📖 Lesson 4.3 – Obstacle Detection Code

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Read obstacle detection signals from an IR sensor

✅ Understand obstacle detection logic

✅ Use conditional statements with sensors

✅ Control an LED based on obstacle detection

✅ Understand real-time decision making in Arduino

✅ Build the foundation for obstacle avoiding robots

1. Introduction

In the previous lesson, we connected the IR sensor to Arduino UNO and displayed sensor status on the Serial Monitor.

Now we will take the next step.

Instead of only displaying messages, Arduino will perform an action whenever an obstacle is detected.

Our goal:

Obstacle Detected

↓

LED ON

No Obstacle

↓

LED OFF

This is the basic principle behind:

• Obstacle Avoiding Robots
• Smart Dustbins
• Automatic Doors
• Automatic Water Dispensers

2. Project Overview

The system works as:

Obstacle
    ↓
IR Sensor
    ↓
Arduino UNO
    ↓
Decision Making
    ↓
LED ON / OFF

3. Components Required

4. Circuit Connections

IR Sensor Module

LED Connection

Circuit Diagram

IR Sensor

VCC -----> 5V
GND -----> GND
OUT -----> D2

LED

D13 -----> Resistor -----> LED -----> GND

5. Understanding Detection Logic

Most IR sensor modules work as:

Arduino continuously checks the sensor output.

Decision Logic

If:

LOW

↓

Obstacle Present

↓

LED ON

If:

HIGH

↓

No Obstacle

↓

LED OFF

6. Algorithm

Step 1

Read IR Sensor Output

↓

Step 2

Is Obstacle Detected?

↓

YES

↓

Turn LED ON

↓

NO

↓

Turn LED OFF

↓

Repeat Forever

7. Arduino Program

int sensorPin = 2;
int ledPin = 13;

void setup()
{
  pinMode(sensorPin, INPUT);
  
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  if(digitalRead(sensorPin) == LOW)
  {
    digitalWrite(ledPin, HIGH);
  }
  else
  {
    digitalWrite(ledPin, LOW);
  }
}

8. Program Explanation

Sensor Pin

int sensorPin = 2;

Stores the IR sensor pin number.

LED Pin

int ledPin = 13;

Stores the LED pin number.

Configure Sensor

pinMode(sensorPin, INPUT);

Sets D2 as input.

Configure LED

pinMode(ledPin, OUTPUT);

Sets D13 as output.

Detect Obstacle

digitalRead(sensorPin)

Reads sensor status.

LED ON

digitalWrite(ledPin, HIGH);

Obstacle detected.

LED OFF

digitalWrite(ledPin, LOW);

No obstacle detected.

9. Testing the Program

Test 1 – No Obstacle

Keep sensor facing open space.

Expected:

LED OFF

Test 2 – Place Hand in Front

Bring your hand within sensor range.

Expected:

LED ON

Test 3 – Remove Hand

Move hand away.

Expected:

LED OFF

10. Enhanced Program with Serial Monitor

int sensorPin = 2;
int ledPin = 13;

void setup()
{
pinMode(sensorPin, INPUT);

pinMode(ledPin, OUTPUT);

Serial.begin(9600);
}

void loop()
{
if(digitalRead(sensorPin) == LOW)
{
digitalWrite(ledPin, HIGH);

Serial.println("Obstacle Detected");
}
else
{
digitalWrite(ledPin, LOW);

Serial.println("No Obstacle");
}

delay(200);
}

Expected Output

Object Present

Obstacle Detected

Object Removed

No Obstacle

11. Understanding Real-Time Detection

Arduino continuously runs:

loop()

thousands of times every second.

This allows the sensor to detect obstacles almost instantly.

12. Testing Different Objects

Try detecting:

Hand

Mobile Phone

Notebook

White Paper

Water Bottle

Observe sensor response.

13. Practical Applications

Obstacle Avoiding Robot

Obstacle Detected

↓

Robot Turns

Smart Dustbin

Hand Detected

↓

Lid Opens

Automatic Water Dispenser

Hand Detected

↓

Pump ON

Conveyor Belt

Object Detected

↓

Counting System

Automatic Door

Person Detected

↓

Door Opens

14. Common Beginner Mistakes

Mistake 1

Using analogRead()

Wrong:

analogRead(sensorPin);

Correct:

digitalRead(sensorPin);

Mistake 2

Wrong Sensor Pin

Verify:

OUT → D2

Mistake 3

LED Wiring Incorrect

Check polarity.

Mistake 4

Ignoring Sensor Calibration

Adjust potentiometer properly.

15. Troubleshooting

LED Never Turns ON

Check:

• Sensor Wiring
• Detection Distance
• Potentiometer Adjustment

LED Always ON

Check:

• Sensor Output Logic
• Potentiometer Setting

No Detection

Check:

• Power Supply
• Sensor Alignment
• Object Distance

Unstable Operation

Check:

• Loose Wires
• Strong Sunlight

16. Mini Challenge

Modify the program so that:

Obstacle Detected

LED Blinks

instead of remaining ON.

Hint:

Use:

digitalWrite();
delay();

📊 Summary

In this lesson, we learned:

✅ Obstacle Detection Logic

✅ IR Sensor Programming

✅ LED Control

✅ Conditional Statements

✅ Real-Time Detection

This lesson demonstrates how Arduino can make decisions and respond automatically when an obstacle is detected.

📖 Key Terms

Obstacle Detection

Detecting nearby objects.

Digital Input

HIGH or LOW signal received by Arduino.

Conditional Statement

Decision-making code using if-else.

Automation

Automatic response without human control.

Real-Time System

System that reacts immediately to changes.

🎯 Quiz

1. Which function reads the IR sensor?

A. analogRead()

B. digitalRead() ✅

C. digitalWrite()

D. Serial.print()

2. What happens when an obstacle is detected?

A. LED OFF

B. LED ON ✅

C. Arduino OFF

D. Sensor OFF

3. Which Arduino pin is connected to the IR sensor output?

A. A0

B. D13

C. D2 ✅

D. D8

4. Which statement is used for decision making?

A. for

B. while

C. if-else ✅

D. setup

5. Which application uses obstacle detection?

A. Smart Dustbin ✅

B. Calculator

C. Keyboard

D. Printer

🏠 Assignment

Task 1

Build the obstacle detection circuit and test it.

Task 2

Display obstacle status on Serial Monitor.

Task 3

Test the sensor with five different objects.

Task 4

Modify the program to blink the LED when an obstacle is detected.

Task 5

Explain how this logic can be used in an obstacle avoiding robot.