ESP32 Forum

Hi,

I have detected an unexpected offset when measuring values with the adc in the module huzzah32 (esp32).

For example, when trying the get the battery value:
- 3781 mV acquired in the ESP32
- 4113 mV measured with the multimeter.

I am taking 3300 mV as reference (VREF) for adc conversions. 12 bit (4095 adc steps).

Being calculaed as follows:
voltage = value * (VREF / ADC_STEPS);

The same happened when using a TMP36 sensor for acquiring temperature values.

TMP36 -> pin 39 (A3 - ADC1)
VBAT/2 -> pin 35 (A13)

Any of you have experienced anything similar?

Regards, Ramon.

"The ADC should be configured before reading is taken." as per the docs, has this been done in your code ?
https://espressif-docs.readthedocs-host ... eading-adc

Hi,

I am using Arduino IDE. The configuration is done out of my scope, but I am assuming full scale 12 bits and 3,3V and no attenuation.

I have tested at 3 points so as to double check:

Vadc_real: 0V -> measured: 0
Vadc_real: 1,78V (through resistor divider) -> measured: 0d1990 (1,60 V)
Vadc_real: 3,3V -> measured: 0d4095 (3,3V)

As you can see there are -180mV offset/linearity error.

Any suggestion will be welcome.

Regards, Ramon.