Most optimal low power mode for frequent sensor data reading

[zazas321]

Hey. We are currently working on the project based on the nRF52840 + external LTE modem.

The nRF52840 is responsible for reading/capturing various sensor data (accelerometer, magnetometer, temperature and etc..) and then sending the data to the cloud every 5-10 seconds.

For our particular application, it is very important to be able to send data very frequently (5-10 seconds) hence we are wondering what would be the most optimal solution for power saving on the nRF52840 side. 

Option 1:

Use low power System ON mode while capturing all the sensor data, communicating with various sensors

Option 2:

Use System OFF mode and wake up every 5 seconds, taking all the measurements and going back to system OFF mode?

I am concerned if it would be efficient to use System OFF mode in our case if we want to collect sensor data frequently (5 seconds) ? Perhaps the start up current consumption is going to be considerably higher than just simply keeping the CPU at System ON low power mode?

I would appreciate any suggestions, thanks in advance!

[Kenneth]

Hello,

You should be using system ON idle mode yes, which draw around ~2uA between sampling the sensor. System OFF is only used if you sleep for more than several minutes, while waiting for a user to press a button or similiar user interaction.

As a side note: I suspect in your case that the the significant current in your application will be due to the LTE modem.

Kenneth

[zazas321]

Thank you very much for the response. It is true that the majority of the current consumption will be due to the LTE modem but I want to optimize the nRF part as much as possible as well even though its going to be considerably lower!

Additionally, I am having issue understanding the System ON power mode as I cannot find enough information about this. I have even created a seperate post about this:

 Where to find information about nRF5X low power modes 

I have managed to find example project to put the system in system off mode but cannot find anything related to system ON mode. Perhaps you would be able to provide some additional information about this ? I would like to test this on the nRF52840DK with the PPK2

[Kenneth]

You should go through nRF Connect SDK Fundamentals course here:
https://academy.nordicsemi.com/ 

Kenneth

[zazas321]

Thats the first thing I did when I picked the nRF52DK but it did not have anything to do with the power saving methods (system ON, system OFF and etc). Perhaps you are talking about some other course?

[Kenneth]

Hello,

Same course yes. The CPU will automatically enter system ON idle when it's not running any code (for instance when all threads are idle and logging is disabled). So seen from application development you don't really do anything explicit to enter system ON idle.

Kenneth