It's not hidden very well [referring to "lies" in the title] when the ESP32's website about the ADC has a graph showing noise of ~10 LSBs normally, which with a

It's not hidden very well [referring to "lies" in the title] when the ESP32's website about the ADC has a graph showing noise of ~10 LSBs normally, which with a proper input capacitor goes down to about 5 LSBs and down to 1 LSB with multisampling. Which is done transparently in hardware. https://docs.espressif.com/projects/esp-idf/en/release-v4.4/esp32/api-reference/peripherals/adc.html https://docs.espressif.com/projects/esp-idf/en/release-v4.4/... It even has almost the same graph showing the linearity and dead zone, none of this is a surprise. It's just not got the best ADC ever and I've chosen different parts because of it before. Other parts have better ADCs... and that Mega has a far lower sampling rate.