A class to take multiple samples of the ESP32 ADC

main.c

#include "SmoothAdc.h"

// define all the channels you want to watch
SmoothAdc<ADC1_CHANNEL_0, ADC1_CHANNEL_3> adc;
esp_adc_cal_characteristics_t adc1_chars;

void setup() {
  Serial.begin(115200);
  // configure and characterize the adc1
  esp_adc_cal_characterize(ADC_UNIT_1, ADC_ATTEN_DB_11, ADC_WIDTH_12Bit, 1100, &adc1_chars);
  adc1_config_width(adc1_chars.bit_width);
  adc1_config_channel_atten(ADC1_CHANNEL_0, adc1_chars.atten);
  adc1_config_channel_atten(ADC1_CHANNEL_3, adc1_chars.atten);
  // start the asynchronious job to sample the adc
  adc.xTaskCreate();
}

void loop() {
  delay(1000);
  auto v1 = esp_adc_cal_raw_to_voltage(adc.sample(0), &adc1_chars);
  Serial.print(v1);
  Serial.print(" ");
  auto v2 = esp_adc_cal_raw_to_voltage(adc.sample(1), &adc1_chars);
  Serial.print(v2);
  Serial.println(" mv");
}

SmoothAdc.h

#pragma once
#include <driver/adc.h>

template<adc1_channel_t... PINS>
class SmoothAdc {
    private:
        const adc1_channel_t pins[sizeof...(PINS)] = {PINS...};
        volatile uint32_t results[sizeof...(PINS)] = {};
        uint16_t reads[sizeof...(PINS)][256] = {};
        uint8_t position = 0;

    public:
        uint16_t sample(size_t pin) {
            return results[pin] / 256;
        }
        
        void xTaskCreate(const UBaseType_t priority = 1, const BaseType_t xCoreID = -1) {
            ::xTaskCreateUniversal(task, "SmoothAdc", 1024, this, priority, NULL, xCoreID);
        }
        
    private:
        void static task (void * parameter) {
            auto self = (SmoothAdc *)parameter;
            for (;;) {
                delay(8 - millis() % 8);
                self->measure();
            }
        }
        
        void measure() {
            for (size_t i = 0; i < sizeof...(PINS); ++i) {
                adc1_get_raw(pins[i]); // ignore the value on first try
                uint16_t read = adc1_get_raw(pins[i]);
                results[i] += read - reads[i][position];
                reads[i][position] = read;
            }
            ++position;
        }
};