Arduino Nano refusing to communicate to UART devices without a computer

Other Hardware General Electronics
1

I have a problem where none of my Arduino nano boards want to communicate to UART devices. When it is powered externally, I wrote a simple program to demonstrate my problem.

void setup() {
Serial.begin(9600);
}

void loop() {
delay(1000);
Serial.write(0x30);
delay(1000);

}

this code works perfectly using a UNO or a mega board. where when it is connected to a standalone power supply the TX pin just constantly spits out the data I However when I upload this exact same code to a arduino NANO it refuses to send anything when it is connected to a power supply. The NANO works perfectly when it is connected to a PC with a USB cable. It cannot be a bad connection since I've checked the output with a scope I tested this with a genuine NANO and a NANO every board, both had the same behaivior. What could be the issue?

2

Have you connected GND between the Nano and the other device?

Regards

3

no, but its not exactly the issue. when I run the code on an UNO board, I scope the TX line + ground it just sends the data, there is no handshake between whatever I connect it to. It just sends it. On the NANO there is nothing, no data

4

If you don't use GND as a reference, how does the receiver detect level changes on its input?

Remove both delay() and you will see Tx LED turn on then send data

5

Note that on the Nano Every, the Rx/Tx pins are Serial1.

Not sure why the genuine Nano does not work, can you post a wiring diagram?

6

Excellent! changing Serial to Serial1 has fixed the issue, and the Nano every board started spitting out the data Thank you very much!

7

Please heed the advice. Serial requires three wires between two devices. TX, RX, and GND. Always.
If they're sharing a power source, of course, then GND is GND. But for two different devices with separate power supplies, you must connect the grounds.

8

obviously yes, tested it with my device, shared ground, TX and RX everything works perfectly. The problem just was that the arduino was not sending anything

9

It cannot be a bad connection since I've checked the output with a scope I tested this with a genuine NANOand a NANO every board, both had the same behavior.

@david_2018 said

Not sure why the genuine Nano does not work, can you post a wiring diagram?

I agree, that the situation with the Classic Nano does not make sense.

Do you have any insight into the problem with the Classic Nano?

10

I have no idea what the problem is with your Nanos, the ones I have have no problems sending data. I just connect Rx, Tx and GND.
I can't add anything else to the matter.

Regards

11

Hi, I have exactly the same issue but the solution about "using Serial1" is quite strange : since when does a nano have a serial1? I tried anyway to use Serial1 with my NANO but obviously I got a "Compilation error: 'Serial1' was not declared in this scope".
So I was unable to send data on RX pin without a connect PC on USB port. I will try a softserial but I don't like to do that without understanding this issue.

12

Serial1 was specifically for a Nano Every, where the Rx/Tx pins are a separate hardware serial port from the Serial used for the USB-to-serial connection to the computer. A classic Nano that uses an atmega328 only has a single hardware serial port, so there is no Serial1.