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I'm trying to start an I2c communication with my Raspberry Pi using the pigpio library. It works fine for me with SPI, but I really do struggle with I2C.

When I use

if (gpioInitialize() < 0) printf("Coudn't initialize gpio");
i2c_handle = i2cOpen(0, 0b1100000, 0);

I always get back -74 as handle, which stands for PI_BAD_I2C_BUS.

Can somebody explain that to me? The bus number I give to the function is 0, that should be totaly valid. But I also tried some different numbers and I always get this same error...

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  • What model Pi are you using? What happens if you try this i2c_handle = i2cOpen(1, 0b1100000, 0);
    – Steve Robillard
    Aug 1, 2017 at 10:45
  • I use a Raspberry Pi 3. No matter what bus number I use, there is always the same return.
    – jusaca
    Aug 1, 2017 at 10:49
  • did you enable i2c in raspi-config?
    – crasic
    Aug 1, 2017 at 23:14
  • Ok, that actually was the problem. Embarrassing. But I don't understand, I didn't enable SPI either, and that worked just fine from the beginning. Can I somehow mark your comment as solution, despite it's not an answer?
    – jusaca
    Aug 2, 2017 at 8:46
  • @crasic, hi, I would like to invite you to post that solution as an answer. Thanks.
    – Ghanima ♦
    Oct 16, 2018 at 19:30

1 Answer 1

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I was getting the same error:

raspberrypi $ python
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 pigpio
>>> mypi = pigpio.pi()
>>> myi2c = mypi.i2c_open(1, 0x1E)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/pigpio.py", line 2644, in i2c_open
    self.sl, _PI_CMD_I2CO, i2c_bus, i2c_address, 4, extents))
  File "/usr/lib/python3/dist-packages/pigpio.py", line 979, in _u2i
    raise error(error_text(v))
pigpio.error: 'bad I2C bus'

And I eventually figured out that you need to enable I2C on the raspberry pi:

sudo raspi-config

And select 5 Interfacing Options -> P5 - I2C -> Yes to enable I2C

You can then check if I2C is enabled by looking in /dev/

raspberrypi $ ls -l /dev/i2c*
crw-rw---- 1 root i2c 89, 1 Apr 14 19:13 /dev/i2c-1
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