SD Card Module suddenly stopped working on Arduino Uno

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1

Hi everyone,

I'm working on a project that uses an Arduino Uno with:

  • A flow meter (YF-S201)
  • An I2C LCD (20x4)
  • An RTC DS3231
  • An SD card module (with AMS1117 voltage regulator)

Everything was working perfectly yesterday — I was logging data to the SD card multiple times. But today, the SD card module refuses to initialize. I get the usual "SD card initialization failed!" message, even with the same code that worked before.

What I've tried so far:

  • Changed the SD card (2GB and 8GB, both FAT32 formatted)
  • Switched CS pin from D10 to D4 (and updated code)
  • Tried two different SD card modules: one 3.3V and one with 5V AMS1117 regulator
  • Used minimal test sketch with SD.begin() and file write
  • Checked and swapped jumper wires
  • Tested with a different Arduino Uno
  • Set pinMode(CS, OUTPUT) before SD.begin()

Wiring (current setup with Arduino Uno):

:small_blue_diamond: Flow Meter YF-S201

  • VCC (Red) → 5V
  • GND (Black) → GND
  • Signal (Yellow) → D2 (interrupt)

:small_blue_diamond: I2C LCD (20x4)

  • VCC → 5V
  • GND → GND
  • SDA → A4
  • SCL → A5

:small_blue_diamond: RTC DS3231

  • VCC → 5V
  • GND → GND
  • SDA → A4
  • SCL → A5

:small_blue_diamond: SD Card Module (AMS1117 version, 5V)

  • VCC → 5V
  • GND → GND
  • CS → D10 (or D4 when testing)
  • MOSI → D11
  • MISO → D12
  • SCK → D13

Here’s the test sketch I’m using:

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

#define SD_CS 10  // or 4 when testing alternative CS

void setup() {
  Serial.begin(9600);
  pinMode(SD_CS, OUTPUT);
  Serial.println("Initializing SD card...");

  if (!SD.begin(SD_CS)) {
    Serial.println("SD card initialization failed!");
    return;
  }

  Serial.println("SD card initialized.");
  File testFile = SD.open("test.txt", FILE_WRITE);
  if (testFile) {
    testFile.println("SD card test successful.");
    testFile.close();
    Serial.println("Write successful.");
  } else {
    Serial.println("Failed to open file for writing.");
  }
}

void loop() {}

It was working fine yesterday, now nothing I try makes it work. Is it possible that the SD card module is damaged somehow? Or could it be SPI interference?

2

Test with one or two of the example sketches that come with the SD library.

If they fail, disconnect everything except the SD card adapter and test again.

3

You cannot connect I/O pins on a 5V Arduino to a 3.3V SD card without using a logic level shifter, as that can damage both the Uno and the SD card module.

Post a link to the product page for SD module, so forum members can determine whether it has a logic level shifter built in.

Tried two different SD card modules: one 3.3V

That may have damaged the Uno.