DrDiettrich:
I only can see Serial.print() in your code. So is the RS232 board connected to RX/TX? And also to Gnd?What if you reduce the baudrate, to make the LED blink longer on a transmission?
RS232 Board connect to default rx-tx pins, yes, and ground i presume. I can try to lower the baudrate. However the product im controlling has baud-rate selection, and is set to the same as in the code
PS: My RS232 board has a switch for enabling/disabling the board, to not stop uploading the code to the Arduino UNO