我来帮你一步步排查这个问题，从硬件到代码逐一分析可能的原因和解决方案：

一、先检查硬件连接与SD卡本身 #

• 接线与兼容性：确认ESP32-CAM和SD卡模块的接线是否正确（AI-Thinker模块默认SD_MMC引脚为GPIO12(D2)、GPIO13(D3)、GPIO14(CMD)，电源必须接3.3V，严禁接5V）。如果是集成了SD卡槽的ESP32-CAM模块，检查卡槽是否接触良好，重新插拔SD卡试试。
• SD卡规格：确保SD卡是32GB及以下的容量（超过32GB的FAT32格式化可能存在兼容性问题），并且是高速卡（Class 10以上最佳）。可以换一张已知能用的SD卡测试，排除卡本身的故障。
• 电源供应：ESP32-CAM拍照时电流需求较高，USB供电可能不足导致SD卡供电异常。建议使用外接3.3V/500mA以上的电源模块供电。

二、代码层面的优化与调试 #

你的代码逻辑没问题，但可以通过调整SD_MMC初始化方式和增加调试信息来定位问题：

1. 修改SD卡初始化代码，增加调试信息 #

将原代码中的SD_MMC初始化部分替换为以下代码，这样能输出更详细的卡状态信息：

Serial.println("Starting SD Card");
// 尝试1线模式初始化（适配多数简易SD模块），如果不行可以把第二个参数改成false用4线模式
if(!SD_MMC.begin("/sdcard", true)){
    Serial.println("SD Card Mount Failed");
    // 打印详细卡类型信息，帮助排查
    uint8_t cardType = SD_MMC.cardType();
    Serial.print("Detected Card Type: ");
    switch(cardType){
        case CARD_NONE: Serial.println("No SD card attached"); break;
        case CARD_MMC: Serial.println("MMC card detected"); break;
        case CARD_SD: Serial.println("Standard SD card detected"); break;
        case CARD_SDHC: Serial.println("SDHC card detected"); break;
        default: Serial.println("Unknown card type");
    }
    return;
}

2. 添加延迟，给硬件上电缓冲时间 #

在相机初始化完成后，添加一点延迟再初始化SD卡，避免硬件还没准备好：

// Init Camera
esp_err_t err = esp_camera_init(&config);
if (err != ESP_OK) {
    Serial.printf("Camera init failed with error 0x%x", err);
    return;
}
delay(500); // 添加这行，给相机和SD卡模块上电缓冲时间

3. 检查GPIO12电平（关键！） #

ESP32的GPIO12引脚电平会影响SD卡的识别模式，启动时如果GPIO12为高电平，可能导致SD卡挂载失败。对于AI-Thinker模块，GPIO12默认应该接下拉电阻，如果你的模块没有，建议手动添加一个10kΩ的下拉电阻到GND，确保启动时GPIO12为低电平。

三、完整修改后的代码参考 #

#include "esp_camera.h"
#include "Arduino.h"
#include "FS.h" // SD Card ESP32
#include "SD_MMC.h" // SD Card ESP32
#include "soc/soc.h" // Disable brownour problems
#include "soc/rtc_cntl_reg.h" // Disable brownour problems
#include "driver/rtc_io.h"
#include <EEPROM.h> // read and write from flash memory

// define the number of bytes you want to access
#define EEPROM_SIZE 1

// Pin definition for CAMERA_MODEL_AI_THINKER
#define PWDN_GPIO_NUM 32
#define RESET_GPIO_NUM -1
#define XCLK_GPIO_NUM 0
#define SIOD_GPIO_NUM 26
#define SIOC_GPIO_NUM 27
#define Y9_GPIO_NUM 35
#define Y8_GPIO_NUM 34
#define Y7_GPIO_NUM 39
#define Y6_GPIO_NUM 36
#define Y5_GPIO_NUM 21
#define Y4_GPIO_NUM 19
#define Y3_GPIO_NUM 18
#define Y2_GPIO_NUM 5
#define VSYNC_GPIO_NUM 25
#define HREF_GPIO_NUM 23
#define PCLK_GPIO_NUM 22

int pictureNumber = 0;

void setup() {
    WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0); //disable brownout detector
    Serial.begin(115200);
    delay(1000); // 给串口和硬件上电缓冲

    camera_config_t config;
    config.ledc_channel = LEDC_CHANNEL_0;
    config.ledc_timer = LEDC_TIMER_0;
    config.pin_d0 = Y2_GPIO_NUM;
    config.pin_d1 = Y3_GPIO_NUM;
    config.pin_d2 = Y4_GPIO_NUM;
    config.pin_d3 = Y5_GPIO_NUM;
    config.pin_d4 = Y6_GPIO_NUM;
    config.pin_d5 = Y7_GPIO_NUM;
    config.pin_d6 = Y8_GPIO_NUM;
    config.pin_d7 = Y9_GPIO_NUM;
    config.pin_xclk = XCLK_GPIO_NUM;
    config.pin_pclk = PCLK_GPIO_NUM;
    config.pin_vsync = VSYNC_GPIO_NUM;
    config.pin_href = HREF_GPIO_NUM;
    config.pin_sscb_sda = SIOD_GPIO_NUM;
    config.pin_sscb_scl = SIOC_GPIO_NUM;
    config.pin_pwdn = PWDN_GPIO_NUM;
    config.pin_reset = RESET_GPIO_NUM;
    config.xclk_freq_hz = 20000000;
    config.pixel_format = PIXFORMAT_JPEG;

    if(psramFound()){
        config.frame_size = FRAMESIZE_UXGA; // FRAMESIZE_ + QVGA|CIF|VGA|SVGA|XGA|SXGA|UXGA
        config.jpeg_quality = 10;
        config.fb_count = 2;
    } else {
        config.frame_size = FRAMESIZE_SVGA;
        config.jpeg_quality = 12;
        config.fb_count = 1;
    }

    // Init Camera
    esp_err_t err = esp_camera_init(&config);
    if (err != ESP_OK) {
        Serial.printf("Camera init failed with error 0x%x", err);
        return;
    }
    delay(500); // 相机初始化后缓冲

    Serial.println("Starting SD Card");
    // 尝试1线模式初始化，若失败可改为false用4线模式
    if(!SD_MMC.begin("/sdcard", true)){
        Serial.println("SD Card Mount Failed");
        uint8_t cardType = SD_MMC.cardType();
        Serial.print("Detected Card Type: ");
        switch(cardType){
            case CARD_NONE: Serial.println("No SD card attached"); break;
            case CARD_MMC: Serial.println("MMC card detected"); break;
            case CARD_SD: Serial.println("Standard SD card detected"); break;
            case CARD_SDHC: Serial.println("SDHC card detected"); break;
            default: Serial.println("Unknown card type");
        }
        return;
    }

    uint8_t cardType = SD_MMC.cardType();
    if(cardType == CARD_NONE){
        Serial.println("No SD Card attached");
        return;
    }

    camera_fb_t * fb = NULL;
    // Take Picture with Camera
    fb = esp_camera_fb_get();
    if(!fb) {
        Serial.println("Camera capture failed");
        return;
    }

    // initialize EEPROM with predefined size
    EEPROM.begin(EEPROM_SIZE);
    pictureNumber = EEPROM.read(0) + 1;

    // Path where new picture will be saved in SD Card
    String path = "/picture" + String(pictureNumber) +".jpg";
    fs::FS &fs = SD_MMC;
    Serial.printf("Picture file name: %s\n", path.c_str());

    File file = fs.open(path.c_str(), FILE_WRITE);
    if(!file){
        Serial.println("Failed to open file in writing mode");
    } else {
        file.write(fb->buf, fb->len); // payload (image), payload length
        Serial.printf("Saved file to path: %s\n", path.c_str());
        EEPROM.write(0, pictureNumber);
        EEPROM.commit();
    }
    file.close();
    esp_camera_fb_return(fb);

    // Turns off the ESP32-CAM white on-board LED (flash) connected to GPIO 4
    pinMode(4, INPUT);
    digitalWrite(4, LOW);
    rtc_gpio_hold_dis(GPIO_NUM_4);

    delay(2000);
    Serial.println("Going to sleep now");
    delay(2000);
    esp_deep_sleep_start();
    Serial.println("This will never be printed");
}

void loop() {
}

按照上面的步骤逐一排查，应该能解决SD卡挂载失败的问题。

内容的提问来源于stack exchange，提问作者Rey