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how to connect ADC voltage divider?

Posted: Tue Feb 12, 2019 8:21 am
by dibalavs
Hello,
I am trying to connect voltage divider to ADC,
The resulting circuit is similar to
Image

But
R1,R2 - 870Kom (I need low power consumption, because of battery powered device).
C1 - 100nF. ( As in ESP recommendations)

As a result, R2 + C1 gives RC oscillator, which oscillate at 1.8Hz
So the resulting voltage measurements have dispersion around 0.4 Volt.
When I log to console raw measurments in cycle, I can see real sinus.

How to correctly connect voltage divider to ESP without such effects?