I'm witnessing some weird notches in the signal I get from ADCs,
I have two lines input and plotting the readings directly ... the signal is somewhat noisy (small ripple on the line) but I get more aggressive artifacts which are not palatable ... they are kind of periodic but not constant :
* DC is clean (3.3v / regulator + cap)
* ADC1_CHANNEL_4 & ADC1_CHANNEL_5
* ADC_ATTEN_DB_11
* ADC_WIDTH_BIT_12
* WIFI is on (AP) and busy streaming ADC readings (but ADC behaves the same when alone)
* i2s is explicitly disabled (but it seem has no effect)
* capture is done in a timer CB (but ADC behaves the same when in a task or main loop)
I tried to extract a pattern from the readings but got nothing too significant, notch is around 2% +/-1% wrt nominal reading, period is about 950ms.
Did someone witness something similar ?
If anybody has a clue where this is coming from, I'd be glad to know
Thanks