Architectures/ARM/i2c

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Introduction

This covers various bits of using i2c on various ARM devices.

Displays

Camera module

On Fedora 29. Add this line

 start_x=1

to /boot/efi/config.txt and load the bcm2835-v4l2 module at boot

 echo bcm2835-v4l2 > /etc/modules-load.d/bcm2835-v4l2.conf

and reboot.

You should now see this device /dev/video0

OLED display on the Raspberry Pi 3

• Tested on Raspberry Pi 3
• Display chipset: ssd1306
• Interface: i2c
• Dimensions: 128 x 64

Create a group that can access the i2c devices without root permissions, and add your user to such group

$ sudo groupadd i2cuser
$ sudo usermod $USER -G i2cuser -a

Create a rule in UDEV, in order to create i2c devices with the right group and permissions

$ echo "SUBSYSTEM==\"i2c-dev\", GROUP=\"i2cuser\", MODE=\"0660\"" | sudo tee /etc/udev/rules.d/50-i2c.rules

Logout from the current session and login again.
Install i2c-tools package

$ sudo dnf install i2c-tools

Verify that the i2c adapter is visible by the system

$ i2cdetect -l -a

The output should be something lik this:

i2c-1	i2c       	bcm2835 I2C adapter             	I2C adapter
i2c-2	i2c       	bcm2835 I2C adapter             	I2C adapter
i2c-0	i2c       	bcm2835 I2C adapter             	I2C adapter

Connect the OLED display to the Raspberry:

GND -> pin 39 VCC -> pin 1 SCL -> pin 5 SDA -> pin 3

Verify that the i2c device is listed

$ i2cdetect -y 1

This should be the output

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

Let's install some packages

$ sudo dnf install git gcc python3-pillow redhat-rpm-config python3-devel zlib-devel libjpeg-devel

You can use the luma Python module https://luma-oled.readthedocs.io/en/latest/intro.html, it seems pretty simple to use

$ pip3 install --upgrade luma.oled --user

Let's clone the luma examples from github

$ git clone https://github.com/rm-hull/luma.examples.git

And test if all is working

$ cd luma.examples/examples
$ python3 ./welcome.py