Here’s the current version of the flow chart of my program design, although it will surely be revised as the program is revised.

I’ve also been thinking about how exactly the tracking of velocity and acceleration is going to work. At a bare minimum, I believe what we specifically want to detect is when the hand moves from negative velocity to positive velocity along the y-axis. A simple switch can watch when the velocity was previously negative and triggers a beat when the velocity turns positive (or above some threshold value to prevent false positives) during each iteration of the main program loop. The amount of acceleration at that point, or how fast the motion is being done, can then determine the volume of the music at that beat.