sketch.pde

#define DELAY 100

#define VOLDOWN 2
#define PREV 3
#define STOP 4
#define PLAY 5
#define NEXT 6
#define VOLUP 7

// Notification led
int led = 13;

int button_state = LOW;

void setup()
{
    // initialize the serial communication: set baud rate
    Serial.begin(9600);

    // Initialize buttons pin modes
    for (int i = 2; i <= 7; i++) {
        pinMode(i, INPUT);
    }

    // Initialize led pin mode
    pinMode(led, OUTPUT);
}

// Blink routine
void blink()
{
    digitalWrite(led, HIGH);
    delay(DELAY);
    digitalWrite(led, LOW);
    delay(DELAY);
}

void handlePin(int pin)
{
    // Read pin state
    button_state = digitalRead(pin);

    // If there were high voltage, i.e. button was pressed
    if (button_state == HIGH) {
        // blink led
        blink();

        // Send throug serial port pin number
        Serial.write(pin);
    } else {
        digitalWrite(led, LOW);
    }
}

// Main cycle
void loop()
{
    int i;
    // Ask each pin
    for (i = 2; i <= 7; i++) {
        handlePin(i);
    }
}