#define adc_disable() (ADCSRA &= ~(1<<ADEN))

const int wakeUpPin = PB0;
const int powerCheckPin = PB1;

// Generally, you should use "unsigned long" for variables that hold time
// The value will quickly become too large for an int to store

unsigned long previousMillis = 0;        // will store last time PB0 went HIGH

// constants won't change:
const long interval = 30000;           // interval to check if sound card is sleeping (milliseconds)

void setup() {
  pinMode(wakeUpPin, OUTPUT);
  pinMode(powerCheckPin, INPUT);

  //Other pins as Input with the purpose of saving energy
  pinMode(PB2, INPUT);
  pinMode(PB3, INPUT);
  pinMode(PB4, INPUT);
  //ADC disabled - energy save
  adc_disable();
}

void loop() {
  while(digitalRead(powerCheckPin)){
    //do nothing while the card is ON (PB1 is HIGH)
  }

  // check to see if it's time to check for voltage in the powerCheckPin;
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval) {
    // save the last time voltage was checked
    previousMillis = currentMillis;

    // try to wakeup the Sound Card with a brief short circuit
    //Provide a 20K resistor to avoid damage the board and USB port
    digitalWrite(wakeUpPin, HIGH);
    delay(10);
    digitalWrite(wakeUpPin, LOW);
  }
}