LED class and methods in Raspberry Pi - Mini Project: Build & Apply

LED class and methods

📖 Scenario: You have a Raspberry Pi connected to an LED light. You want to control the LED by turning it on and off using a simple program.

🎯 Goal: Create a class called LED that can turn the LED on and off using methods. Then, use this class to turn the LED on and off.

📋 What You'll Learn

Create a class named LED

Add an __init__ method that takes a pin number and stores it

Add a method turn_on that prints "LED on pin X is ON" where X is the pin number

Add a method turn_off that prints "LED on pin X is OFF" where X is the pin number

Create an instance of LED with pin number 17

Call turn_on and turn_off methods on the instance

💡 Why This Matters

🌍 Real World

Controlling hardware like LEDs on a Raspberry Pi is common in home automation and robotics projects.

💼 Career

Understanding how to create classes and methods to control hardware devices is useful for embedded systems and IoT developer roles.

1

Create the LED class with an __init__ method

Create a class called LED with an __init__ method that takes a parameter pin and stores it in self.pin.

Raspberry Pi

# Your code here

Hint

Remember, the __init__ method sets up the object with the pin number.

2

Add methods to turn the LED on and off

Add a method turn_on that prints "LED on pin {self.pin} is ON" and a method turn_off that prints "LED on pin {self.pin} is OFF" inside the LED class.

Raspberry Pi

class LED:
    def __init__(self, pin):
        self.pin = pin

# Your code here

Hint

Use print(f"LED on pin {self.pin} is ON") inside turn_on and similar for turn_off.

3

Create an LED instance with pin 17

Create an instance of the LED class named led with the pin number 17.

Raspberry Pi

class LED:
    def __init__(self, pin):
        self.pin = pin

    def turn_on(self):
        print(f"LED on pin {self.pin} is ON")

    def turn_off(self):
        print(f"LED on pin {self.pin} is OFF")

# Your code here

Hint

Use led = LED(17) to create the LED object.

4

Turn the LED on and off using the methods

Call the turn_on method on led to turn the LED on, then call the turn_off method on led to turn the LED off. Print the output.

Raspberry Pi

class LED:
    def __init__(self, pin):
        self.pin = pin

    def turn_on(self):
        print(f"LED on pin {self.pin} is ON")

    def turn_off(self):
        print(f"LED on pin {self.pin} is OFF")

led = LED(17)

# Your code here

Hint

Use led.turn_on() and led.turn_off() to show the LED status.

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