I must be being dumb.  Help!!!!!!!!!!!!!!!!


I have been struggling big time getting serial communication to work from an Arduino.

I have wired a 9pin serial cable as per http://www.arduino.cc/en/Tutorial/ArduinoSoftwareRS232 under the 'cable' header.

I have connected to an old machine that has a known to be working com port. I can connect to another device t :'(o the COM port and talk to that no problem.


Arduino RS-232 CONNECTOR
Digital 0 (RX) 2
Digital 1 (TX) 3

I have set hyper-terminal up as 9600 baud, 8 data bits, 1 stop bit, no parity, no hardware flow control.

I have a LED on pin 13 that blinks (see the code below), but I get no serial comms at all...

byte high = 0;

void setup()                    // run once, when the sketch starts
  pinMode(13, OUTPUT);
  high = 0;

void loop()                     // run over and over again
  if (high == 0)
    digitalWrite(13, HIGH);
    high = 1;
    digitalWrite(13, LOW);
    high = 0;
   Serial.print("HELLO WORLD");

Does anyone please have any ideas. I'm currently totally stumped.

Thanks in advance!


Have you disconnected the USB cable?
Have you checked the levels on your max232 with a multimeter?
If you disconnect the breadboard from the Arduino, you should be able to check that you get +/12V swings on the outputs of the max232 when you apply 0 and 5V to the inputs.


The answer was in the post subject... I was being dumb!

I was working on a wrong assumption that the Rx/Tx pins on the Arduino were capable of talking directly to a COM port....

Somehow I didn't damage anything in the process of doing so.

A quick trip to jaycar (Aussie electronics components store) for a MAX232, some caps and a 9 pin connector and an actual RTFM of the page I linked to got me working.

I do think it's worth pointing out in the documentation that a chip like the 232 is required even when using the hardware RS-232 on the Arduino. I got it into my head that this was only needed if you were using 'random' digital pins. I'm a software guy, so that's my feeble excuse! Thanks to this fabulous Arduino stuff, my weak of electrical knowledge gets exposed on a regular basis!

Thanks for you for your really quick response. Next time, you'll want to be sure to check if I'm being stupid or not before posing any diagnostic questions :slight_smile: