The board layout and the source code is all available on GitHub. Because the switches are analog, they are bidirectional. That is, it isn’t really connecting one output to 32 inputs.

which forms a variable resistor you can read with an Arduino analog input. You can see the entire thing in the video below. The source code is simple at this point — eventually, he plans to ...

To interface an analog input or output component with ... with building circuits and writing codes for hardware control, then ...

The Nano includes 14 digital pins (for both digital input and digital output components) and eight analog pins ... The Nano uses the Arduino IDE with the Arduino code language (based on C++).