Reading from SHT4x (I2C) with ESP32

[affsantos]

Hello,

I would like to read the temperature and humidity from SHT41 sensor with a ESP32 using I2C.

So far, I can see the sensor using i2c.scan() with the correct address (0x44). I can also write to the sensor without errors (using i2c.writeto()) but as soon I try to read from the sensor (using i2c.readfrom()) then I get the following error:

OSError: [Errno 19] ENODEV

Here is the code I am using (it fails when running the i2c.readfrom()):

    import machine
    import time

    i2c = machine.I2C(scl=machine.Pin(5), sda=machine.Pin(4))

    print('Scan i2c bus...')
    devices = i2c.scan()

    if len(devices) == 0:
      print("No i2c device !")
    else:
      print('i2c devices found:',len(devices))

      for device in devices:  
        print("Decimal address: ",device," | Hexa address: ",hex(device))
        
        
    SHT4x_ADDRESS = 0x44
    SHT4X_MEASURE = bytearray('\xFD')  

    i2c.writeto(SHT4x_ADDRESS, SHT4X_MEASURE)
    time.sleep_ms(10)
    unit = i2c.readfrom(SHT4x_ADDRESS, 6)

This code returns:

Scan i2c bus...
i2c devices found: 1
Decimal address:  68  | Hexa address:  0x44
Traceback (most recent call last):
File "<stdin>", line 23, in main
OSError: [Errno 19] ENODEV

Link to sensor datasheet: https://download.mikroe.com/documents/d ... asheet.pdf

Note: I found another person, in the old forum, having a similar issue but I could not find a solution for this problem.

What I tried:

• Different sensor (I have 2xSHT41, both same error)
• Different ESP32 and also tried with an old ESP8266, same error
• Add a pullup 1k resistor (same error) and 10k resistor (can't find the sensor anymore)
• Tried both I2C and SoftI2C libraries, same error.

Thanks in advance

[jimmo]

Just reading the Adafruit driver for this sensor it looks like you're doing the right thing. The only thing I can see different is they trigger a soft reset by sending b'\x94' before the first read.

[jimmo]

Ahhh no I see it -- bytearray('\xFD') is not what you want. This is actually the bytes 0xc3, 0xbd which is the utf-8 representation of 0xfd.

You need to use bytearray(b'\xFD') (note the b prefix), but even better you don't actually need the bytearray at all -- just write SHT4X_MEASURE = b'\xFD'.

[jimmo]

CPython doesn't allow you to create a bytearray from a string like this, so I raised #9863 to try and avoid this trap!

[affsantos]

Thank you @jimmo for the help. I will keep an eye on your PR #9863!

[jimmo]

You don't need that PR though, that's just to prevent someone else running into the same surprise.

If you change your code as suggested then it should work.

[affsantos]

Thanks for the reply @jimmo.
I tried both SHT4X_MEASURE = bytearray(b'\xFD') and SHT4X_MEASURE = b'\xFD' but I got exactly the same error as before.

I also tried to implement the soft reset that you mentioned but I still get the same error. Below the code that I tried with the soft reset:

    SHT4X_RESET = b'\x94'
    SHT4x_ADDRESS = 0x44
    SHT4X_MEASURE = b'\xFD'
    
    i2c.writeto(SHT4x_ADDRESS, SHT4X_RESET)
    time.sleep_ms(10)
    i2c.writeto(SHT4x_ADDRESS, SHT4X_MEASURE)
    time.sleep_ms(10)
    unit = i2c.readfrom(SHT4x_ADDRESS, 6)