Writing data to SD card in Arduino - Mini Project: Build & Apply

Writing data to SD card

📖 Scenario: You are building a simple Arduino project that saves sensor readings to an SD card. This helps you keep a record of data over time, just like writing notes in a notebook.

🎯 Goal: Learn how to write text data to an SD card using Arduino. You will create a program that saves a message to a file on the SD card.

📋 What You'll Learn

Use the SD library to work with the SD card

Initialize the SD card in the setup() function

Create or open a file called data.txt on the SD card

Write a line of text to the file

Close the file after writing

💡 Why This Matters

🌍 Real World

Saving sensor data or logs to an SD card is common in projects like weather stations, data loggers, or portable devices that need to keep records without a computer.

💼 Career

Understanding how to write data to external storage like SD cards is useful for embedded systems developers, IoT engineers, and anyone working with hardware data collection.

1

Set up SD card and chip select pin

Write #include <SD.h> at the top and create an integer variable called chipSelect with the value 10.

Arduino

#include 
// Your code here

Need a hint?

Use #include <SD.h> to include the SD library. The chip select pin is usually 10 on many Arduino boards.

2

Initialize the SD card in setup()

Write a setup() function that starts serial communication at 9600 baud and uses SD.begin(chipSelect) to initialize the SD card. If initialization fails, print "Initialization failed!" to serial. If it succeeds, print "Initialization done.".

Arduino

#include 
int chipSelect = 10;

void setup() {
  // Your code here
}

void loop() {
}

Need a hint?

Use Serial.begin(9600); to start serial communication. Use if (!SD.begin(chipSelect)) to check if SD card initializes.

3

Open file and write data

Inside setup(), after successful initialization, create a File object called dataFile by opening "data.txt" in write mode using SD.open(). Then write the text "Hello, SD card!" to dataFile. Finally, close dataFile.

Arduino

#include 
int chipSelect = 10;

void setup() {
  Serial.begin(9600);
  if (!SD.begin(chipSelect)) {
    Serial.println("Initialization failed!");
    return;
  }
  Serial.println("Initialization done.");
  
  // Open file and write data here
}

void loop() {
}

Need a hint?

Use SD.open("data.txt", FILE_WRITE) to open the file for writing. Use println() to write a line. Always close the file after writing.

4

Print confirmation message

After writing and closing the file, print "Data written to data.txt" to the serial monitor.

Arduino

#include 
int chipSelect = 10;

void setup() {
  Serial.begin(9600);
  if (!SD.begin(chipSelect)) {
    Serial.println("Initialization failed!");
    return;
  }
  Serial.println("Initialization done.");
  
  File dataFile = SD.open("data.txt", FILE_WRITE);
  if (dataFile) {
    dataFile.println("Hello, SD card!");
    dataFile.close();
  } else {
    Serial.println("Error opening data.txt");
  }
  // Print confirmation message here
}

void loop() {
}

Need a hint?

Use Serial.println("Data written to data.txt"); to show the message.