NANO + separate USB-SERIAL converter issue

Hi everyone

Im trying connect my nano through separate USB-TTL (CH340 Robotdyn)

NANO alone is working fine w/ incorporate serial (also CH340)

when I connect usb-ttl robotdyn (its recognized as COM3)

Dyn --- Nano
Gnd - Gnd
5v - Vin
Rx - Tx
Tx - Rx

but no luck. rx/tx LEDs on Dyn and on Nano is not blinking. Arduino serial terminal doesnt show anything
also I tried Putty - its open serial window but I cannot enter any message. Cursor is frozen on the top left corner. and cursor is not blinking

I don't see Rx/Tx-leds on the Dyn so that will indeed not blink.

I also don't see a 5V/3V3 selecter although I do see a 5V and 3V3 output. This suggests that the Tx is a 3V3 line. Might have trouble overpowering the CH340 on the Nano.

But, let's start at the beginning first. Do a simple loopback test on the Dyn.

Do not connect 5V to VIN. Connect GND and RX and TX only. Let each board receive 5 volts from USB.

septillion, about loop back thank you will try after work
do you think that 5v is just power and rx/tx is 3.3v ? hmmm... may be.. I did not think about that

Perehama, if I connect power on nano from usb then it automatically can send/receive either and serial signal via usb
and i cannot determine if those signal have been sent via Dyn or via Nano internal converter :slight_smile:

alexblade:
Perehama, if I connect power on nano from usb then it automatically can send/receive either and serial signal via usb
and i cannot determine if those signal have been sent via Dyn or via Nano internal converter :slight_smile:

You cannot use the serial monitor on COM1 or whatever the FDTI is set to? and Termite or PUTTY or MTTY etc for COM3?

I got you. you mean that internal for example willbe COM3 , external COM4... and connect terminal to COM4
thank you. need to try

so, loopback is working fine

also I tried as said Perehama, Nano connect to COM3 (power)
Dyn connect to COM4 (power)
Dyn - Nano
Gnd - Gnd
Rx - Tx
Tx - Rx

Serial monitor on COM3 is working fine as expected
after that change port in arduino to COM4
Serial monitor on COM4 is not working
:frowning:

could someone help me ?
may be hypothetic

Ahh, yeah, 5V to Vin is no good.

Can you try connecting the Nano to the Dyn and no USB to the Nano?

And to be sure, not working = not receiving anything? And what kind of program are you running from which you expect data?

And took a quick look at the schematic of the converter and the UART runs at 5V. (Aka, bad news if you where planning to use it on a 3V3 board!)

"Can you try connecting the Nano to the Dyn and no USB to the Nano?"

yes, I have connected so from the beginning
Dyn --- Nano
Gnd - Gnd
5v - Vin
Rx - Tx
Tx - Rx

Dyn to PC (COM3)
nothing in serial monitor.

"And what kind of program are you running"

just simple sketch aka loopback in the NANO

while (Serial.available()) Serial.write(Serial.read());

If I have connected NANO using internal usb + this sketch, so all data I have sent via Serial monitor I can receive it back. Serial is working.

"bad news if you where planning to use it on a 3V3 board!"

yes, bad news, but Nano is 5V so should be ok for this particular case?

"Ahh, yeah, 5V to Vin is no good."

why?

Don't use Vin if you power it 5V! Use the 5V/Vcc pin. Vin goes to the voltage regulator and it needs more then 5V to give a stable 5V out.

But there are no Vcc.. only Vin and
Out +5V
Out +3.3V

ok, looks like RAW is Vin, and Vcc is USB power line.
in any case, I have tried power to usb and connect just rx/tx/gnd (post #6) with no luck

is there are chance that rx/tx pins cannot be used w/o usb, I mean only when usb data line are connected then rx/tx pins also is available

It should just work.

And the 5V pin is the Vcc, not Vusb. And it's not only an output :wink: Aka, use that to feed 5V.

Another test you can try:

  • Tie the Nano Reset to GND (to keep Nano in reset)
  • Connect Dyn Rx to Nano Rx (yes, rx to rx)
  • Connect Dyn Tx to Nano Tx

If you now open two Serial programs (like two instances of Putty) to both COM ports set to the same baudrate. you should be able to talk between them. Aka, sort of an extended loopback test.

damn damn :slight_smile:
about power - working and with 5v pin and with Vin - weired but workin'

about data pins

I have connected rx-rx
and tx-tx

and serial monitor is working fine :slight_smile:

so looks like on Nano or on Dyn is mistake printing labels ?

alexblade:
I have connected rx-rx
and tx-tx

and serial monitor is working fine :slight_smile:

Aka, you can send text to the Nano COM and receive it on the Dyn COM and the other way around?

alexblade:
so looks like on Nano or on Dyn is mistake printing labels ?

Mistake printing labels? What do you mean?

What do you mean?

typo. wrong designation. where is written (on the board near pin) "rx" should be "tx" and vice versa. but how detect who is wrong? I have no other usb-ttl

you can send text to the Nano COM and receive it on the Dyn COM and the other way around?

On Nano I just used rx/tx/gnd/Vin pins, I have not touch usb.
and yes I can receive/send data

other question about weird behavior of putty. (arduino serial monitor working fine) on putty serial connection -
when I just type one letter it automatically goes to serial . I mean on arduino serial I can type as many as I want symbols and when I want send I should press enter. On putty w/o enter each symbol automatically goes to serial. is it possible to fix this ? (last version of putty)

I have no clue anymore what you tested and what's doing what, sorry...

And don't think Putty has a "send on enter" option. But really, you should not need it.

septillion, on Nano , if we need to send/receive serial data usually we should use USB port.
but on Nano also exist rx/tx pins. if they exists, so they should work also. I tested those pins. if board can send/receive serial data through rx/tx pins (not by USB). so if we want to check those pins we should use separate usb-ttl.
initially I have connected external usb-ttl (aka Dyn) with Nano as
rx <- tx
tx -> tx
as expected yes. and serial doesnt work

but on the nano or on the Dyn was typo. label was not correct. after that I have change connection
rx - rx
tx - tx
serial starts working


Putty:
I think "send on enter" should be. otherwise how communicate with GSM modem for example?
if I want send AT command, but A and T will be sent separately. like
A
error: no A command
T
error: no T command

Ahh, so problem is fixed :slight_smile: I never saw a Nano with an error so I'm with the Dyn. Maybe they tried to "help" by labeling it with the pins you should connect it to. If you want to check it, simply write a sketch that sends data. If you still receive data if the Rx-Rx line is unplugged it's the Dyn that's labeled wrong.

About Putty/Serial, that should not happen. Serial has (by design) no concept of lines or "chunks" of data. It just sends a byte at a time, only separated by time. For example, you can't see the difference between:

Serial.print("AT");
//and 
Serial.print("A");
Serial.print("T");

They only thing that does make a change is the ASCII concept of a line. Aka, a line is over after a new line ('\n'), carriage return ('\r') or both characters. And I think most devices would rely on that. Unless they are pretty stupid and rely on a (very short!) time out (aka, time passed between characters) to sense the end of a command. But that would be pretty stupid because that might also happen when you do want to send them right after each other but the computer or micro controller got busy right in the middle and delayed the second part a bit.

Maybe they tried to "help" by labeling it with the pins you should connect it to.

ha may be :slight_smile:

thank you

about putty - hm, make sense.... need to check :slight_smile: