Multiple LED patterns in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LED blinking code?

Consider this Python code controlling an LED connected to GPIO pin 17 on a Raspberry Pi. What will be the LED's behavior?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)

for _ in range(3):
    GPIO.output(17, GPIO.HIGH)
    time.sleep(0.5)
    GPIO.output(17, GPIO.LOW)
    time.sleep(0.5)

GPIO.cleanup()

A The LED stays off and never turns on.

B The LED stays on continuously for 3 seconds.

C The LED blinks on and off 6 times, each state lasting 0.5 seconds.

D The LED blinks on and off 3 times, each state lasting 0.5 seconds.

💡 Hint

Look at the loop and the sleep durations to understand how many times the LED changes state.

The loop runs 3 times. Each iteration turns the LED on for 0.5 seconds, then off for 0.5 seconds, resulting in 3 blinks.

❓ Predict Output

intermediate

What pattern does this LED sequence produce?

This code controls two LEDs connected to GPIO pins 17 and 27. What is the resulting LED pattern?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.setup(27, GPIO.OUT)

for _ in range(2):
    GPIO.output(17, GPIO.HIGH)
    GPIO.output(27, GPIO.LOW)
    time.sleep(1)
    GPIO.output(17, GPIO.LOW)
    GPIO.output(27, GPIO.HIGH)
    time.sleep(1)

GPIO.cleanup()

A LED on pin 17 and LED on pin 27 alternate turning on every second, repeating twice.

B Only the LED on pin 17 blinks twice; the other stays off.

C Both LEDs turn on and off together twice with 1 second intervals.

D Both LEDs stay off the entire time.

💡 Hint

Check which LED is on and off in each step inside the loop.

The code turns on LED 17 while LED 27 is off for 1 second, then switches states for 1 second, repeating twice.

🔧 Debug

advanced

Why does this LED pattern code raise an error?

Examine this code snippet intended to blink an LED connected to GPIO pin 22. Why does it raise an error?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.OUT)

for i in range(3):
    GPIO.output(22, GPIO.HIGH)
    time.sleep(0.3)
    GPIO.output(22, GPIO.LOW)
    time.sleep(0.3)

GPIO.cleanup()

A SyntaxError due to missing colon after the for loop declaration.

B RuntimeError because GPIO pin 22 is not set up correctly.

C TypeError because time.sleep() is called with a float instead of an integer.

D NameError because GPIO is not imported.

💡 Hint

Check the for loop syntax carefully.

The for loop line is missing a colon at the end, causing a SyntaxError.

🚀 Application

advanced

How many LED blinks occur in this pattern?

This code runs a pattern on an LED connected to GPIO pin 5. How many times does the LED blink (turn on then off) before the program ends?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(5, GPIO.OUT)

for i in range(2):
    for j in range(3):
        GPIO.output(5, GPIO.HIGH)
        time.sleep(0.2)
        GPIO.output(5, GPIO.LOW)
        time.sleep(0.2)
    time.sleep(0.5)

GPIO.cleanup()

A 5 blinks

B 6 blinks

C 2 blinks

D 3 blinks

💡 Hint

Count the inner loop blinks and multiply by the outer loop iterations.

The inner loop blinks 3 times per outer loop iteration. The outer loop runs twice, so total blinks = 3 * 2 = 6.

🧠 Conceptual

expert

What is the main advantage of using PWM for LED brightness control on Raspberry Pi?

Pulse Width Modulation (PWM) is often used to control LED brightness. What is the key advantage of using PWM instead of just turning the LED on and off quickly?

A PWM makes the LED blink faster so it appears to be a different color.

B PWM increases the voltage to the LED to make it brighter than normal.

C PWM allows smooth brightness control by varying the on/off ratio without changing voltage, saving power and reducing heat.

D PWM is used to change the LED's physical size by controlling current.

💡 Hint

Think about how brightness changes without damaging the LED or wasting energy.

PWM changes the fraction of time the LED is on, controlling brightness smoothly without increasing voltage or current, which saves power and reduces heat.