SD card module wiring in Arduino - Time & Space Complexity

Time Complexity: SD card module wiring

O(n)

Understanding Time Complexity

When working with an SD card module on Arduino, it's important to understand how the wiring affects the speed of communication.

We want to know how the time to read or write data changes as the amount of data grows.

Scenario Under Consideration

Analyze the time complexity of reading data from an SD card using SPI communication.

#include <SPI.h>
#include <SD.h>

File dataFile;

void setup() {
  SD.begin(10); // CS pin 10
  dataFile = SD.open("data.txt");
}

void loop() {
  if (dataFile) {
    while (dataFile.available()) {
      char c = dataFile.read();
      // process character
    }
    dataFile.close();
  }
  while(1); // stop
}
    

This code reads a file character by character from the SD card connected via SPI.

Identify Repeating Operations

Look at what repeats as the program runs.

• Primary operation: Reading each character from the SD card inside the while loop.
• How many times: Once for every character in the file until the end.

How Execution Grows With Input

As the file size grows, the number of characters to read grows too.

Input Size (n)	Approx. Operations
10 characters	10 reads
100 characters	100 reads
1000 characters	1000 reads

Pattern observation: The time to read grows directly with the number of characters.

Final Time Complexity

Time Complexity: O(n)

This means the time to read the file grows in a straight line with the file size.

Common Mistake

[X] Wrong: "Reading from the SD card takes the same time no matter how big the file is."

[OK] Correct: Each character must be read one by one, so bigger files take more time.

Interview Connect

Understanding how data size affects reading time helps you design better programs that handle files efficiently on Arduino.

Self-Check

What if we read the file in larger chunks instead of one character at a time? How would the time complexity change?