@Emmanuel-Goudot Yes, that's the piece of code below, which works for my DHT22 on a Lopy. It is buried far below in a thread, where two people fight to get it running(https://forum.pycom.io/topic/1172/pure-python-library-for-reading-dht-sensor-on-pycom-boards). No clue what their problem is, since I consider it solved, even if not bullet proof.
import time
from machine import enable_irq, disable_irq, Pin
class DTHResult:
'DHT sensor result returned by DHT.read() method'
ERR_NO_ERROR = 0
ERR_MISSING_DATA = 1
ERR_CRC = 2
error_code = ERR_NO_ERROR
temperature = -1
humidity = -1
def __init__(self, error_code, temperature, humidity):
self.error_code = error_code
self.temperature = temperature
self.humidity = humidity
def is_valid(self):
return self.error_code == DTHResult.ERR_NO_ERROR
class DTH:
'DHT sensor (dht11, dht21,dht22) reader class for Pycom'
__pin = Pin('P3', mode=Pin.OPEN_DRAIN)
__dhttype = 0
def __init__(self, pin, sensor=0):
self.__pin = pin
self.__pin(1)
self.__dhttype = sensor
def read(self):
time.sleep(1)
# send initial high
#self.__send_and_sleep(1, 25000)
# pull down to low
#self.__send_and_sleep(0, 40000)
# collect data into an array
data = self.__collect_input()
# parse lengths of all data pull up periods
pull_up_lengths = self.__parse_data_pull_up_lengths(data)
# if bit count mismatch, return error (4 byte data + 1 byte checksum)
print(pull_up_lengths)
if len(pull_up_lengths) != 40:
return DTHResult(DTHResult.ERR_MISSING_DATA, 0, 0)
# calculate bits from lengths of the pull up periods
bits = self.__calculate_bits(pull_up_lengths)
# we have the bits, calculate bytes
the_bytes = self.__bits_to_bytes(bits)
print(the_bytes)
# calculate checksum and check
checksum = self.__calculate_checksum(the_bytes)
if the_bytes[4] != checksum:
return DTHResult(DTHResult.ERR_CRC, 0, 0)
# ok, we have valid data, return it
[int_rh, dec_rh, int_t, dec_t, csum] = the_bytes
if self.__dhttype==0: #dht11
rh = int_rh #dht11 20% ~ 90%
t = int_t #dht11 0..50°C
else: #dht21,dht22
rh = ((int_rh * 256) + dec_rh)/10
t = (((int_t & 0x7F) * 256) + dec_t)/10
if (int_t & 0x80) > 0:
t *= -1
return DTHResult(DTHResult.ERR_NO_ERROR, t, rh)
def __send_and_sleep(self, output, mysleep):
self.__pin(output)
time.sleep_us(mysleep)
def __collect_input(self):
# collect the data while unchanged found
unchanged_count = 0
# this is used to determine where is the end of the data
max_unchanged_count = 100
last = -1
data = []
m = [1]*500 # needs long sample size to grab all the bits from the DHT
self.__pin(0)
time.sleep_us(20000)
self.__pin(1)
irqf = disable_irq()
for i in range(len(m)):
m[i] = self.__pin() ## sample input and store value
enable_irq(irqf)
for i in range(len(m)):
current = m[i]
data.append(current)
if last != current:
unchanged_count = 0
last = current
else:
unchanged_count += 1
if unchanged_count > max_unchanged_count:
break
#print(data)
return data
def __parse_data_pull_up_lengths(self, data):
STATE_INIT_PULL_DOWN = 1
STATE_INIT_PULL_UP = 2
STATE_DATA_FIRST_PULL_DOWN = 3
STATE_DATA_PULL_UP = 4
STATE_DATA_PULL_DOWN = 5
state = STATE_INIT_PULL_UP
lengths = [] # will contain the lengths of data pull up periods
current_length = 0 # will contain the length of the previous period
for i in range(len(data)):
current = data[i]
current_length += 1
if state == STATE_INIT_PULL_DOWN:
if current == 0:
# ok, we got the initial pull down
state = STATE_INIT_PULL_UP
continue
else:
continue
if state == STATE_INIT_PULL_UP:
if current == 1:
# ok, we got the initial pull up
state = STATE_DATA_FIRST_PULL_DOWN
continue
else:
continue
if state == STATE_DATA_FIRST_PULL_DOWN:
if current == 0:
# we have the initial pull down, the next will be the data pull up
state = STATE_DATA_PULL_UP
continue
else:
continue
if state == STATE_DATA_PULL_UP:
if current == 1:
# data pulled up, the length of this pull up will determine whether it is 0 or 1
current_length = 0
state = STATE_DATA_PULL_DOWN
continue
else:
continue
if state == STATE_DATA_PULL_DOWN:
if current == 0:
# pulled down, we store the length of the previous pull up period
lengths.append(current_length)
state = STATE_DATA_PULL_UP
continue
else:
continue
return lengths
def __calculate_bits(self, pull_up_lengths):
# find shortest and longest period
shortest_pull_up = 1000
longest_pull_up = 0
for i in range(0, len(pull_up_lengths)):
length = pull_up_lengths[i]
if length < shortest_pull_up:
shortest_pull_up = length
if length > longest_pull_up:
longest_pull_up = length
# use the halfway to determine whether the period it is long or short
halfway = shortest_pull_up + (longest_pull_up - shortest_pull_up) / 2
bits = []
for i in range(0, len(pull_up_lengths)):
bit = False
if pull_up_lengths[i] > halfway:
bit = True
bits.append(bit)
return bits
def __bits_to_bytes(self, bits):
the_bytes = []
byte = 0
for i in range(0, len(bits)):
byte = byte << 1
if (bits[i]):
byte = byte | 1
else:
byte = byte | 0
if ((i + 1) % 8 == 0):
the_bytes.append(byte)
byte = 0
#print(the_bytes)
return the_bytes
def __calculate_checksum(self, the_bytes):
return the_bytes[0] + the_bytes[1] + the_bytes[2] + the_bytes[3] & 255
