[nRF52] Best practise for ultra low power SAADC 4 channel conversion

[Mateusz Gancarczyk]

What is the best practise for multichannel SAADC conversion in ultra low power devices? For example I have to measured 4 channel in interval 250ms. Below what I try:

1. I'm set RTC for interupt 250ms. In RTC handler I initialized SAADC channel 0 and start conversion. In SAADC end of conversion handler i uintialized SAADC, get result from channel 0 and initialized for channel 1 and start conversion. Same for channels 3 and 4 but in channel 4 I'm not start new conversion but Im set RTC for 333ms Handler. I try it and I get strange result.

If I have only one channel I've get current consuption:

avarage current is around 10uA ( it's ok for my aplication ). but if I enabled conversion for 4 channel, one by one ( as I descripted above ) I've got something like that:

Current is 2 times higher! I don't know why density of the current spikes is in that level.

Mayby I should use PPI? i read this topic: devzone.nordicsemi.com/.../

or maybe different method?

[Jørgen Holmefjord]

Hi,

It seems there is some issues with using scan mode when the low-power mode in the SAADC driver is enabled. I will look into this.

I ported the method used in the saadc_low_power example from SDK 11, and added this to SDK 13 example:

main.c

This gives me an average current draw of just over 4 uA.

Best regards,

Jørgen

[Jørgen Holmefjord]

No, there is not.. But I made one for you: saadc_low_power_multichannel.zip

[Simon]

Hi  Jørgen

Would it be possible for you to create also a armgcc version for the pca10056? That would be great :-)

[Jørgen Holmefjord]

It could, but I think you should be able to manage this yourself:

• Copy pca10056 directory from default saadc peripheral example in SDK 15 into the project dir I uploaded.
• Copy config directory from pca10040/blank directory into pca10056/blank directory (overwrite existing sdk_config.h file).
• Add the three missing source files to the makefile:
  • $(SDK_ROOT)/integration/nrfx/legacy/nrf_drv_clock.c \
  • $(SDK_ROOT)/modules/nrfx/drivers/src/nrfx_clock.c \
  • $(SDK_ROOT)/modules/nrfx/drivers/src/nrfx_rtc.c \