Rerouting AT interface for power measurement using external supply

[Frikkie Badenhorst]

Hi there,

We received your devkits on Friday, 25th of June and started evaluation of the modules this morning (Magnus Pederson and Brian Kim @ Nordic arranged the devkits for us). We are able to successfully connect to the network and do current measurements. Since we are on a tight schedule, I was hoping you could assist with the following simple issue:

We will be using a supply voltage of around 3.3 - 3.6V, and would thus want to evaluate the power consumption at that supply. For this, we add an external supply to P21 and bridge SB20. We then add a current meter (Nordic PPK2) to P22. We do however only want to evaluate the power profile of the nRF9160 chip, and not the interface MCU. We thus put SW6 in the "right" position.

When this is the case, the UART interfaces are not available on the USB connector. Also when having the USB cable connected, the supply voltage is 5V, so we do not want to have the USB cable connected at all. Thus to communicate via the serial interface with the nRF9160, we will need to reroute the UART pins to the external connectors. We can then use a serial-to-usb adapter to communicate using a simple terminal program (TeraTerm).

Could you please advise as to what would be the quickest way to do this? Which UART port is the AT interface (UART0/1/2)? I guess we will also have to disable HW flow control for this test as our Serial to USB adapter has only a TX, RX and GND wire.

We are reaching out simply to speed up the evaluation process.

Thanks in advance!

Kind regards,

Frikkie Badenhorst

[Stian Røed Hafskjold]

Hi, please follow my guide here on how to measure current on the nRF9160 DK: https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/hardware-design/posts/getting-started-with-current-measurements-on-the-nrf9160

I think the easiest way is using the SMU method, then you can supply P22 directly with the voltage you need and measure current at the same time. You leave the USB cable plugged in for UART/debugging, and the USB will then power everything on the DK except the nRF91 VDD itself. So there will be now leakage current from the nRF91 to the rest of the DK, nor will the nRF91 be powered by the USB.

No modifications to the DK are needed, and SW6 can be left in the default position.

[Frikkie Badenhorst]

Hi Stian, 

Thank you for your response. Yes the SMU looks as if it will work.

Also, what application can we flash onto the the SiP in order to do manual current testing? 

We currently have the asset tracker application flashed onto the module, however we are having issues installing the nRD Connect SDK and getting it running with SEGGER Embedded Studio (I have created a seperate ticked for that), so thus for now cannot create our own custom apps.

Should simply erasing the firmware on the app processor be fine?

[Stian Røed Hafskjold]

I don't think we have any precompiled examples in the SDK, but I could probably create some hex files for you if you want.

I would recommend starting with the UDP sample. It transfers a UDP packet at a regular interval and going into PSM or eDRX idle between the transfers. It's power optimized and easily configurable from the .conf file. If you want I can create a hex file with the parameters you want.

Alternatively, you can use the Serial LTE Modem application. This is based on using a terminal to submit AT commands to the modem over UART, so you can set up your own test environment. Then before doing current measurements you can issue the AT+XSLEEP command to turn off UART and putting the nRF91 in the lowest power mode.

[Frikkie Badenhorst]

Setting up our own test environment, is exactly what we want to do and the Serial LTE Modem application sounds perfect. As mentioned, for now we are having issues installing the SDK and SES.

Would you be so kind to provide me with the HEX files of this application, which I can use with the Programmer tool provided in nRF Connect for Desktop to flash the app?

Thanks so much, Stian.

[Frikkie Badenhorst]

Hi Stian, will you be able to provide the hex files of the Serial LTE Modem app? It is very urgent as we need to do testing on the hardware as soon as possible. 

We are having issues with installing the SDK and SES as mentioned here, https://devzone.nordicsemi.com/f/nordic-q-a/76895/zephyr-base-not-set-and-open-ide-not-present-in-toolchain-manager/317882#317882 , so cant build the application ourselves.

Thanks a lot for your help so far!

Regards,

Frikkie

[Stian Røed Hafskjold]

Hi, sorry for the late reply. Here a hex file for you: 3005.merged.hex

It is currently consuming 30 uA in idle, after calling AT#XSLEEP=0, ideally you should see around 2-3 uA. So I will have to look into what changes they made in the newest NCS release v1.6.0 in order to get it down to the expected idle current. Anyways, you should be able to get started with the hex I posted above, and I will get back to you shortly with an updated one.

[Frikkie Badenhorst]

Thank you Stian! Looking forward to seeing the device in operation!

Please keep me updated on the updated hex file, thanks

[Frikkie Badenhorst]

Hi Stian,

after calling AT#XSLEEP, how can we wake the device/UARTs up again so that we can send some more AT commands?

[Stian Røed Hafskjold]

Hi, button 1 on the DK should wake the device up again

[Frikkie Badenhorst]

Thanks Stian.

I have accidentally closed the ticket, but I believe you are still preparing the update LTE Serial Modem app which will allow the expected idle current.

[Stian Røed Hafskjold]

Yes, here is a new hex file with the expected idle current: 8547.merged.hex