DistanceSensor (ultrasonic) in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ultrasonic sensor reading code?

Consider this Python code snippet using the DistanceSensor from gpiozero on a Raspberry Pi. What will it print?

Raspberry Pi

from gpiozero import DistanceSensor
sensor = DistanceSensor(echo=17, trigger=4)
distance = sensor.distance
print(round(distance, 2))

A A float number representing distance in meters, rounded to 2 decimals

B An integer number representing distance in centimeters

C A string describing the distance like 'Distance: 0.5m'

D A runtime error because sensor.distance is not a valid attribute

💡 Hint

Check the distance attribute of the DistanceSensor class in gpiozero.

The distance attribute returns a float representing the distance in meters. The code rounds it to 2 decimals and prints it as a number.

🧠 Conceptual

intermediate

Which pin is used as the trigger in this DistanceSensor setup?

Given this setup: DistanceSensor(echo=18, trigger=23), which GPIO pin sends the ultrasonic pulse?

A GPIO 18

B Neither, pins must be specified differently

C Both GPIO 18 and 23

D GPIO 23

💡 Hint

Remember: trigger pin sends the pulse, echo pin listens.

The trigger pin is the one that sends the ultrasonic pulse. Here it is GPIO 23.

🔧 Debug

advanced

Why does this DistanceSensor code raise an AttributeError?

Look at this code snippet:

from gpiozero import DistanceSensor
sensor = DistanceSensor(echo=27, trigger=22)
print(sensor.get_distance())

Why does it raise AttributeError: 'DistanceSensor' object has no attribute 'get_distance'?

A Because the pins 27 and 22 are invalid GPIO pins

B Because the sensor must be initialized with <code>DistanceSensor(trigger=22, echo=27)</code> instead

C Because the DistanceSensor class uses the attribute <code>distance</code>, not a method <code>get_distance()</code>

D Because the gpiozero library is not imported correctly

💡 Hint

Check the official gpiozero DistanceSensor API for available methods and attributes.

The DistanceSensor class provides a distance attribute, not a get_distance() method. Calling the latter causes AttributeError.

📝 Syntax

advanced

Which option correctly initializes a DistanceSensor with trigger on GPIO 5 and echo on GPIO 6?

Choose the correct Python code snippet that creates a DistanceSensor object with trigger pin 5 and echo pin 6.

A sensor = DistanceSensor(echo=5, trigger=6)

B sensor = DistanceSensor(trigger=5, echo=6)

C sensor = DistanceSensor(5, 6)

D sensor = DistanceSensor(trigger_pin=5, echo_pin=6)

💡 Hint

Check the parameter names in the DistanceSensor constructor.

The correct parameter names are trigger and echo. Option B uses them correctly.

🚀 Application

expert

How many distance readings will this code collect in 5 seconds?

Consider this code snippet:

from gpiozero import DistanceSensor
import time
sensor = DistanceSensor(echo=24, trigger=25)
start = time.time()
readings = []
while time.time() - start < 5:
    readings.append(sensor.distance)
print(len(readings))

Assuming the loop runs as fast as possible, how many readings will be collected approximately?

A About 50 readings (due to sensor measurement delay)

B About 100 readings (limited by sensor response time)

C About 5000 readings (one per millisecond)

D Exactly 5 readings (one per second)

💡 Hint

Think about how fast the ultrasonic sensor can measure distance and how fast the loop can run.

The DistanceSensor updates roughly every 0.1 seconds due to sensor timing, so about 50 readings in 5 seconds.