ESP32-PaxCounter/src/adcread.cpp

#ifdef HAS_BATTERY_PROBE

#include "globals.h"
#include <driver/adc.h>
#include <esp_adc_cal.h>

#define DEFAULT_VREF    1100    // to be done: use adc2_vref_to_gpio() to obtain a better estimate
#define NO_OF_SAMPLES   64      // we do multisampling

// Local logging tag
static const char TAG[] = "main";

static void print_char_val_type(esp_adc_cal_value_t val_type)
{
    if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
        ESP_LOGI(TAG,"ADC calibration using efuse Two Point Value");
    } else if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
        ESP_LOGI(TAG,"ADC calibration using eFuse Vref");
    } else {
        ESP_LOGI(TAG,"ADC calibration using default Vref");
    }
}

uint16_t read_voltage(void)
{
    static const adc1_channel_t channel = HAS_BATTERY_PROBE;
    static const adc_atten_t atten = ADC_ATTEN_DB_11;
    static const adc_unit_t unit = ADC_UNIT_1;

    //configure ADC1
    ESP_ERROR_CHECK(adc1_config_width(ADC_WIDTH_BIT_12));
    ESP_ERROR_CHECK(adc1_config_channel_atten(channel, atten));

    //calibrate ADC1
    esp_adc_cal_characteristics_t *adc_chars = (esp_adc_cal_characteristics_t *) calloc(1, sizeof(esp_adc_cal_characteristics_t));
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize(unit, atten, ADC_WIDTH_BIT_12, DEFAULT_VREF, adc_chars);
    print_char_val_type(val_type);
    
    //multisample ADC1
    uint32_t adc_reading = 0;
    for (int i = 0; i < NO_OF_SAMPLES; i++) {
            adc_reading += adc1_get_raw(channel);
    }

    adc_reading /= NO_OF_SAMPLES;

    //Convert adc_reading to voltage in mV
    uint32_t voltage = esp_adc_cal_raw_to_voltage(adc_reading, adc_chars);
    #ifdef BATT_FACTOR
        voltage *= BATT_FACTOR;
    #endif
    ESP_LOGI(TAG,"Raw: %d / Voltage: %dmV", adc_reading, voltage);
    return voltage;
}
#endif // HAS_BATTERY_PROBE