Ultrasonic distance sensor (HC-SR04) in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the trigger pin for the HC-SR04 sensor.

Arduino

const int trigPin = [1];

Drag options to blanks, or click blank then click option'

A2

B5

C13

D9

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing an analog pin instead of a digital pin for the trigger.

Using the same pin number for both trigger and echo.

The trigger pin is set to digital pin 9 to send the ultrasonic pulse.

2fill in blank

medium

Complete the code to set the echo pin as an input in the setup function.

Arduino

pinMode([1], INPUT);

Drag options to blanks, or click blank then click option'

AechoPin

BtrigPin

CledPin

DbuttonPin

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the trigger pin as input instead of output.

Using a pin variable that is not defined.

The echo pin must be set as an input to read the returning ultrasonic pulse.

3fill in blank

hard

Fix the error in the code to send a 10 microsecond pulse to the trigger pin.

Arduino

digitalWrite(trigPin, HIGH);
delayMicroseconds([1]);
digitalWrite(trigPin, LOW);

Drag options to blanks, or click blank then click option'

A1

B100

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using delay() instead of delayMicroseconds().

Using too long or too short pulse duration.

The HC-SR04 sensor requires a 10 microsecond pulse on the trigger pin to start measurement.

4fill in blank

hard

Fill both blanks to correctly calculate the distance in centimeters from the duration.

Arduino

long duration = pulseIn([1], HIGH);
float distance = duration [2] 58.2;

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AechoPin

B*

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying duration instead of dividing.

Using the trigger pin instead of echo pin for pulseIn.

The pulseIn function measures the time on the echo pin. Distance is calculated by dividing duration by 58.2.

5fill in blank

hard

Fill all three blanks to complete the loop that reads distance and prints it to the serial monitor.

Arduino

digitalWrite([1], LOW);
delayMicroseconds(2);
digitalWrite([2], HIGH);
delayMicroseconds(10);
digitalWrite([2], LOW);

long duration = pulseIn([3], HIGH);
float distance = duration / 58.2;
Serial.print("Distance: ");
Serial.print(distance);
Serial.println(" cm");

Drag options to blanks, or click blank then click option'

AtrigPin

BechoPin

Attempts:

3 left

💡 Hint

Common Mistakes

Using echo pin to send pulse instead of trigger pin.

Mixing up the order of setting pins HIGH and LOW.

The trigger pin is first set LOW, then HIGH for 10 microseconds, then LOW again to send the pulse. The echo pin is used to measure the pulse duration.

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