZ = const(0x01)
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_MAX31865_CONFIG_FILT60HZ = const(0x00)
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_MAX31865_RTDMSB_REG = const(0x01)
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_MAX31865_RTDLSB_REG = const(0x02)
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_MAX31865_HFAULTMSB_REG = const(0x03)
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_MAX31865_HFAULTLSB_REG = const(0x04)
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_MAX31865_LFAULTMSB_REG = const(0x05)
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_MAX31865_LFAULTLSB_REG = const(0x06)
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_MAX31865_FAULTSTAT_REG = const(0x07)
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_MAX31865_FAULT_HIGHTHRESH = const(0x80)
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_MAX31865_FAULT_LOWTHRESH = const(0x40)
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_MAX31865_FAULT_REFINLOW = const(0x20)
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_MAX31865_FAULT_REFINHIGH = const(0x10)
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_MAX31865_FAULT_RTDINLOW = const(0x08)
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_MAX31865_FAULT_OVUV = const(0x04)
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_RTD_A = 3.9083e-3
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_RTD_B = -5.775e-7
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#pylint: enable=bad-whitespace
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class MAX31865:
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"""Driver for the MAX31865 thermocouple amplifier."""
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# Class-level buffer for reading and writing data with the sensor.
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# This reduces memory allocations but means the code is not re-entrant or
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# thread safe!
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_BUFFER = bytearray(3)
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def __init__(self, spi, cs, *, rtd_nominal=100, ref_resistor=430.0, wires=2):
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self.rtd_nominal = rtd_nominal
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self.ref_resistor = ref_resistor
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self._device = spi_device.SPIDevice(spi, cs, baudrate=500000,
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polarity=0, phase=1)
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# Set wire config register based on the number of wires specified.
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if wires not in (2, 3, 4):
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raise ValueError('Wires must be a value of 2, 3, or 4!')
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config = self._read_u8(_MAX31865_CONFIG_REG)
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if wires == 3:
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config |= _MAX31865_CONFIG_3WIRE
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else:
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# 2 or 4 wire
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config &= ~_MAX31865_CONFIG_3WIRE
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self._write_u8(_MAX31865_CONFIG_REG, config)
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# Default to no bias and no auto conversion.
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self.bias = False
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self.auto_convert = False
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# pylint: disable=no-member
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def _read_u8(self, address):
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# Read an 8-bit unsigned value from the specified 8-bit address.
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with self._device as device:
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self._BUFFER[0] = address & 0x7F
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device.write(self._BUFFER, end=1)
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device.readinto(self._BUFFER, end=1)
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return self._BUFFER[0]
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def _read_u16(self, address):
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# Read a 16-bit BE unsigned value from the specified 8-bit address.
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with self._device as device:
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self._BUFFER[0] = address & 0x7F
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device.write(self._BUFFER, end=1)
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device.readinto(self._BUFFER, end=2)
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return (self._BUFFER[0] << 8) | self._BUFFER[1]
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def _write_u8(self, address, val):
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# Write an 8-bit unsigned value to the specified 8-bit address.
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with self._device as device:
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self._BUFFER[0] = (address | 0x80) & 0xFF
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self._BUFFER[1] = val & 0xFF
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device.write(self._BUFFER, end=2)
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# pylint: enable=no-member
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@property
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def bias(self):
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"""The state of the sensor's bias (True/False)."""
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return bool(self._read_u8(_MAX31865_CONFIG_REG) & _MAX31865_CONFIG_BIAS)
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@bias.setter
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def bias(self, val):
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config = self._read_u8(_MAX31865_CONFIG_REG)
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if val:
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config |= _MAX31865_CONFIG_BIAS # Enable bias.
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else:
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config &= ~_MAX31865_CONFIG_BIAS # Disable bias.
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self._write_u8(_MAX31865_CONFIG_REG, config)
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@property
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def auto_convert(self):
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"""The state of the sensor's automatic conversion
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mode (True/False).
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"""
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return bool(self._read_u8(_MAX31865_CONFIG_REG) & _MAX31865_CONFIG_MODEAUTO)
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@auto_convert.setter
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def auto_convert(self, val):
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config = self._read_u8(_MAX31865_CONFIG_REG)
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if val:
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config |= _MAX31865_CONFIG_MODEAUTO # Enable auto convert.
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else:
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config &= ~_MAX31865_CONFIG_MODEAUTO # Disable auto convert.
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self._write_u8(_MAX31865_CONFIG_REG, config)
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@property
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def fault(self):
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"""The fault state of the sensor. Use ``clear_faults()`` to clear the
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fault state. Returns a 6-tuple of boolean values which indicate if any
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faults are present:
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- HIGHTHRESH
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- LOWTHRESH
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- REFINLOW
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- REFINHIGH
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- RTDINLOW
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- OVUV
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"""
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faults = self._read_u8(_MAX31865_FAULTSTAT_REG)
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#pylint: disable=bad-whitespace
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highthresh = bool(faults & _MAX31865_FAULT_HIGHTHRESH)
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lowthresh = bool(faults & _MAX31865_FAULT_LOWTHRESH)
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refinlow = bool(faults & _MAX31865_FAULT_REFINLOW)
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refinhigh = bool(faults & _MAX31865_FAULT_REFINHIGH)
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rtdinlow = bool(faults & _MAX31865_FAULT_RTDINLOW)
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ovuv = bool(faults & _MAX31865_FAULT_OVUV)
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#pylint: enable=bad-whitespace
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return (highthresh, lowthresh, refinlow, refinhigh, rtdinlow, ovuv)
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def clear_faults(self):
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"""Clear any fault state previously detected by the sensor."""
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config = self._read_u8(_MAX31865_CONFIG_REG)
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config &= ~0x2C
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config |= _MAX31865_CONFIG_FAULTSTAT
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self._write_u8(_MAX31865_CONFIG_REG, config)
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def read_rtd(self):
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"""Perform a raw reading of the thermocouple and return its 15-bit
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value. You'll need to manually convert this to temperature using the
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nominal value of the resistance-to-digital conversion and some math. If you just want
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temperature use the temperature property instead.
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"""
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self.clear_faults()
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self.bias = True
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time.sleep(0.01)
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config = self._read_u8(_MAX31865_CONFIG_REG)
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config |= _MAX31865_CONFIG_1SHOT
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self._write_u8(_MAX31865_CONFIG_REG, config)
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time.sleep(0.065)
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rtd = self._read_u16(_MAX31865_RTDMSB_REG)
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# Remove fault bit.
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rtd >>= 1
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return rtd
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@property
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def resistance(self):
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"""Read the resistance of the RTD and return its value in Ohms."""
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resistance = self.read_rtd()
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resistance /= 32768
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resistance *= self.ref_resistor
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return resistance
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@property
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def temperature(self):
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"""Read the temperature of the sensor and return its value in degrees
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Celsius.
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"""
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# This math originates from:
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# http://www.analog.com/media/en/technical-documentation/application-notes/AN709_0.pdf
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# To match the naming from the app note we tell lint to ignore the Z1-4
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# naming.
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# pylint: disable=invalid-name
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raw_reading = self.resistance
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Z1 = -_RTD_A
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Z2 = _RTD_A * _RTD_A - (4 * _RTD_B)
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Z3 = (4 * _RTD_B) / self.rtd_nominal
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Z4 = 2 * _RTD_B
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temp = Z2 + (Z3 * raw_reading)
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temp = (math.sqrt(temp) + Z1) / Z4
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if temp >= 0:
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return temp
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rpoly = raw_reading
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temp = -242.02
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temp += 2.2228 * rpoly
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rpoly *= raw_reading # square
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temp += 2.5859e-3 * rpoly
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rpoly *= raw_reading # ^3
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temp -= 4.8260e-6 * rpoly
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rpoly *= raw_reading # ^4
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temp -= 2.8183e-8 * rpoly
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rpoly *= raw_reading # ^5
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temp += 1.5243e-10 * rpoly
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return temp
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