uart console not working when connecting the nrf9160 DK to the battery.

[J0sh1101]

Hey,

with the help of the devzone community I configured the overlay to use the uart2 for the zehyr console. The aurt2 TX is on the pin 0.24. This pin is then connected to the UART-to-USB converter UM232R USB, where it then goes to the PC. When I power the nrf9160 DK via USB (J6), everything works. The serial terminal works as it should. I get this output:

*** Booting Zephyr OS build v3.3.99-ncs1 ***
[00:00:00.303,802] <inf> aero_sens: Start v.4, baord: nrf9160dk_nrf9160

[00:00:00.544,921] <inf> nrf_modem_lib_trace: Trace thread ready
[00:00:00.546,539] <inf> nrf_modem_lib_trace: Trace level override: 2

However, when I connect the nrf9160 DK to the battery at P21, I get nothing on the serial port. I add the picture so that everyone understands.

The LED of the debugger only blinks in a quite high frequency. My setup is as follows: I have a 1500 mAh 3.7 battery that I connect to a TI TPS62840 step-down converter (green board) that gives me 3.3V. With this I then go to the P21. I also measured the output voltage of the converter and it looks good:

What am I missing?

Thanks for the help.

[Sigurd Hellesvik]

Hi,

Can you try to use a bench power supply on the same voltage of the battery in place of the battery?

If that does not work, can you try to change the bench power supply to 3V (if that works for your other circuit)?

Regards,
Sigurd Hellesvik

[J0sh1101]

Hi,

I did what you said. I replaced the battery with the power supply, then removed the entire circuit and added only the power supply, and it still remained the same. No change.

I then came up with the idea of adding an LED toggle. The application toggled the LED even when it was powered from the external power supply, but the UART didn't work. Here is an image of it:

When I connected the USB micro to the J6 while it was powered by the power supply, then suddenly the UART was active again.

Is there a jumper or line I need to trim to make it work?

Is this reproduceable on your side or am I only one getting this? 

Thanks for the help.

[Sigurd Hellesvik]

I see that you only use one line forUART, which I assume is TX.
What do you connect the UART reader to?
Could it be that the USB connection provides ground to an eventual laptop that is no longer present when you use only power supply?

In addition, can you measure GND and VDD on the DK Power Supply and USB, so we can see what the difference is?

[J0sh1101]

Hi,

Sigurd Hellesvik said:

I see that you only use one line forUART, which I assume is TX.

Yes, that is correct. 

Sigurd Hellesvik said:

What do you connect the UART reader to?

to the PC.

Sigurd Hellesvik said:

Could it be that the USB connection provides ground to an eventual laptop that is no longer present when you use only power supply?

Yes, you are right. I only realized after you said it that the reference to common ground was missing.

After I connected the two grounds, the UART reader worked again. Thanks!