home-assistant.io/source/_includes/common-tasks/enable_i2c.md

Enable I2C

Home Assistant using the {% term "Home Assistant Operating System" %} which is a managed environment, which means you can't use existing methods to enable the I2C bus on a Raspberry Pi. In order to use I2C devices you will have to

• Enable I2C for the Home Assistant Operating System
• Setup I2C devices e.g. sensors

Enable I2C with an SD card reader

Access the boot partition

You will need:

• SD card reader
• SD card with {% term "Home Assistant Operating System" %} flashed on it

Shutdown/turn-off your Home Assistant installation and unplug the SD card. Plug the SD card into an SD card reader and find a drive/file system named hassos-boot. The file system might be shown/mounted automatically. If not, use your operating systems disk management utility to find the SD card reader and make sure the first partition is available.

Add files to enable I2C

• In the root of the hassos-boot partition, add a new folder called CONFIG.
• In the CONFIG folder, add another new folder called modules.
• Inside the modules folder add a text file called rpi-i2c.conf with the following content:

  i2c-dev
  

• In the root of the hassos-boot partition, edit the file called config.txt add two lines to it:

  dtparam=i2c_vc=on
  dtparam=i2c_arm=on
  

Start with the new OS configuration

• Insert the SD card back into your Raspberry Pi.
• On startup, the hassos-config.service will automatically pickup the new rpi-i2c.conf configuration.
• Another reboot might be necessary to make sure the just imported rpi-i2c.conf is present at boot time.

Enable I2C via Home Assistant Operating System Terminal

Alternatively, by attaching a keyboard and screen to your device, you can access the physical terminal to the {% term "Home Assistant Operating System" %}.

You can enable I2C via this terminal:

• Login as root.

• Type login and press enter to access the shell.

• Type the following to enable I2C, you may need to replace sda1 with sdb1 or mmcblk0p1 depending on your platform:

  mkdir /tmp/mnt
  mount /dev/sda1 /tmp/mnt
  mkdir -p /tmp/mnt/modules
  echo -ne i2c-dev>/tmp/mnt/modules/rpi-i2c.conf
  echo dtparam=i2c_vc=on >> /tmp/mnt/config.txt
  echo dtparam=i2c_arm=on >> /tmp/mnt/config.txt
  sync
  reboot
  

Troubleshooting

After rebooting the host there should be i2c-0 and similar device files in /dev. If such device files are missing, enabling I2C failed for some reason. You can check the status of I2C kernel modules by using lsmod | grep i2c in the terminal. If they are loaded, you should find at least the entry i2c_dev. Active usage of the modules is indicated by a number, e.g. i2c_dev 20480 2 would indicate two active I2C device files.

An active I2C can also be checked with a multi meter showing 3.3 V on the I2C pins GPIO2 and GPIO3.