mimicking DVM 10 to 11MΩ input impedance on microcontroller analogue input
You can just add a Rail-to-rail CMOS-input op-amp as a unity-gain buffer. If you need gain (for a lower input range than the ADC reference), add a couple of resistors in a typical non-inverting amplifier configuration. Best to put 100nF or so across the op-amp power supply pins.



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For more than the ADC reference (like 30V) you need to add an voltage divider at the input where the 10M resistor is. For example if your ADC reference is 5V you could use 9M + 1M for 50V full-scale. The impedance seen by the source is 10M.



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