Here’s a little Spintronics keyboard (spin-synth?)! It’s approximately one equal temperament octave from C4-C5 (as best as I could get with the available values of the Spintronic resistors, not perfect, put pretty close, at least on my computer). The keyboard has both momentary contact operation (like a normal piano) as well as the ability to sustain notes.
There are transistors laid out in a standard keyboard pattern, pull down on the right-hand side to sound the note, release to shut it off.
Below the transistors is a corresponding row of switches. Turn them on to hold a note.