DHT11 not working properly

[yeyeto2788]

Using version 3.5.8 in a loop it almost never gets a reading with the following code:

import time
import board
import adafruit_dht

dhtDevice = adafruit_dht.DHT11(board.PG6)


for try_number in range(1,200):
  print(f"Try number {try_number}")
  try:
    print(f"Got temp of: {dhtDevice.temperature}")
    print(f"And hum of: {dhtDevice.humidity}")
    break
  except RuntimeError as e:
    print(e)
    time.sleep(2.1)
  else:
    time.sleep(2.1)
  print("\n")

The weird part is that using the version 3.5.5 it actually get the readings correctly.

More data:
Python: 3.8.5
SBC: Orange Pi Lite
Installed libraries:

Adafruit-Blinka==6.4.1
adafruit-circuitpython-busdevice==5.0.6
adafruit-circuitpython-dht==3.5.5
adafruit-circuitpython-mcp3xxx==1.4.5
Adafruit-PlatformDetect==3.4.0
Adafruit-PureIO==1.1.8
appdirs==1.4.4
attrs==20.3.0
bcrypt==3.2.0
cached-property==1.5.2
certifi==2019.11.28
cffi==1.14.3
chardet==3.0.4
cryptography==3.2.1
dbus-python==1.2.16
distlib==0.3.1
distro==1.5.0
distro-info===0.23ubuntu1
docker==4.3.1
docker-compose==1.27.4
dockerpty==0.4.1
docopt==0.6.2
filelock==3.0.12
idna==2.8
iotop==0.6
jsonschema==3.2.0
mudpi==0.10.0
paho-mqtt==1.5.1
paramiko==2.7.2
pycparser==2.20
pyftdi==0.52.9
PyGObject==3.36.0
PyNaCl==1.4.0
pyrsistent==0.17.3
pyserial==3.5
python-apt==2.0.0+ubuntu0.20.4.4
python-dotenv==0.15.0
pyusb==1.1.1
PyYAML==5.3.1
redis==3.5.3
requests==2.22.0
requests-unixsocket==0.2.0
six==1.14.0
texttable==1.6.3
unattended-upgrades==0.1
urllib3==1.25.8
virtualenv==20.1.0
websocket-client==0.57.0

[jposada202020]

Thanks, for the report, @yeyeto2788
Triggering time was changed in version 3.5.6, and corrected in 3.5.7 to improve trigger reading time in the DHT11. So in you case, this change is not working correctly? DHT11 needs more time to react after the initial signal, so this was taken into consideration. Could you try to change the value as show in the code below, and put the old value. to see if it works.

V3.5.6

Adafruit_CircuitPython_DHT/adafruit_dht.py

Line 142 in 85b6a36

time.sleep(self._trig_wait // 1000000)

V3.5.7

Adafruit_CircuitPython_DHT/adafruit_dht.py

Line 142 in ceb883d

time.sleep(self._trig_wait / 1000000)

[yeyeto2788]

Hey @jposada202020,

Thanks for the quick reply. I try both versions you mentioned and none of those worked. The code/wiring still remain the same but changing the library version give a completely different output

import time
import board
import adafruit_dht

dhtDevice = adafruit_dht.DHT11(board.PG6)


for try_number in range(1,200):
  print(f"Try number {try_number}")
  try:
    print(f"Got temp of: {dhtDevice.temperature}")
    print(f"And hum of: {dhtDevice.humidity}")
    break
  except RuntimeError as e:
    print(e)
    time.sleep(2.1)
  else:
    time.sleep(2.1)
  print("\n")

V3.5.7

(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ pip install adafruit-circuitpython-dht==3.5.7
Collecting adafruit-circuitpython-dht==3.5.7
  Downloading adafruit-circuitpython-dht-3.5.7.tar.gz (28 kB)
Requirement already satisfied: Adafruit-Blinka in ./venv/lib/python3.8/site-packages (from adafruit-circuitpython-dht==3.5.7) (6.4.1)
Requirement already satisfied: Adafruit-PureIO>=1.1.7 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.7) (1.1.8)
Requirement already satisfied: Adafruit-PlatformDetect>=3.1.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.7) (3.4.0)
Requirement already satisfied: pyftdi>=0.40.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.7) (0.52.9)
Requirement already satisfied: pyserial>=3.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.7) (3.5)
Requirement already satisfied: pyusb>=1.0.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.7) (1.1.1)
Building wheels for collected packages: adafruit-circuitpython-dht
  Building wheel for adafruit-circuitpython-dht (setup.py) ... done
  Created wheel for adafruit-circuitpython-dht: filename=adafruit_circuitpython_dht-3.5.7-py3-none-any.whl size=6837 sha256=64936289ef4ee9d95648779129c46efd18e8aaab255f6156d5a1735d1977b4e8
  Stored in directory: /home/yeyeto2788/.cache/pip/wheels/30/3e/2b/c43aa6a3c0afd819cf5cadd2089a674b9f2a580e1b3ef25b0b
Successfully built adafruit-circuitpython-dht
Installing collected packages: adafruit-circuitpython-dht
  Attempting uninstall: adafruit-circuitpython-dht
    Found existing installation: adafruit-circuitpython-dht 3.5.6
    Uninstalling adafruit-circuitpython-dht-3.5.6:
      Successfully uninstalled adafruit-circuitpython-dht-3.5.6


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
A full buffer was not returned. Try again.


Try number 2
A full buffer was not returned. Try again.


Try number 3
A full buffer was not returned. Try again.


Try number 4
A full buffer was not returned. Try again.


Try number 5
A full buffer was not returned. Try again.
^CTraceback (most recent call last):
  File "test.py", line 11, in <module>
    print(f"Got temp of: {dhtDevice.temperature}")
  File "/home/yeyeto2788/workspace/mudpi-core/venv/lib/python3.8/site-packages/adafruit_dht.py", line 244, in temperature
    self.measure()
  File "/home/yeyeto2788/workspace/mudpi-core/venv/lib/python3.8/site-packages/adafruit_dht.py", line 200, in measure
    raise RuntimeError("A full buffer was not returned. Try again.")
RuntimeError: A full buffer was not returned. Try again.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    time.sleep(2.1)
KeyboardInterrupt

V3.5.6

(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ pip install adafruit-circuitpython-dht==3.5.6
Collecting adafruit-circuitpython-dht==3.5.6
  Using cached adafruit_circuitpython_dht-3.5.6-py3-none-any.whl
Requirement already satisfied: Adafruit-Blinka in ./venv/lib/python3.8/site-packages (from adafruit-circuitpython-dht==3.5.6) (6.4.1)
Requirement already satisfied: pyftdi>=0.40.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.6) (0.52.9)
Requirement already satisfied: Adafruit-PureIO>=1.1.7 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.6) (1.1.8)
Requirement already satisfied: Adafruit-PlatformDetect>=3.1.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.6) (3.4.0)
Requirement already satisfied: pyusb>=1.0.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.6) (1.1.1)
Requirement already satisfied: pyserial>=3.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.6) (3.5)
Installing collected packages: adafruit-circuitpython-dht
  Attempting uninstall: adafruit-circuitpython-dht
    Found existing installation: adafruit-circuitpython-dht 3.5.7
    Uninstalling adafruit-circuitpython-dht-3.5.7:
      Successfully uninstalled adafruit-circuitpython-dht-3.5.7
      
(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py ) 

Try number 1
DHT sensor not found, check wiring


Try number 2
DHT sensor not found, check wiring


Try number 3
DHT sensor not found, check wiring


Try number 4
DHT sensor not found, check wiring
^CTraceback (most recent call last):
  File "test.py", line 11, in <module>
    print(f"Got temp of: {dhtDevice.temperature}")
  File "/home/yeyeto2788/workspace/mudpi-core/venv/lib/python3.8/site-packages/adafruit_dht.py", line 244, in temperature
    self.measure()
  File "/home/yeyeto2788/workspace/mudpi-core/venv/lib/python3.8/site-packages/adafruit_dht.py", line 196, in measure
    raise RuntimeError("DHT sensor not found, check wiring")
RuntimeError: DHT sensor not found, check wiring

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    time.sleep(2.1)
KeyboardInterrupt

V3.5.5

(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ pip install adafruit-circuitpython-dht==3.5.5
Collecting adafruit-circuitpython-dht==3.5.5
  Using cached adafruit_circuitpython_dht-3.5.5-py3-none-any.whl
Requirement already satisfied: Adafruit-Blinka in ./venv/lib/python3.8/site-packages (from adafruit-circuitpython-dht==3.5.5) (6.4.1)
Requirement already satisfied: Adafruit-PlatformDetect>=3.1.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.5) (3.4.0)
Requirement already satisfied: pyftdi>=0.40.0 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.5) (0.52.9)
Requirement already satisfied: Adafruit-PureIO>=1.1.7 in ./venv/lib/python3.8/site-packages (from Adafruit-Blinka->adafruit-circuitpython-dht==3.5.5) (1.1.8)
Requirement already satisfied: pyserial>=3.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.5) (3.5)
Requirement already satisfied: pyusb>=1.0.0 in ./venv/lib/python3.8/site-packages (from pyftdi>=0.40.0->Adafruit-Blinka->adafruit-circuitpython-dht==3.5.5) (1.1.1)
Installing collected packages: adafruit-circuitpython-dht
  Attempting uninstall: adafruit-circuitpython-dht
    Found existing installation: adafruit-circuitpython-dht 3.5.6
    Uninstalling adafruit-circuitpython-dht-3.5.6:
      Successfully uninstalled adafruit-circuitpython-dht-3.5.6
(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
DHT sensor not found, check wiring


Try number 2
Got temp of: 22
And hum of: 20

So I looked what was on the library of the 3.5.5 version and this is what I found:

(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ find ./ -name adafruit*dht*
./venv/lib/python3.8/site-packages/__pycache__/adafruit_dht.cpython-38.pyc
./venv/lib/python3.8/site-packages/adafruit_dht.py
(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sed -n -e 138,152p ./venv/lib/python3.8/site-packages/adafruit_dht.py
            dhtpin.value = True
            time.sleep(0.1)
            dhtpin.value = False
            time.sleep(0.001)
            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

And this might correspond to Line 141 on commit e22d289ab480468fa305a451e3b9c1961c7f0fb2

To summarize I don't really see a difference on using self._trig_wait/1000000 which will give you 0.0018 and it is on version 3.5.7 than using just 0.001. I mean, is that sensitive to time the sensor? 🤔

[jposada202020]

@yeyeto2788 No problem,
Interesting, actually for the DHT11 will be 0.018 = it comes from here

Adafruit_CircuitPython_DHT/adafruit_dht.py

Line 265 in ceb883d

super().__init__(True, pin, 18000, use_pulseio)

. The interesting thing here is that in your case, the wait time of 0.001 works better.
In a note, yes 3.5.6 would not work as the waiting time was 0 as you get an python int division. That was my mistake.
Could you make some test changing the value, maybe hardcoded it. it is very interesting. maybe is something that I am not seeing.
I did as you can see in here some testing, so for me the library works in both sensors. with the trigger time https://github.com/jposada202020/DHT_Investigation
But I am very curious

[yeyeto2788]

Sure, so want me to try out your script (modified with the pin used on my SBC) or you just want me to manually change the values on the library itself? It is almost the same as mine except for the checksum.

[jposada202020]

Both :) but for this case it would be better to verify the library behaviour, understand why when we use 0.001 works and when we use the division in the trigger do not. So if you could manually change the library values that would really helpful.

[yeyeto2788]

Based on your script

I get this output:

(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test_a.py
DHT sensor not found, check wiring
DHT sensor not found, check wiring
Temp: 69.8 F / 21.0 C    Humidity: 20%
Traceback (most recent call last):
  File "test_a.py", line 34, in <module>
    print(f"Cycle: {i}--Checksum Errors: {dhtDevice.checksum_test}--Data Buffer Error: {dhtDevice.data_buffer_test}"
AttributeError: 'DHT11' object has no attribute 'checksum_test'

I also tried with manual changes and my code and the results are below.

0.001 Gives 3 out of 10 reads

141             # Using the time to pull-down the line according to DHT Model
142             time.sleep(0.001)
143             timestamp = time.monotonic()  # take timestamp


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
Got temp of: 21
And hum of: 20


Try number 2
DHT sensor not found, check wiring


Try number 3
DHT sensor not found, check wiring


Try number 4
DHT sensor not found, check wiring


Try number 5
DHT sensor not found, check wiring


Try number 6
DHT sensor not found, check wiring


Try number 7
Got temp of: 21
And hum of: 20


Try number 8
Got temp of: 21
And hum of: 20


Try number 9
DHT sensor not found, check wiring


Try number 10
DHT sensor not found, check wiring

0.0001 Gives 2 out of 10

141             # Using the time to pull-down the line according to DHT Model
142             time.sleep(0.0001)
143             timestamp = time.monotonic()  # take timestamp
144             dhtval = True  # start with dht pin true because its pulled up
145             dhtpin.direction = Direction.INPUT


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
DHT sensor not found, check wiring


Try number 2
DHT sensor not found, check wiring


Try number 3
Got temp of: 21
And hum of: 20


Try number 4
DHT sensor not found, check wiring


Try number 5
Got temp of: 21
And hum of: 20


Try number 6
DHT sensor not found, check wiring


Try number 7
DHT sensor not found, check wiring


Try number 8
DHT sensor not found, check wiring


Try number 9
DHT sensor not found, check wiring


Try number 10
DHT sensor not found, check wiring

0.1 Gives NO reads

142             time.sleep(0.1)
143             timestamp = time.monotonic()  # take timestamp
144             dhtval = True  # start with dht pin true because its pulled up
145             dhtpin.direction = Direction.INPUT
146
147             try:
148                 dhtpin.pull = Pull.UP
149             # Catch the NotImplementedError raised because
150             # blinka.microcontroller.generic_linux.libgpiod_pin does not su>


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
A full buffer was not returned. Try again.


Try number 2
A full buffer was not returned. Try again.


Try number 3
A full buffer was not returned. Try again.


Try number 4
A full buffer was not returned. Try again.


Try number 5
A full buffer was not returned. Try again.


Try number 6
A full buffer was not returned. Try again.


Try number 7
A full buffer was not returned. Try again.


Try number 8
A full buffer was not returned. Try again.


Try number 9
A full buffer was not returned. Try again.


Try number 10
A full buffer was not returned. Try again.

0.002 Gives 8 of 10

141             # Using the time to pull-down the line according to DHT Model
142             time.sleep(0.002)
143             timestamp = time.monotonic()  # take timestamp
144             dhtval = True  # start with dht pin true because its pulled up
145             dhtpin.direction = Direction.INPUT
146
147             try:
148                 dhtpin.pull = Pull.UP
149             # Catch the NotImplementedError raised because
150             # blinka.microcontroller.generic_linux.libgpiod_pin does not su>
151             # internal pull resistors.


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
Got temp of: 21
And hum of: 20


Try number 2
DHT sensor not found, check wiring


Try number 3
Got temp of: 21
And hum of: 20


Try number 4
Got temp of: 21
And hum of: 20


Try number 5
Got temp of: 21
And hum of: 20


Try number 6
Got temp of: 21
And hum of: 20


Try number 7
Got temp of: 21
And hum of: 20


Try number 8
DHT sensor not found, check wiring


Try number 9
Got temp of: 21
And hum of: 20


Try number 10
Got temp of: 21
And hum of: 20

0.00185 BEST RESULTS 😄

141             # Using the time to pull-down the line according to DHT Model
142             time.sleep(0.00185)
143             timestamp = time.monotonic()  # take timestamp
144             dhtval = True  # start with dht pin true because its pulled up
145             dhtpin.direction = Direction.INPUT
146
147             try:
148                 dhtpin.pull = Pull.UP
149             # Catch the NotImplementedError raised because
150             # blinka.microcontroller.generic_linux.libgpiod_pin does not su>
151             # internal pull resistors.


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
Got temp of: 21
And hum of: 20


Try number 2
Got temp of: 21
And hum of: 20


Try number 3
Got temp of: 21
And hum of: 20


Try number 4
DHT sensor not found, check wiring


Try number 5
Got temp of: 21
And hum of: 20


Try number 6
Got temp of: 21
And hum of: 20


Try number 7
Got temp of: 21
And hum of: 20


Try number 8
Got temp of: 21
And hum of: 20


Try number 9
Got temp of: 21
And hum of: 20


Try number 10
Got temp of: 21
And hum of: 20

I hope it gives you an idea more or less on timing. Of course I haven't test it on other boards so would be great to test same timings on other boards.

[jposada202020]

@yeyeto2788 did you try with the division :) why on earth it does not work hen dividing, do we need to use an if statemt. 😄 Thanks for testing. so timing is good, at least. why is not working with the class attribute ❓ 😞

[jposada202020]

@yeyeto2788 by the way thanks for testing :)

[yeyeto2788]

@jposada202020 I forgot about it 😛

Here you have the test:

141             # Using the time to pull-down the line according to DHT Model
142             time.sleep(self._trig_wait / 1000000)
143             timestamp = time.monotonic()  # take timestamp
144             dhtval = True  # start with dht pin true because its pulled up
145             dhtpin.direction = Direction.INPUT
146
147             try:
148                 dhtpin.pull = Pull.UP
149             # Catch the NotImplementedError raised because
150             # blinka.microcontroller.generic_linux.libgpiod_pin does not su>
151             # internal pull resistors.


(venv) yeyeto2788@orangepilite:~/workspace/mudpi-core$ sudo /home/yeyeto2788/workspace/mudpi-core/venv/bin/python test.py
Try number 1
DHT sensor not found, check wiring


Try number 2
A full buffer was not returned. Try again.


Try number 3
A full buffer was not returned. Try again.


Try number 4
Got temp of: 21
And hum of: 20


Try number 5
A full buffer was not returned. Try again.


Try number 6
A full buffer was not returned. Try again.


Try number 7
A full buffer was not returned. Try again.


Try number 8
A full buffer was not returned. Try again.


Try number 9
A full buffer was not returned. Try again.


Try number 10
A full buffer was not returned. Try again.

So the thing is that it is actually working but giving more false positives or false reads using that conversion time.sleep(self._trig_wait / 1000000) which will be 0.018.

NOTE: This is a total different number to let's say 0.00185 which was the most promising number to return more reads.

[jposada202020]

@yeyeto2788 :) are you sure that you have a DHT11, if so, it is pretty good.... 💨 , look at page 5 of this datasheet https://osoyoo.com/driver/DHT11-datasheet.pdf

[yeyeto2788]

I hope it is a DHT11 because it actually looks like one, my sensor is this one which was bought on other site.

Regarding that datasheet it states the following:

the programme of MCU will set Data Single-bus voltage level from high to low
and this processmust take at least 18ms to ensure DHT’s detection of MCU's signal

So it has to be AT LEAST 18ms and I'm actually getting better results with less than that (1.85ms)🤮

If you need me to test something else just let me know.

P.D: I can also contact me through Discord and probably it would be more faster.

[jposada202020]

@yeyeto2788 Thanks. See.. 👀 that is why I am so confused. I will contact you in the Adafruit discord :)

[jposada202020]

@yeyeto2788 Hello I tried to contact you in the Adafruit discord channel. but there are two people with the same nickname, if you could leave me a message in the help-with-circuitpython channel, I can trace it. Thanks I have an idea of what to do but I would need your help, and need to discuss also what your think and feedback. thanks