Ultrasonic distance sensor (HC-SR04) in Arduino - Mini Project: Build & Apply

Ultrasonic distance sensor (HC-SR04)

📖 Scenario: You want to measure the distance to an object using an ultrasonic sensor (HC-SR04) connected to an Arduino board. This sensor sends out sound waves and listens for the echo to calculate how far the object is.

🎯 Goal: Build a simple Arduino program that reads the distance from the HC-SR04 sensor and prints the distance in centimeters to the Serial Monitor.

📋 What You'll Learn

Use pins 9 for triggerPin and 10 for echoPin.

Create a variable to store the duration of the echo pulse.

Calculate the distance in centimeters using the duration.

Print the distance to the Serial Monitor.

💡 Why This Matters

🌍 Real World

Ultrasonic sensors are used in robots, parking sensors, and obstacle detection to measure distances without touching objects.

💼 Career

Understanding how to read sensor data and process it is important for embedded systems and robotics jobs.

1

Set up sensor pins

Create two integer variables called triggerPin and echoPin and set them to 9 and 10 respectively.

Arduino

# Your code here

Hint

Use int to create the variables and assign the numbers 9 and 10.

2

Configure pins in setup

In the setup() function, set triggerPin as an output and echoPin as an input. Also, start the serial communication at 9600 baud using Serial.begin(9600);.

Arduino

int triggerPin = 9;
int echoPin = 10;

void setup() {
  // Your code here
}

Hint

Use pinMode() to set pin modes and Serial.begin(9600); to start serial communication.

3

Measure distance in loop

In the loop() function, send a 10 microsecond pulse to triggerPin, then read the pulse duration from echoPin using pulseIn(). Calculate the distance in centimeters by dividing the duration by 58 and store it in an integer variable called distance.

Arduino

int triggerPin = 9;
int echoPin = 10;

void setup() {
  pinMode(triggerPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  // Send pulse and measure duration
  // Calculate distance
}

Hint

Send a short pulse on triggerPin, then use pulseIn() to measure the echo time. Divide by 58 to get centimeters.

4

Print the distance

Add a line in the loop() function to print the distance variable to the Serial Monitor using Serial.println(distance);.

Arduino

int triggerPin = 9;
int echoPin = 10;

void setup() {
  pinMode(triggerPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);

  long duration = pulseIn(echoPin, HIGH);
  int distance = duration / 58;
  // Print the distance
}

Hint

Use Serial.println(distance); to show the distance on the Serial Monitor.

Practice

1. What is the main purpose of the trigger pin on the HC-SR04 ultrasonic sensor?

easy

A. To send a short ultrasonic pulse to start distance measurement

B. To receive the echo signal from the object

C. To power the sensor

D. To reset the sensor

Solution

1. Step 1: Understand the role of the trigger pin

   The trigger pin is used to send a short pulse that starts the ultrasonic burst.

2. Step 2: Differentiate from echo pin

   The echo pin listens for the returning pulse, not the trigger pin.

3. Final Answer:

   To send a short ultrasonic pulse to start distance measurement -> Option A

4. Quick Check:

   Trigger pin sends pulse = A [OK]

Hint: Trigger pin sends pulse, echo pin listens [OK]

Common Mistakes:

• Confusing trigger with echo pin
• Thinking trigger powers the sensor
• Assuming trigger resets the sensor

2. Which Arduino function is used to measure the duration of the echo pulse from the HC-SR04 sensor?

easy

A. digitalWrite()

B. pulseIn()

C. analogRead()

D. delay()

Solution

1. Step 1: Identify function to measure pulse duration

   The pulseIn() function measures the length of a pulse on a pin.

2. Step 2: Exclude other functions

   digitalWrite() sets pin output, analogRead() reads analog values, delay() pauses execution.

3. Final Answer:

   pulseIn() -> Option B

4. Quick Check:

   pulseIn measures pulse length = B [OK]

Hint: Use pulseIn() to measure echo pulse duration [OK]

Common Mistakes:

• Using digitalWrite() to read pulse
• Confusing analogRead() with pulse measurement
• Using delay() instead of measuring pulse

3. What will be the output distance (in cm) if the measured echo time is 1160 microseconds? Use the formula: distance = (echoTime / 2) / 29.1.

medium

A. 80 cm

B. 40 cm

C. 10 cm

D. 20 cm

Solution

1. Step 1: Calculate half of echo time

   Half of 1160 microseconds is 580 microseconds.

2. Step 2: Divide by 29.1 to get distance

   580 / 29.1 ≈ 19.93 cm, approximately 20 cm.

3. Final Answer:

   20 cm -> Option D

4. Quick Check:

   (1160/2)/29.1 ≈ 20 cm [OK]

Hint: Divide echo time by 2 and then by 29.1 [OK]

Common Mistakes:

• Forgetting to divide echo time by 2
• Using wrong divisor instead of 29.1
• Mixing units of time and distance

4. Identify the error in this Arduino code snippet for HC-SR04 distance measurement:

digitalWrite(triggerPin, HIGH);
delayMicroseconds(10);
digitalWrite(triggerPin, LOW);
echoTime = pulseIn(echoPin, LOW);

medium

A. echoTime should be declared as int, not long

B. delayMicroseconds should be delay()

C. pulseIn should measure HIGH pulse, not LOW

D. triggerPin should be set LOW before HIGH

Solution

1. Step 1: Check pulseIn usage

   The echo pulse is HIGH when the echo is received, so pulseIn should measure HIGH pulse.

2. Step 2: Verify other code parts

   delayMicroseconds(10) is correct for 10 microseconds pulse; triggerPin sequence is correct; echoTime type depends on usage but not an error here.

3. Final Answer:

   pulseIn should measure HIGH pulse, not LOW -> Option C

4. Quick Check:

   pulseIn measures HIGH pulse = D [OK]

Hint: pulseIn(echoPin, HIGH) to measure echo pulse [OK]

Common Mistakes:

• Measuring LOW pulse instead of HIGH
• Using delay() instead of delayMicroseconds()
• Setting triggerPin LOW before HIGH incorrectly

5. You want to measure distance continuously and print it every second using HC-SR04. Which code snippet correctly triggers the sensor and calculates distance in cm?

hard

A. digitalWrite(triggerPin, LOW);
delayMicroseconds(2);
digitalWrite(triggerPin, HIGH);
delayMicroseconds(10);
digitalWrite(triggerPin, LOW);
echoTime = pulseIn(echoPin, HIGH);
distance = (echoTime / 2) / 29.1;

B. digitalWrite(triggerPin, HIGH);
delayMicroseconds(10);
digitalWrite(triggerPin, LOW);
echoTime = pulseIn(echoPin, LOW);
distance = echoTime * 29.1 / 2;

C. digitalWrite(triggerPin, LOW);
delay(10);
digitalWrite(triggerPin, HIGH);
echoTime = pulseIn(echoPin, HIGH);
distance = (echoTime / 2) / 29.1;

D. digitalWrite(triggerPin, HIGH);
delayMicroseconds(2);
digitalWrite(triggerPin, LOW);
echoTime = pulseIn(echoPin, HIGH);
distance = (echoTime * 2) / 29.1;

Solution

1. Step 1: Check trigger pulse sequence

   The correct sequence is to set trigger LOW for 2 microseconds, then HIGH for 10 microseconds, then LOW again.

2. Step 2: Verify echo measurement and distance formula

   pulseIn measures HIGH pulse duration; distance = (echoTime / 2) / 29.1 converts time to cm correctly.

3. Final Answer:

   Code snippet C correctly triggers and calculates distance -> Option A

4. Quick Check:

   Trigger LOW-2us-HIGH-10us-LOW, pulseIn HIGH, distance formula = C [OK]

Hint: Trigger LOW-2us, HIGH-10us, then LOW; measure HIGH pulse [OK]

Common Mistakes:

• Skipping initial LOW trigger pulse
• Measuring LOW pulse instead of HIGH
• Incorrect distance formula with wrong multiplication/division