i2c problem

I'm having problems with i2c, and after a couple of hours trying all the options that Google throws up, I'm stumped.

Pi 3 4.14.79-v7+

sudo i2cdetect -y 1 Error: could not open file '/dev/i2c/1': No such file or directory

cat /etc/modules i2c-bcm2708 i2c-dev

tail /boot/config.txt

dtparam=i2c=on dtparam=i2c_arm=on dtparam=i2c_vc device_tree_param=i2c=on1=on dtparam=spi=on dtparam=i2s=on

/etc/modprobe.d/raspi-blacklist.conf is empty

Any suggestions ?

TIA

Adrian

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Is this an original model B with 256MB of RAM? If so it only has bus 0.

---druck

What does "i2cdetect -l" show?

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Lew Pitcher 
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On a sunny day (Sun, 27 Jan 2019 17:19:34 +0000) it happened Adrian wrote in :

Well, I use a lot of i2c also on raspberry, and I use a C library for that do the I/O not via the dedicated pins but via any pin I want. I2c is largely time insensitive (as for example to a task switch) so it always works. Want the library? I can publish the c code here. I use actualy 3 pins, scl (output), sda_in (input), and sda_pulldown (output via pulldown diode connected to sda line). If you scroll down on this page you see a circuit diagram with 2 separate i2c busses:

actualy the library is the .tgz link at the bottom of the page. Saved time, uses a hundred of more times...

All assuming you know C.and hardware.

Pi 3 with 1GB

Adrian

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i2c-0 i2c bcm2835 I2C adapter I2C adapter

Adrian

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Hello Vince,

Yes, with several reboots afterwards.

Adrian

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It's interesting, I've never user i2c on my RPi (3+) but after enabling it via raspi-config (didn't reboot) I have /dev/i2c-1 but not /dev/i2c/1. So why the difference?

Why i2c-bcm2708? I have only i2c-dev in /etc/modules. i2c-bcm2708 isn't loaded but i2c-bcm2835 is.

Of these I have only dtparam=i2c_arm=on.

I have /dev/i2c-0

I've added i2c-bcm2835 (and rebooted), and still no luck.

Adrian

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First thing I'd suggest you try would be 'sudo i2cdetect -y 0'. Don't know why, but that sure seems to be indicated.

Thanks.

That works. I get blanks in the first three cells, and the last 8 cells, otherwise it is "--".

Adrian

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In message , Adrian writes

A bit more digging.

I'm trying to listen to a BME280 sensor (temperature, pressure and humidity), and there is some Python code available to do so. That uses /dev/i2c/1, however, if I alter the code slightly, and tell it to use a different port (so it points to /dev/i2c-0), I get a different error (no great surprise) :

Traceback (most recent call last): File "bme280_sensor.py", line 9, in bme280.load_calibration_params(bus, address) File "/usr/local/lib/python3.5/dist-packages/bme280/__init__.py", line

155, in load_calibration_params compensation_params.dig_T1 = read.unsigned_short(0x88) File "/usr/local/lib/python3.5/dist-packages/bme280/reader.py", line 40, in unsigned_short return self._bus.read_word_data(self._address, register) & 0xffff File "/usr/local/lib/python3.5/dist-packages/smbus2/smbus2.py", line 410, in read_word_data ioctl(self.fd, I2C_SMBUS, msg) OSError: [Errno 121] Remote I/O error

sudo i2cdetect -y 0 gives me :

0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- --

So, does that suggest that the bus is working, or that that I've got the right bus, but there is no data or what ?

Thanks

Adrian

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[Snip]

It looks like the internal i2c bus 0 is enabled, and not the external bus 1, which your sensor will be connected to.

Try going back to a stock config.txt and cmdline.txt from a Raspbian image, reboot, use raspi-config to enable i2c, reboot again.

---druck

Thanks.

I've done that, and now I get /dev/i2c-1 present (but not 0 !)

Running the python code, I now get readings from the sensors.

Problem resolved. Many thanks to those who've contributed.

Adrian

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