Why the Serial monitor could print when BT connecting on?

The bluetooth doesn't pair and connect to the computer only connect to the arduino.
It can't receive data from monitor but can Serial.print to the monitor ,why?
I thought it couldn't R&T both when the other UART devices connecting to the arduino?

You need to post the code you are using.
And please use the code button </>so your code looks like thisand is easy to copy to a text editor

AND you need to post a diagram (a photo of a pencil drawing would be best) showing how you have everything connected.

…R

Still getting my feet wet with bluetooth but if I recall correctly from my recent tries:

if the BT module is a slave, it can only be paired with one master.

I might be wrong though.

Bluetooth Tx connect to the arduino pin 0,Rx connect to arduino pin1.

void setup() {
  Serial.begin(9600);
  Serial.println("EEEEEEEEEEEE");// could show on the monitor
} 
  
 
void loop(){
   if(Serial.available())// send to arduino,
   Serial.print(Serial.read());//fail to show on the monitor.
}

I think it maybe like this: When I want to send data to arduino from the monitor,the Tx of USB is sending data ,but Tx of BT still remain HIGH, so the data line still HIGH?
When I want to send data to the monitor from the arduino,both Rx of BT & UBS only PULL-HIGH, it change when Tx of arduino change,so sending data from arduino is fine.

yangkai:
Bluetooth Tx connect to the arduino pin 0,Rx connect to arduino pin1.

That means that you are trying to use pins 0 and 1 for two things at the same time which does not work well.

Assuming you are using an Uno I sugggest you use SoftwareSerial to create a separate serial connection on two other pins for your Bluetooth device.

...R
Serial Input Basics

Thanks, I already done !

Glad to hear you have it working.

...R

I think having Bluetooth and monitor working together is fine,. so long as you don’t want to do anything with the monitor. And why would you anyway? This can be useful for beginners when checking, say, Arduino <> Android. You get to see what’s going on with both.