ser=serial.Serial(port='/dev/ttyS0', baudrate=9600, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_WO, bytesize=serial.EIGHTBITS)

while True:
    x = ser.readline()
    print(x)

void setup()
{
    Serial3.begin(9600);
}

void loop()
{
    Serial3.println("hello raspberry");
}