Issue
I have a Raspberry Pi 4 connected with a DHT22 sensor, and I want to read data from my sensor.
So I installed the library Adafruit_DHT
sudo pip3 install Adafruit_DHT
then, I navigate to the directory Adafruit_Python_DHT/examples/
, and then,
since I have a DHT22 sensor connected to GPIO pi n° 4,
I run
python AdafruitDHT.py 22 4
and I get
(lab_app) root@Raspberry100:/var/www/lab_app/Adafruit_Python_DHT/examples# python AdafruitDHT.py 2302 4
Traceback (most recent call last):
File "AdafruitDHT.py", line 41, in <module>
humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 94, in read_retry
humidity, temperature = read(sensor, pin, platform)
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 80, in read
platform = get_platform()
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 63, in get_platform
raise RuntimeError('Unknown platform.')
RuntimeError: Unknown platform.
(lab_app) root@Raspberry100:/var/www/lab_app/Adafruit_Python_DHT/examples# python AdafruitDHT.py 22 4
Traceback (most recent call last):
File "AdafruitDHT.py", line 41, in <module>
humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 94, in read_retry
humidity, temperature = read(sensor, pin, platform)
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 80, in read
platform = get_platform()
File "/var/www/lab_app/lib/python3.8/site-packages/Adafruit_DHT-1.4.0-py3.8-linux-armv7l.egg/Adafruit_DHT/common.py", line 63, in get_platform
raise RuntimeError('Unknown platform.')
RuntimeError: Unknown platform.
(lab_app) root@Raspberry100:/var/www/lab_app/Adafruit_Python_DHT/examples#
Since the traceback indicates
'Unknown platform.'
I did a little research on the github repository of Adafruit_Python_DHT library, and I found the script Adafruit_Python_DHT/Adafruit_DHT/common.py
.
Here I see there is an If/elif structure def get_platform()
that aims to identify the device calling the library, but there is value assignment only for RPi 1, 2 and 3, while RPi 4 is missing.
So I bet this is the reason why the error unknown platform
occurs.
I navigated the library source code and I found out the directory Adafruit_Python_DHT/Adafruit_DHT/
, in which the last commit says "included Raspberry Pi 4".
Here is a module platform_detect.py
that seems to be designed to somehow "upgrade" the library in order to recognize Raspberry Pi 4.
So I tryed to "upgrade" my library by doing this:
In (lab_app) root@Raspberry100:/var/www/lab_app/Adafruit_Python_DHT/Adafruit_DHT#
,
I run
platform_detect.py
And I don't get any output from the prompt, so I guess everything has gone right.
Then I navigate to the directory Adafruit_Python_DHT/examples/
and run again
python AdafruitDHT.py 22 4
but I still get the same error.
So how can I get data from a DHT22 sensor connected to GPIO pi n° 4 by using Adafruit_Python_DHT library?
Solution
Thank Tms91 for posting this solution as it helped find the heart of a problem I've been running into with the DHT22 sensor.
I was having issues reading the DHT22 sensor on a Raspberry Pi 4B.
The platform_detect.py
file returns a value to the Adafruit_DHT routine read_retry()
call to identify the platform being used (should return 3
for RPi4) when it tries to read temp and humidity.
A modification to your solution that worked for me was to add the BCM (Broadcom chip identifier) value for RPi 4B to the platform_detect.py
file, (rather than failing out and supplying a value)
For example:
{your path}/Adafruit_Python_DHT/Adafruit_DHT/
Edit platform_detect.py
: - in the function pi_version()
[around line 112 ] add the BCM device value for RPI-4b (BCM2711
) to the if/elif list of BCM types. For Raspberry Pi 4B, BCM2711
is an updated value to check for:
# Adding the following elif to accommodate RPi4B Broadcomchip
elif match.group(1) == 'BCM2711':
# Pi 4B
return 3
No need to change the final else statement or edit the common.py
file.
Next, return to the {your path}/Adafruit_python_DHT/folder
and, as Tms91 suggested, run the setup.py
again:
python3 setup.py install
to re-install the platform_detect.py
file.
I'm guessing this might work for other similar platform errors if you're able to find the right value for your platform.
Answered By - Quisp