I²C PWM Board

ROS2 node for controlling PWM boards based on the PCA9685 chip with an I²C interface. Primary use is for controlling RC Servos and DC motors via PWM. This is based on ros-i2cpwmboard (OUTDATED) with updates to make it work on ROS2.

To see a practical use of this project, see the SMOV project.

Documentation

At present, there is no complete new documentation for the project. However, you can access the documentation for the old version of the project (the changes to be made to the terminal are minimal, as it uses ROS1, and the core functionality remains the same). You can access it by clicking here or here.

Functionalities

The calibration package will help you find the centre and critical values of your servos. Click here to take a look.

When you launch the program, you can now choose your I²C bus. Here's an example:

ros2 run i2c_pwm_board controller 1 # The "1" tells the program to open the i2c-1/ bus, but you can change it to your desired bus.

This will be particularly useful for opening several buses between programs, and for easily adapting to the RPi Zero, which has an i2c-0/ bus by default.

It works as follows: If you want to open i2c-1 (RPi default, except for the RPi Zero), it will start the topics under the main_ prefix. Otherwise, if you open another bus, it will start the topics under the secondary_ prefix.
You can therefore currently only control two boards at a time.

Examples

# Setting PWM frequency to 50Hz.
ros2 service call /set_pwm_frequency i2c_pwm_board_msgs/srv/IntValue "{value: 50}"

# Configuring two servos.
ros2 service call /config_servos i2c_pwm_board_msgs/srv/ServosConfig "servos: [{servo: 1, center: 333, range: 100, direction: -1},{servo: 2, center: 336, range: 108, direction: 1}]"

# Configuring those two servos on differential mode.
ros2 service call /config_drive_mode i2c_pwm_board_msgs/srv/DriveMode "{mode: differential, rpm: 56.0, radius: 0.0055, track: 0.015, scale: 1.0,servos: [{servo: 1, position: 1}, {servo: 2, position: 2}]}"

# Drive both servos forward using proportional value between [-1; 1].
ros2 topic pub -1 /servos_proportional i2c_pwm_board_msgs/msg/ServoArray "{servos:[{servo: 1, value: 0.40}, {servo: 2, value: 0.40}]}"

Installation

You need to have ROS2 installed (of course) and these packages provided by the default desktop installation below :

• rclcpp, std_msgs, std_srvs, geometry_msgs
• rosidl_default_generators, rosidl_default_runtime
• Have python3-colcon-common-extensions installed
• Have libi2c-dev and i2c-tools installed
• Have the xmlrpcpp package

Clone it

You can clone and run this package by copying the command below :

• Note that if you want to run this project, you have to clone the xmlrpcpp packages :

git clone --recursive https://github.com/vertueux/i2c_pwm_board.git

Install automatically

You can install the i2c library and colcon by running the install scripts located at scripts/install_dependencies.sh. Simply just copy & paste this code :

cd scripts/
chmod +x install_dependencies.sh
./install_dependencies

Configure Ubuntu

Make sure that both I²C and SPI are enabled by default. Check the file /boot/firmware/syscfg.txt and see if you have the following lines :

dtparam=i2c_arm=on
dtparam=spi=on

If not, maybe you can append them on /boot/firmware/usercfg.txt and reboot, and hopefully, that works. If that doesn't work, maybe do sudo apt update && sudo full-upgrade -y and see if there are any distro updates needed.

• Refer to this post.

You can also add the following line to /boot/config.txt :

dtparam=i2c_arm=on

As well as this line to /etc/modules :

i2c-dev

• Refer to this post.

---

With raspi-config, you can enable i2c by navigating to Interface Options->Advanced->I²C and then enable it.

Testing I²C

Now when you log in you can type the following command to see all the connected devices

sudo i2cdetect -y 1 # Or 0, depends on the device you use.

Build it

source /opt/ros/humble/setup.bash # With Debian binaries 
cd /i2c_pwm_board/
colcon build --packages-select i2c_pwm_board i2c_pwm_board_msgs xmlrpcpp
source install/setup.bash # Do not change directory

Run it

In order to run the project, you just have to perform this command :

ros2 run i2c_pwm_board controller # You can add your I²C bus address as a digit (like 1 to open i2c-1/).