PCA9685 - ROS2 Driver with ros2_control Integration

Overview

This repository contains a ROS2 package for controlling the PCA9685 PWM driver using both:

• A ROS2 native service-based interface (legacy control)
• A ROS2 Control hardware interface (recommended for modern robot systems)

It is designed primarily for servo motor control.

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Hardware

Tested setup:

• Raspberry Pi 4B (4GB RAM)
• OS: ros-realtime-rpi4-image
• ROS2: Humble
• PCA9685 16-channel PWM driver (I2C)
• Servo: TowerPro SG90

Reference: - https://www.nxp.com/products/pca9685 - https://www.towerpro.com.tw/product/sg90-7/

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Package Modes

This package supports two operation modes:

1. Legacy ROS2 Service Mode

• Node: ros2_pca9685
• Control method: ROS2 Service (/pca9685/set_pwm)
• Suitable for simple direct control or testing

2. ROS2 Control Hardware Interface (Recommended)

• Integrates with ros2_control
• Exposes:
  • Command interfaces (position)
  • State interfaces (position feedback = commanded value)
• Works with controller_manager and standard ROS2 controllers

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Installation

Clone into your ROS2 workspace:

cd ~/ros2_ws/src
git clone <your-repo-url>

Build:

cd ~/ros2_ws
colcon build --packages-select ros2_pca9685

Source:

source install/setup.bash

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Running Legacy Service Node

Launch driver node:

ros2 launch ros2_pca9685 ros2_pca9685.launch.py

Check service:

ros2 service list

Call service:

ros2 service call /pca9685/set_pwm ros2_pca9685/srv/SetPwm "channel_num: 1
target_position: 170"

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ROS2 Control Setup

Important Concept

The hardware interface does NOT start controller_manager automatically.

User is responsible for:

• Starting controller_manager
• Loading controllers (e.g. joint_trajectory_controller, forward_command_controller)
• Providing URDF + ros2_control tags

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Step 1: Add ros2_control to URDF

Example snippet:

<ros2_control name="PCA9685System" type="system">
  <hardware>
    <plugin>ros2_pca9685/PCA9685Hardware</plugin>
  </hardware>

  <joint name="servo_joint_1">
    <command_interface name="position" />
    <state_interface name="position" />
  </joint>
</ros2_control>

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Step 2: Start controller_manager

ros2 run controller_manager ros2_control_node   --ros-args --params-file config/controllers.yaml

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Step 3: Load Controllers

ros2 control load_controller joint_state_broadcaster
ros2 control load_controller forward_command_controller

Activate:

ros2 control switch_controller   --activate forward_command_controller   --activate joint_state_broadcaster

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Step 4: Send Commands

ros2 topic pub /forward_command_controller/commands std_msgs/msg/Float64MultiArray "data: [1.57, 0.78]"

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Internal Behavior

• write(): converts rad to PWM duty cycle
• read(): echoes command (no encoder feedback)

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Architecture

MoveIt / User Node
|
controller_manager
|
ros2_control hardware interface
|
PCA9685 PWM Driver
|
Servo Motor

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License

BSD 3-Clause License

Copyright (c) 2026 Mezael Docoy