Arduino pro mini serial output gibberish

Hi all,

I used a arduino pro mini to develop my project.
My serial output keep giving me gibberish. like "A咢�聙�AC@�聙場聙場1熿1熦 bAC bAC bAC bAC b". And I don't have this problem a few days ago. I change the baud rate to 4800,9600,115200 and the problem exists. Even if I run the simple code blew. So I change to a arduino UNO and it didn't have this problem.

void setup() {
  Serial.begin(9600);// put your setup code here, to run once:
}

void loop() {
  Serial.println("YES");
}

And I don't have this problem a few days ago.

Perhaps you have a hardware problem like a lose or mispositioned wire or connection.

So if the Uno didn’t have the problem what system did?

zoomkat:
Perhaps you have a hardware problem like a lose or mispositioned wire or connection.

Well, The only hardware thing I did is de-soldering the on-board greed power LED. And I used a FTDI cable to program the board. The sketch can be uploaded to the board without error.

Grumpy_Mike:
So if the Uno didn’t have the problem what system did?

I think the error comes from the pro mini board itself, the hardware problem.

channinglin:
Well, The only hardware thing I did is de-soldering the on-board greed power LED. And I used a FTDI cable to program the board. The sketch can be uploaded to the board without error.

Next time just put a bit of black paint on the LED. :slight_smile:

...R

channinglin:
Well, The only hardware thing I did is de-soldering the on-board greed power LED. And I used a FTDI cable to program the board. The sketch can be uploaded to the board without error.

Do you mean:- The sketch could be uploaded to the board without error.

If so it looks like you have messed up something more than just the LED.

Grumpy_Mike:
Do you mean:- The sketch could be uploaded to the board without error.

If so it looks like you have messed up something more than just the LED.

Hi all,

I think I have found the answer. When I upload the sketch, I choose "ATmega328 3.3V 8Mhz", and it gives me the gibberish. But if I switch to "ATmega328 5V 16Mhz" then it works without serial gibberish.

However, I think my board is a 3.3V board. I used a 3.3V FTDI cable to program it and 3.7V lipo battery to power it......

The key is the clock speed, not the voltage. If the clock speed is set wrong then the baud rate is calculated wrong and you get gibberish from the serial line.

Set the serial monitor baud rate to half that of the rate set in the code and the gibberish will be replaced with real data.