SPI with SD card module in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does SPI stand for and why is it used with an SD card module?

SPI stands for Serial Peripheral Interface. It is used with an SD card module to allow fast and simple communication between the Arduino and the SD card using a few wires.

beginner

Name the four main SPI pins used to connect an Arduino to an SD card module.

The four main SPI pins are: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCK (Serial Clock), and CS (Chip Select).

beginner

What is the role of the CS (Chip Select) pin in SPI communication with an SD card?

The CS pin tells the SD card when it should listen to the Arduino. When CS is LOW, the SD card is active and communicates; when HIGH, it ignores signals.

beginner

In Arduino code, which library is commonly used to work with SD cards over SPI?

The SD library is commonly used to read and write files on SD cards using SPI communication.

beginner

Why do you need to call SD.begin(CS_pin) in your Arduino sketch?

Calling SD.begin(CS_pin) initializes the SD card and SPI communication. It sets up the card to be ready for reading or writing files.

Which SPI pin sends data from the Arduino to the SD card?

A SCK

B MISO

C MOSI

D CS

MOSI stands for Master Out Slave In, so it sends data from the Arduino (master) to the SD card (slave).

What happens when the CS pin is set HIGH during SPI communication?

A Arduino resets

B SD card listens to Arduino

C SPI clock stops

D SD card ignores communication

When CS is HIGH, the SD card ignores SPI communication and does not respond.

Which Arduino library helps you work with SD cards over SPI?

A SD

B SPI

C Wire

D EEPROM

The SD library provides easy functions to read and write files on SD cards using SPI.

What is the purpose of the SCK pin in SPI?

A Provide clock signal

B Send data to Arduino

C Select the device

D Send data from Arduino

SCK provides the clock signal that synchronizes data transfer between Arduino and SD card.

Before reading or writing files, what must you do in your Arduino sketch?

A Set MOSI HIGH

B Call SD.begin(CS_pin)

C Reset Arduino

D Call SPI.end()

Calling SD.begin(CS_pin) initializes the SD card and SPI communication.

Explain how SPI communication works between an Arduino and an SD card module.

Think about how the Arduino talks to the SD card using a few wires and a clock.

Describe the steps to initialize and write a file to an SD card using Arduino SPI.

Start from setting up the card to saving your data safely.

Practice

1. What is the main purpose of using SPI when working with an SD card module on Arduino?

easy

A. To enable fast communication between Arduino and the SD card

B. To power the SD card module

C. To store data permanently on the Arduino board

D. To convert analog signals to digital

Solution

1. Step 1: Understand SPI role

   SPI is a communication protocol that allows fast data transfer between devices.

2. Step 2: Connect Arduino and SD card

   SPI connects Arduino to the SD card module to send and receive data quickly.

3. Final Answer:

   To enable fast communication between Arduino and the SD card -> Option A

4. Quick Check:

   SPI = fast communication [OK]

Hint: SPI is for fast data transfer, not power or storage [OK]

Common Mistakes:

• Confusing SPI with power supply
• Thinking SPI stores data on Arduino
• Mixing SPI with analog-to-digital conversion

2. Which of the following is the correct way to initialize the SD card module using SPI on Arduino if the chip select pin is 10?

easy

A. SD.start(10);

B. SD.begin(10);

C. SD.open(10);

D. SD.init(10);

Solution

1. Step 1: Recall SD library initialization

   The SD library uses SD.begin(chipSelectPin) to start communication.

2. Step 2: Match correct function and parameter

   SD.begin(10) correctly initializes the SD card with pin 10 as chip select.

3. Final Answer:

   SD.begin(10); -> Option B

4. Quick Check:

   SD.begin(pin) initializes SD card [OK]

Hint: Use SD.begin() with chip select pin to start SD card [OK]

Common Mistakes:

• Using SD.start() which does not exist
• Confusing SD.open() with initialization
• Using SD.init() which is not a valid method

3. What will be the output on the Serial Monitor after running this Arduino code snippet?

if (SD.begin(10)) {
  Serial.println("SD card initialized.");
} else {
  Serial.println("Initialization failed.");
}

medium

A. SD card initialized.

B. Initialization failed.

C. Compilation error

D. No output

Solution

1. Step 1: Understand SD.begin() return value

   SD.begin(10) returns true if the SD card initializes successfully.

2. Step 2: Check the if condition and output

   If true, it prints "SD card initialized." to Serial Monitor.

3. Final Answer:

   SD card initialized. -> Option A

4. Quick Check:

   SD.begin(10) true prints initialization message [OK]

Hint: SD.begin() returns true if SD card is ready [OK]

Common Mistakes:

• Assuming SD.begin() always fails
• Expecting no output without Serial.begin() (assumed present)
• Confusing SD.open() with SD.begin()

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

SD.begin(10);
File dataFile = SD.open("log.txt", FILE_WRITE);
if (dataFile) {
  dataFile.println("Hello World");
}
// Missing dataFile.close();

medium

A. SD.open() is used incorrectly

B. Missing SD.begin() before opening file

C. println() cannot be used with File

D. File is not closed after writing

Solution

1. Step 1: Check file handling steps

   After writing to a file, it must be closed to save data properly.

2. Step 2: Identify missing close()

   The code writes but does not call dataFile.close(), risking data loss.

3. Final Answer:

   File is not closed after writing -> Option D

4. Quick Check:

   Always close files after writing [OK]

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

Common Mistakes:

• Forgetting to call SD.begin() before open
• Thinking println() is invalid for File
• Ignoring file close causes data loss

5. You want to write multiple sensor readings to an SD card file named "data.txt" every 5 seconds. Which approach correctly uses SPI with the SD card module to do this efficiently?

hard

A. Call SD.begin(10) once in setup(), open the file, write readings, close file each time in loop()

B. Call SD.begin(10) once in setup(), open file once in setup(), write readings and close file each time in loop()

C. Call SD.begin(10) once in setup(), open and close the file each time in loop() before writing readings

D. Call SD.begin(10) inside loop(), open file once in setup(), write readings without closing file

Solution

1. Step 1: Understand SD.begin() usage

   SD.begin() should be called once in setup() to initialize the card.

2. Step 2: Manage file open/close in loop()

   Opening and closing the file each time in loop() ensures data is saved and file is not locked.

3. Step 3: Avoid keeping file open across loops

   Keeping file open without closing risks data loss or corruption if power fails.

4. Final Answer:

   Call SD.begin(10) once in setup(), open and close the file each time in loop() before writing readings -> Option C

5. Quick Check:

   Initialize once, open/close file each write [OK]

Hint: Init SD once; open and close file each write cycle [OK]

Common Mistakes:

• Calling SD.begin() repeatedly wastes time
• Leaving file open across loop iterations
• Opening file only once and never closing