# SPDX-FileCopyrightText: 2017 Mike McWethy for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""
:mod:`adafruit_dhtlib`
======================
CircuitPython support for the DHT11 and DHT22 temperature and humidity devices.
* Author(s): Mike McWethy
**Hardware:**
* Adafruit `DHT22 temperature-humidity sensor + extras
<https://www.adafruit.com/product/385>`_ (Product ID: 385)
* Adafruit `DHT11 basic temperature-humidity sensor + extras
<https://www.adafruit.com/product/386>`_ (Product ID: 386)
**Software and Dependencies:**
* Adafruit CircuitPython firmware for the supported boards:
https://circuitpython.org/downloads
"""
import array
import time
from os import uname
from digitalio import DigitalInOut, Direction, Pull
_USE_PULSEIO = False
try:
from pulseio import PulseIn
_USE_PULSEIO = True
except (ImportError, NotImplementedError):
pass # This is OK, we'll try to bitbang it!
try:
# Used only for typing
from typing import Union
from microcontroller import Pin
except ImportError:
pass
__version__ = "0.0.0+auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_DHT.git"
[docs]
class DHTBase:
"""base support for DHT11 and DHT22 devices
:param bool dht11: True if device is DHT11, otherwise DHT22.
:param ~board.Pin pin: digital pin used for communication
:param int trig_wait: length of time to hold trigger in LOW state (microseconds)
:param bool use_pulseio: False to force bitbang when pulseio available (only with Blinka)
"""
__hiLevel = 51
def __init__(
self, dht11: bool, pin: Pin, trig_wait: int, use_pulseio: bool, *, max_pulses: int = 81
):
self._dht11 = dht11
self._pin = pin
self._trig_wait = trig_wait
self._max_pulses = max_pulses
self._last_called = 0
self._humidity = None
self._temperature = None
self._use_pulseio = use_pulseio
if "Linux" not in uname() and not self._use_pulseio:
raise ValueError("Bitbanging is not supported when using CircuitPython.")
# We don't use a context because linux-based systems are sluggish
# and we're better off having a running process
if self._use_pulseio:
self.pulse_in = PulseIn(self._pin, maxlen=self._max_pulses, idle_state=True)
self.pulse_in.pause()
[docs]
def exit(self) -> None:
"""Cleans up the PulseIn process. Must be called explicitly"""
if self._use_pulseio:
self.pulse_in.deinit()
def _pulses_to_binary(self, pulses: array.array, start: int, stop: int) -> int:
"""Takes pulses, a list of transition times, and converts
them to a 1's or 0's. The pulses array contains the transition times.
pulses starts with a low transition time followed by a high transistion time.
then a low followed by a high and so on. The low transition times are
ignored. Only the high transition times are used. If the high
transition time is greater than __hiLevel, that counts as a bit=1, if the
high transition time is less that __hiLevel, that counts as a bit=0.
start is the starting index in pulses to start converting
stop is the index to convert upto but not including
Returns an integer containing the converted 1 and 0 bits
"""
binary = 0
hi_sig = False
for bit_inx in range(start, stop):
if hi_sig:
bit = 0
if pulses[bit_inx] > self.__hiLevel:
bit = 1
binary = binary << 1 | bit
hi_sig = not hi_sig
return binary
def _get_pulses_pulseio(self) -> array.array:
"""_get_pulses implements the communication protocol for
DHT11 and DHT22 type devices. It sends a start signal
of a specific length and listens and measures the
return signal lengths.
return pulses (array.array uint16) contains alternating high and low
transition times starting with a low transition time. Normally
pulses will have 81 elements for the DHT11/22 type devices.
"""
pulses = array.array("H")
if self._use_pulseio:
# The DHT type device use a specialize 1-wire protocol
# The microprocessor first sends a LOW signal for a
# specific length of time. Then the device sends back a
# series HIGH and LOW signals. The length the HIGH signals
# represents the device values.
self.pulse_in.clear()
self.pulse_in.resume(self._trig_wait)
# loop until we get the return pulse we need or
# time out after 1/4 second
time.sleep(0.25)
self.pulse_in.pause()
while self.pulse_in:
pulses.append(self.pulse_in.popleft())
return pulses
def _get_pulses_bitbang(self) -> array.array:
"""_get_pulses implements the communication protcol for
DHT11 and DHT22 type devices. It sends a start signal
of a specific length and listens and measures the
return signal lengths.
return pulses (array.array uint16) contains alternating high and low
transition times starting with a low transition time. Normally
pulses will have 81 elements for the DHT11/22 type devices.
"""
pulses = array.array("H")
with DigitalInOut(self._pin) as dhtpin:
# we will bitbang if no pulsein capability
transitions = []
# Signal by setting pin high, then low, and releasing
dhtpin.direction = Direction.OUTPUT
dhtpin.value = True
time.sleep(0.1)
dhtpin.value = False
# Using the time to pull-down the line according to DHT Model
time.sleep(self._trig_wait / 1000000)
timestamp = time.monotonic() # take timestamp
dhtval = True # start with dht pin true because its pulled up
dhtpin.direction = Direction.INPUT
try:
dhtpin.pull = Pull.UP
# Catch the NotImplementedError raised because
# blinka.microcontroller.generic_linux.libgpiod_pin does not support
# internal pull resistors.
except NotImplementedError:
dhtpin.pull = None
while time.monotonic() - timestamp < 0.25:
if dhtval != dhtpin.value:
dhtval = not dhtval # we toggled
transitions.append(time.monotonic()) # save the timestamp
# convert transtions to microsecond delta pulses:
# use last 81 pulses
transition_start = max(1, len(transitions) - self._max_pulses)
for i in range(transition_start, len(transitions)):
pulses_micro_sec = int(1000000 * (transitions[i] - transitions[i - 1]))
pulses.append(min(pulses_micro_sec, 65535))
return pulses
[docs]
def measure(self) -> None:
"""measure runs the communications to the DHT11/22 type device.
if successful, the class properties temperature and humidity will
return the reading returned from the device.
Raises RuntimeError exception for checksum failure and for insufficient
data returned from the device (try again)
"""
delay_between_readings = 2 # 2 seconds per read according to datasheet
# Initiate new reading if this is the first call or if sufficient delay
# If delay not sufficient - return previous reading.
# This allows back to back access for temperature and humidity for same reading
if (
self._last_called == 0
or (time.monotonic() - self._last_called) > delay_between_readings
):
self._last_called = time.monotonic()
new_temperature = 0
new_humidity = 0
if self._use_pulseio:
pulses = self._get_pulses_pulseio()
else:
pulses = self._get_pulses_bitbang()
# print(len(pulses), "pulses:", [x for x in pulses])
if len(pulses) < 10:
# Probably a connection issue!
raise RuntimeError("DHT sensor not found, check wiring")
if len(pulses) < 80:
# We got *some* data just not 81 bits
raise RuntimeError("A full buffer was not returned. Try again.")
buf = array.array("B")
for byte_start in range(0, 80, 16):
buf.append(self._pulses_to_binary(pulses, byte_start, byte_start + 16))
if self._dht11:
# humidity is 1 byte
new_humidity = buf[0]
# temperature is 1 byte for integral and 1 byte for 1st decimal place
new_temperature = buf[2] + (buf[3] & 0x0F) / 10
else:
# humidity is 2 bytes
new_humidity = ((buf[0] << 8) | buf[1]) / 10
# temperature is 2 bytes
# MSB is sign, bits 0-14 are magnitude)
new_temperature = (((buf[2] & 0x7F) << 8) | buf[3]) / 10
# set sign
if buf[2] & 0x80:
new_temperature = -new_temperature
# calc checksum
chk_sum = 0
for b in buf[0:4]:
chk_sum += b
# checksum is the last byte
if chk_sum & 0xFF != buf[4]:
# check sum failed to validate
raise RuntimeError("Checksum did not validate. Try again.")
if new_humidity < 0 or new_humidity > 100:
# We received unplausible data
raise RuntimeError("Received unplausible data. Try again.")
self._temperature = new_temperature
self._humidity = new_humidity
@property
def temperature(self) -> Union[int, float, None]:
"""temperature current reading. It makes sure a reading is available
Raises RuntimeError exception for checksum failure and for insufficient
data returned from the device (try again)
"""
self.measure()
return self._temperature
@property
def humidity(self) -> Union[int, float, None]:
"""humidity current reading. It makes sure a reading is available
Raises RuntimeError exception for checksum failure and for insufficient
data returned from the device (try again)
"""
self.measure()
return self._humidity
[docs]
class DHT11(DHTBase):
"""Support for DHT11 device.
:param ~board.Pin pin: digital pin used for communication
"""
def __init__(self, pin: Pin, use_pulseio: bool = _USE_PULSEIO):
super().__init__(True, pin, 18000, use_pulseio)
[docs]
class DHT22(DHTBase):
"""Support for DHT22 device.
:param ~board.Pin pin: digital pin used for communication
"""
def __init__(self, pin: Pin, use_pulseio: bool = _USE_PULSEIO):
super().__init__(False, pin, 1000, use_pulseio)
[docs]
class DHT21(DHTBase):
"""Support for DHT21/AM2301 device.
:param ~board.Pin pin: digital pin used for communication
"""
# DHT21/AM2301 is sending three more dummy bytes after the "official" protocol.
# Pulseio will take only the last pulses up to maxPulses.
# If that would be 81, the dummy pulses will be read and the real data would be truncated.
# Hence setting maxPulses to 129, taking both real data and dummy bytes into buffer.
def __init__(self, pin: Pin, use_pulseio: bool = _USE_PULSEIO):
super().__init__(False, pin, 1000, use_pulseio, max_pulses=129)
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