[HowTo] Raspberry Pi Temperature and Humidity Sensor (DHT22/DHT11/AM2302)

[monkstone]

Difficulty: ★★☆☆☆

There is some misleading advice out there, suggesting the need for a 10k ohm resistor. But the the three lead DHT22 comes with an inbuilt resistor, which seems to do the job, also the majority of advice is for RaspberryPI OS. I thought I would share my experience:

1. I suggest connecting to pin 1 for 3.3 volt supply (RaspberryPi3/4), pin 11 for gpio17 and pin 9 for gnd.

2. You should also install software from Adafruit, use pacman to install pip and gcc if needed.

   sudo pip3 install Adafruit_DHT
   

3. You need a python script to access the sensor

   import Adafruit_DHT
   
   DHT_SENSOR = Adafruit_DHT.AM2302
   DHT_PIN = 17
   
   while True:
       humidity, temperature = Adafruit_DHT.read_retry(DHT_SENSOR, DHT_PIN)
   
       if humidity is not None and temperature is not None:
           print("Temp={0:0.1f}*C  Humidity={1:0.1f}%".format(temperature, humidity))
       else:
           print("Failed to retrieve data from humidity sensor")
   

4. Unfortunately you need root permission to access the sensor, therefore I:

   • copied 60-rpi.gpio-common.rules from RaspberryOS to /lib/udev/rules.d

     SUBSYSTEM=="bcm2835-gpiomem", KERNEL=="gpiomem", GROUP="dialout", MODE="0660"
     SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:dialout /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
     SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:dialout /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
     

   • created a dialout group and added myself as user, and now I don’t need root privileges.

     groupadd dialout
     usermod --append dialout $USER