Using multiple libraries together in Arduino - Step-by-Step Execution

Concept Flow - Using multiple libraries together

Start Program

↓

Include Library A

↓

Include Library B

↓

Initialize Objects from A and B

↓

Setup: Initialize both libraries

↓

Loop: Use functions from both libraries

↓

Repeat Loop

The program starts by including multiple libraries, then initializes their objects, sets them up, and uses their functions together in the main loop.

Execution Sample

Arduino

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

LiquidCrystal_I2C lcd(0x27,16,2);

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

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

This code uses Wire and LiquidCrystal_I2C libraries together to display 'Hello' on an LCD screen.

Execution Table

Step	Action	Library/Function	Result/State
1	Include Wire library	Wire	Wire functions available
2	Include LiquidCrystal_I2C library	LiquidCrystal_I2C	LCD functions available
3	Create lcd object	LiquidCrystal_I2C lcd	lcd ready to control LCD
4	Call Wire.begin()	Wire.begin()	I2C bus initialized
5	Call lcd.init()	lcd.init()	LCD initialized
6	Call lcd.backlight()	lcd.backlight()	LCD backlight turned on
7	Set cursor to (0,0)	lcd.setCursor(0,0)	Cursor at first row, first column
8	Print 'Hello' on LCD	lcd.print("Hello")	'Hello' displayed on LCD
9	Loop repeats	loop()	Display stays on, ready for updates

💡 Loop runs continuously; program does not exit.

Variable Tracker

Variable	Start	After setup	After loop 1	After loop 2
lcd	Not created	Created and initialized	Cursor at (0,0), 'Hello' displayed	Cursor at (0,0), 'Hello' displayed

Key Moments - 3 Insights

Why do we need to call Wire.begin() before using the LCD?

Wire.begin() initializes the I2C communication bus that the LCD uses; without it, the LCD library cannot communicate with the hardware. See execution_table step 4.

Can we use functions from both libraries in the same loop?

Yes, after initialization, you can call functions from both libraries anytime, as shown in execution_table steps 7 and 8.

What happens if we forget to call lcd.init()?

The LCD will not initialize properly and may not display anything. This is shown in execution_table step 5 where lcd.init() prepares the LCD.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state after calling Wire.begin()?

A LCD backlight turned on

B I2C bus initialized

C Cursor set to (0,0)

D LCD initialized

💡 Hint

Check execution_table step 4 for Wire.begin() result.

At which step is the LCD backlight turned on?

A Step 6

B Step 5

C Step 7

D Step 8

💡 Hint

Look at execution_table for lcd.backlight() call.

If we remove Wire.begin(), what will likely happen?

A LCD will display 'Hello' normally

B Program will not compile

C LCD will not initialize or display correctly

D Backlight will turn on but no text

💡 Hint

Refer to key_moments about Wire.begin() importance.

Concept Snapshot

Using multiple libraries together:
- Include each library with #include
- Create objects for each library as needed
- Initialize each library in setup()
- Use functions from all libraries in loop()
- Ensure dependencies (like Wire.begin()) are called first

Full Transcript

This example shows how to use two Arduino libraries together: Wire and LiquidCrystal_I2C. First, both libraries are included. Then, an lcd object is created from LiquidCrystal_I2C. In setup(), Wire.begin() initializes the I2C bus, which is required for the LCD to communicate. Then lcd.init() and lcd.backlight() prepare the LCD screen. In the loop(), the cursor is set and the text 'Hello' is printed on the LCD. The loop repeats continuously, keeping the display on. Key points include calling Wire.begin() before using the LCD and initializing each library properly. This allows functions from both libraries to work together smoothly.

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