Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

WestCoastDaz — Tue, 16 May 2017 20:11:02 GMT

Joe,

The current is 3mA now because the debugger is connected and the debug engine is running. I forgot about that when I suggested using RTT. There really isn't a low current way to log data without modifying the logging library to disable the UART after all data is flushed or toggle unused GPIOs.

Sorry for the confusion.

The check is to the left of my initial answer, please check it only if you felt I answered your question:)

Cheers, Darren

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

Joe — Tue, 16 May 2017 20:02:25 GMT

Actually, a folowup question :)

I now switch to using RTT like you suggested. In sdk_config.h, I set NRF_LOG_BACKEND_SERIAL_USES_UART to 0, and NRF_LOG_BACKEND_SERIAL_USES_RTT to 1. When I run JLinkRTTViewer, the output is nice and quick. However, now my idle/sleep current is ~3mA. Have you had similar experience? Do I need to turn off the RTT before going to sleep?

I am new to the forum, where is the check you want me to click?

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

WestCoastDaz — Tue, 16 May 2017 19:39:51 GMT

Joe,

My pleasure! If I answered your question would you mind clicking the check.

Thanks

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

Joe — Tue, 16 May 2017 19:24:50 GMT

Thanks, Darren!

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

WestCoastDaz — Tue, 16 May 2017 18:18:25 GMT

Joe, the UART it's self takes 55uA but it turns on the peripheral clock which is where the majority of the current is coming from. You should be able to un-init the UART using the SDK. You will likely have to dig through the logging library to find out which UART calls a being made and then use them. If you want to quickly check then you may want to try RTT based logging as I highlighted above. We switched to it and haven't looked back.

Darren

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

Joe — Tue, 16 May 2017 18:10:09 GMT

Hi Darren,

I am suspecting the UART is drawing the current, but the data sheet says 55 uA, not 400 uA. Do you know of a way in runtime to disable the UART to reduce the sleep current?

BTW, I am using SDK 12.2.0 and PCA10040.

Joseph

RE: Sleep current with NRF_LOG_ENABLED or without NRF_LOG_ENABLED

WestCoastDaz — Tue, 16 May 2017 17:59:09 GMT

Joe,

Without knowing exactly how you have sdk_config.h setup my guess is the additional sleep current is due to the UART quiescent current. In our tests it adds ~400uA static quiescent current. If you have a Segger debugger you can switch to RTT logging which is a lot faster than using the UART and it frees up your UART for other tasks.

Darren