scan for available ports. return a list of tuples (num, name)
    Returns:

def scan():
    """
    scan for available ports. return a list of tuples (num, name)
    Returns:

    """
    available = []
    for i in range(256):
        try:
            s = serial.Serial('COM'+str(i))
            available.append((i, s.portstr))
            s.close()
        except serial.SerialException:
            pass
    return available