Trying to read from a voltage divider circuit using two 240 Ohm resistors. Getting a reading of 6.0, when it should be 1.65. Circuit is powered by a bench 3.3V and both the Huzzah32 and circuit are grounded. Using USB for the Huzzah32. Any thoughts?

  void setup() 
void loop() 
  int sensorValue = analogRead(A9);
  float voltage = sensorValue * (3.3 / 1023.0);

circuit diagram

  • Please add the schema. Commented Oct 21, 2020 at 7:10
  • My multimeter reads the correct Vout... Commented Oct 21, 2020 at 8:03
  • this gets me closer, but still low... float voltage = (sensorValue * 3.3) / (4095); Commented Oct 21, 2020 at 8:26
  • ESP32 chips have a problem with ADC and WIFI at the same time. Maybe disable WIFI ?
    – tavis
    Commented Oct 21, 2020 at 9:01
  • both the Huzzah32 and circuit are grounded ... are the grounds joined? ... your schematic does not show a common ground
    – jsotola
    Commented Oct 21, 2020 at 16:54

1 Answer 1


First, ESP32 ADC is 12-bit, not 10-bit. therefore the formula should be:

float voltage = sensorValue * (3.3 / 4096.0);

Secondly, ESP32 ADC is not really linear, and tend to have lower reading than the actual value. You will need to do some calibration if you want to get a more accurate reading. You can take a look at my github on esp32-adc-calibrate.

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