ADC Input Issue. Input pulls sometimes low

[MaxRPEng]

Hello,

i have a strange issue with my analog input.
Every few seconds (not the same database) my signal is getting pulled low.

But i dont know why. The external signal is stable, i tested it with a oscilloscope.

I meassure the voltage of a piezo ceramic.

please see my oscilloscope print. It looks like a discharge of my filter cap and after thati charges again.

I am pretty shure that is is not related to the external circutry.

I use P0.03 as analog input

Any ideas?

[Akadir]

Hello @MaxRPEng,

I am interested in ADC at Bluetooth , can you share your code or some reference codes?

[ketiljo]

The internal capacitor of the ADC will load the circuit when the acquisition starts. So if you have a very high impedance source, the voltage will drop when the ADC is turned on and starts to sample. Use a small capacitor near the pin to buffer the voltage. Same principle as here: https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/measuring-lithium-battery-voltage-with-nrf51