SAADC on NRF52832 returns strange values intermittent

[Mike]

Hi,

I see intermittent incorrect values from the saadc. The code is described here.

The graf shows battery voltage in mV over about 4 days with one sample per minute. Note the 3 samples that are off. I'm aware that there's no calibration done in the code, but I suspect that has nothing to do with this (the periodic fluctuations are well correlated to the temperature).

Am I doing something wrong?

Thanks, Mike

[Mike]

Not yet, i want to understand the root cause first. Could this have something to do with RF rx/tx, i.e. that saadc sample at the instant RF is active? I checked VDD again, and there is no ripple on the supply rail of that magnitude during RF rx/tx (using a 100MHz scope with trigger set properly). Could it be interference /inside/ the nRF52832 chip that cause this? Note that saadc sample NRF_SAADC_INPUT_VDD which is internal.