DistanceSensor (ultrasonic) in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the DistanceSensor class from gpiozero.

Raspberry Pi

from gpiozero import [1]

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

ADistanceSensor

BLED

CButton

DMotor

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the wrong class like LED or Button.

Forgetting to import the class.

The DistanceSensor class is imported from the gpiozero library to use the ultrasonic sensor.

2fill in blank

medium

Complete the code to create a DistanceSensor object with trigger pin 17 and echo pin 18.

Raspberry Pi

sensor = DistanceSensor(trigger=[1], echo=18)

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

A27

B22

C17

D23

Attempts:

3 left

💡 Hint

Common Mistakes

Using the echo pin number for trigger.

Using a wrong pin number.

The trigger pin is set to GPIO 17 as specified.

3fill in blank

hard

Fix the error in the code to print the distance in centimeters.

Raspberry Pi

print(f"Distance: {sensor.[1] * 100:.1f} cm")

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

Adistance

Bvalue

Cdistance_cm

Ddistance_in

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent property like 'distance_cm'.

Not multiplying by 100 to convert meters to centimeters.

The distance property returns the distance in meters. Multiplying by 100 converts it to centimeters.

4fill in blank

hard

Fill both blanks to create a dictionary of distances for sensors on pins 5 and 6, only if distance is less than 0.5 meters.

Raspberry Pi

distances = {pin: sensor.distance for pin in [5, 6] if sensor.distance [1] [2]

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

A<

B0.5

C>

D1.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<'.

Using the wrong threshold value.

The condition checks if the distance is less than 0.5 meters.

5fill in blank

hard

Fill all three blanks to create a dictionary with pin numbers as keys, distances in cm as values, only for distances greater than 0.2 meters.

Raspberry Pi

dist_cm = {pin: sensor.[1] * 100 for pin in [7, 8] if sensor.[2] > [3]

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

Adistance

C0.2

D0.5

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names.

Using wrong threshold values.

The dictionary comprehension converts distance to centimeters and filters distances greater than 0.2 meters.

Practice

1. What does the DistanceSensor measure using ultrasonic waves?

easy

A. The speed of sound in water

B. The temperature of the air

C. The distance to an object without touching it

D. The brightness of a light source

Solution

1. Step 1: Understand the sensor's purpose

   The DistanceSensor uses sound waves to detect how far an object is without physical contact.

2. Step 2: Identify the correct measurement type

   It measures distance, not temperature, speed, or brightness.

3. Final Answer:

   The distance to an object without touching it -> Option C

4. Quick Check:

   DistanceSensor measures distance = C [OK]

Hint: Remember: ultrasonic means measuring distance by sound [OK]

Common Mistakes:

• Confusing distance with temperature
• Thinking it measures speed or light
• Assuming physical contact is needed

2. Which of the following is the correct way to create a DistanceSensor object in Python on Raspberry Pi?

easy

A. sensor = DistanceSensor(trigger=17, echo=4)

B. sensor = DistanceSensor(echo=17, trigger=4)

C. sensor = DistanceSensor(4, 17)

D. sensor = DistanceSensor(echo=4, trigger=17)

Solution

1. Step 1: Recall parameter names for DistanceSensor

   The DistanceSensor constructor expects named parameters: echo and trigger pins.

2. Step 2: Match correct pin assignments

   sensor = DistanceSensor(echo=17, trigger=4) correctly assigns echo=17 and trigger=4 as named arguments.

3. Final Answer:

   sensor = DistanceSensor(echo=17, trigger=4) -> Option B

4. Quick Check:

   Use named pins echo=17, trigger=4 = A [OK]

Hint: Use named arguments echo and trigger in correct order [OK]

Common Mistakes:

• Swapping echo and trigger pins
• Passing pins without names
• Using wrong pin numbers

3. What will the following code print if the sensor measures 0.25 meters?

from gpiozero import DistanceSensor
sensor = DistanceSensor(echo=17, trigger=4)
distance_cm = sensor.distance * 100
print(round(distance_cm))

medium

A. 25

B. 0.25

C. 250

D. 2.5

Solution

1. Step 1: Understand sensor.distance value

   The sensor.distance returns distance in meters as a float, here 0.25 meters.

2. Step 2: Convert meters to centimeters and round

   Multiplying 0.25 by 100 gives 25 centimeters, then rounding keeps it 25.

3. Final Answer:

   25 -> Option A

4. Quick Check:

   0.25 m * 100 = 25 cm [OK]

Hint: Multiply meters by 100 to get centimeters [OK]

Common Mistakes:

• Printing meters instead of centimeters
• Multiplying by 1000 instead of 100
• Not rounding the result

4. Identify the error in this code snippet using DistanceSensor:

from gpiozero import DistanceSensor
sensor = DistanceSensor(echo=4, trigger=17)
print(sensor.distance * 100)

medium

A. Echo and trigger pins are swapped

B. Missing import statement

C. sensor.distance returns centimeters directly

D. Print statement syntax error

Solution

1. Step 1: Check pin assignments

   The echo pin should be connected to the sensor's echo pin, trigger to trigger pin. Usually, echo=17 and trigger=4 is standard, so swapping is likely wrong.

2. Step 2: Verify other code parts

   Import is correct, sensor.distance returns meters (not centimeters), and print syntax is valid.

3. Final Answer:

   Echo and trigger pins are swapped -> Option A

4. Quick Check:

   Pin swap error = D [OK]

Hint: Echo pin usually higher number than trigger [OK]

Common Mistakes:

• Confusing echo and trigger pins
• Assuming distance returns centimeters
• Forgetting to import gpiozero

5. You want to measure distance in centimeters and print only integer values every second. Which code snippet correctly does this using DistanceSensor?

hard

A. from gpiozero import DistanceSensor
import time
sensor = DistanceSensor(echo=17, trigger=4)
while True:
print(sensor.distance)
time.sleep(1)

B. from gpiozero import DistanceSensor
sensor = DistanceSensor(echo=17, trigger=4)
print(round(sensor.distance))

C. from gpiozero import DistanceSensor
import time
sensor = DistanceSensor(echo=4, trigger=17)
while True:
print(sensor.distance * 100)
time.sleep(1)

D. from gpiozero import DistanceSensor
import time
sensor = DistanceSensor(echo=17, trigger=4)
while True:
print(int(sensor.distance * 100))
time.sleep(1)

Solution

1. Step 1: Check pin assignments and imports

   from gpiozero import DistanceSensor import time sensor = DistanceSensor(echo=17, trigger=4) while True: print(int(sensor.distance * 100)) time.sleep(1) correctly imports time, sets echo=17 and trigger=4, which is standard.

2. Step 2: Verify distance calculation and printing

   It multiplies sensor.distance (meters) by 100 to get centimeters, converts to int for integer output, and prints every second with time.sleep(1).

3. Step 3: Compare with other options

   from gpiozero import DistanceSensor sensor = DistanceSensor(echo=17, trigger=4) print(round(sensor.distance)) prints once and rounds meters, not centimeters. from gpiozero import DistanceSensor import time sensor = DistanceSensor(echo=4, trigger=17) while True: print(sensor.distance * 100) time.sleep(1) swaps pins and prints float centimeters. from gpiozero import DistanceSensor import time sensor = DistanceSensor(echo=17, trigger=4) while True: print(sensor.distance) time.sleep(1) prints meters, not centimeters.

4. Final Answer:

   from gpiozero import DistanceSensor import time sensor = DistanceSensor(echo=17, trigger=4) while True: print(int(sensor.distance * 100)) time.sleep(1) -> Option D

5. Quick Check:

   Correct pins, int centimeters, 1-second delay = A [OK]

Hint: Multiply by 100, convert to int, use sleep(1) for timing [OK]

Common Mistakes:

• Swapping echo and trigger pins
• Not converting meters to centimeters
• Printing only once instead of every second