Electronic – Arduino Uno R3 hardware serial: peripheral interfering with the USB/Serial-converter

arduinohardwareportserialuart

I like to use the hardware serial port (pin 0 RX and 1 TX) to connect a bluetooth module.
Internally these pins are also connected to the onboard USB to serial converter microcontroller which is used to flash the ATMega328 using the bootstrap code.

enter image description here
(From http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf)

Now these two signals would interfer, I think.

Can the RX/TX pins be used to interface with an UART peripheral?
If, what should one do to avoid colliding signals?

I couldn't find examples in my Arduino books and with Google that used the hardware serial port of the Uno R3 to connect peripherals.

Edit 1:

Let me add the following: I don't want to use the Serial monitor (of the Arduino IDE) and the peripheral (Bluetooth module) at the same time. I don't expect that it can be used at the same time. The device should run without USB connected. The Bluetooth module, in this case, will be used to remotely and wirelessly control the Arduino.

Even when not using both together, I suspect the ATMega16U and the periperal might interfer.

And: I know, there's a shield and also an "ArduinoBT", but I don't want to use them as long as it's possible to do this with the hardware serial port of the Uno.

Edit 2:

The peripheral (Bluetooth) module operates at 3.3V while the Arduino operates at 5V.

Best Answer

Those two resistors, marked RN4A and RN4B, are used to protect the uart line from conflicts, while also assigning priority to the external header. They act like weak pullups, in that anything before (In this case, left of) the resistors will only affect the line after them, if the lines are not being used.

Anything serial connection plugged into the header, will take priority over the Arduino's usb/serial connection, as they can directly power the lines.

But this will also provide issues during programming, so use an enable pin, or power switch, or simply remove the bluetooth module while programming.

Related Solutions

Electronic – Arduino Uno R3: Directly supply regulated 5V to 5V pin

Here's a less formal way to look at it: Providing power directly to the +5V pin is (almost) exactly what happens when the Uno is powered over USB. As USB power is perfectly fine, by design, then your setup should be OK too.

External regulated +5V can be supplied to the USBVCC net just as well, for example by using an USB-B cable.

As per the second question, you should not connect to V_in. NCP1117's output may then become an alternative, competing power-source and this is best to be avoided.

Electronic – arduino – Can the Arduino Leonardo act as a keyboard, mouse, and serial port at the same time

It looks like the keyboard and mouse example on the arduino site already has a method for reading the serial port.



/*
  KeyboardAndMouseControl

 Controls the mouse from five pushbuttons on an Arduino Leonardo or Micro.

 Hardware:
 * 5 pushbuttons attached to D2, D3, D4, D5, D6


 The mouse movement is always relative. This sketch reads 
 four pushbuttons, and uses them to set the movement of the mouse.

 WARNING:  When you use the Mouse.move() command, the Arduino takes
 over your mouse!  Make sure you have control before you use the mouse commands.

 created 15 Mar 2012
 modified 27 Mar 2012
 by Tom Igoe

 this code is in the public domain

 */

// set pin numbers for the five buttons:
const int upButton = 2;     
const int downButton = 3;        
const int leftButton = 4;
const int rightButton = 5;
const int mouseButton = 6;

void setup() { // initialize the buttons' inputs:
  pinMode(upButton, INPUT);       
  pinMode(downButton, INPUT);       
  pinMode(leftButton, INPUT);       
  pinMode(rightButton, INPUT);       
  pinMode(mouseButton, INPUT);

  Serial.begin(9600);
  // initialize mouse control:
  Mouse.begin();
  Keyboard.begin();
}

void loop() {

right here:


  // use serial input to control the mouse:
  if (Serial.available() > 0) {
    char inChar = Serial.read();

    switch (inChar) {   
    case 'u':
      // move mouse up
      Mouse.move(0, -40);
      break; 
    case 'd':
      // move mouse down
      Mouse.move(0, 40);
      break;
    case 'l':
      // move mouse left
      Mouse.move(-40, 0);
      break;
    case 'r':
      // move mouse right
      Mouse.move(40, 0);
      break;
    case 'm':
      // perform mouse left click
      Mouse.click(MOUSE_LEFT);
      break;
    }
  }

  // use the pushbuttons to control the keyboard:
  if (digitalRead(upButton) == HIGH) {
    Keyboard.write('u'); 
  }
  if (digitalRead(downButton) == HIGH) {
    Keyboard.write('d'); 
  }
  if (digitalRead(leftButton) == HIGH) {
    Keyboard.write('l'); 
  }
  if (digitalRead(rightButton) == HIGH) {
    Keyboard.write('r'); 
  }
  if (digitalRead(mouseButton) == HIGH) {
    Keyboard.write('m'); 
  }

}

If you can read the serial port, it seems like you can write to it too. I don't have a leonardo board to test this out myself, but inside of the loop() function you should be able to add something like


Serial.print("hello world");

and verify this while the Mouse and Keyboard are running too.