ROS2 driver for a very simple I2C device

The custom I2C device has one register at an address 0x42 or 0x43 that can only be written to with values in the range 0 to 7. The address can be changed by modifying the code. The ROS2 driver will send data values in the range 0 to 7 to address 0x42 and data values greater that or equal to 8 to address 0x43 after subtracting 8.

ROS topic and message

The topic used is /pi2c.

The message used is std_msgs/msgs/UInt8. Values in the range 0 to 15 are sent to the device. Other values are ignored.

Installation

This driver using the Python SMBUS package to interface with the I2C on the RPi. Install it using:

sudo apt install python3-smbus2

Clone this repo in a ROS2 workspace and then build and run. See below for example commands:

cd ~/ws/src
git clone https://github.com/RealRobotics/pi2c-driver-ros2
cd ~/ws
colcon build --packages-select pi2c_driver
ros2 launch pi2c_driver pi2c_driver.launch.py

When successful started, you should see output like this:

[INFO] [launch]: All log files can be found below /home/pipebot/.ros/log/2024-04-22-20-18-56-873873-skatebot1-7672
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [pi2c_driver_exec-1]: process started with pid [7673]
[pi2c_driver_exec-1] [INFO] [1713813538.509213956] [pi2c]: PI2C started...

Verify that you can see the topic using:

$ ros2 topic list
/parameter_events
/pi2c
/rosout

Testing

To send a command to the I2C device from the command line use this command:

$ ros2 topic pub -1 /pi2c std_msgs/UInt8 "{data: 14}"
publisher: beginning loop
publishing #1: std_msgs.msg.UInt8(data=14)

The driver can emit one of three messages.

# Value in range and device present
[pi2c_driver_exec-1] [INFO] [1713820461.992177218] [pi2c]: Written 14 to address 68
# Value out of range
[pi2c_driver_exec-1] [WARN] [1713820470.863957176] [pi2c]: Value 24 exceeds maximum value of 15. Ignoring...
# No I2C device
[pi2c_driver_exec-1] [ERROR] [1713813552.280648022] [pi2c]: Failed to write value 14 to I2C device: [Errno 121] Remote I/O error

Acknowledgments

© 2024, University of Leeds.

The author, A. Blight, has asserted his moral rights.