Send once [Uno + Sparkfun MIDI Breakout]

sonvivant:
Also, further to a comment from Nick Gammon earlier in this thread, the buttons are on pull-down, not pull-up. (Is pull-up better and why?)

void setup() {

MIDI.begin();   
  // initialize the pushbutton pin as an input:
  pinMode(buttonStop, INPUT); 
  pinMode(buttonGo, INPUT);
  pinMode(buttonLast, INPUT);
  pinMode(buttonNext, INPUT); 
}

...

The simplest thing is to have the buttons wired, from the pin to ground, so when you press it, the pin is grounded. To make this work you need pull-up, eg.

void setup() {
  
  MIDI.begin();     	
  // initialize the pushbutton pin as an input:
  pinMode(buttonStop, INPUT_PULLUP);  
  pinMode(buttonGo, INPUT_PULLUP);
  pinMode(buttonLast, INPUT_PULLUP);
  pinMode(buttonNext, INPUT_PULLUP); 
}

...

Now the (weak) pull-up keeps the pins high, and when you push the button they go low. So you look for a high -> low transition.