SPI with SD card module in Arduino - Step-by-Step Execution

Concept Flow - SPI with SD card module

Start SPI Communication

↓

Initialize SD Card

↓

Check if SD Card is present

Yes | No↓

Open/Create File

↓

Write/Read Data

↓

Close File

↓

End SPI Communication

This flow shows how Arduino uses SPI to talk to the SD card: start SPI, initialize SD, check card, read/write files, then close.

Execution Sample

Arduino

SPI.begin();
if (!SD.begin(10)) {
  Serial.println("SD fail");
  return;
}
File dataFile = SD.open("test.txt", FILE_WRITE);
if (dataFile) dataFile.println("Hello SPI");
dataFile.close();

This code starts SPI, initializes the SD card on pin 10, writes "Hello SPI" to test.txt, then closes the file.

Execution Table

Step	Action	Evaluation/Condition	Result/Output
1	SPI.begin()	Start SPI bus	SPI bus ready
2	SD.begin(10)	Check SD card on CS pin 10	SD card detected (True)
3	SD.open("test.txt", FILE_WRITE)	Open file for writing	File opened successfully
4	dataFile.println("Hello SPI")	Write string to file	String written to file
5	dataFile.close()	Close the file	File closed
6	End	All steps done	Program ends successfully

💡 Program stops after writing and closing the file successfully

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
SPI bus	Not started	Started	Started	Started	Started
SD card status	Unknown	Detected (True)	Detected	Detected	Detected
dataFile	None	None	File object	File object	Closed file

Key Moments - 3 Insights

Why does the program stop if SD.begin(10) returns false?

Because SD.begin(10) checks if the SD card is connected and ready. If it returns false (see step 2 in execution_table), the program prints "SD fail" and stops to avoid errors.

What happens if SD.open() fails to open the file?

If SD.open() fails, the file object is invalid and writing will not happen. The program should check if the file opened successfully before writing (step 3 in execution_table).

Why do we call dataFile.close() after writing?

Closing the file (step 5) saves the data properly and frees resources. Without closing, data might not be saved correctly.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of SD.begin(10) at step 2?

A SPI bus not started

B SD card not detected (False)

C SD card detected (True)

D File opened

💡 Hint

Check the 'Result/Output' column at step 2 in execution_table

At which step does the program write data to the SD card?

A Step 4

B Step 3

C Step 1

D Step 5

💡 Hint

Look for the action 'dataFile.println' in execution_table

If SD.begin(10) returned false, what would happen to the variable 'dataFile'?

A It would be a valid file object

B It would remain None

C It would be closed

D It would contain the string 'Hello SPI'

💡 Hint

Refer to variable_tracker and key_moments about SD.begin failure

Concept Snapshot

SPI with SD card module in Arduino:
- Use SPI.begin() to start SPI bus
- Use SD.begin(CS_pin) to initialize SD card
- Check SD.begin result before proceeding
- Open files with SD.open(filename, mode)
- Write/read data, then close file with file.close()
- Always check for errors to avoid crashes

Full Transcript

This visual execution shows how Arduino communicates with an SD card using SPI. First, SPI.begin() starts the SPI bus. Then SD.begin(10) initializes the SD card on chip select pin 10 and checks if the card is present. If the card is detected, the program opens a file named test.txt for writing. It writes the string "Hello SPI" to the file, then closes the file to save data properly. If the SD card is not detected, the program prints an error and stops. Variables like SPI bus status, SD card status, and file object change step by step as shown. Key moments include why the program stops if SD card is missing, why to check file open success, and why closing the file is important. The quiz questions help reinforce understanding of these steps.