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]

Thanks for your reply Jørgen.

As described in the linked post, VDD is the supply voltage to nRF52832 from the battery:

  ch.pin_p = NRF_SAADC_INPUT_VDD;
  ch.pin_n = NRF_SAADC_INPUT_DISABLED;

The battery voltage does not dip according to an external adc that measure current and voltage to the pcb, so it's something in saadc that creates this.

I use i2c to gather data from 2 other sensors. Those sensors are disabled at the time VDD is measured (via a FET switch), and is switched on in firmware after VDD is measured.