📖 Lesson 4.2 – IR Sensor Circuit

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Connect an IR Obstacle Sensor with Arduino UNO

✅ Understand sensor wiring

✅ Read sensor output using Arduino

✅ Display detection status on Serial Monitor

✅ Test object detection

✅ Verify proper sensor operation

1. Introduction

In the previous lesson, we learned:

• What an IR Sensor is
• How infrared reflection works
• Parts of an IR Sensor Module
• Applications of IR Sensors

Now it is time to connect the sensor with Arduino UNO and observe how it detects obstacles.

This lesson forms the foundation for:

• Obstacle Detection Systems
• Obstacle Avoiding Robots
• Smart Dustbins
• Automatic Water Dispensers

2. Project Overview

The system works as:

Obstacle
    ↓
IR Sensor
    ↓
Arduino UNO
    ↓
Serial Monitor

When an object comes in front of the sensor, Arduino will detect it and display a message.

3. Components Required

4. Understanding the IR Sensor Pins

Most IR obstacle sensors have three pins:

5. Arduino Connections

Circuit Diagram

IR Sensor Module        Arduino UNO

VCC      ----------->    5V

GND      ----------->    GND

OUT      ----------->    D2

6. Why Use Digital Pin D2?

The IR sensor provides:

HIGH

or

LOW

output.

Therefore we use:

digitalRead()

instead of:

analogRead()

Digital Pin D2 reads these signals easily.

7. Understanding Sensor Output

Most IR modules work as:

This may vary slightly depending on the sensor module.

Example

No object present:

HIGH

Arduino interprets:

No Obstacle

Object detected:

LOW

Arduino interprets:

Obstacle Detected

8. Arduino Program

int sensorPin = 2;
int sensorValue;

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

  Serial.begin(9600);
}

void loop()
{
  sensorValue = digitalRead(sensorPin);

  Serial.println(sensorValue);

  delay(200);
}

9. Program Explanation

Define Sensor Pin

int sensorPin = 2;

Stores the sensor pin number.

Configure Input Pin

pinMode(sensorPin, INPUT);

Sets D2 as an input pin.

Read Sensor Output

sensorValue = digitalRead(sensorPin);

Reads HIGH or LOW from the sensor.

Display Value

Serial.println(sensorValue);

Shows the reading on Serial Monitor.

10. Uploading the Program

Step 1

Connect Arduino UNO.

Step 2

Open Arduino IDE.

Step 3

Select:

Tools → Board → Arduino UNO

Step 4

Select Correct COM Port.

Step 5

Upload Program.

Step 6

Open Serial Monitor.

Step 7

Set Baud Rate:

9600

11. Testing the Sensor

Test 1 – No Obstacle

Keep sensor facing open space.

Serial Monitor:

1
1
1
1

Meaning:

HIGH

No obstacle detected.

Test 2 – Hand Detection

Place your hand in front of the sensor.

Serial Monitor:

0
0
0
0

Meaning:

LOW

Obstacle detected.

12. Improved Program

Instead of displaying 0 and 1:

int sensorPin = 2;

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

  Serial.begin(9600);
}

void loop()
{
  if(digitalRead(sensorPin) == LOW)
  {
    Serial.println("Obstacle Detected");
  }
  else
  {
    Serial.println("No Obstacle");
  }

  delay(300);
}

Output

No Object

No Obstacle

Object Present

Obstacle Detected

13. Testing Different Objects

Try detecting:

Hand

Notebook

Mobile Phone

White Paper

Black Object

Observe detection performance.

14. Adjusting Sensor Sensitivity

Use the blue potentiometer.

Clockwise

Increase detection range.

Anti-Clockwise

Decrease detection range.

Test until stable detection is achieved.

15. Observation Table

16. Real-World Applications

This same circuit is used in:

Obstacle Avoiding Robots

Smart Dustbins

Automatic Water Dispensers

Industrial Object Counters

Automatic Doors

Conveyor Systems

17. Common Beginner Mistakes

Mistake 1

Connecting OUT to the wrong pin.

Correct:

OUT → D2

Mistake 2

Using:

analogRead()

instead of:

digitalRead()

Mistake 3

Testing under direct sunlight.

IR performance may reduce.

Mistake 4

Ignoring sensitivity adjustment.

18. Troubleshooting

No Output

Check:

• Power Supply
• Wiring
• COM Port

Always Detecting Obstacle

Check:

• Potentiometer Adjustment
• Sensor Placement

Never Detecting Obstacle

Check:

• Wiring
• Detection Range
• Object Distance

Unstable Detection

Check:

• Loose Wires
• Strong Sunlight

📊 Summary

In this lesson, we learned:

✅ IR Sensor Wiring

✅ Arduino Connection

✅ Digital Input Reading

✅ Serial Monitor Output

✅ Obstacle Detection Testing

✅ Sensor Calibration

The IR sensor can now successfully detect nearby objects and communicate that information to Arduino.

📖 Key Terms

Digital Output

HIGH or LOW signal from the sensor.

Obstacle Detection

Detecting nearby objects without contact.

Calibration

Adjusting sensor sensitivity.

Reflection

IR light bouncing back from an object.

Digital Input

Arduino reading HIGH or LOW signals.

🎯 Quiz

1. Which Arduino pin is used in this lesson?

A. A0

B. D13

C. D2 ✅

D. D8

2. Which function reads the IR sensor output?

A. analogRead()

B. digitalRead() ✅

C. digitalWrite()

D. Serial.read()

3. What output is usually generated when an obstacle is detected?

A. HIGH

B. LOW ✅

C. 1023

D. Analog Signal

4. Which pin of the sensor connects to Arduino 5V?

A. GND

B. OUT

C. VCC ✅

D. D2

5. Why is calibration important?

A. To upload code

B. To improve detection performance ✅

C. To increase memory

D. To reduce voltage

🏠 Assignment

Task 1

Connect the IR sensor module and verify obstacle detection.

Task 2

Display “Obstacle Detected” and “No Obstacle” on Serial Monitor.

Task 3

Test the sensor with five different objects.

Task 4

Adjust the potentiometer and observe detection range changes.

Task 5

Create an observation table showing object detection results.