SPI with SD card module in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this SPI initialization code?

Consider the following Arduino code snippet initializing SPI for an SD card module. What will be printed on the Serial Monitor?

Arduino

void setup() {
  Serial.begin(9600);
  if (!SD.begin(10)) {
    Serial.println("Initialization failed!");
  } else {
    Serial.println("Initialization done.");
  }
}

void loop() {}

A Initialization done.

B Initialization failed!

C No output, program stuck.

D Compilation error.

💡 Hint

Check if the SD card module is connected correctly and the chip select pin matches.

If the SD card is not connected or the chip select pin is wrong, SD.begin() returns false, printing "Initialization failed!".

🧠 Conceptual

intermediate

Which SPI mode is typically used by SD card modules?

SPI communication has four modes (0 to 3) defined by clock polarity and phase. Which mode is standard for SD card modules?

A Mode 0 (CPOL=0, CPHA=0)

B Mode 1 (CPOL=0, CPHA=1)

C Mode 2 (CPOL=1, CPHA=0)

D Mode 3 (CPOL=1, CPHA=1)

💡 Hint

SD cards use SPI mode where clock idles low and data is sampled on the rising edge.

SD cards use SPI Mode 0, where clock polarity is 0 (idle low) and clock phase is 0 (data sampled on rising edge).

🔧 Debug

advanced

Why does this SD card write code fail to save data?

Examine the code below that attempts to write "Hello" to a file on the SD card. Why does it fail to save the data?

Arduino

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

File myFile;

void setup() {
  Serial.begin(9600);
  if (!SD.begin(10)) {
    Serial.println("SD init failed");
    return;
  }
  myFile = SD.open("test.txt", FILE_WRITE);
  if (myFile) {
    myFile.print("Hello");
    Serial.println("Write done");
    myFile.close();
  } else {
    Serial.println("Error opening file");
  }
}

void loop() {}

A The SPI library is missing initialization.

B The chip select pin 10 is incorrect for SD.begin().

C The file mode FILE_WRITE is invalid.

D The file is not closed after writing, so data is not saved.

💡 Hint

Think about what happens after writing to a file on SD cards.

Data is buffered and only saved when the file is closed. Missing myFile.close() causes data loss.

📝 Syntax

advanced

What error does this SPI transfer code produce?

Look at the code snippet below. What error will it cause when compiled?

Arduino

byte data = SPI.transfer();

A Runtime error: null pointer exception

B No error, returns 0 by default

C Compilation error: missing argument for SPI.transfer()

D Compilation error: SPI library not included

💡 Hint

Check the required parameters for SPI.transfer().

SPI.transfer() requires one byte argument to send. Calling it without arguments causes a compile error.

🚀 Application

expert

How many files are created by this SD card code?

Given the code below, how many files will be created on the SD card after running setup() once?

Arduino

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

void setup() {
  Serial.begin(9600);
  SD.begin(10);
  for (int i = 0; i < 3; i++) {
    String filename = "file" + String(i) + ".txt";
    File f = SD.open(filename.c_str(), FILE_WRITE);
    if (f) {
      f.println("Data " + String(i));
      f.close();
    }
  }
}

void loop() {}

A 3 files named file0.txt, file1.txt, file2.txt

B No files created due to missing SD card check

C 1 file named file2.txt only

D Infinite files created due to loop error

💡 Hint

Look at the loop and how filenames are generated.

The loop runs 3 times creating 3 different files with names file0.txt, file1.txt, and file2.txt.