EEPROM for storing settings in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is EEPROM in Arduino?

EEPROM is a small memory inside the Arduino that keeps data even when the power is off. It is used to save settings or information that should stay after the board is turned off.

beginner

How do you write a byte to EEPROM in Arduino?

Use the function EEPROM.write(address, value); where address is the memory location and value is the byte to store.

beginner

How do you read a byte from EEPROM in Arduino?

Use the function EEPROM.read(address); to get the byte stored at the given address.

intermediate

Why should you limit EEPROM writes?

EEPROM has a limited number of write cycles (usually 100,000). Writing too often can wear it out and cause data loss.

intermediate

How can you store multiple settings in EEPROM?

You can store each setting at a different address or use a structure and save it as bytes. Remember to read and write each setting carefully to avoid overwriting.

What happens to EEPROM data when Arduino is powered off?

A Data is erased automatically

B Data is copied to RAM

C Data becomes random

D Data is saved and remains intact

EEPROM keeps data even when power is off, unlike RAM which loses data.

Which function writes a byte to EEPROM in Arduino?

A EEPROM.read()

B EEPROM.write()

C EEPROM.store()

D EEPROM.save()

EEPROM.write(address, value) stores a byte at the specified address.

What is a common limit of EEPROM write cycles?

A 100,000 times

B 100 times

C 10,000 times

D 10 times

EEPROM typically supports about 100,000 write cycles before wearing out.

How do you read a byte from EEPROM?

A EEPROM.write(address)

B EEPROM.get(address)

C EEPROM.read(address)

D EEPROM.load(address)

EEPROM.read(address) returns the byte stored at the given address.

What is a good practice when storing multiple settings in EEPROM?

A Use different addresses or a structure for each setting

B Avoid reading settings

C Write settings every second

D Store all settings at the same address

Using different addresses or a structure prevents overwriting and keeps data organized.

Explain how EEPROM can be used to save and retrieve a user setting on Arduino.

Think about how to save a value and get it back even after turning off the Arduino.

Describe why it is important to limit the number of writes to EEPROM and how you might do that in a program.

Consider the lifespan of EEPROM and how to avoid unnecessary writes.

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