OSError: [Errno 5] EIO

[rkappel]

Hello,

I tried to use your library to read a DHT20 sensor and did just basically copy/paste everything using Thonny.

When running the sample code I get the error below. A simple LED blink test program works, though.

Many Thanks for your help in advance.

René

Traceback (most recent call last):
File "", line 11, in
File "dht20.py", line 18, in init
File "dht20.py", line 28, in is_ready
OSError: [Errno 5] EIO

[flrrth]

Hi, this could be caused by a poor connection somewhere in your breadboard. Rewiring your entire circuit could solve it.

[Pokinatcha]

pico-dht20/dht20/dht20.py

Lines 25 to 29 in 90540b7

	@property
	def is_ready(self) -> bool:
	"""Check if the DHT20 is ready."""
	self._i2c.writeto(self._address, bytearray(b'\x71'))
	return self._i2c.readfrom(self._address, 1)[0] == 0x18

Hi, change the comparison in the return of is_ready to:
return self._i2c.readfrom(self._address, 1)[0] & 0x18 == 0x18

and it should work.
But there are several flaws in this library. According to the datasheet, the waiting time after triggering a measurement (0xAC) must be at least 80ms, not 50ms as here. The initialization sequence of the calibration (0x1B, 0x1C, 0x1E) differs from the reference implementation of the manufacturer ASAIR.

[rkappel]

Hi,

I soldered the connections properly and now it works fine. I did not need to change the code in the library.

Many Thanks for your prompt response and the follow-up.

Best Regards,
René

[fxschmidt]

Hi,
I get the same error as Rene, but my wiring was okay. For me the solution was to substitute I2C(...) with SoftI2C(...). I found this solution in the MicroPython forum. Therefore my code to run the measurements is:

from machine import Pin, SoftI2C
from utime import sleep

from dht20 import DHT20


i2c0_sda = Pin(4)
i2c0_scl = Pin(5)
i2c0 = SoftI2C( sda=i2c0_sda, scl=i2c0_scl)
sleep(0.2)

dht20 = DHT20(0x38, i2c0)

while True:
    measurements = dht20.measurements
    print(f"Temperature: {measurements['t']} °C, humidity: {measurements['rh']} %RH")
    sleep(1)

I also added theses two additional lines in the dht20.py file:

# https://github.com/flrrth/pico-dht20

from machine import I2C
from utime import sleep_ms


class DHT20:
    """Class for the DHT20 Temperature and Humidity Sensor.

    The datasheet can be found at http://www.aosong.com/userfiles/files/media/Data%20Sheet%20DHT20%20%20A1.pdf
    """
    
    def __init__(self, address: int, i2c: I2C):
        self._address = address
        self._i2c = i2c
        sleep_ms(100)
        
        # Added Columns
        self._i2c.writeto(0x38, bytearray(b'\x71'))
        sleep_ms(200)