Earlier this year (during quarantine) I bought an Autoharp with the plan of modifying it so that it could play entire scales rather than just 1 chord at a time.
I bought 12 additional blank felt bars, and my gf helped me to cut the felt on each so that 1 bar mutes 1 pitch class (i.e. all octaves of a note) when its button is depressed.
I was so jazzed when the project worked as planned! Luckily I have small hands, so I’m able to push down 5 buttons at once, allowing the remaining 7 notes of the chroma to ring out when the instrument is strummed / plucked / picked.
I created a visual interface to help me figure out which button-depression-combinations correlates to which scale, and wrapped it within my Scale Navigator web app. As I select the scale with Scale Navigator open on my iPad, the Autoharp visual interface shows me which buttons to press to stay harmonically synchronized with the current scale.