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Unable to read cape sensors via i2cget

Former Member

As noted in this forum post, I have the weather cape working, but am only able to read the sensor values by reading data directly from locations like /sys/bus/i2c/devices/1-0077/pressure0_input.

 

I believe this is because i2cdetect shows them as busy (UU), but I'm unsure how to get whatever drivers or software has hold of them to let them go so I can access them directly.  Any hints appreciated.

  • Hi Josh,

     

    See here: http://elinux.org/CircuitCo:BeagleBone_Weather

    There should already be a driver loaded for it when you plug it in, and to read any of the sensors you just need to access the files in the path

    /sys/bus/i2c/devices/i2c-1 which is the way this driver talks to user space applications. The 'cat' command can be used to view the sensor values

    from the command line. You shouldn't (need to) use Python I2C commands - this low-layer access is being handled by the driver.

     

    With Python, there will be a way to do a cat xyz shell command and capture the response. I don't know the way to do that however - I'm not knowledgeable in Python.

    Check out 'python exec shell command stdout' or similar in google, this will reveal how to do this.

  • in reply to shabaz

    Hey thanks for the speedy reply.

     

    Yes I am able to access that data via python by subbing out to the shell.  So my scripts are working. However I'd prefer to use the i2c libraries available to python for other beagleboard sensors, rather than sub to the shell.  I was hoping I could either disable the driver and still access the i2c data directly, and/or the driver would allow me to access it w/o keeping it blocked/busy.

  • in reply to Former Member

    You'd have to investigate if capemgr allows that; it might not. One possible way would be to erase (or remove) the EEPROM on the cape, but you may prefer an alternative method.

    Python is so slow that I don't think there will be an improvement in speed by accessing I2C data directly (and weather changes slowly anyway).

    You don't have to use 'cat' - I just though that might be easier. You could open a file in Python and read it, which would be the correct way to do it (but I don't know how to

    do that in Python..).