raspberry_pi_button

Overview

A ROS package to interface a button to a ROS topics using a Raspberry Pi GPIO. Provides an easy way to create button boxes and integrate them within ROS.

Example of button box using a Raspberry Pi 3B+ and homemade case

License

MIT

Installation

Package has to be launched from a Raspberry Pi. Has been tested on Raspberry Pi 3B+.

Dependencies

• Robot Operating System (ROS)

• RPi.GPIO

  Install using sudo apt install rpi.gpio

Building

To build the package, clone the current repository in your catkin workspace and build it.

cd catkin_ws/src
git clone https://github.com/RBinsonB/ros_raspberry_pi_button.git

Build your workspace with either catkin_make or catkin build

cd ...
catkin_make

Setting up hardware

Connect any number of buttons to GPIO pins of the Raspberry Pi. Each button should supply 5V (from the Raspberry Pi 5V pins or other) to the input pin. The code provided here will read the pin value and uses Raspberry Pi internal pull-down resistors.

Button wiring example for two buttons and a Raspberry Pi 3B+

Setting up the Raspberry Pi ROS environment

It is assumed that the ROS master is running on another computer on the same network. The Raspberry Pi ROS environment needs to be set accordingly.

• From the Raspberry Pi Set the ROS_MASTER_URI to the ROS master computer IP and port (replacing by the proper ROS master computer IP): export ROS_MASTER_URI=http://<ros-master-ip>:11311

  Set the ROS_IP to the Raspberry Pi IP (replacing by the proper Raspberry Pi IP): export ROS_IP=<rpi-ip>

• From the ROS master computer

  Set the ROS_IP to the ROS master computer IP (replacing by the proper ROS master computer IP): export ROS_IP=<ros-master-ip>

Usage

Configuration is done with ROS parameters. Each button need the private parameters /input_pin and /topic_id grouped under the button name. For example to setup a button named button_1, reading value from a button connected to GPIO 4 and publishing it on the topic button_state, the parameters should be:

~/button_1/input_pin: 4
~/button_1/topic_id: button_state

YAML config files help setting up multiple buttons. An example config files for a box of two buttons can be found at /config/button_box_example.yaml

To launch, simply run the node button_node.py (with the previously stated parameters as private parameters) while a ROS master core is running. For each button the state will be published as a boolean to the specified ROS topic.

Example

An example launch file for a box of two buttons (connected on GPIO 4 and 27) can be found at /launch/button_box_example.launch and run using the following command:

roslaunch raspberry_pi_button button_box_example.launch

Checking that button state are being published can be done by running:

rostopic list

The following topics should appear in the list.

/button_1
/button_2

Checking each button state can be done by running the following:

rostopic echo /button_1

and

rostopic echo /button_2

Config files

• button_box_example.yaml Example of configuration file for a box of two buttons connected to GPIO 4 and 27.

Launch files

• button_box_example.launch: Example of implementation of a box of two buttons. Run the button node with associated configuration to track the state of two buttons and publish the states to ROS topics.

Nodes

button_node.py

Track every configured button state and publish it over ROS as a Bool message. Message is latched and only published when button is changing state.

Published Topics

• topic_id (std_msgs/Bool, latched)

  Button state (True when circuit close, False when circuit open). Topic name is to be configured by the parameter topic_id and is subject to change. Each configured button gets its own state publisher topic.

Parameters

• ~/button_name/input_pin (int)

  Button input pin using BCM numbering. button_name can be configured to any name. Parameter needed for each button.

• ~/button_name/topic_id (string)

  Button state topic. button_name can be configured to any name. Parameter needed for each button.