It's been a while since I've done serial over the Arduino, but something here is definitely weird.
This code:
void setup() { Serial.begin(300); } void loop() { Serial.println(","); }
produces the following repeating string of gibberish:
???à?æ???à?æ???à?æ???à?æ???à?æ???à?æ...
The serial monitor is at 300 baud right now, but I've also tried running and monitoring the sketch at 9600 to no avail. What gives?
Try putting a small delay (only maybe 20ms) into your 'loop' function. Just as a debugging step, to see what happens. Sometimes, serial interfaces can get mis-synchronised if there are never any pauses between characters. Do let us know the outcome!
Hm, same thing:
??à?æ???à?æ???à?æ???à?æ???à?æ???à?æ???
Ah. I had the wrong board selected from the Tools -> Board menu.