Using Arduino Uno RX and TX pins while COmport through USB

Other Hardware 3rd Party Boards
1

Hello,

Is it possible to control e.g. a wifi module using the hardware TX/RX pins while you at the same time have the USB cable connected to the PC and just watching the commands being transmitted from the arduino to the wifi module and vice versa on a serial monitor? I.e. you do not type any commands or such in the Serial Monitor. Just passively watching the communication for debugging purposes.

I'm playing with my Arduino uno again after some years of absence and I'm currenlty not sure if my arduino is broken or if this has never worked. In the serial console, I do see the commands transmitted from the arduino but I do not see any replies from the wifi module.

2

hnrkssn:
In the serial console, I do see the commands transmitted from the arduino but I do not see any replies from the wifi module.

That is exactly what you should expect :slight_smile:
There are resistors on the RX/TX connections between ATmega328p (the "Arduino") and the ATmega16U2 (it does the USB to UART communication).
rx_tx_resistors.png
The resistors are there so that you can use the UNO's pins D0 and D1 also for serial communication with other modules but the UART to USB converter, just like you do with the wifi module.
UART is no bus, it is thought for point to point communication, but you can do some listening. And that is what you are doing. But with this wiring you can only hear one partner, in this case it is the ATmega328p, but not the other (the replies of the wifi module).

3

If you need both serial for a WiFi adapter, and serial monitor, you need to either:

  • Use SoftwareSerial (with all it's limitations and problems) for the WiFi serial
  • Use an Arduino based on the 32u4, and connect to Serial1 (the "Serial" on the 32u4 is the USB virtual serial port).
  • Use an Arduino with more than one serial port (Ex: Mega2560, third party board based on 1284p, etc)
  • Use software serial and an external serial adapter for the serial monitor, instead of the on-board USB serial adapter.
4

Thanks for your replies. Perfect explanations!