PWMLED for brightness in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the PWMLED class from gpiozero.

Raspberry Pi

from gpiozero import [1]

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

ALED

BPWMLED

CButton

DOutputDevice

Attempts:

3 left

💡 Hint

Common Mistakes

Importing LED instead of PWMLED

Importing Button which is unrelated

Importing OutputDevice which is too general

We import PWMLED to control LED brightness using pulse-width modulation.

2fill in blank

medium

Complete the code to create a PWMLED object on GPIO pin 17.

Raspberry Pi

led = PWMLED([1])

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

A18

B27

C22

D17

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin 18 or 22 which are valid pins but not the one asked

Using pin 27 which is higher than 22

GPIO pin 17 is used to connect the LED for brightness control.

3fill in blank

hard

Fix the error in setting the LED brightness to 50%.

Raspberry Pi

led.value = [1]

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

A0.5

B50

C1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 50 which is out of range

Using 5 which is too high

Using 1 which is full brightness

The brightness value must be between 0.0 (off) and 1.0 (full brightness). 50% brightness is 0.5.

4fill in blank

hard

Fill both blanks to create a dictionary of LED brightness for words longer than 3 letters.

Raspberry Pi

brightness = {word: [1] for word in words if len(word) [2] 3}

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

Alen(word)

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '==' which filter wrong words

Using word instead of len(word) for brightness

We use len(word) to get brightness and filter words longer than 3 with >.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping uppercase words to brightness values greater than 0.3.

Raspberry Pi

brightness = [1]: [2] for word in words if [2] [3] 0.3}

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

Aword.upper()

Bword

C>

Dlen(word)

Attempts:

3 left

💡 Hint

Common Mistakes

Using word as the value instead of len(word)

Using '<' instead of '>' in filter

Using word instead of word.upper() as key

Keys are uppercase words (word.upper()), values are brightness (len(word)), filtered by brightness > 0.3.

Practice

1. What does the PWMLED class control on a Raspberry Pi?

easy

A. The speed of the Raspberry Pi fan

B. The color of an LED by mixing red, green, and blue lights

C. The temperature of the Raspberry Pi CPU

D. The brightness of an LED by changing how long it is on and off quickly

Solution

1. Step 1: Understand PWMLED purpose

   PWMLED is used to control LED brightness by adjusting the time it stays on and off rapidly.

2. Step 2: Compare options

   Only The brightness of an LED by changing how long it is on and off quickly describes brightness control using on/off timing, which matches PWMLED's function.

3. Final Answer:

   The brightness of an LED by changing how long it is on and off quickly -> Option D

4. Quick Check:

   PWMLED controls brightness = A [OK]

Hint: PWM means brightness by fast on/off timing [OK]

Common Mistakes:

• Confusing brightness with color control
• Thinking PWMLED controls temperature or fan speed

2. Which of the following is the correct way to set the brightness of a PWMLED named led to half brightness?

easy

A. led.set_brightness = 0.5

B. led.brightness(0.5)

C. led.brightness = 0.5

D. led.brightness = 50

Solution

1. Step 1: Recall PWMLED brightness syntax

   Brightness is set by assigning a float between 0 and 1 to the brightness attribute.

2. Step 2: Check each option

   led.brightness = 0.5 uses correct attribute assignment with 0.5 (half brightness). Others use wrong syntax or wrong value type.

3. Final Answer:

   led.brightness = 0.5 -> Option C

4. Quick Check:

   Set brightness by attribute = C [OK]

Hint: Use led.brightness = value between 0 and 1 [OK]

Common Mistakes:

• Calling brightness like a function
• Using integer 50 instead of 0.5
• Trying to assign to a method

3. What will be the output behavior of this code snippet?

from gpiozero import PWMLED
import time
led = PWMLED(17)
led.brightness = 0.2
time.sleep(2)
led.brightness = 0.8
time.sleep(2)
led.off()

medium

A. LED glows dimly for 2 seconds, then brightly for 2 seconds, then turns off

B. LED glows brightly for 2 seconds, then dimly for 2 seconds, then turns off

C. LED stays off the whole time

D. Code causes an error because brightness is set incorrectly

Solution

1. Step 1: Analyze brightness settings

   First brightness is 0.2 (dim), then after 2 seconds it changes to 0.8 (bright).

2. Step 2: Understand timing and off command

   Each brightness level lasts 2 seconds, then LED is turned off.

3. Final Answer:

   LED glows dimly for 2 seconds, then brightly for 2 seconds, then turns off -> Option A

4. Quick Check:

   Brightness changes 0.2 to 0.8 then off = A [OK]

Hint: Brightness values control glow level over time [OK]

Common Mistakes:

• Mixing order of brightness values
• Thinking brightness values cause errors
• Assuming LED stays on after off()

4. Identify the error in this code that tries to set LED brightness:

from gpiozero import PWMLED
led = PWMLED(18)
led.brightness(0.7)

medium

A. Using parentheses after brightness instead of assignment

B. Wrong pin number for PWMLED

C. Missing import for time module

D. PWMLED does not support brightness control

Solution

1. Step 1: Check how brightness is set

   Brightness is an attribute, so it should be assigned a value, not called like a function.

2. Step 2: Verify other options

   Pin 18 is valid, time module is not needed here, and PWMLED supports brightness.

3. Final Answer:

   Using parentheses after brightness instead of assignment -> Option A

4. Quick Check:

   brightness is attribute, not method = D [OK]

Hint: Set brightness with =, not parentheses [OK]

Common Mistakes:

• Calling brightness like a function
• Assuming pin number causes error
• Thinking time import is required here

5. You want to smoothly increase an LED's brightness from off to full over 5 seconds using PWMLED. Which code snippet correctly achieves this?

hard

A. from gpiozero import PWMLED
import time
led = PWMLED(21)
for i in range(5):
led.brightness = i
time.sleep(1)
led.off()

B. from gpiozero import PWMLED
import time
led = PWMLED(21)
for i in range(6):
led.brightness = i / 5
time.sleep(1)
led.off()

C. from gpiozero import PWMLED
import time
led = PWMLED(21)
for i in range(0, 1, 0.2):
led.brightness = i
time.sleep(1)
led.off()

D. from gpiozero import PWMLED
import time
led = PWMLED(21)
for i in range(5):
led.brightness = 1 - i / 5
time.sleep(1)
led.off()

Solution

1. Step 1: Understand brightness range and timing

   Brightness must go from 0 to 1 in steps over 5 seconds, so dividing i by 5 in 6 steps (0 to 5) works.

2. Step 2: Check each code snippet

   from gpiozero import PWMLED
   import time
   led = PWMLED(21)
   for i in range(6):
       led.brightness = i / 5
       time.sleep(1)
   led.off()

   correctly uses i/5 for brightness from 0 to 1 in 1-second steps.

   from gpiozero import PWMLED
   import time
   led = PWMLED(21)
   for i in range(5):
       led.brightness = i
       time.sleep(1)
   led.off()

   sets brightness to integers >1 (invalid).

   from gpiozero import PWMLED
   import time
   led = PWMLED(21)
   for i in range(0, 1, 0.2):
       led.brightness = i
       time.sleep(1)
   led.off()

   uses range with float step (invalid syntax).

   from gpiozero import PWMLED
   import time
   led = PWMLED(21)
   for i in range(5):
       led.brightness = 1 - i / 5
       time.sleep(1)
   led.off()

   decreases brightness instead of increasing.

3. Final Answer:

   Code that increases brightness smoothly from 0 to 1 over 5 seconds using i/5 steps -> Option B

4. Quick Check:

   Brightness from 0 to 1 in steps = B [OK]

Hint: Divide loop index by max steps for smooth brightness [OK]

Common Mistakes:

• Using integer brightness values >1
• Trying to use float step in range (not allowed)
• Decreasing brightness instead of increasing