i2c address not being recognized?

[maha-haji]

Hi,

I have no issues using the HTU21D, but when I run [hex(x) for x in i2c.scan()] it does not show up in my list of i2c device addresses (i.e. I do not see '0x40' anywhere). Running sudo i2cdetect -y 1 in the command line, it does show up correctly.

Any suggestions on what I might be doing wrong?

Thanks!

[ladyada]

the sensor works fine when you use it, do other i2c items appear? what ocmputer and os are you using

[maha-haji]

yes, I also have a BMP280 that I can see the i2c address of, as well as a BNO055. I'm using a Raspberry Pi 4 Model B, running the latest Raspbian OS

[ladyada]

could be it doesnt like how we scan for devices, its not a 'standard' thing

[caternuson]

Any special reason for the current use of read_byte() in the scan() function? It seems like most other scans use a test write instead of a read, and success if simply getting an ACK at given address.

I just did quick test changing to using quick_write: https://github.com/adafruit/Adafruit_Python_PureIO/blob/f4d0973da05b8b21905ff6bab69cdb652128f342/Adafruit_PureIO/smbus.py#L278 and it seems to work.

Pi 4 with a HTU21D on I2C:

(blinka) pi@raspberrypi:~ $ python3
Python 3.7.3 (default, Dec 20 2019, 18:57:59) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import board
>>> i2c = board.I2C()
>>> i2c.scan()
[64]
>>> 

[makermelissa]

No idea 🤷‍♀️. It's been that way for quite a while.

[ladyada]

there was a reason for this, i think... beaglebone did not have the ability to write without data?

[kaolpr]

Well, I came across that issue too. @ladyada what would you say on giving an option to scan using write? It would require modification of busio.py along with microcontroller files. Microcontrollers not supporting write without data can raise an exception.

[ladyada]

the best thing we can do is if you have something in busio.py that determines the platform its running on and doesn't do a bus-scan that way for whatever platform it doesnt work.

for the individual chips that freak out we use the probe=false 'don't try to scan me while creating the busdevice' https://docs.circuitpython.org/projects/busdevice/en/latest/api.html

[kaolpr]

Well, I was rather thinking of changing busio.I2C.scan method definition to include with_write: bool=False or sth similar.

[ladyada]

we'd rather not change the API as its platform dependent and we don't have it in main CircuitPython - you can add platform dependant code within the scan function - that's the PR we'd accept to review!