Serial.println() sending output to both Serial and Serial3 unexpectedly on Mega

Using Arduino Programming Questions
1

Hi,
I am using Serial and Serial3 ports for output on a Mega2560. When I initialize just the Serial port (connected to USB), anytime I send Serial.print(), it also sends to Serial3 which is connected to a Bluetooth HM-10 module. Serial3 seems to be ignored on initialization and doesn't output anything to either Serial (usb) or Serial3 devices.

My Serial3 device is connected to pins 15 and 14.

void setup(){
  Serial.begin(9600);
  // Serial3.begin(9600); // initing this does not change behavior
}

void loop(){
  Serial.println("To USB - Serial");  // sends to both Serial (USB) and Serial3 (BT device)
  // Serial3.println("To Bluetooth - Serial3"); // message never sends
}

Anybody heard of this?

thanks

2

How do you know it sends to the Bluetooth device? Where is the output from the Bluetooth device appearing?

Post diagram showing how everything is connected. A photo of a simple pencil drawing is best. Please DO NOT use Fritzing.

...R

3

Hi -

Attached is a basic diagram of the serial wiring.
I also have sensors connected to A1-A4, A8-A11, plus I2C on D20,D21 (all powered by 3.3V)

I know Bluetooth is receiving these messages because I have HM-10 paired to the Bluetooth Serial app on my iPhone (screenshot attached).

bfbt.jpg
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IMG_0066.jpg
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4

Try changing the baud rate on one of them. :slight_smile:

5

Try changing the baud rate on one of them

doesn't help. still outputs to both.

6

digitoxin9:
doesn't help. still outputs to both.

At which rate? :slight_smile: The purpose is to narrow it down, not fix it magically.

7

Images from Reply #2 so we don't have to download them. See this Image Guide

f3047f1da242780e5e0df6328292fef21aca37cb.jpg
f3047f1da242780e5e0df6328292fef21aca37cb.jpg1080×619 211 KB

7c7bec6d83be6a5dc7994a45187db93d870da147.jpg
7c7bec6d83be6a5dc7994a45187db93d870da147.jpg1242×2208 378 KB

...R

8

What happens if you connect the Bluetooth module to Serial1 or Serial2?

Also, add delay(500); into loop()

Also Also, add Serial.println("Test A starting"); into setup() so you can verify that the correct program is actually loaded.

...R

9

Just asking...
Have you selected the correct (Mega) target in the Arduino IDE ?
You haven't fiddled with any of the Arduino library installation, or edited the .H files - have you?

10

:-X facepalm.

after following the connections again, i saw that the HM-10 was connected to Serial pins 0,1 instead of Serial3 14,15. now it works as expected.

thanks for your suggestions!

11

Thanks for the feedback.

And welcome to the club :slight_smile:

...R

12