EEPROM for storing settings in Arduino - Time & Space Complexity

Time Complexity: EEPROM for storing settings

O(n)

Understanding Time Complexity

When using EEPROM to save settings on an Arduino, it's important to know how the time to save or read data changes as the amount of data grows.

We want to understand how the program's running time changes when storing more settings.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

#include <EEPROM.h>

void saveSettings(int* settings, int size) {
  for (int i = 0; i < size; i++) {
    EEPROM.write(i, settings[i]);
  }
}
    

This code saves an array of settings into EEPROM memory, one byte at a time.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Writing each setting byte to EEPROM inside a for-loop.
• How many times: The loop runs once for each setting, so it repeats size times.

How Execution Grows With Input

As the number of settings increases, the time to save them grows in a straight line.

Input Size (n)	Approx. Operations
10	10 writes to EEPROM
100	100 writes to EEPROM
1000	1000 writes to EEPROM

Pattern observation: Doubling the number of settings doubles the time needed to save them.

Final Time Complexity

Time Complexity: O(n)

This means the time to save settings grows directly with the number of settings you want to store.

Common Mistake

[X] Wrong: "Writing one byte to EEPROM takes the same time no matter how many bytes I write overall."

[OK] Correct: Each byte write takes time, so writing more bytes adds up and takes longer overall.

Interview Connect

Understanding how saving data scales helps you design efficient programs that handle settings well, a useful skill in many embedded projects.

Self-Check

"What if we only write to EEPROM when a setting changes? How would the time complexity change?"

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