Short answer

ESP32 SD card mount fails. What should I check on the board?

  • Use 3.3 V logic cards and level shifting if the slot sees 5 V. Many modules die on the first mount attempt.
  • SPI vs SDMMC pin maps differ. Wrong CMD/CLK/DAT0 is the usual schematic miss.
  • Long wires and missing pull-ups cause intermittent mounts. Keep the slot close to the MCU.
  • Format and card class matter less than power and pins. Fix the rail and CS before chasing filesystem flags.

中文

短答

ESP32 挂不上 SD 卡，板上先查什么？

  • 卡和电平按 3.3 V 逻辑来；卡槽若碰到 5 V 要电平转换。很多模组第一次 mount 就挂。
  • SPI 与 SDMMC 脚定义不同。CMD/CLK/DAT0 画错最常见。
  • 线太长、缺上拉会导致间歇失败。卡槽尽量靠近 MCU。
  • 先电源和片选，再纠结文件系统参数。格式和速度等级往往不是第一因。