Sparkfun RedBoard serial monitor problem

[Lagom]

I unpacked a class-pack of sparkfun RedBoards. To check them, I run the dummy code below. USB connection to laptop with original cable from each pack. With the serial monitor open, same baud rate, I get an inverted question mark and the serial printing occurs twice. In WOKWI only once. If I press the reset button on the RedBoard, serial printing only occurs once with 8 out of the 10 class-pack RedBoards. Any ideas for what's going on? Laptop issue? Cable issue? RedBoard issue? Thanks!

boolean hasRun = false;

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  function();
}

void function()
{
  if (hasRun == false)
  {
    int someValue = analogRead(A0);
    Serial.print("I ran only once ");
    Serial.print(someValue);
  }
  hasRun = true;
}

[Lagom]

After uploading with the serial monitor window open, closing the serial monitor and then opening it often results in a single execution as expected, but not always. When double printing, the analogRead values are different, so the code gets executed twice for sure.

[ec2021]

Hi @Lagom,

that sounds really weird ...

Looks like other people also had problems with RedBoards and Serial. Not sure whether it helps you but you may have a look here [RedBoard Artemis Nano Serial NOT Working - SparkFun Electronics Forum](RedBoard Artemis Nano Serial NOT Working - SparkFun Electronics Forum

That's all I found in a hurry.

Good luck!

[Lagom]

All right, I will check it out. At least all 10 boards serial print only once after the reset button is pressed.

[LarryD]

Opening the serial monitor restarts the Arduino, there might be something left in the output buffer causing the problem.

Might be best to:

• Power on the Arduino
• Open the serial monitor
• Clear the serial monitor screen
• Press the reset switch on the Arduino

BTW

Consider this one change:

boolean hasRun = false;

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  function();
}

void function()
{
  if (hasRun == false)
  {
    hasRun = true;
    int someValue = analogRead(A0);
    Serial.print("I ran only once ");
    Serial.print(someValue);
  }

}

[Lagom]

Thanks, that four-step sequence of actions works with all 10 RedBoards.