EEPROM read and write in Arduino - Mini Project: Build & Apply

EEPROM read and write

📖 Scenario: You are working on an Arduino project that needs to save a small number permanently, even when the power is off. This is useful for storing settings or counters that should not reset every time the board restarts.

🎯 Goal: Learn how to write a number to the Arduino's EEPROM memory and then read it back to use in your program.

📋 What You'll Learn

Create a variable to hold the number to save

Create a variable for the EEPROM address

Write the number to EEPROM at the given address

Read the number back from EEPROM

Print the read number to the Serial Monitor

💡 Why This Matters

🌍 Real World

Saving settings or counters that must stay even when the Arduino is turned off, like user preferences or device calibration data.

💼 Career

Understanding EEPROM read/write is important for embedded systems programming and IoT device development where persistent storage is needed.

1

Create the number and EEPROM address variables

Create an int variable called numberToSave and set it to 123. Also create an int variable called eepromAddress and set it to 0.

Arduino

# Create 'numberToSave' and 'eepromAddress' variables
// Your code here

Hint

Use int numberToSave = 123; and int eepromAddress = 0; to create the variables.

2

Include EEPROM library and start Serial communication

Add #include <EEPROM.h> at the top. In setup(), start Serial communication at 9600 baud.

Arduino

#include 

int numberToSave = 123;
int eepromAddress = 0;

void setup() {
  Serial.begin(9600);
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Remember to include the EEPROM library and start Serial in setup().

3

Write the number to EEPROM and read it back

In setup(), write numberToSave to EEPROM at eepromAddress using EEPROM.write(). Then read the value back into an int variable called readNumber using EEPROM.read().

Arduino

#include 

int numberToSave = 123;
int eepromAddress = 0;

void setup() {
  Serial.begin(9600);
  // Write numberToSave to EEPROM
  // Read value back into readNumber
  // Your code here
}

void loop() {
}

Hint

Use EEPROM.write(address, value) to save and EEPROM.read(address) to read.

4

Print the read number to Serial Monitor

Add a Serial.println() statement in setup() to print the readNumber variable.

Arduino

#include 

int numberToSave = 123;
int eepromAddress = 0;

void setup() {
  Serial.begin(9600);
  EEPROM.write(eepromAddress, numberToSave);
  int readNumber = EEPROM.read(eepromAddress);
  // Print readNumber
  // Your code here
}

void loop() {
}

Hint

Use Serial.println(readNumber); to show the saved number.

Practice

1. What does EEPROM.write(address, value) do in Arduino?

easy

A. Stores a byte value at the specified EEPROM address

B. Reads a byte value from the specified EEPROM address

C. Deletes all data from EEPROM

D. Initializes the EEPROM memory

Solution

1. Step 1: Understand EEPROM.write function

   The function EEPROM.write(address, value) saves a byte value at the given address in EEPROM memory.

2. Step 2: Differentiate from EEPROM.read

   EEPROM.read(address) is used to read data, not write it.

3. Final Answer:

   Stores a byte value at the specified EEPROM address -> Option A

4. Quick Check:

   EEPROM.write saves data [OK]

Hint: Write saves data, read retrieves data from EEPROM [OK]

Common Mistakes:

• Confusing write with read function
• Thinking EEPROM.write clears memory
• Assuming EEPROM.write initializes EEPROM

2. Which of the following is the correct syntax to read a byte from EEPROM at address 10?

easy

A. EEPROM.get(10);

B. EEPROM.write(10);

C. EEPROM.readByte(10);

D. EEPROM.read(10);

Solution

1. Step 1: Identify correct EEPROM read syntax

   The correct function to read a byte from EEPROM is EEPROM.read(address).

2. Step 2: Check options for exact match

   Only EEPROM.read(10); matches the correct syntax.

3. Final Answer:

   EEPROM.read(10); -> Option D

4. Quick Check:

   EEPROM.read(address) reads byte [OK]

Hint: Use EEPROM.read(address) to get stored byte [OK]

Common Mistakes:

• Using EEPROM.write to read data
• Using non-existent EEPROM.readByte function
• Confusing EEPROM.get with EEPROM.read

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

EEPROM.write(5, 42);
byte val = EEPROM.read(5);
Serial.println(val);

medium

A. 0

B. 42

C. 5

D. Undefined behavior

Solution

1. Step 1: Write value 42 at EEPROM address 5

   The code stores the byte 42 at address 5 using EEPROM.write(5, 42);.

2. Step 2: Read the value back from address 5

   EEPROM.read(5) reads the stored value, which is 42.

3. Final Answer:

   42 -> Option B

4. Quick Check:

   Write 42, read 42 [OK]

Hint: Write then read same address returns stored value [OK]

Common Mistakes:

• Assuming EEPROM.read returns address instead of value
• Forgetting to write before reading
• Expecting default 0 without writing

4. Identify the error in this code snippet:

EEPROM.write(1024, 100);
byte val = EEPROM.read(1024);
Serial.println(val);

medium

A. Serial.println cannot print byte values

B. EEPROM.write requires two arguments

C. Address 1024 is out of EEPROM range

D. EEPROM.read cannot be assigned to byte

Solution

1. Step 1: Check EEPROM address range

   Typical Arduino EEPROM size is 1024 bytes, so address 1024 is out of range (valid addresses are 0-1023).

2. Step 2: Validate other code parts

   EEPROM.write has correct arguments, EEPROM.read returns byte, and Serial.println can print bytes.

3. Final Answer:

   Address 1024 is out of EEPROM range -> Option C

4. Quick Check:

   EEPROM address must be within 0-1023 [OK]

Hint: EEPROM addresses start at 0, max 1023 on typical boards [OK]

Common Mistakes:

• Using address equal to EEPROM size
• Assuming EEPROM size is larger than actual
• Misunderstanding Serial.println capabilities

5. You want to store a user's high score (an integer between 0 and 1000) in EEPROM. Which approach correctly saves and reads this value?

hard

A. Use EEPROM.put(address, highScore); and EEPROM.get(address, highScore);

B. Use EEPROM.write(address, highScore); and EEPROM.read(address);

C. Use EEPROM.write(address, highScore % 256); only

D. Use EEPROM.read(address); to save and EEPROM.write(address, highScore); to read

Solution

1. Step 1: Understand data size and EEPROM functions

   High score is an integer (2 bytes), so EEPROM.write (1 byte) is insufficient to store full value.

2. Step 2: Use EEPROM.put and EEPROM.get for multi-byte data

   EEPROM.put(address, highScore); saves the entire integer, and EEPROM.get(address, highScore); reads it back correctly.

3. Final Answer:

   Use EEPROM.put(address, highScore); and EEPROM.get(address, highScore); -> Option A

4. Quick Check:

   Use put/get for multi-byte data [OK]

Hint: Use EEPROM.put/get for integers, write/read for bytes [OK]

Common Mistakes:

• Using EEPROM.write for multi-byte integers
• Not reading back with EEPROM.get
• Mixing read and write roles