Source code for adafruit_ds18x20

# SPDX-FileCopyrightText: 2017 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT

"""
`adafruit_ds18x20`
====================================================

Driver for Dallas 1-Wire temperature sensor.

* Author(s): Carter Nelson

**Software and Dependencies:**

* Adafruit CircuitPython firmware for the supported boards:
  https://circuitpython.org/downloads

"""

__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_DS18x20.git"

import time
from micropython import const
from adafruit_onewire.device import OneWireDevice

_CONVERT = b"\x44"
_RD_SCRATCH = b"\xBE"
_WR_SCRATCH = b"\x4E"
_CONVERSION_TIMEOUT = const(1)
RESOLUTION = (9, 10, 11, 12)
# Maximum conversion delay in seconds, from DS18B20 datasheet.
_CONVERSION_DELAY = {9: 0.09375, 10: 0.1875, 11: 0.375, 12: 0.750}


[docs]class DS18X20: """Class which provides interface to DS18X20 temperature sensor :param bus: The bus the DS18X20 is connected to :param int address: The device address. **Quickstart: Importing and using the device** Here is an example of using the :class:`DS18X20` class. First you will need to import the libraries to use the sensor .. code-block:: python import board from adafruit_onewire.bus import OneWireBus from adafruit_ds18x20 import DS18X20 Once this is done you can define your :class:`adafruit_onewire.bus.OneWireBus` object and define your sensor object .. code-block:: python ow_bus = OneWireBus(board.D5) ds18 = DS18X20(ow_bus, ow_bus.scan()[0]) Now you have access to the :attr:`temperature` attribute .. code-block:: python temperature = ds18.temperature """ def __init__(self, bus, address): if address.family_code == 0x10 or address.family_code == 0x28: self._address = address self._device = OneWireDevice(bus, address) self._buf = bytearray(9) self._conv_delay = _CONVERSION_DELAY[12] # pessimistic default else: raise ValueError("Incorrect family code in device address.") @property def temperature(self): """The temperature in degrees Celsius.""" self._convert_temp() return self._read_temp() @property def resolution(self): """The programmable resolution. 9, 10, 11, or 12 bits.""" return RESOLUTION[self._read_scratch()[4] >> 5 & 0x03] @resolution.setter def resolution(self, bits): if bits not in RESOLUTION: raise ValueError("Incorrect resolution. Must be 9, 10, 11, or 12.") self._buf[0] = 0 # TH register self._buf[1] = 0 # TL register self._buf[2] = RESOLUTION.index(bits) << 5 | 0x1F # configuration register self._write_scratch(self._buf) def _convert_temp(self, timeout=_CONVERSION_TIMEOUT): with self._device as dev: dev.write(_CONVERT) start_time = time.monotonic() if timeout > 0: dev.readinto(self._buf, end=1) # 0 = conversion in progress, 1 = conversion done while self._buf[0] == 0x00: if time.monotonic() - start_time > timeout: raise RuntimeError( "Timeout waiting for conversion to complete." ) dev.readinto(self._buf, end=1) return time.monotonic() - start_time def _read_temp(self): # pylint: disable=invalid-name buf = self._read_scratch() if self._address.family_code == 0x10: if buf[1]: t = buf[0] >> 1 | 0x80 t = -((~t + 1) & 0xFF) else: t = buf[0] >> 1 return t - 0.25 + (buf[7] - buf[6]) / buf[7] t = buf[1] << 8 | buf[0] if t & 0x8000: # sign bit set t = -((t ^ 0xFFFF) + 1) return t / 16 def _read_scratch(self): with self._device as dev: dev.write(_RD_SCRATCH) dev.readinto(self._buf) return self._buf def _write_scratch(self, buf): with self._device as dev: dev.write(_WR_SCRATCH) dev.write(buf, end=3)
[docs] def start_temperature_read(self): """Start asynchronous conversion, returns immediately. Returns maximum conversion delay [seconds] based on resolution.""" with self._device as dev: dev.write(_CONVERT) return _CONVERSION_DELAY[self.resolution]
[docs] def read_temperature(self): """Read the temperature. No polling of the conversion busy bit (assumes that the conversion has completed).""" return self._read_temp()