Using multiple libraries together in Arduino - Time & Space Complexity

Time Complexity: Using multiple libraries together

O(n)

Understanding Time Complexity

When using multiple libraries in Arduino, it's important to understand how the program's running time changes as more libraries are added or used together.

We want to know how the total work grows when combining different library functions.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

#include <Wire.h>
#include <SPI.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Wire.begin();
  SPI.begin();
  lcd.init();
  lcd.backlight();
}

void loop() {
  lcd.setCursor(0, 0);
  lcd.print("Hello");
  delay(1000);
}
    

This code uses three libraries to control hardware: Wire for I2C, SPI for SPI communication, and LiquidCrystal_I2C for the LCD display.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The loop() function runs repeatedly, calling lcd.print() each time.
• How many times: The loop runs forever, repeating the print operation every second.

How Execution Grows With Input

Here, the input size is not a variable like an array length, but the number of library calls and their internal operations.

Input Size (number of library calls)	Approx. Operations
1	Small number of operations for one library call
3	Sum of operations from all three libraries
10	Sum grows roughly linearly with number of calls

Pattern observation: The total work grows roughly in a straight line as more library calls are added.

Final Time Complexity

Time Complexity: O(n)

This means the total running time grows linearly with the number of library calls made in the program.

Common Mistake

[X] Wrong: "Adding more libraries does not affect the program speed because they run independently."

[OK] Correct: Each library call adds work that the microcontroller must do, so more libraries or calls increase total execution time.

Interview Connect

Understanding how multiple libraries affect program speed helps you write efficient Arduino code and shows you can think about how different parts of a program work together.

Self-Check

"What if we replaced the lcd.print() call with a function that updates multiple sensors? How would the time complexity change?"

Practice

1. Which of the following is the correct way to include multiple libraries in an Arduino sketch?

easy

A. Use multiple #include statements at the top of the sketch.

B. Write all library code inside the loop() function.

C. Include only one library and call others inside it.

D. Use #import instead of #include for multiple libraries.

Solution

1. Step 1: Understand library inclusion syntax

   Arduino uses #include to add libraries at the top of the sketch.

2. Step 2: Confirm multiple libraries usage

   You can add multiple #include lines, one for each library needed.

3. Final Answer:

   Use multiple #include statements at the top of the sketch. -> Option A

4. Quick Check:

   Multiple #include lines = correct way [OK]

Hint: Always put each library in its own #include line at the top [OK]

Common Mistakes:

• Trying to include libraries inside functions
• Using #import instead of #include
• Combining all libraries into one include

2. Which of these is the correct syntax to include the Wire and LiquidCrystal libraries in an Arduino sketch?

easy

A. #include "Wire"
#include "LiquidCrystal"

B. #include
#include

C. #import
#import

D. include
include

Solution

1. Step 1: Check correct include syntax

   The correct way is #include <LibraryName.h> with angle brackets and .h extension.

2. Step 2: Verify options

   #include #include uses correct syntax; others use wrong keywords or missing .h or wrong quotes.

3. Final Answer:

   #include <Wire.h>\n#include <LiquidCrystal.h> -> Option B

4. Quick Check:

   #include with angle brackets and .h = correct [OK]

Hint: Use #include with angle brackets and .h [OK]

Common Mistakes:

• Using #import instead of #include
• Omitting the .h extension
• Using double quotes instead of angle brackets

3. Given this Arduino code snippet using two libraries:

#include <Wire.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  Wire.begin();
  lcd.begin(16, 2);
  lcd.print("Hi");
}

void loop() {
  // nothing here
}

What will be displayed on the LCD when the Arduino runs?

medium

A. Nothing will display because Wire library is not used in loop.

B. The LCD will show random characters.

C. A compile error due to missing Wire usage.

D. The text "Hi" on the LCD screen.

Solution

1. Step 1: Analyze library initialization

   Wire library is started with Wire.begin() in setup; LiquidCrystal is initialized and prints "Hi".

2. Step 2: Check output on LCD

   Since lcd.print("Hi") runs in setup, "Hi" appears on the LCD screen.

3. Final Answer:

   The text "Hi" on the LCD screen. -> Option D

4. Quick Check:

   lcd.print("Hi") = "Hi" shown [OK]

Hint: Look for lcd.print() calls to find displayed text [OK]

Common Mistakes:

• Assuming Wire must be used in loop to avoid errors
• Thinking missing loop code means no output
• Confusing compile errors with unused library warnings

4. This Arduino sketch uses two libraries but does not work as expected:

#include <Wire.h>
#include <Adafruit_Sensor.h>

void setup() {
  Wire.begin();
  sensor.begin();
}

void loop() {
  sensor.read();
}

What is the main problem here?

medium

A. Adafruit_Sensor.h does not exist as a library.

B. Wire.begin() must be called inside loop, not setup.

C. The sensor object is not declared before use.

D. Missing #include for the sensor's specific library.

Solution

1. Step 1: Check object declaration

   The code calls sensor.begin() and sensor.read() but never declares or creates a sensor object.

2. Step 2: Verify library usage

   Without declaring sensor, the code will not compile or run correctly.

3. Final Answer:

   The sensor object is not declared before use. -> Option C

4. Quick Check:

   Objects must be declared before calling methods [OK]

Hint: Always declare objects before calling their methods [OK]

Common Mistakes:

• Thinking Wire.begin() must be in loop
• Assuming header file alone creates objects
• Ignoring missing object declarations

5. You want to use both the Servo and SoftwareSerial libraries in your Arduino project to control a servo motor and communicate via serial. Which of the following is the best approach to combine them correctly?

hard

A. Include both libraries at the top, create objects for each, initialize in setup(), and use their functions in loop().

B. Include only the Servo library and call SoftwareSerial functions inside Servo methods.

C. Use #include for Servo in setup() and SoftwareSerial in loop().

D. Combine both libraries into one custom library before including.

Solution

1. Step 1: Properly include and declare libraries

   Both libraries must be included at the top with #include and objects created for Servo and SoftwareSerial.

2. Step 2: Initialize and use in setup() and loop()

   Initialize both in setup() and call their functions as needed in loop() to run both tasks simultaneously.

3. Final Answer:

   Include both libraries at the top, create objects for each, initialize in setup(), and use their functions in loop(). -> Option A

4. Quick Check:

   Include, declare, initialize, then use both libraries [OK]

Hint: Include and initialize all libraries before using their functions [OK]

Common Mistakes:

• Trying to include libraries inside functions
• Assuming one library can call another's functions
• Delaying includes until inside setup or loop