IR sensor for obstacle detection in Arduino - Mini Project: Build & Apply

IR Sensor for Obstacle Detection

📖 Scenario: You are building a simple robot that can detect obstacles using an IR sensor. The sensor will tell the robot if something is close by, so it can stop or change direction.

🎯 Goal: Create a program that reads the IR sensor value and prints Obstacle detected when an obstacle is close, or No obstacle when the path is clear.

📋 What You'll Learn

Use a variable called irSensorPin to store the IR sensor input pin number.

Use a variable called threshold to set the distance limit for obstacle detection.

Read the sensor value using digitalRead(irSensorPin).

Use an if statement to check if the sensor detects an obstacle.

Print Obstacle detected or No obstacle accordingly.

💡 Why This Matters

🌍 Real World

IR sensors are used in robots and devices to detect objects and avoid collisions.

💼 Career

Understanding sensor input and conditional logic is important for embedded systems and robotics jobs.

1

Set up the IR sensor pin

Create a variable called irSensorPin and set it to 7. Then set the pin mode of irSensorPin to INPUT inside the setup() function.

Arduino

int irSensorPin = 7;

void setup() {
  // Set irSensorPin as input
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use pinMode(irSensorPin, INPUT); inside setup() to prepare the sensor pin.

2

Add a threshold variable

Create a variable called threshold and set it to 1. This will be used to decide if an obstacle is detected.

Arduino

int irSensorPin = 7;
int threshold = 1;  // Your code here

void setup() {
  pinMode(irSensorPin, INPUT);
}

void loop() {
  
}

Hint

The threshold variable helps decide when the sensor detects an obstacle.

3

Read sensor and check for obstacle

Inside the loop() function, read the sensor value into a variable called sensorValue using digitalRead(irSensorPin). Then use an if statement to check if sensorValue equals threshold.

Arduino

int irSensorPin = 7;
int threshold = 1;

void setup() {
  pinMode(irSensorPin, INPUT);
}

void loop() {
  int sensorValue = digitalRead(irSensorPin);  // Your code here
  if (sensorValue == threshold) {
    // Your code here
  }
}

Hint

Use digitalRead(irSensorPin) to get the sensor value and compare it with threshold.

4

Print obstacle detection result

Inside the if block, print Obstacle detected using Serial.println(). Add an else block to print No obstacle when the sensor value does not equal threshold.

Arduino

int irSensorPin = 7;
int threshold = 1;

void setup() {
  pinMode(irSensorPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  int sensorValue = digitalRead(irSensorPin);
  if (sensorValue == threshold) {
    // Your code here
  } else {
    // Your code here
  }
}

Hint

Use Serial.println() to show messages on the serial monitor. Add a small delay to avoid flooding the output.

Practice

1. What does an IR sensor detect in an obstacle detection system?

easy

A. Visible light intensity

B. Magnetic fields around objects

C. Sound waves bouncing off objects

D. Reflected infrared light from nearby objects

Solution

1. Step 1: Understand IR sensor function

   IR sensors emit infrared light and detect the light reflected back from objects.

2. Step 2: Identify what is detected

   The sensor measures reflected infrared light, not visible light, sound, or magnetic fields.

3. Final Answer:

   Reflected infrared light from nearby objects -> Option D

4. Quick Check:

   IR sensor = reflected infrared light [OK]

Hint: IR sensors detect reflected infrared light, not visible or sound [OK]

Common Mistakes:

• Confusing IR sensor with light or sound sensors
• Thinking it detects visible light
• Assuming it detects magnetic fields

2. Which Arduino code snippet correctly reads an analog IR sensor value from pin A0?

easy

A. int sensorValue = analogRead(A0);

B. int sensorValue = digitalRead(A0);

C. int sensorValue = analogWrite(A0);

D. int sensorValue = digitalWrite(A0);

Solution

1. Step 1: Identify correct function for analog reading

   analogRead(pin) reads analog sensor values from specified pin.

2. Step 2: Check pin and function usage

   Pin A0 is analog input; analogRead(A0) is correct syntax.

3. Final Answer:

   int sensorValue = analogRead(A0); -> Option A

4. Quick Check:

   Use analogRead for analog sensors [OK]

Hint: Use analogRead() for analog sensor pins like A0 [OK]

Common Mistakes:

• Using digitalRead() for analog sensors
• Using analogWrite() which is for output
• Using digitalWrite() which is for digital output

3. What will be printed if the IR sensor value is 350 and the threshold is 300 in this code?

int sensorValue = 350;
int threshold = 300;
if(sensorValue > threshold) {
  Serial.println("No obstacle");
} else {
  Serial.println("Obstacle detected");
}

medium

A. Error

B. No obstacle

C. 350

D. Obstacle detected

Solution

1. Step 1: Compare sensorValue with threshold

   350 is greater than 300, so condition sensorValue > threshold is true.

2. Step 2: Determine printed output

   Since condition is true, code prints "No obstacle".

3. Final Answer:

   No obstacle -> Option B

4. Quick Check:

   350 > 300 = true, prints "No obstacle" [OK]

Hint: Check if sensor value is above threshold for output [OK]

Common Mistakes:

• Confusing greater than with less than
• Expecting sensor value to print
• Thinking else block runs when condition is true

4. Identify the error in this Arduino code for obstacle detection:

int sensorPin = A0;
int threshold = 400;
void setup() {
  Serial.begin(9600);
}
void loop() {
  int sensorValue = digitalRead(sensorPin);
  if(sensorValue < threshold) {
    Serial.println("Obstacle detected");
  }
  delay(100);
}

medium

A. Using digitalRead instead of analogRead for analog sensor

B. Missing Serial.begin in setup()

C. Incorrect delay value

D. Threshold comparison operator is wrong

Solution

1. Step 1: Check sensor reading function

   IR sensor outputs analog values, so analogRead() must be used, not digitalRead().

2. Step 2: Verify other code parts

   Serial.begin is present, delay is reasonable, comparison operator is correct.

3. Final Answer:

   Using digitalRead instead of analogRead for analog sensor -> Option A

4. Quick Check:

   Analog sensor needs analogRead() [OK]

Hint: Use analogRead() for analog sensors, not digitalRead() [OK]

Common Mistakes:

• Using digitalRead for analog sensor pins
• Forgetting Serial.begin() (not the case here)
• Misusing delay() values

5. You want to detect obstacles only when the IR sensor value is between 200 and 400. Which code snippet correctly implements this?

hard

A. if(sensorValue < 200 && sensorValue > 400) { Serial.println("Obstacle detected"); }

B. if(sensorValue >= 200 || sensorValue <= 400) { Serial.println("Obstacle detected"); }

C. if(sensorValue > 200 && sensorValue < 400) { Serial.println("Obstacle detected"); }

D. if(sensorValue == 200 && sensorValue == 400) { Serial.println("Obstacle detected"); }

Solution

1. Step 1: Understand range condition

   To detect values between 200 and 400, sensorValue must be greater than 200 AND less than 400.

2. Step 2: Analyze each option

   if(sensorValue < 200 && sensorValue > 400) { Serial.println("Obstacle detected"); }: impossible condition (< 200 && > 400); if(sensorValue >= 200 || sensorValue <= 400) { Serial.println("Obstacle detected"); } uses || which allows all values; if(sensorValue > 200 && sensorValue < 400) { Serial.println("Obstacle detected"); }: > 200 && < 400 correct; if(sensorValue == 200 && sensorValue == 400) { Serial.println("Obstacle detected"); } checks equality to both values simultaneously, impossible.

3. Final Answer:

   if(sensorValue > 200 && sensorValue < 400) { Serial.println("Obstacle detected"); } -> Option C

4. Quick Check:

   Use AND (&&) for range checks [OK]

Hint: Use && to check sensor value within a range [OK]

Common Mistakes:

• Using || instead of && for range
• Checking impossible conditions
• Using equality instead of range