main.cpp

#include <cmath>
#include <string>
#include <Arduino.h>
#include <esp_adc_cal.h>
#include "driver/adc.h"

#if CONFIG_IDF_TARGET_ESP32
static const adc_bits_width_t width = ADC_WIDTH_BIT_12;
#elif CONFIG_IDF_TARGET_ESP32S2
static const adc_bits_width_t width = ADC_WIDTH_BIT_13;
#endif

esp_adc_cal_characteristics_t *adc_chars;


void setup() {
    Serial.begin(115200);

    adc_chars = new esp_adc_cal_characteristics_t();

    //pinMode(8, INPUT);
    adc1_config_channel_atten(ADC1_CHANNEL_4, ADC_ATTEN_DB_0);
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize(ADC_UNIT_1, ADC_ATTEN_DB_0, width, 5000, adc_chars);
    delay(5000);

    //Check type of calibration value used to characterize ADC
    if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
        Serial.println("eFuse Vref");
    } else if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
        Serial.println("Two Point");
    } else {
        Serial.println("Default");
    }
}

void loop() {
    uint32_t reading =  adc1_get_raw(ADC1_CHANNEL_4);
    auto output_voltage = esp_adc_cal_raw_to_voltage(reading, adc_chars);

    Serial.print(output_voltage);
    Serial.println("mV");
    delay(1000);
}