Made by our makers

// PID line following — the values that finally worked for me
const float Kp = 0.08, Ki = 0.0002, Kd = 0.9;
int baseSpeed = 140;          // was 200 — too fast for the hairpin

void loop() {
  int error = readLinePosition() - 3500;   // 0..7000, centre = 3500
  integral += error;
  int correction = Kp * error + Ki * integral + Kd * (error - lastError);
  lastError = error;

  // Slow down when we are far off the line; speed up on the straights.
  int speed = baseSpeed - min(abs(error) / 40, 60);
  setMotors(speed + correction, speed - correction);
}

// Non-blocking debounce — no delay(), the loop stays responsive.
class Button {
  uint8_t pin; bool stable = HIGH, last = HIGH; unsigned long changedAt = 0;
public:
  explicit Button(uint8_t p) : pin(p) { pinMode(p, INPUT_PULLUP); }

  // Returns true once per physical press.
  bool pressed() {
    bool now = digitalRead(pin);
    if (now != last) { last = now; changedAt = millis(); }
    if (millis() - changedAt > 25 && now != stable) {
      stable = now;
      return stable == LOW;       // active-low with INPUT_PULLUP
    }
    return false;
  }
};