Mini Pro Serial port running at half speed

Using Arduino IDE 1.x
1

So this is odd...
I pulled two Arduino Mini Pro's (3.3V - 8kHz) out of my bin to use them and I was having difficulty even getting a "Hello World" sketch to work properly on either. I put the same sketch on an Uno and it worked fine. After noodling around it was clear that I have to set the serial monitor on my laptop to twice the baud rate as I specify in the sketch. When I do that it works fine. I'm guessing the problem is either that the serial port on both mini's is running at the wrong rate or the Arduino ide (mac) is mismatched for the mini.

I put the mini on a logic analyzer and and it confirmed that the data is coming out at 14400 even though I initialized the serial port at 28800 so I guess it's something in the mini.

Any ideas?

2

(3.3V - 8kHz)

Eight what?

3

Ooops, 8 MHz...

4

Any ideas?

probably the signature of the Arduino in the source code of the serial port is missing the particular type.

You can check the clock freq.

void setup()
{
  Serial.begin(14400);
  Serial.print("FREQ CPU: ");
  Serial.println(F_CPU);
}

void loop(){}
5

I see that this issue is quite old but no definitive resolution was ever submitted. If I am wrong in posting to the topic and should start a new topic (Per the warning msg) please let me know and I will learn the details.

I happened on this original post because it's the exact problem I was experiencing. Rob Tillaart's suggestion to use F_CPU was key. When I did that, the output was 16 Mhz though I am using a 8 Mhz, 3V Pro Mini. Just as the OP had described, only by setting the Serial Monitor to 4800 (for coded Serial.begin(9600) for example) would produce readable text. As it turns out, in the Arduino IDE, there are two choices for Pro Mini boards. The default is the 5V/16 Mhz board. If this is not changed to the 8 Mhz choice, this Serial Print baud mismatch reveals itself.