DHT does not work with root user using Raspberry Zero WH

[JavanXD]

I am using a clean Raspberry Pi OS install (version: 2021-03-04-raspbian-buster) on a Raspberry Zero WH. You can download the image or you can check the used install instructions here.

I installed the following two packages: sudo pip3 install adafruit-circuitpython-dht && sudo apt-get install libgpiod2

PoC:

import logging
import adafruit_dht
import time
import board
import digitalio

logger = logging.getLogger('HoneyPi.read_dht')
if __name__ == '__main__':
    try:

        SENSOR_PIN = digitalio.Pin(4) # change GPIO pin
        dht = adafruit_dht.DHT22(SENSOR_PIN, use_pulseio=True)

        timer = 0
        while timer <= 10:
            try:
                temperature = dht.temperature
                temperature_f = temperature * (9 / 5) + 32
                humidity = dht.humidity

                print("Temp: {:.1f} F / {:.1f} °C    Humidity: {}% ".format(temperature_f, temperature, humidity))

                break # break while if it worked
            except RuntimeError as error:
                # Errors happen fairly often, DHT's are hard to read, just keep going
                print(error.args[0])
                time.sleep(2.0)
                timer = timer + 2

            if timer > 10: # end reached
                print("Loop finished. Error.")

    except (KeyboardInterrupt, SystemExit):
       pass

    except RuntimeError as error:
        logger.error("RuntimeError in DHT measurement: " + error.args[0])

    except Exception as e:
       logger.exception("Unhandled Exception in DHT measurement")

(full script)

Console:

pi@HoneyPi:~/HoneyPi/rpi-scripts $ sudo -u root python3 read_dht.py
RuntimeError in DHT measurement: Timed out waiting for PulseIn message. Make sure libgpiod is installed.
pi@HoneyPi:~/HoneyPi/rpi-scripts $ sudo -u pi python3 read_dht.py
Temp: 78.3 F / 25.7 °C    Humidity: 66.2% 

Notes:
yes, root user is part of gpio group (sudo usermod -aG gpio root)

I noticed that I am not the only one affected by this issue:

• https://stackoverflow.com/questions/63292226/dht22-works-as-user-but-not-as-sudo-on-pi-zero-w August-2020
• https://forums.adafruit.com/viewtopic.php?f=19&t=160892&start=15#p804598 March-2020
• https://forums.adafruit.com/viewtopic.php?f=24&t=168136#p823332 July-2020

I have been using the Adafruit_DHT library for a long time but because you stopped fixing issues such as this I've migrated to your new library. Unfortunately it turns out that you do not fix issues for Raspi Zero. What I am supposed to use now? Please fix this issue.

[alaub81]

I have a similar issue with adafruit-circuitpython-hcsr04 on a raspberry pi zero w. It works as the normal pi user, but not with sudo or as root user.

I installed:

pip3 install adafruit-circuitpython-hcsr04

and my simple script looks like this:

#!/usr/bin/python3

import time
import board
import adafruit_hcsr04

sonar = adafruit_hcsr04.HCSR04(trigger_pin=board.D5, echo_pin=board.D6)

while True:
    try:
        print("Distance: %.2f cm" % sonar.distance)
    except RuntimeError:
        print("Retrying!")
    time.sleep(1)

I got the same error when I start the script as root user:

RuntimeError: Timed out waiting for PulseIn message. Make sure libgpiod is installed.

[JavanXD]

@alaub81 I created this support request in the Adafruit forum: https://forums.adafruit.com/viewtopic.php?f=24&t=183236&p=890751#p890221 I would recommend to you to save yourself some time and use another library.