Assuming you are able to assemble it yourself, you can do as the author did - use two scrabblepad PCBs: https://donutcables.com/products/scrabblepad-pcb-extras

Assuming you are able to assemble it yourself, you can do as the author did - use two scrabblepad PCBs: https://donutcables.com/products/scrabblepad-pcb-extras https://donutcables.com/products/scrabblepad-pcb-extras