USB to TTL Serial Adapter not showing any output

Hello everyone!

I’m using an FTDI RS232 USB Serial Adapter and would like to read the output of the serial.

It works plug-and-play on my Ubuntu Laptop and Mac by simply running screen <DEVICE PATH> 115200.

On the Jetson, the USB Serial is recognised and the drivers also seem to be working, judging from my dmesg outputs:

[ 4498.788522] usb 1-2.3: Manufacturer: FTDI
[ 4498.792972] ftdi_sio 1-2.3:1.0: FTDI USB Serial Device converter detected
[ 4498.794093] usb 1-2.3: FTDI USB Serial Device converter now attached to ttyUSB0

I am running the same screen command on the Jetson (with correct permission!) and it just gives me a blank screen and no output. When I type a character the TX LED on the FTDI USB board lights up but I just don’t receive anything.

If anyone has got any ideas about how I can resolve this, it would be greatly appreciated!

Are you able to get this cable:
Connect to uart pins on the 40-pin header and check if you can see the log?

@DaneLLL Thanks for your response!

I could order it, but it seems to have the same hardware inside as my current dongle:

It works perfectly fine on all other machines, just the Jetson doesn’t show any output.

Could you open the ttyUSB0 node before you power on the jetson and see if it will print log?

Just to clarify, there is an external device that sends valid RS232 to the USB to TTL USB Dongle.
I can read out this serial perfectly fine on all other devices (Raspberry Pi, MacBook, Ubuntu Laptop) but it does not output anything on the Jetson and just shows a blank screen.

@WayneWWW Could you clarify what you mean by this?

If you read the log after the board is already boot up for quite long time, and it is your “first boot” without configuring any user account, then your uart will stuck and give no output and cannot handle any input either.

Thus, make sure you are doing “open the serial console, wait and power on the board”. The purpose is just to prevent this case.

If you still cannot see any log print in above case, check whether your pin is connected wrong or not.

@WayneWWW I’m not quite sure how I can start reading the output on the Jetson when it is turned off.
Again, to clarify: The Jetson is the receiver of the Serial. The USB Converter is plugged into the Jetson USB Port and I am logging on to the Jetson and reading this Serial Output with a regular “screen” command. 😅

Oh ok, So you want jetson to read the log from other device but not check the log from jetson. Is that what you are doing?

@WayneWWW Yes exactly. sorry for being unclear. That’s exactly what I am trying. An external device outputs Serial and I want to read it on the Jetson.

Perhaps the settings differ (the default) when plugged in to the Jetson. Most Jetson side UARTs will default to 115200 8N1. Some incorrect settings for a mismatch of settings across the two ends of the UART will put out garbage, but many times such a mismatch will have no output at all.

Thanks for everyone’s help. In the end this was actually a hardware issue that was not related to the Jetson.
The Jetson and the Serial Output device were at different ground voltage levels and putting a USB Isolator (to galvanically isolate the two devices and grounds) solved the issue for us.

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