Measure voltage with esp32

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1

i try to measure voltage with esp32 with this formula:

esp32_voltage * (analogRead / 1023) * 13.1951
i get 13.1951 from (R1+R2)/R2

  analogReadResolution(10); // Set analog read resolution: 6biots(0-63),  8 bits(0-255), 10 bits (0-1023)

 float result = (3.3 * ((float)analogRead(35) / 1023)) * 13.1951;

here is schematic

voltage
voltage907×527 10.5 KB

in my case AnalogRead is 236 and input voltage is 12.24v
but based on this formula result is10.0v and not around 12

2

What is the max input of your A/D and is there any resistor dividers in front of it already installed on the ESP module.

3

@arpa123
Use analogReadMilliVolts();
analogRead is un-calibrated and will give you the wrong answer.

4

max 42V

5

Post a link to technical details on your board.

6

i connected io35 to volage_measure label (schematic image above)

7

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