Le't say I want to communicate with another device using Serial communication.
Can I use the Arduino Uno as basically a "Usb to Serial" adapter? meaning If Arduino
is connected to my PC with USB, whatever that goes form my PC to Arduino
also comes out from the RX pin?
I tried connecting a LED to the RX pin but it's constantly on. The little LED light on the board marked "RX" does flicker when I send inputs through USB but my LED connected to RX pin is just always On.
Can I use the Arduino as explained above?
If not then the RX/TX pins are not fully connected to the USB?
Uno, I edited the question.
meres34880:
Can I use the Arduino Uno as basically a "Usb to Serial" adapter? meaning If Arduino
is connected to my PC with USB, whatever that goes form my PC to Arduino
also comes out from the RX pin?
Possibly - read on.
I tried connecting a LED to the RX pin but it's constantly on.
On the Uno there is another microprocessor that converts between USB and the Rx and Tx of the Atmega 328. The Tx of the converter (i.e. what comes from the PC) connects to the Rx of the Atmega 328.
In a serial system the Tx line (in this case, from the converter) is always HIGH when it is idle which is why your LED connected to the Rx is always ON. It does not signify that the serial connection is not working.
In the other direction if the Atmega 328 is using Serial it will set its Tx pin HIGH when idle. And that may interfere with your proposed usage. I think if you upload a program to the Atmega 328 that does not use Serial and sets the Rx and Tx pins as INPUT what you want to do should work. Carefully removing the Atmega 328 from the Uno would be another option.
My advice would be to invest in a USB-TTL cable.
...R
You could connect the Reset pin to Gnd, takes the 328P out of the picture.
Then Rx, Tx can be used for other devices if desired.
Or just spring for an FTDI Module, $6.90 here. I bought 10 a while ago and I use them constantly. My current project is using 3 of them! One on the 1284P Serial to talk to my laptop, 2nd on Serial1 to talk to an RPi, 3rd on Sparkfun Fingerprint scanner to talk to the RPi (vs attempting to secure USB wires to pads on the bottom of the scanner to a USB-A connector, which I don't have, or chopping up a cable).
I use the FTDI's 3.3V to power the fingerprint scanner.
https://www.tinyosshop.com/index.php?route=product/product&product_id=600&filter_name=ft
There's also a version with a Mini-B connector (vs Micro-B) that comes with a cable.
"Can I use the Arduino Uno as basically a "Usb to Serial" adapter? meaning If Arduino
is connected to my PC with USB, whatever that goes form my PC to Arduino
also comes out from the RX pin?"
To some extent you probably can for simple communication testing. The resting state of TTL rx and tx pins is +5v (RS232 is inverted). I have not tried any programming operations with such a setup, so I cant speak to the result and have not tried holding the arduino in a reset mode. The rx pin on the arduino is the arduino rx and tx of the serial monitor/pc. The tx pin on the arduino is the arduino tx and is also the rx of the serial monitor/pc. This is sometimes useful in troubleshooting serial communication issues between the arduino and other connected serial devices.