Writing data to SD card in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the SD card.

Arduino

#include <SD.h>
const int chipSelect = 4;

void setup() {
  Serial.begin(9600);
  if (!SD.[1](chipSelect)) {
    Serial.println("Initialization failed!");
    return;
  }
  Serial.println("Initialization done.");
}

void loop() {}

Drag options to blanks, or click blank then click option'

Abegin

Binit

Cstart

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Using SD.init() instead of SD.begin()

Forgetting to pass the chip select pin

Calling the function outside setup()

The SD library uses SD.begin() to initialize the card with the chip select pin.

2fill in blank

medium

Complete the code to open a file named "data.txt" for writing.

Arduino

File dataFile = SD.[1]("data.txt", FILE_WRITE);

Drag options to blanks, or click blank then click option'

Awrite

Bcreate

Cread

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Using SD.read() which is for reading files

Using SD.write() which is for writing data to files, not opening

Using SD.create() which does not exist

The SD library uses SD.open() to open files. FILE_WRITE mode opens the file for writing.

3fill in blank

hard

Fix the error in the code to write "Hello" to the file.

Arduino

if (dataFile) {
  dataFile.[1]("Hello");
  dataFile.close();
} else {
  Serial.println("Error opening file");
}

Drag options to blanks, or click blank then click option'

Aopen

Bprint

Cwrite

Dprintln

Attempts:

3 left

💡 Hint

Common Mistakes

Using write() which writes bytes, not strings

Using println() which adds a newline

Using open() which is for opening files

The File object uses print() to write text data to the file.

4fill in blank

hard

Fill both blanks to write a number and close the file properly.

Arduino

File dataFile = SD.open("numbers.txt", FILE_WRITE);
if (dataFile) {
  dataFile.[1](123);
  dataFile.[2]();
} else {
  Serial.println("Failed to open file");
}

Drag options to blanks, or click blank then click option'

Aprint

Bclose

Cwrite

Dflush

Attempts:

3 left

💡 Hint

Common Mistakes

Using print() for numbers without conversion

Forgetting to close the file

Using flush() instead of close()

Use write() to write the number as bytes and close() to close the file.

5fill in blank

hard

Fill all three blanks to write multiple lines and close the file.

Arduino

File dataFile = SD.open("log.txt", FILE_WRITE);
if (dataFile) {
  dataFile.[1]("Line 1");
  dataFile.[2]("Line 2");
  dataFile.[3]();
} else {
  Serial.println("Cannot open file");
}

Drag options to blanks, or click blank then click option'

Aprint

Bprintln

Cclose

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using print() without newlines

Using write() which writes bytes

Forgetting to close the file

Use println() to write lines with newlines and close() to close the file.

Practice

1. What is the correct way to open a file for writing data on an SD card in Arduino?

easy

A. Use SD.close(filename)

B. Use SD.read(filename)

C. Use SD.open(filename, FILE_WRITE)

D. Use SD.format()

Solution

1. Step 1: Understand file opening modes

   To write data, the file must be opened in write mode, which is done using FILE_WRITE.

2. Step 2: Identify the correct function call

   The function SD.open(filename, FILE_WRITE) opens the file for writing. Other options do not open files for writing.

3. Final Answer:

   Use SD.open(filename, FILE_WRITE) -> Option C

4. Quick Check:

   Open file for writing = SD.open(filename, FILE_WRITE) [OK]

Hint: Use FILE_WRITE with SD.open() to write files [OK]

Common Mistakes:

• Using SD.read() to open file for writing
• Forgetting FILE_WRITE mode
• Trying to write without opening file

2. Which of the following is the correct syntax to write the string "Hello" followed by a newline to a file named "log.txt" on the SD card?

easy

A. file.write("Hello");

B. file.println("Hello");

C. file.print("Hello");

D. file.read("Hello");

Solution

1. Step 1: Identify the write functions

   To write text with a newline, file.println() is used. file.print() writes without newline, file.write() writes bytes.

2. Step 2: Choose the function that writes string with newline

   file.println("Hello") writes "Hello" followed by a newline, which is common for logging.

3. Final Answer:

   file.println("Hello"); -> Option B

4. Quick Check:

   Write string with newline = file.println() [OK]

Hint: Use file.println() to write string with newline [OK]

Common Mistakes:

• Using file.read() to write data
• Confusing file.write() with file.print()
• Forgetting to add newline if needed

3. What will be the output on the SD card file after running this code snippet?

File file = SD.open("data.txt", FILE_WRITE);
if (file) {
  file.println("Line 1");
  file.println("Line 2");
  file.close();
}

medium

A. No output because file.close() is missing

B. Line 1\nLine 2\n

C. Line 1Line 2

D. Line 1
Line 2

Solution

1. Step 1: Understand file writing with println()

   Each call to file.println() writes the string plus a newline character.

2. Step 2: Check file closing

   The file is closed properly with file.close(), so data is saved.

3. Final Answer:

   Line 1 Line 2 -> Option D

4. Quick Check:

   file.println() adds newline, file.close() saves data [OK]

Hint: file.println() adds newline; always close file to save [OK]

Common Mistakes:

• Thinking file.close() is missing
• Assuming println() does not add newline
• Confusing escape sequences with actual newlines

4. Identify the error in this Arduino code snippet for writing to an SD card:

if (!SD.begin()) {
  Serial.println("Initialization failed!");
}
File file = SD.open("test.txt", FILE_WRITE);
file.println("Data");
// Missing file.close()

medium

A. File is not closed after writing, risking data loss

B. Serial.println() cannot be used with SD cards

C. FILE_WRITE is not a valid mode for SD.open()

D. SD.begin() should be called after opening the file

Solution

1. Step 1: Check SD initialization

   SD.begin() is correctly called before opening the file.

2. Step 2: Identify missing file.close()

   The file is opened and written to, but not closed, which can cause data not to be saved properly.

3. Final Answer:

   File is not closed after writing, risking data loss -> Option A

4. Quick Check:

   Always close file after writing to save data [OK]

Hint: Always close files after writing to save data [OK]

Common Mistakes:

• Forgetting to close the file
• Calling SD.begin() after opening file
• Misunderstanding FILE_WRITE mode

5. You want to write multiple sensor readings to a file on the SD card, but only if the SD card initializes successfully. Which of the following code snippets correctly implements this logic?

hard

A. if (SD.begin()) {
File dataFile = SD.open("readings.txt", FILE_WRITE);
if (dataFile) {
dataFile.println(sensorValue);
dataFile.close();
}
} else {
Serial.println("SD init failed");
}

B. File dataFile = SD.open("readings.txt", FILE_WRITE);
if (dataFile) {
if (SD.begin()) {
dataFile.println(sensorValue);
}
dataFile.close();
}

C. if (!SD.begin()) {
Serial.println("SD init failed");
} else {
File dataFile = SD.open("readings.txt");
dataFile.println(sensorValue);
dataFile.close();
}

D. SD.begin();
File dataFile = SD.open("readings.txt", FILE_WRITE);
dataFile.println(sensorValue);
dataFile.close();

Solution

1. Step 1: Check SD initialization before file operations

   The correct code first calls and checks SD.begin() before attempting to open the file.

2. Step 2: Proper file open, write, close, and error handling

   Open with SD.open("readings.txt", FILE_WRITE), verify with if (dataFile), write dataFile.println(sensorValue), dataFile.close(), and print error if init fails.

3. Final Answer:

   if (SD.begin()) { File dataFile = SD.open("readings.txt", FILE_WRITE); if (dataFile) { dataFile.println(sensorValue); dataFile.close(); } } else { Serial.println("SD init failed"); } -> Option A

4. Quick Check:

   Check SD.begin() first, then open, write, close file [OK]

Hint: Always check SD.begin() before file operations [OK]

Common Mistakes:

• Opening file before SD.begin()
• Not closing file after writing
• Ignoring SD initialization failure