[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?

[Mateusz Gancarczyk]

I'm afraid it's not working :/ Current consumption for one channel is 4uA but for 4 channels above 1mA. I download SAADC low power example from GitHub: github.com/.../saadc_low_power and modify for 4 channels. I disabled burst mode and oversample:

#define SAADC_SAMPLES_IN_BUFFER 4 
#define SAADC_OVERSAMPLE NRF_SAADC_OVERSAMPLE_DISABLED 
#define SAADC_BURST_MODE 0 

I also disable UART_PRINTING_ENABLED and all LED blinking. In this link: www.dropbox.com/.../saadc_low_power.rar you can download modifiy example. What I'm doing wrong?