i3-ws-display

Display active i3 workspaces on a 7-segment display

A set of programs and configuration files for displaying i3 workspaces on a display controlled by an Arduino Nano.

Background

I started using a secondary monitor and didn't want to waste screen real estate for a status bar on it. However, peeking at the other monitor to see which workspaces are active felt awkward. This led me to create this project. The end result is a 4-digit 7-segment display that shows the active workspaces, mounted on top of my external monitor. It also shows if a workspace is visible by lighting up the dot after the corresponding workspace number.

There is no real reason to be limited to a 4-digit display, or in fact - a 7-segment display. I have workspaces 4-7 mapped to my external display. This setup works quite well for me.

Hardware setup

You'll need:

• Arduino Nano. Technically any Arduino should work, but then you'll have to rewrite the pin mappings/use a library for the 7-segment display.
• 7-segment display module. Mine is labelled HS420561K-32. It's a 4-digit common-cathode unit. It's important that there is a dot after every digit so you can indicate the currently visible workspace.
• Four 220-ohm resistors and wires to connect it all up

Setup

Connect the display to your Arduino. If you want the numbers on the display to align left, change the align_to_right symbol to false in uc/src/main.cpp. Then flash the file to your Arduino using PlatformIO. To do that, run the following commands in the root directory of the project:

cd uc
pio run -t upload

Wiring for a common-cathode display with the following pin arrangement (according to the typical segment identification):
Top row - 1, a, f, 2, 3, b
Bottom row - e, d, DP, c, g, 4

Software setup

Arch Linux users can use the provided PKGBUILD.

Dependencies

A compiler with C++17 support (clang-5+, gcc-7+), cmake 3.11+, git

pkgconf
libserial
jsoncpp
sigc++

This project also uses the i3ipcpp library which is pulled and built automatically by cmake.

Building

Run the following commands:

cd linux
mkdir build && cd build
cmake ..
make
sudo make install

Configuration

Run ws-display --help to see available configuration options.

You'll probably want to write an udev rule for the Arduino. Otherwise it might not always get bound to the same /dev node.
Unfortunately the Arduino Nano does not have a serial id, so it's difficult to write an udev rule for it. I found that the easiest way was to tie it to a USB hub port. This works as long as the Arduino is always plugged into the same USB port.
I won't go into writing udev rules here, see the 97-ws-display.rules file for an example. I found this post helpful.

If the Arduino will always be connected to your machine you could (and should) just start ws-display from your i3 config.

I have a laptop and a docking station to which the Arduino is connected to so I'm using a systemd user service for starting and stopping ws-display. The systemd user service starts ws-display as soon as the Arduino becomes available. The service also depends on a custom i3.target which gets started by i3:

exec_always --no-startup-id systemctl --user restart i3.target

I also put systemctl --user stop i3.target in a script that runs when i3 exits. See the systemd/ws-display.service and systemd/i3.target files.