📘 Lesson P7 – Functions in Arduino Programming

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Understand what functions are

✅ Understand why functions are important

✅ Create custom functions

✅ Call functions correctly

✅ Pass parameters to functions

✅ Return values from functions

✅ Organize large Arduino programs

✅ Improve code readability and reusability

1. Introduction

Imagine you are building a robot.

The robot needs to:

• Move Forward
• Move Backward
• Turn Left
• Turn Right
• Stop

One approach is to write the motor control code repeatedly whenever needed.

Example:

digitalWrite(IN1,HIGH);
digitalWrite(IN2,LOW);
digitalWrite(IN3,HIGH);
digitalWrite(IN4,LOW);

Again…

digitalWrite(IN1,HIGH);
digitalWrite(IN2,LOW);
digitalWrite(IN3,HIGH);
digitalWrite(IN4,LOW);

Again…

digitalWrite(IN1,HIGH);
digitalWrite(IN2,LOW);
digitalWrite(IN3,HIGH);
digitalWrite(IN4,LOW);

This makes programs:

❌ Long

❌ Difficult to read

❌ Difficult to maintain

Instead, we use:

Functions

2. What is a Function?

A function is a reusable block of code designed to perform a specific task.

Think of a function as a machine.

Input

↓

Processing

↓

Output

Whenever needed, we simply call the function.

Real-Life Example

Imagine a remote control.

When you press:

Volume Up

The TV performs a predefined task.

You do not manually increase the volume each time.

Similarly:

A function stores instructions that can be used repeatedly.

3. Why Functions are Important

Functions help:

✅ Reduce code duplication

✅ Improve readability

✅ Simplify debugging

✅ Make programs modular

✅ Reuse code

Professional programmers use functions extensively.

4. Functions Already Used in Arduino

You are already using functions.

Example:

void setup()
{

}

setup() is a function.

void loop()
{

}

loop() is also a function.

Other examples:

digitalWrite();




analogRead();




Serial.println();

These are built-in functions provided by Arduino.

5. Anatomy of a Function

Example:

void blinkLED()
{
digitalWrite(13,HIGH);
delay(500);

digitalWrite(13,LOW);
delay(500);
}

A function has:

Return Type

void

Function Name

blinkLED

Parentheses

()

Function Body

{

}

Contains instructions.

6. Creating Your First Function

Example:

void sayHello()
{
   Serial.println("Hello Students");
}

This function prints a message.

7. Calling a Function

Creating a function does not automatically execute it.

We must call it.

Example:

void sayHello()
{
   Serial.println("Hello Students");
}

void setup()
{
   Serial.begin(9600);

   sayHello();
}

void loop()
{

}

Output:

Hello Students

Program Flow

Power ON

↓

setup()

↓

sayHello()

↓

Print Message

↓

loop()

8. LED Blink Function Example

void blinkLED()
{
   digitalWrite(13,HIGH);
   delay(500);

   digitalWrite(13,LOW);
   delay(500);
}

Call it:

void loop()
{
   blinkLED();
}

Result:

LED continuously blinks.

9. Function Parameters

Sometimes functions need input values.

These inputs are called:

Parameters

Example

Suppose we want to display different numbers.

void displayNumber(int number)
{
Serial.println(number);
}

Calling:

displayNumber(10);

Output:

10

Calling:

displayNumber(25);

Output:

25

How Parameters Work

Function:

void displayNumber(int number)

Parameter:

number

receives data sent during the function call.

10. Multiple Parameters

Functions can receive multiple values.

Example:

void addNumbers(int a, int b)
{
int result = a + b;

Serial.println(result);
}

Call:

addNumbers(5,3);

Output:

8

11. Return Values

Some functions send data back.

Example:

int addNumbers(int a, int b)
{
   return a + b;
}

Call:

int result;

result = addNumbers(10,20);

Result:

30

Understanding return

The keyword:

return

sends a value back to the caller.

Example

int square(int num)
{
   return num * num;
}

Call:

int result = square(5);

Output:

25

12. Void Functions

Many functions do not return anything.

Example:

void turnOnLED()
{
   digitalWrite(13,HIGH);
}

Here:

void

means:

Returns nothing.

13. Functions with Return Values

Example:

int getDistance()
{
   return 25;
}

This function returns an integer.

Other examples:

float getTemperature()
{
   return 30.5;
}

bool isDoorOpen()
{
return true;
}

14. Variable Scope

Variables created inside a function exist only inside that function.

Example:

void test()
{
int number = 10;
}

Outside the function:

number

cannot be used.

This is called:

Local Scope

Global Variables

Variables created outside functions are available everywhere.

Example:

int count = 0;

void setup()
{

}

void loop()
{

}

This is called:

Global Scope

15. Function Prototype

Sometimes functions are written below setup() and loop().

Arduino often handles this automatically.

Example:

void blinkLED();

void setup()
{

}

This declaration is called a:

Function Prototype

16. Real Project Example

Obstacle Avoiding Robot

Instead of writing motor code repeatedly:

void moveForward()
{
// Motor code
}

void stopRobot()
{
// Motor code
}

void turnLeft()
{
// Motor code
}

Now the program becomes:

if(distance < 10)
{
stopRobot();
}
else
{
moveForward();
}

Much easier to understand.

17. Common Beginner Mistakes

Mistake 1

Creating function but never calling it.

Example:

void hello()
{
Serial.println("Hello");
}

Nothing happens unless:

hello();

is called.

Mistake 2

Missing parentheses.

Wrong:

hello;

Correct:

hello();

Mistake 3

Wrong parameter count.

Function:

addNumbers(int a,int b)

Wrong:

addNumbers(5);

Mistake 4

Forgetting return value.

Example:

int square(int x)
{
}

Must return something.

18. Best Practices

✅ Give meaningful names

Good:

moveForward()

Bad:

abc()

✅ Keep functions small

✅ One function = One task

✅ Reuse functions whenever possible

✅ Add comments for complex functions

19. Real-World Applications

Functions are used in:

Line Follower Robots

followLine()

Smart Irrigation

checkMoisture()

Home Automation

turnOnLight()

Weather Station

readTemperature()

Water Dispenser

dispenseWater()

📊 Summary

In this lesson, we learned:

✅ What functions are

✅ Creating functions

✅ Calling functions

✅ Parameters

✅ Return values

✅ Local and Global Variables

✅ Function prototypes

Functions make Arduino programs cleaner, easier to understand, and easier to maintain, especially in large projects.

📖 Key Terms

Function

A reusable block of code.

Parameter

Input value passed to a function.

Return Value

Data sent back by a function.

Void

Function returns nothing.

Local Variable

Variable available only inside a function.

Global Variable

Variable available throughout the program.

Function Call

Executing a function.

🎯 Quiz

1. What is a function?

A. Variable

B. Reusable block of code ✅

C. Sensor

D. Loop

2. Which keyword means “returns nothing”?

A. int

B. bool

C. void ✅

D. char

3. What is a parameter?

A. Output

B. Input value to a function ✅

C. Loop variable

D. Comment

4. Which keyword sends a value back?

A. send

B. output

C. return ✅

D. print

5. Why are functions useful?

A. Reduce repeated code ✅

B. Increase wiring

C. Power Arduino

D. Create sensors

🏠 Assignment

Task 1

Create a function named showName() that prints your name.

Task 2

Create a function named blinkLED() that blinks an LED once.

Task 3

Create a function that adds two numbers and displays the result.

Task 4

Create a function that returns the square of a number.

Task 5

Design functions for a robot:

• moveForward()
• moveBackward()
• turnLeft()
• turnRight()
• stopRobot()

Explain what each function should do.