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Update enable_i2c.md (#17005)

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Co-authored-by: Stefan Agner <stefan@agner.ch>
Co-authored-by: Franck Nijhof <frenck@frenck.nl>
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## Enable I2C ## Enable I2C
Home Assistant using the Home Assistant Operating System is a managed environment, which means you can't use existing methods to enable the I2C bus on a Raspberry Pi. Home Assistant using the 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
### Step by step instructions ### Enable I2C with an SD card reader
#### Access the boot partition
You will need: You will need:
- SD card reader - SD card reader
- SD card with Home Assistant Operating System flashed on it - SD card with Home Assistant Operating System flashed on it
#### Step 1 - Access the Home Assistant Operating System boot partition
Shutdown/turn-off your Home Assistant installation and unplug the SD card. 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 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, `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 use your operating systems disk management utility to find the SD card reader
and make sure the first partition is available. and make sure the first partition is available.
#### Step 2 - Add files to enable I2C #### Add files to enable I2C
- In the root of the `hassos-boot` partition, add a new folder called `CONFIG`. - In the root of the `hassos-boot` partition, add a new folder called `CONFIG`.
- In the `CONFIG` folder, add another new folder called `modules`. - In the `CONFIG` folder, add another new folder called `modules`.
@ -32,7 +33,7 @@ and make sure the first partition is available.
dtparam=i2c_arm=on dtparam=i2c_arm=on
``` ```
#### Step 3 - Start with the new configuration #### Start with the new OS configuration
- Insert the SD card back into your Raspberry Pi. - Insert the SD card back into your Raspberry Pi.
- On startup, the `hassos-config.service` will automatically pickup the new - On startup, the `hassos-config.service` will automatically pickup the new
@ -40,9 +41,7 @@ and make sure the first partition is available.
- Another reboot might be necessary to make sure the just imported `rpi-i2c.conf` is - Another reboot might be necessary to make sure the just imported `rpi-i2c.conf` is
present at boot time. present at boot time.
The I2C devices should now be present under /dev. ### Enable I2C via Home Assistant Operating System Terminal
### From Home Assistant Operating System Terminal
Alternatively, by attaching a keyboard and screen to your device, you can access the physical terminal to the Home Assistant Operating System. Alternatively, by attaching a keyboard and screen to your device, you can access the physical terminal to the Home Assistant Operating System.
@ -62,3 +61,9 @@ You can enable i2c via this terminal:
sync sync
reboot 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 check with a multi meter showing 3.3 V on the I2C pins GPIO2 and GPIO3.