Activity 2: Distance Sensors

Overview

In this activity, you will wire and experiment with two types of distance sensors: an ultrasonic sensor (HC-SR04) and an infrared (IR) obstacle detection sensor. You’ll test how each sensor responds to different objects, surfaces, and distances. This is a team demonstration activity where you’ll show your understanding of sensor operation and explore their strengths and limitations.

Teams: Work in groups of 2-3 students

Due Date: Sunday, February 2nd by 11:50 AM

Learning Objectives

By completing this activity, you will:

• Wire and operate ultrasonic and IR distance sensors
• Understand how different sensors detect obstacles
• Explore sensor performance across various conditions
• Learn when to use each sensor type in robotics applications

Requirements

What You Must Demonstrate

1. Wire both sensors correctly to Arduino Uno
2. Show both sensors working with Serial Monitor output
3. Conduct at least 2 experiments per sensor from the suggested list below
4. Explain your findings to the instructor

Grading Criteria

This is a Class Activity worth points toward your participation grade.

Grading Rubric (Pass/Fail with feedback):

To Pass: You must achieve at least 70% overall. Both sensors must be functional.

Part 1: Ultrasonic Sensor (HC-SR04)

Understanding Ultrasonic Sensors

The HC-SR04 uses sound waves (40 kHz ultrasonic) to measure distance:

• Sends out a sound pulse
• Measures time for echo to return
• Calculates distance: distance = (time × speed_of_sound) / 2

Specifications:

• Range: 2 cm to 400 cm
• Accuracy: ±3 mm
• Beam angle: ~15°

Wiring the HC-SR04

Components:

• Arduino Uno
• HC-SR04 ultrasonic sensor
• 4 jumper wires
• Breadboard (optional)

Arduino Code for HC-SR04

// HC-SR04 Ultrasonic Sensor
#define TRIG_PIN 9
#define ECHO_PIN 10

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.println("HC-SR04 Test - Distance in cm:");
}

void loop() {
  // Send trigger pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  // Measure echo duration
  long duration = pulseIn(ECHO_PIN, HIGH);
  
  // Calculate distance in cm
  float distance = duration * 0.034 / 2;
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  delay(500);
}

Part 2: Infrared (IR) Obstacle Sensor

Understanding IR Sensors

Digital IR sensors emit infrared light and detect reflections:

• Output: HIGH (1) when no obstacle detected, LOW (0) when obstacle is present
• The sensor compares reflected IR light intensity to an internal threshold
• If reflection is strong enough (object is close/reflective), output goes LOW
• If reflection is weak (object far/absent), output stays HIGH

Key Component - Potentiometer:

• Small adjustable screw or dial on the sensor
• Controls the sensitivity threshold - how much reflected light triggers detection
• Turn clockwise → sensor becomes more sensitive (detects from farther away)
• Turn counter-clockwise → sensor becomes less sensitive (only detects very close objects)
• This lets you tune the sensor for your specific use case

Typical range: 2-30 cm (adjustable via potentiometer)

Wiring the IR Sensor

Components:

• Arduino Uno
• IR obstacle detection sensor
• 3 jumper wires

Arduino Code for IR Sensor

// Digital IR Obstacle Sensor
#define IR_PIN 2

void setup() {
  Serial.begin(9600);
  pinMode(IR_PIN, INPUT);
  Serial.println("IR Sensor Test:");
}

void loop() {
  int sensorState = digitalRead(IR_PIN);
  
  Serial.print("Sensor value: ");
  Serial.print(sensorState);
  Serial.print(" - ");
  
  if (sensorState == LOW) {
    Serial.println("OBSTACLE DETECTED!");
  } else {
    Serial.println("Clear");
  }
  
  delay(300);
}

Tip: The IR sensor outputs binary (0 or 1) values. Adjust the potentiometer to set when it switches from 0→1:

• Clockwise rotation = more sensitive = detects farther away
• Counter-clockwise = less sensitive = only detects very close objects
• Find the “sweet spot” for your detection distance by testing with an object and slowly turning the potentiometer

Part 3: Suggested Experiments

For Ultrasonic Sensor:

1. Distance Test: Measure objects at 10cm, 30cm, 50cm, 100cm - how accurate is it?
2. Surface Test: Try flat wall, angled surface (45°), soft material (cloth/foam)
3. Object Size: Test with large box, thin object (pencil), your hand
4. Material Test: Compare wood, metal, cardboard, plastic

For IR Sensor:

1. Distance Range: Find minimum and maximum detection distances
2. Color Test: Try white paper, black paper, colored objects
3. Surface Test: Compare matte vs. glossy/reflective surfaces
4. Angle Test: Move object side-to-side to find detection angle

Choose at least 2 experiments per sensor to demonstrate.

Part 4: Demonstration Checklist

When demonstrating to the instructor, be ready to:

• ✓ Show both sensors wired correctly
• ✓ Display Serial Monitor output for both sensors
• ✓ Demonstrate at least 2 experiments per sensor
• ✓ Explain what you observed and why
• ✓ Answer questions about sensor behavior

Troubleshooting

Ultrasonic Sensor Issues

IR Sensor Issues

Resources

• HC-SR04 Datasheet
• Arduino pulseIn() Documentation

Good luck exploring robot perception! 🤖📏