Time and storage

microSD card with ESP32

A microSD card gives a display board real storage for logs, images or audio. Many display boards already have a slot, so check the board page first. Its pins are often wired through the board and shared with the display or other parts, so the example pins below are only a starting point.

A separate reader connects over SPI at 3.3 V. Look for a module with pull-ups on the data lines, and avoid ones without them. Modules with a regulator accept 5 V on VCC, but feeding 5 V to a direct adapter can damage the card, so read the module. Sources agree that FAT32 on cards up to 32 GB is the reliable choice. Larger cards often ship as exFAT, which the ESP32 does not read by default.

Writes are slow compared with RAM, and a long write can stall a display task. Log small batches, close or flush the file, and keep heavy file work away from the drawing loop. If power is cut while writing, the file can be damaged, so do not rely on the card as the only copy of important data.

#include <SPI.h>
#include <SD.h>

const int SCK_PIN = 12, MISO_PIN = 13, MOSI_PIN = 11, CS_PIN = 10;

void setup() {
  Serial.begin(115200);
  SPI.begin(SCK_PIN, MISO_PIN, MOSI_PIN, CS_PIN);
  if (!SD.begin(CS_PIN)) {
    Serial.println("Card not found: check wiring and FAT32");
    return;
  }
  File f = SD.open("/log.txt", FILE_APPEND);
  if (f) {
    f.printf("boot at %lu ms\n", millis());
    f.close();
  }
  Serial.printf("Card size: %llu MB\n", SD.cardSize() / (1024 * 1024));
}

void loop() {}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.