I am using a variac to take 0 to 120 Vac and rectify it so that I can get 0 to 5 Vdc for an analog input to my Arduino. I have attached my circuit. The precision rectifer was tested (in Tina TI). With a 169 (peak to peak) Vac from the variac I get about 12 Vac on the secondary of the transformer. Rectified output is approximately 8 Vdc. I then use the voltage divider to get 5 Vdc with the variac at max. My question is, what will the loading effect of the analog input on the Arduino be? I can't find or don't know what I am looking at to see a spec for input resistance. The Arduino is an ATmega328. I assume that the loading would be minimal and I could compensate with the pot in the voltage divider. Is that a bad assumption or is there a better way of converting the 0 to 8 into 0 to 5? Also what do you think of my filter cap sizing. I get about 40mv of ripple. Is there a point of diminishing returns on filter cap sizing? A larger cap reduces the ripple more, but haves a longer charge time on power up.
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