DHT 11 sensor not found, check wiring

Question

I am using raspberry pi 4 model b and sensor DHT 11 for checking the humidity and temperature. When I am using the code DHT.py, the result is:

1604263139.922  4 3 0.0 0.0
1604263142.192  4 3 0.0 0.0
1604263144.463  4 3 0.0 0.0
1604263146.732  4 3 0.0 0.0
1604263149.002  4 3 0.0 0.0
1604263151.273  4 3 0.0 0.0
1604263153.544  4 3 0.0 0.0
1604263155.816  4 3 0.0 0.0

but when I run my own code by using the command of python3 q1.py -f 5 -p 20 -o test.csv :

from board import D4
import adafruit_dht
import argparse
import datetime

parser = argparse.ArgumentParser()

parser.add_argument('-f',type=float)
parser.add_argument('-p',type=float)
parser.add_argument('-o',type=str)

args = parser.parse_args()

num_samples = int(args.p / args.f )


dht_device = adafruit_dht.DHT11(D4)

fp = open(args.o, 'w')

for i in range(num_samples):
    now = datetime.datetime.now()
    temperature = dht_device.temperature
    humidity = dht_device.humidity
    ptint(now.day,temperature,humidity,file = fp)
    time.sleep(args.f)
    
fp.close()

the error is :

Traceback (most recent call last):
  File "q1.py", line 23, in <module>
    temperature = dht_device.temperature
  File "/home/pi/WORK_DIR/py37/lib/python3.7/site-packages/adafruit_dht.py", line 253, in temperature
    self.measure()
  File "/home/pi/WORK_DIR/py37/lib/python3.7/site-packages/adafruit_dht.py", line 205, in measure
    raise RuntimeError("DHT sensor not found, check wiring")
RuntimeError: DHT sensor not found, check wiring

the datasheet of sensor is DFR0067 DFROBOT

boot/config.txt

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
dtparam=i2c_arm=on
#dtparam=i2s=on
dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d

Answer 1

I think (unless you have not corrected it yet) you have your wires wrong. The green one is the signal (data) and you have it connected to the 3V3.

Source: DFRobot - SEN0137 DHT22 Temperature and humidity module

Hint: Try running it in the loop like in the dht_simpletest.py - as @Milliways mentioned the python library is not stable.

Running in the loop and printing exceptions will give you more debug info - for my Pi Zero v1.3 this message was printed among others - misreported, see: issue-33.

Answer 2

The Adafruit code is notoriously unreliable.

I use Joan's code, but have written a wrapper around it to facilitate getting a single reading.

This is easy to modify and include in your own code.

https://raspberrypi.stackexchange.com/a/117225/8697