MicroSD Card Module — SPI SD Card Breakout

Overview

The MicroSD Card Module is an SPI-based breakout board designed to interface standard MicroSD (SDSC) and MicroSDHC memory cards with 5 V or 3.3 V microcontrollers. Because native SD cards operate exclusively at 3.3 V logic and draw up to 200 mA during burst writes, this module includes an onboard 3.3 V low-dropout (LDO) linear regulator (e.g. AMS1117-3.3) and a quad buffer level shifter IC (such as the 74LVC125A or 74HC4050).

It is standard equipment in DIY datalogging projects, weather stations, flight recorders, and audio playback systems built on Arduino, ESP32, and Raspberry Pi platforms.

Quick reference


Operating voltage (`VCC`)	4.5 V to 5.5 V (or 3.3 V direct)
Logic level	3.3 V and 5 V tolerant (onboard level shifter)
Interface	SPI Mode 0 ( $CPOL=0, CPHA=0$ )
Supported card types	MicroSD ( $\le 2\text{ GB}$ ), MicroSDHC ( $\le 32\text{ GB}$ )
File system format	FAT16 / FAT32
Peak current draw	~100 mA to 200 mA during write operations

Pinout

The module exposes a standard 6-pin 0.1" (2.54 mm) right-angle or straight header:

Pin	Name	Type	Description
1	`GND`	Power	Ground (0 V)
2	`VCC`	Power	Supply input (+4.5 V to +5.5 V DC)
3	`MISO`	Output	Master In Slave Out — SPI data line from card to MCU
4	`MOSI`	Input	Master Out Slave In — SPI data line from MCU to card
5	`SCK`	Input	Serial Clock — SPI clock signal driven by MCU
6	`CS`	Input	Chip Select — Active-Low SPI slave select signal

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{CC}$	4.5	5.0	5.5	V	Powered via onboard regulator
Logic Input High	$V_{IH}$	2.0	3.3 / 5.0	5.5	V	`MOSI`, `SCK`, `CS` pins
Logic Input Low	$V_{IL}$	-0.5	0	0.8	V	`MOSI`, `SCK`, `CS` pins
Operating Current (Idle)	$I_{idle}$	—	0.2	2.0	mA	Standby mode
Operating Current (Write)	$I_{write}$	—	80	200	mA	Peak burst write current
SPI Clock Speed	$f_{SCK}$	—	4	25	MHz	Microcontroller dependent
Operating Temperature	$T_{opr}$	-20	—	70	°C	Ambient temperature

Communication & protocol

The module communicates via standard 4-wire SPI (Mode 0: active-high clock, data sampled on leading rising edge).

Card Initialization: The host MCU sends 80+ clock pulses on SCK with CS held high to force the SD card into SPI mode, followed by software reset command CMD0.
SPI Voltage Shifting: Incoming 5 V logic signals from the MCU (MOSI, SCK, CS) pass through the onboard 74LVC125 level shifter down to 3.3 V. The MISO output line drives 3.3 V logic, which is correctly recognized as a High state by 5 V TTL microcontrollers (Arduino Uno V_IH_min = 3.0 V).

Wiring

Module Pin	Arduino Uno	ESP32	Notes
`VCC`	5V	5V / 3.3V	Connect to 5 V rail for onboard regulator
`GND`	GND	GND	Shared system ground
`MISO`	D12	GPIO 19	Hardware SPI MISO pin
`MOSI`	D11	GPIO 23	Hardware SPI MOSI pin
`SCK`	D13	GPIO 18	Hardware SPI Clock pin
`CS`	D4 (or D10)	GPIO 5	Configurable Chip Select pin

Warning

Cheap resistor-divider clones hazard:

Some low-cost clone boards substitute the level-shifter IC with cheap passive resistor dividers ( $1\text{ k}\Omega / 2.2\text{ k}\Omega$ ). Resistor dividers distort SPI clock edges at frequencies above 4 MHz, causing random file corruption and card initialization failures (SD initialization failed).
Ensure your module uses an active IC buffer (74LVC125 / 74HC4050).

Example

cpp

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

const int chipSelect = 4;

void setup() {
  Serial.begin(9600);
  while (!Serial) { ; }

  Serial.print("Initializing SD card...");
  if (!SD.begin(chipSelect)) {
    Serial.println("Initialization failed!");
    return;
  }
  Serial.println("Initialization done.");

  File dataFile = SD.open("datalog.txt", FILE_WRITE);
  if (dataFile) {
    dataFile.println("Timestamp,Temperature_C");
    dataFile.println("1000,24.5");
    dataFile.close();
    Serial.println("Data written to datalog.txt");
  } else {
    Serial.println("Error opening datalog.txt");
  }
}

void loop() {
  // Main execution loop
}

Common mistakes

Formatting cards $>32\text{ GB}$ with exFAT: MicroSD card libraries on 8-bit MCUs (such as standard Arduino SD.h) only support FAT16 and FAT32 file systems. MicroSDXC cards ( $>32\text{ GB}$ ) formatted in exFAT fail to initialize.
Powering from weak 3.3 V rails: MicroSD cards draw up to 200 mA during write operations. Powering VCC from a low-current 3.3 V MCU pin (e.g. older FTDI adapters or Nano 3.3 V pins limited to 50 mA) causes brownout resets.
Leaving CS unhandled on shared SPI buses: When sharing the SPI bus with displays or sensors (e.g. Ethernet shields, OLEDs), ensure all CS pins have pull-up resistors so inactive devices release the MISO line.

Notes

MicroSD vs MicroSDHC: MicroSDHC cards ( $4\text{ GB}$ to $32\text{ GB}$ ) use block addressing (512-byte blocks) rather than byte addressing.

Interface	SPI
Package	Breakout Module (6-pin 0.1" header)