Pop'n Music is a rhythm game by Konami which uses 9 100mm circular buttons for gameplay.
It is largely considered the easiest DIY controller to make due to its straightforward construction and wiring.
The best code to use is from CrazyRedMachine: https://github.com/CrazyRedMachine/UltimatePopnController
This codebase features two versions:
- Arduino Due code for replicating the buttons and lights inside a real Pop'n Music cabinet
- Arduino Leonardo code for DIY controllers
Buttons and Electronics
You will need 9 100mm circular buttons, follow the link for where to buy.
Typically, most controllers will also feature 2 additional buttons for other options. 33mm square buttons are common, but you can use any button.
See Choosing a Board for information on which board to use, but typically an Arduino Leonardo or Arduino Micro (or clones) is going to be the easiest work with.
Dimensions and Artwork
You can find official dimensions and replica artwork from CrazyRedMachine: https://github.com/CrazyRedMachine/PopnPanel
The controller itself will be a simple box. Not all 100mm buttons are the same length, so be sure to measure yours before starting construction. Simple plans are included in the link above.