Still stumbling a bit with the Arduino code. I had a breadboard prototype working last week with two sensors, two LEDs and a buzzer. But when I expanded the prototype to include 11 sensors and LEDs, the code no longer works as intended. Most notably, the buzzer appears to be trying to play more than one note at a time.
Digging through one of my bins I found a good candidate for the "screen" that will show the LEDs when keys are pushed: the translucent front plate that went over the CRT on an old oscilloscope. It's the perfect size and I've decided to expand the matrix of LEDs to an 5x4 array to make it seem more natural.