EEPROM for storing settings in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this EEPROM read code?

Consider the following Arduino code that writes and then reads a byte from EEPROM address 10. What will be printed on the Serial Monitor?

Arduino

  #include <EEPROM.h>

  void setup() {
    Serial.begin(9600);
    EEPROM.write(10, 42);
    byte val = EEPROM.read(10);
    Serial.println(val);
  }

  void loop() {}

A Compilation error

B 42

C 255

D 0

💡 Hint

EEPROM.write stores a byte at the given address, and EEPROM.read retrieves it.

The code writes the value 42 to EEPROM address 10, then reads it back and prints it. So the output is 42.

🧠 Conceptual

intermediate

How many bytes does EEPROM store in a typical Arduino Uno?

What is the size of the EEPROM memory available on a standard Arduino Uno board?

A 512 bytes

B 2048 bytes

C 1024 bytes

D 256 bytes

💡 Hint

Check the Arduino Uno specifications for EEPROM size.

The Arduino Uno has 1024 bytes of EEPROM memory available for storing data.

🔧 Debug

advanced

Why does this EEPROM update code not update the stored value?

The following code is intended to update the EEPROM value at address 5 to 100, but the stored value never changes. What is the problem?

Arduino

  #include <EEPROM.h>

  void setup() {
    Serial.begin(9600);
    byte current = EEPROM.read(5);
    if (current != 100) {
      EEPROM.update(5, 100);
    }
    Serial.println(EEPROM.read(5));
  }

  void loop() {}

A EEPROM.write only works once after reset; subsequent writes are ignored.

B The code is correct; the value should update to 100.

C EEPROM.write is asynchronous and needs EEPROM.commit() to save changes.

D EEPROM.update does not update if the value is the same, so no change occurs.

💡 Hint

EEPROM.update only writes if the new value differs from the stored one to reduce wear.

EEPROM.update checks if the new value differs before writing to avoid unnecessary wear. If the value is already 100, it won't write again.

📝 Syntax

advanced

What error does this EEPROM code produce?

What error will this Arduino code produce when compiled?

Arduino

  #include <EEPROM.h>

  void setup() {
    EEPROM.write(1024, 123);
  }

  void loop() {}

A Runtime error: Address out of range

B No error, writes 123 at address 1024

C Compilation error: invalid address

D Undefined behavior, may overwrite memory

💡 Hint

EEPROM size limits valid addresses.

The Arduino Uno EEPROM size is 1024 bytes, so address 1024 is out of range. This causes a runtime error or unexpected behavior.

🚀 Application

expert

How to store and retrieve a struct in EEPROM?

You want to save a struct with multiple settings to EEPROM and read it back. Which code snippet correctly stores and retrieves the struct?

Arduino

  struct Settings {
    int volume;
    bool enabled;
  };

  Settings settings = {10, true};

  void saveSettings() {
    // ???
  }

  void loadSettings() {
    // ???
  }

A Use EEPROM.put(0, settings) to save and EEPROM.get(0, settings) to load.

B Use EEPROM.write(0, settings) to save and EEPROM.read(0) to load.

C Convert struct to string and store with EEPROM.writeString(), then parse on load.

D Use EEPROM.update(0, settings) to save and EEPROM.read(0) to load.

💡 Hint

EEPROM.put and EEPROM.get handle complex data types like structs.

EEPROM.put writes the entire struct to EEPROM starting at the given address. EEPROM.get reads it back. EEPROM.write and EEPROM.read only handle single bytes.

Practice

1. What is the main purpose of using EEPROM in an Arduino program?

easy

A. To increase the speed of the program

B. To store data permanently even when the power is off

C. To connect to the internet

D. To control the brightness of an LED

Solution

1. Step 1: Understand EEPROM functionality

   EEPROM memory keeps data saved even if the Arduino loses power.

2. Step 2: Compare options with EEPROM purpose

   Only To store data permanently even when the power is off describes permanent data storage, which matches EEPROM use.

3. Final Answer:

   To store data permanently even when the power is off -> Option B

4. Quick Check:

   EEPROM stores permanent data = A [OK]

Hint: EEPROM saves data without power loss [OK]

Common Mistakes:

• Confusing EEPROM with RAM (temporary memory)
• Thinking EEPROM speeds up the program
• Mixing EEPROM with internet or LED control

2. Which of the following is the correct syntax to write the value 42 to EEPROM address 10?

easy

A. EEPROM.save(42, 10);

B. EEPROM.read(10, 42);

C. EEPROM.write(10, 42);

D. EEPROM.store(10, 42);

Solution

1. Step 1: Recall EEPROM write syntax

   The correct function to save data is EEPROM.write(address, value);.

2. Step 2: Match syntax with options

   Only EEPROM.write(10, 42); uses EEPROM.write with correct parameter order.

3. Final Answer:

   EEPROM.write(10, 42); -> Option C

4. Quick Check:

   Write uses EEPROM.write(address, value) = D [OK]

Hint: Use EEPROM.write(address, value) to save data [OK]

Common Mistakes:

• Using EEPROM.read() to write data
• Using non-existent functions like EEPROM.store()
• Swapping address and value parameters

3. What will be the output of this Arduino code snippet?

EEPROM.write(5, 100);
int val = EEPROM.read(5);
Serial.println(val);

medium

A. Error

B. 0

C. 5

D. 100

Solution

1. Step 1: Understand EEPROM write and read

   The code writes 100 to address 5, then reads from address 5.

2. Step 2: Predict Serial output

   Reading address 5 returns 100, so Serial.println prints 100.

3. Final Answer:

   100 -> Option D

4. Quick Check:

   Write 100, read 100 = A [OK]

Hint: Read returns last written value at address [OK]

Common Mistakes:

• Expecting read to return address instead of value
• Confusing EEPROM.read() with EEPROM.write()
• Assuming default value 0 without write

4. Identify the error in this code that tries to save a setting to EEPROM:

int setting = 25;
EEPROM.read(0, setting);

medium

A. Using EEPROM.read() instead of EEPROM.write() to save data

B. Wrong address used, should be 1 instead of 0

C. Missing semicolon after variable declaration

D. EEPROM.read() requires three parameters

Solution

1. Step 1: Check function purpose

   EEPROM.read() reads data; EEPROM.write() saves data.

2. Step 2: Identify misuse in code

   The code uses EEPROM.read() with two parameters, which is incorrect for saving.

3. Final Answer:

   Using EEPROM.read() instead of EEPROM.write() to save data -> Option A

4. Quick Check:

   Write needs EEPROM.write(), not EEPROM.read() = C [OK]

Hint: Use EEPROM.write() to save, EEPROM.read() to get data [OK]

Common Mistakes:

• Confusing read and write functions
• Passing wrong number of parameters
• Assuming EEPROM.read() can save data

5. You want to save a user volume setting (0-255) in EEPROM address 20 and read it back on startup. Which code snippet correctly does this?

hard

A. EEPROM.write(20, volume);
int vol = EEPROM.read(20);

B. EEPROM.read(20, volume);
int vol = EEPROM.write(20);

C. EEPROM.save(20, volume);
int vol = EEPROM.load(20);

D. EEPROM.write(volume, 20);
int vol = EEPROM.read(volume);

Solution

1. Step 1: Save volume to EEPROM address 20

   Use EEPROM.write(20, volume); to store the value.

2. Step 2: Read volume back from address 20

   Use EEPROM.read(20); to get the saved value.

3. Final Answer:

   EEPROM.write(20, volume); int vol = EEPROM.read(20); -> Option A

4. Quick Check:

   Write then read from same address = B [OK]

Hint: Write then read from same EEPROM address [OK]

Common Mistakes:

• Swapping address and value parameters
• Using non-existent EEPROM.save() or EEPROM.load()
• Reading before writing data