ESP32 ADC 电量 esp32 adc速度

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mob64ca13fe62db 2024-05-11 23:06:49

文章标签 ESP32 ADC 电量 iot 嵌入式硬件 sed #include 文章分类 架构后端开发

一、目的

本篇主要介绍ESP32的ADC功能，ESP32有两个ADC模块，分别为ADC1/ADC2，每个ESP32系列具有的通道数不一样，详情请看下表。

在WiFi在使用时，ADC2的使用受到一些限制，实际应用场景中一般只使用ADC1即可。

二、介绍

ADC的IO引脚分配

ESP32系列（下表来自ESP-IDF开发文档）

GPIO	Analog Function	RTC GPIO	Comments
GPIO0	ADC2_CH1	RTC_GPIO11	Strapping pin
GPIO1			TXD
GPIO2	ADC2_CH2	RTC_GPIO12	Strapping pin
GPIO3			RXD
GPIO4	ADC2_CH0	RTC_GPIO10
GPIO5			Strapping pin
GPIO6			SPI0/1
GPIO7			SPI0/1
GPIO8			SPI0/1
GPIO9			SPI0/1
GPIO10			SPI0/1
GPIO11			SPI0/1
GPIO12	ADC2_CH5	RTC_GPIO15	Strapping pin; JTAG
GPIO13	ADC2_CH4	RTC_GPIO14	JTAG
GPIO14	ADC2_CH6	RTC_GPIO16	JTAG
GPIO15	ADC2_CH3	RTC_GPIO13	Strapping pin; JTAG
GPIO16			SPI0/1
GPIO17			SPI0/1
GPIO18
GPIO19
GPIO21
GPIO22
GPIO23
GPIO25	ADC2_CH8	RTC_GPIO6
GPIO26	ADC2_CH9	RTC_GPIO7
GPIO27	ADC2_CH7	RTC_GPIO17
GPIO32	ADC1_CH4	RTC_GPIO9
GPIO33	ADC1_CH5	RTC_GPIO8
GPIO34	ADC1_CH6	RTC_GPIO4	GPI
GPIO35	ADC1_CH7	RTC_GPIO5	GPI
GPIO36	ADC1_CH0	RTC_GPIO0	GPI
GPIO37	ADC1_CH1	RTC_GPIO1	GPI
GPIO38	ADC1_CH2	RTC_GPIO2	GPI
GPIO39	ADC1_CH3	RTC_GPIO3	GPI

从上表我们可以看到ADC1可以使用的IO引脚为GPIO32-GPIO39总共8个通道。

ESP32S2系列（下表来自ESP-IDF开发文档）

GPIO	Analog Function	RTC GPIO	Comment
GPIO0		RTC_GPIO0	Strapping pin
GPIO1	ADC1_CH0	RTC_GPIO1
GPIO2	ADC1_CH1	RTC_GPIO2
GPIO3	ADC1_CH2	RTC_GPIO3
GPIO4	ADC1_CH3	RTC_GPIO4
GPIO5	ADC1_CH4	RTC_GPIO5
GPIO6	ADC1_CH5	RTC_GPIO6
GPIO7	ADC1_CH6	RTC_GPIO7
GPIO8	ADC1_CH7	RTC_GPIO8
GPIO9	ADC1_CH8	RTC_GPIO9
GPIO10	ADC1_CH9	RTC_GPIO10
GPIO11	ADC2_CH0	RTC_GPIO11
GPIO12	ADC2_CH1	RTC_GPIO12
GPIO13	ADC2_CH2	RTC_GPIO13
GPIO14	ADC2_CH3	RTC_GPIO14
GPIO15	ADC2_CH4	RTC_GPIO15
GPIO16	ADC2_CH5	RTC_GPIO16
GPIO17	ADC2_CH6	RTC_GPIO17
GPIO18	ADC2_CH7	RTC_GPIO18
GPIO19	ADC2_CH8	RTC_GPIO19
GPIO20	ADC2_CH9	RTC_GPIO20
GPIO21		RTC_GPIO21
GPIO26			SPI0/1
GPIO27			SPI0/1
GPIO28			SPI0/1
GPIO29			SPI0/1
GPIO30			SPI0/1
GPIO31			SPI0/1
GPIO32			SPI0/1
GPIO33
GPIO34
GPIO35
GPIO36
GPIO37
GPIO38
GPIO39			JTAG
GPIO40			JTAG
GPIO41			JTAG
GPIO42			JTAG
GPIO43
GPIO44
GPIO45			Strapping pin
GPIO46			GPI；Strapping pin

从上表我们可以看到ADC1可以使用的IO引脚为GPIO1-GPIO10总共10个通道。

ESP32S3系列（下表来自ESP-IDF开发文档）

GPIO	Analog Function	RTC GPIO	Comment
GPIO0		RTC_GPIO0	Strapping pin
GPIO1	ADC1_CH0	RTC_GPIO1
GPIO2	ADC1_CH1	RTC_GPIO2
GPIO3	ADC1_CH2	RTC_GPIO3	Strapping pin
GPIO4	ADC1_CH3	RTC_GPIO4
GPIO5	ADC1_CH4	RTC_GPIO5
GPIO6	ADC1_CH5	RTC_GPIO6
GPIO7	ADC1_CH6	RTC_GPIO7
GPIO8	ADC1_CH7	RTC_GPIO8
GPIO9	ADC1_CH8	RTC_GPIO9
GPIO10	ADC1_CH9	RTC_GPIO10
GPIO11	ADC2_CH0	RTC_GPIO11
GPIO12	ADC2_CH1	RTC_GPIO12
GPIO13	ADC2_CH2	RTC_GPIO13
GPIO14	ADC2_CH3	RTC_GPIO14
GPIO15	ADC2_CH4	RTC_GPIO15
GPIO16	ADC2_CH5	RTC_GPIO16
GPIO17	ADC2_CH6	RTC_GPIO17
GPIO18	ADC2_CH7	RTC_GPIO18
GPIO19	ADC2_CH8	RTC_GPIO19	USB-JTAG
GPIO20	ADC2_CH9	RTC_GPIO20	USB-JTAG
GPIO21		RTC_GPIO21
GPIO26			SPI0/1
GPIO27			SPI0/1
GPIO28			SPI0/1
GPIO29			SPI0/1
GPIO30			SPI0/1
GPIO31			SPI0/1
GPIO32			SPI0/1
GPIO33			SPI0/1
GPIO34			SPI0/1
GPIO35			SPI0/1
GPIO36			SPI0/1
GPIO37			SPI0/1
GPIO38
GPIO39
GPIO40
GPIO41
GPIO42
GPIO43
GPIO44
GPIO45			Strapping pin
GPIO46			Strapping pin
GPIO47
GPIO48

从上表我们可以看到ADC1可以使用的IO引脚为GPIO1-GPIO10总共10个通道。

ADC的参考电压

ESP32默认的参考电压是1.1V（每个芯片间有差异，非精准），所以只能测量0-1.1V的电压；

ADC的量程设置

为了能够测量更大量程的电压，需要使用其衰减配置；每个通道都可以单独配置

/**
 * @brief ADC attenuation parameter. Different parameters determine the range of the ADC. See ``adc1_config_channel_atten``.
 */
typedef enum {
    ADC_ATTEN_DB_0   = 0,  ///<No input attenumation, ADC can measure up to approx. 800 mV
    ADC_ATTEN_DB_2_5 = 1,  ///<The input voltage of ADC will be attenuated extending the range of measurement by about 2.5 dB (1.33 x)
    ADC_ATTEN_DB_6   = 2,  ///<The input voltage of ADC will be attenuated extending the range of measurement by about 6 dB (2 x)
    ADC_ATTEN_DB_11  = 3,  ///<The input voltage of ADC will be attenuated extending the range of measurement by about 11 dB (3.55 x)
} adc_atten_t;

每个配置推荐的输入范围

ESP32 ADC 电量 esp32 adc速度_sed

ADC最小化噪声

1.在输入引脚接一个100nF的陶瓷电容

2.多次采样取平均

ADC的校准方式

不同芯片的参考电压不一样（1000mV - 1200mV），所以建议进行硬件校准

/**
 * @brief Type of calibration value used in characterization
 */
typedef enum {
    ESP_ADC_CAL_VAL_EFUSE_VREF = 0,         /**< Characterization based on reference voltage stored in eFuse*/
    ESP_ADC_CAL_VAL_EFUSE_TP = 1,           /**< Characterization based on Two Point values stored in eFuse*/
    ESP_ADC_CAL_VAL_DEFAULT_VREF = 2,       /**< Characterization based on default reference voltage*/
    ESP_ADC_CAL_VAL_EFUSE_TP_FIT = 3,       /**< Characterization based on Two Point values and fitting curve coefficients stored in eFuse */
    ESP_ADC_CAL_VAL_MAX,
    ESP_ADC_CAL_VAL_NOT_SUPPORTED = ESP_ADC_CAL_VAL_MAX,
} esp_adc_cal_value_t;

ESP32支持ESP_ADC_CAL_VAL_EFUSE_TP/ESP_ADC_CAL_VAL_EFUSE_VREF

ESP32S2支持ESP_ADC_CAL_VAL_EFUSE_TP

ESP32S3支持ESP_ADC_CAL_VAL_EFUSE_TP_FIT

ESP_ADC_CAL_VAL_EFUSE_TP根据EFUSE里面两个采样值进行校准（150mV/850mV）

ESP_ADC_CAL_VAL_EFUSE_VREF根据EFUSE里面的参考电压校准

ESP_ADC_CAL_VAL_EFUSE_TP_FIT根据EFUSE里面两个采样点和特性曲线校准

有些ESP32模组出厂时已经做了校准，我们可以通过工具查看

ADC相关的efuse设置

$espefuse.py -p /dev/cu.SLAB_USBtoUART adc_info
Connecting......
Detecting chip type... Unsupported detection protocol, switching and trying again...
Connecting......
Detecting chip type... ESP32
espefuse.py v4.1

=== Run "adc_info" command ===
ADC VRef calibration: 1128mV

通过espefuse.py adc_info命令我们可以看到我的ESP32模组默认支持VRef校验。

如果不支持VRef校准输出如下

ADC VRef calibration: None (1100 mV nominal)

如果支持两点校准，输出如下

ADC VRef calibration: 1149 mV
ADC readings stored in efuse BLK3:
    ADC1 Low reading  (150 mV): 306
    ADC1 High reading (850 mV): 3153
    ADC2 Low reading  (150 mV): 389
    ADC2 High reading (850 mV): 3206

三、实战

接口说明

1.检查是否支持指定的校准方式

esp_err_t esp_adc_cal_check_efuse(esp_adc_cal_value_t value_type);

2.设置采样量化位数

esp_err_t adc1_config_width(adc_bits_width_t width_bit);

3.设置指定通道的衰减

esp_err_t adc1_config_channel_atten(adc1_channel_t channel, adc_atten_t atten);

4.获取指定通道校准特征值

esp_adc_cal_value_t esp_adc_cal_characterize(adc_unit_t adc_num,
adc_atten_t atten,
adc_bits_width_t bit_width,
uint32_t default_vref,
esp_adc_cal_characteristics_t *chars);

5.获取指定通道的采样值

int adc1_get_raw(adc1_channel_t channel);

6.根据校准特征值获取实际电压值

uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc_reading, const esp_adc_cal_characteristics_t *chars);

参考代码

/* ADC1 Example

   This example code is in the Public Domain (or CC0 licensed, at your option.)

   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/
#include <stdio.h>
#include <stdlib.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/gpio.h"
#include "driver/adc.h"
#include "esp_adc_cal.h"

#define DEFAULT_VREF    1100        //Use adc2_vref_to_gpio() to obtain a better estimate
#define NO_OF_SAMPLES   64          //Multisampling

static esp_adc_cal_characteristics_t *adc_chars;
#if CONFIG_IDF_TARGET_ESP32
static const adc_channel_t channel = ADC_CHANNEL_6;     //GPIO34 if ADC1, GPIO14 if ADC2
static const adc_bits_width_t width = ADC_WIDTH_BIT_12;
#elif CONFIG_IDF_TARGET_ESP32S2
static const adc_channel_t channel = ADC_CHANNEL_6;     // GPIO7 if ADC1, GPIO17 if ADC2
static const adc_bits_width_t width = ADC_WIDTH_BIT_13;
#endif
static const adc_atten_t atten = ADC_ATTEN_DB_0;
static const adc_unit_t unit = ADC_UNIT_1;


static void check_efuse(void)
{
#if CONFIG_IDF_TARGET_ESP32
    //Check if TP is burned into eFuse
    if (esp_adc_cal_check_efuse(ESP_ADC_CAL_VAL_EFUSE_TP) == ESP_OK) {
        printf("eFuse Two Point: Supported\n");
    } else {
        printf("eFuse Two Point: NOT supported\n");
    }
    //Check Vref is burned into eFuse
    if (esp_adc_cal_check_efuse(ESP_ADC_CAL_VAL_EFUSE_VREF) == ESP_OK) {
        printf("eFuse Vref: Supported\n");
    } else {
        printf("eFuse Vref: NOT supported\n");
    }
#elif CONFIG_IDF_TARGET_ESP32S2
    if (esp_adc_cal_check_efuse(ESP_ADC_CAL_VAL_EFUSE_TP) == ESP_OK) {
        printf("eFuse Two Point: Supported\n");
    } else {
        printf("Cannot retrieve eFuse Two Point calibration values. Default calibration values will be used.\n");
    }
#else
#error "This example is configured for ESP32/ESP32S2."
#endif
}


static void print_char_val_type(esp_adc_cal_value_t val_type)
{
    if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
        printf("Characterized using Two Point Value\n");
    } else if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
        printf("Characterized using eFuse Vref\n");
    } else {
        printf("Characterized using Default Vref\n");
    }
}


void app_main(void)
{
    //Check if Two Point or Vref are burned into eFuse
    check_efuse();

    //Configure ADC
    if (unit == ADC_UNIT_1) {
        adc1_config_width(width);
        adc1_config_channel_atten(channel, atten);
    } else {
        adc2_config_channel_atten((adc2_channel_t)channel, atten);
    }

    //Characterize ADC
    adc_chars = calloc(1, sizeof(esp_adc_cal_characteristics_t));
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize(unit, atten, width, DEFAULT_VREF, adc_chars);
    print_char_val_type(val_type);

    //Continuously sample ADC1
    while (1) {
        uint32_t adc_reading = 0;
        //Multisampling
        for (int i = 0; i < NO_OF_SAMPLES; i++) {
            if (unit == ADC_UNIT_1) {
                adc_reading += adc1_get_raw((adc1_channel_t)channel);
            } else {
                int raw;
                adc2_get_raw((adc2_channel_t)channel, width, &raw);
                adc_reading += raw;
            }
        }
        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);
        printf("Raw: %d\tVoltage: %dmV\n", adc_reading, voltage);
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

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