Ini
[env:leonardo]
platform = atmelavr
board = leonardo
framework = arduino
lib_deps = mheironimus/Joystick@^2.1.1
build_flags = -D USB_VID=0x1209 -D USB_PID=0x32D4

Cpp
#include <Arduino.h>
#include <Joystick.h>

Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID, JOYSTICK_TYPE_JOYSTICK,
  7, 0, true, false, false, false, false, false, false, false, false, false, false);

constexpr uint8_t BTN[7] = {4, 12, 6, 8, 9, 10, 5};
constexpr uint8_t ENC_A = 3, ENC_B = 2, ENC_I = 0;
constexpr uint16_t DEBOUNCE_US = 1000;
volatile int16_t encoderDelta = 0;
volatile uint8_t prevAB = 0;

void encoderISR() {
  uint8_t ab = (digitalRead(ENC_A) << 1) | digitalRead(ENC_B);
  static const int8_t qdec[16] = {0,-1,1,0, 1,0,0,-1, -1,0,0,1, 0,1,-1,0};
  encoderDelta += qdec[(prevAB << 2) | ab];
  prevAB = ab;
}

void setup() {
  for (uint8_t p : BTN) pinMode(p, INPUT_PULLUP);
  pinMode(ENC_A, INPUT); pinMode(ENC_B, INPUT); pinMode(ENC_I, INPUT);
  prevAB = (digitalRead(ENC_A) << 1) | digitalRead(ENC_B);
  attachInterrupt(digitalPinToInterrupt(ENC_A), encoderISR, CHANGE);
  attachInterrupt(digitalPinToInterrupt(ENC_B), encoderISR, CHANGE);
  Joystick.setXAxisRange(-32767, 32767);
  Joystick.begin(false);
}

void loop() {
  static bool stable[7] = {false};
  static bool candidate[7] = {false};
  static uint32_t changedAt[7] = {};
  uint32_t now = micros();
  bool dirty = false;
  for (uint8_t i=0; i<7; ++i) {
    bool pressed = !digitalRead(BTN[i]);
    if (pressed != candidate[i]) { candidate[i] = pressed; changedAt[i] = now; }
    if (candidate[i] != stable[i] && uint32_t(now-changedAt[i]) >= DEBOUNCE_US) {
      stable[i] = candidate[i]; Joystick.setButton(i, stable[i]); dirty = true;
    }
  }
  noInterrupts(); int16_t d = encoderDelta; encoderDelta = 0; interrupts();
  if (d) {
    static int16_t turntable = 0;
    turntable = int16_t(uint16_t(turntable) + uint16_t(d)); // wrapping position axis
    Joystick.setXAxis(turntable);
    dirty = true;
  }
  if (dirty) Joystick.sendState();
}

• Hardware: each button has 100 Ω series + 1 nF shunt (100 ns pole), small enough not to add perceptible rhythm-game latency; C12–C18 may be DNP for firmware-only filtering.
• Firmware: 1.0 ms stable-time debounce, independently tracked for all seven buttons; no blocking delays.
• Encoder: no millisecond debounce. Both edges use interrupt-driven 4-state transition table; illegal transitions contribute zero.

• 16 MHz external crystal; bootloader/fuses must select external crystal and disable clock divide-by-8.
• Blank ATmega32U4-AU ships without a USB bootloader. Program Caterina-compatible bootloader or application through J2 ICSP first.
• The starter exposes the turntable as a wrapping signed X position axis, which is broadly compatible and fully functional. Software that requires a relative axis can replace only the HID descriptor/report layer while retaining the same ISR and encoderDelta logic.

Bash
pio run
pio run -t upload