Adding an external serial console port to NanoPi R6S

I had no trouble with my first experience with NanoPi R6S while installing and running the FriendlyWrt/OpenWrt 22.03 image, but that was another story when testing Ubuntu or Debian as the mini PC would not boot at all after flashing the images with eFlasher apparently successfully, but suspiciously fast (under 2 seconds).

I spent nearly four hours trying the different images and then the Rockchip Windows utility, but all my attempts failed, and FriendlyElec was not overly helpful. So I decided to connect a serial console to see what was going on. The NanoPi R6S comes with a 3-pin header for the serial console, but it’s not populated.

serial console port NanoPi R6S

So I soldering one, but not at the top of the bottom, and instead at the bottom since it would allow me to still use the metal enclosure to cool the processor.

3-pin serial console header soldered to NanoPi R6S

Some readers, or at least one, often complain about the lack of external access to the serial console in routers to debug issues without having to disconnect the device and open it up. But with the NanoPi R6S, it’s fairly easy to create to add an external serial console port by soldering the header on the bottom side of the board and then making a hole in the bottom plate.

UART console opening

I used a power drill and a file tool, and the result is functional but not exactly neat. People with better skills than me or a CNC machine could make something neater.

GND Tx Rx markings

I’ll also pretend I did not center the hole on purpose in order to be able to see the markings (GND, Tx, Rx).

NanoPi R6S DIY external UART console

But it does the job and we can now access the serial console without having to tear down the router, simply connect Tx, Rx, and GND to a USB to TTL debug board with jumper wires and we are good to go. I had to cut the headers by about 1 mm to prevent them from touching the desk once we are not using the serial console anymore. A plastic cover would be nice, and looking around in my office, plastic bits covering HDMI cables seem to be good candidates for this purpose, provided we make a hole of the right size.

It works within the eFlasher utility or when I boot the FrienlyWrt/OpenWrt image using 1,500,000 bps baudrate stipulated in the wiki:

But there’s no output at all with Ubuntu or Debian. So something must be wrong while flashing the image inside the eFlasher utility especially since it just takes one or two seconds to complete the “firmware upgrade”, I’m guessing some issues with the MicroSD card (I/O errors or too small), but that will be for another day.

I hope FriendlyElec considers providing easy access to the serial console in their future routers, as it should cost close to nothing to implement a solution as described above.

[Update: Pastrav has come up with a nicer way to add a serial port to NanoPi R6S using a 2.5mm audio connector attached to the hole reserved for an antenna. See comments for details.

NanoPi R6S audio jack serial port


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