LED class and methods in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to turn the LED on.

Raspberry Pi

led = LED(17)
led.[1]()

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

Ablink

Boff

Con

Dtoggle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'off' instead of 'on' will turn the LED off.

Using 'blink' or 'toggle' will not simply turn the LED on.

The on() method turns the LED on.

2fill in blank

medium

Complete the code to make the LED blink once.

Raspberry Pi

led = LED(18)
led.[1](1)

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

Ablink

Btoggle

Coff

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' will keep the LED on without blinking.

Using 'off' will turn the LED off.

Using 'toggle' switches the LED state but does not blink.

The blink() method makes the LED blink. The argument 1 means blink once.

3fill in blank

hard

Fix the error in the code to toggle the LED state.

Raspberry Pi

led = LED(22)
led.[1]()

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

Atoggle

Bblink

Con

Doff

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'blink' will make the LED flash instead of toggling.

Using 'on' or 'off' sets the LED to a fixed state.

The toggle() method changes the LED from on to off or off to on.

4fill in blank

hard

Fill both blanks to create a dictionary with LED pins and the results of LED methods on those pins.

Raspberry Pi

led_states = {17: LED(17).[1](), 18: LED(18).[2]()}

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

Ais_lit

Bon

Coff

Dtoggle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'is_lit' will turn the LED on instead of checking.

Using 'toggle' will change the LED state instead of turning it off.

The is_lit() method checks if the LED is on, and off() turns the LED off.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension with LED pin names and states.

Raspberry Pi

led_status = {{ [1]: LED([3]).[2]() for [3] in [17, 18, 22] }}

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

Apin

Bis_lit

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for key and loop variable causes errors.

Using 'on' or 'off' instead of 'is_lit' changes LED state instead of checking.

The dictionary uses the pin number as key (pin), calls is_lit() to get the LED state, and loops over pins using pin.

Practice

1.

What does the on() method of an LED class typically do in Raspberry Pi programming?

easy

A. Turns the LED light on

B. Turns the LED light off

C. Makes the LED blink continuously

D. Cleans up the GPIO pins

Solution

1. Step 1: Understand the purpose of on() method

   The on() method is designed to switch the LED light to the ON state.

2. Step 2: Compare with other methods

   Other methods like off() turn the LED off, and blink() makes it blink. Cleanup is done separately.

3. Final Answer:

   Turns the LED light on -> Option A

4. Quick Check:

   on() means LED ON [OK]

Hint: Remember: on() means light ON, off() means light OFF [OK]

Common Mistakes:

• Confusing on() with off()
• Thinking on() cleans GPIO pins
• Assuming on() makes LED blink

2.

Which of the following is the correct way to create an LED object on GPIO pin 17 using the gpiozero library?

from gpiozero import LED

led = ?

easy

A. LED(17)

B. LED.pin(17)

C. LED[17]

D. LED{17}

Solution

1. Step 1: Recall LED object creation syntax

   In gpiozero, you create an LED by calling LED(pin_number), e.g., LED(17).

2. Step 2: Check other options for syntax errors

   Options A, B, and D use invalid Python syntax for object creation.

3. Final Answer:

   LED(17) -> Option A

4. Quick Check:

   LED(pin) = LED(17) [OK]

Hint: Use parentheses with pin number: LED(17) [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Trying to call a method like LED.pin()
• Using curly braces which are invalid here

3.

What will be the output of this code snippet controlling an LED?

from gpiozero import LED
from time import sleep

led = LED(22)
led.on()
sleep(1)
led.off()
print('LED state:', led.is_lit)

medium

A. SyntaxError

B. LED state: True

C. LED state: None

D. LED state: False

Solution

1. Step 1: Trace the LED state changes

   The LED is turned on, then after 1 second turned off before printing.

2. Step 2: Check the printed LED state

   After led.off(), led.is_lit is False, so output is 'LED state: False'.

3. Final Answer:

   LED state: False -> Option D

4. Quick Check:

   LED off means is_lit = False [OK]

Hint: Check final LED state after all commands run [OK]

Common Mistakes:

• Assuming LED stays on after off()
• Confusing is_lit property value
• Expecting syntax error due to sleep

4.

Identify the error in this code that tries to blink an LED on pin 5:

from gpiozero import LED
from time import sleep

led = LED(5)
led.blink(on_time=0.5, off_time=0.5)
sleep(2)
led.off()

medium

A. Missing led.on() before blink

B. Should call led.close() to clean GPIO

C. No error; code works correctly

D. blink() method requires a times argument

Solution

1. Step 1: Review the code for GPIO cleanup

   The code blinks the LED and turns it off but does not release GPIO resources.

2. Step 2: Identify missing cleanup step

   Proper practice is to call led.close() to free GPIO pins after use.

3. Final Answer:

   Should call led.close() to clean GPIO -> Option B

4. Quick Check:

   Always close GPIO pins after use [OK]

Hint: Always close() LEDs to free GPIO pins [OK]

Common Mistakes:

• Thinking blink() needs on() first
• Assuming blink() requires times argument
• Ignoring GPIO cleanup after program

5.

You want to create a program that blinks two LEDs on pins 17 and 27 alternately every 0.5 seconds for 5 seconds total. Which code snippet correctly implements this using the LED class?

from gpiozero import LED
from time import sleep

led1 = LED(17)
led2 = LED(27)

start = 0
while start < 5:
    led1.on()
    led2.off()
    sleep(0.5)
    led1.off()
    led2.on()
    sleep(0.5)
    start += 1

led1.off()
led2.off()
led1.close()
led2.close()

hard

A. Should use blink() method instead of manual on/off

B. The loop runs too long; should use start < 10

C. This code blinks LEDs alternately for 5 seconds correctly

D. Missing sleep between led1.off() and led2.on()

Solution

1. Step 1: Analyze the loop timing and LED control

   The loop runs 5 times, each iteration takes 1 second (two 0.5s sleeps), total 5 seconds blinking alternately.

2. Step 2: Check LED on/off sequence and cleanup

   LED1 and LED2 turn on/off alternately with proper sleep delays, and GPIO pins are closed at the end.

3. Final Answer:

   This code blinks LEDs alternately for 5 seconds correctly -> Option C

4. Quick Check:

   Loop count x sleep = total blink time [OK]

Hint: Count loop x sleep to verify total blink time [OK]

Common Mistakes:

• Miscounting total blink duration
• Forgetting to close GPIO pins
• Assuming blink() method is mandatory