punchy.ino

#include "MIDIUSB.h"

const byte TOTAL_BUTTONS = 16;
const byte BUTTONS_PIN[TOTAL_BUTTONS] = {2,3,4,5,6,7,8,9,10,11,12,A0,A1,A2,A3,A4};
const byte BUTTONS_PITCH[TOTAL_BUTTONS] = {36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};

void setup() {
  for (byte i = 0; i < TOTAL_BUTTONS; i++) {
    pinMode(BUTTONS_PIN[i], INPUT_PULLUP);
  }
}

void loop() {
  for (byte i = 0; i < TOTAL_BUTTONS; i++) {
    byte buttonState = digitalRead(BUTTONS_PIN[i]);
    byte pitch = BUTTONS_PITCH[i];
    
    delay(2); // See https://arduino.cc/en/Tutorial/Debounce

    if (buttonState == LOW) {
      noteOn(pitch);
    } else {
      noteOff(pitch);
    }
  }
}

void noteOn(byte pitch) {
  MidiUSB.sendMIDI({0x09, 0x90, pitch, 127});
  MidiUSB.flush();
}

void noteOff(byte pitch) {
  MidiUSB.sendMIDI({0x08, 0x80, pitch, 0});
  MidiUSB.flush();
}