First GPIO program (LED blink) in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Raspberry Pi GPIO LED blink code?

Consider this Python code to blink an LED connected to GPIO pin 17 on a Raspberry Pi. What will it print to the console?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

for i in range(3):
    GPIO.output(17, GPIO.HIGH)
    print("LED ON")
    time.sleep(0.5)
    GPIO.output(17, GPIO.LOW)
    print("LED OFF")
    time.sleep(0.5)

GPIO.cleanup()

A LED ON\nLED OFF\nLED ON\nLED OFF\nLED ON\nLED OFF

B LED ON\nLED ON\nLED ON\nLED OFF\nLED OFF\nLED OFF

C LED ON\nLED OFF\nLED ON\nLED ON\nLED OFF\nLED OFF

D LED OFF\nLED ON\nLED OFF\nLED ON\nLED OFF\nLED ON

💡 Hint

Each loop turns the LED ON then OFF once, printing messages accordingly.

The loop runs 3 times. Each time it prints "LED ON" then "LED OFF". So the output repeats these two lines 3 times.

🧠 Conceptual

intermediate

Which GPIO mode is used in this code and why?

In the code below, what does GPIO.setmode(GPIO.BCM) mean?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)

A It initializes the GPIO pins as input by default.

B It sets pin numbering to use the physical pin numbers on the header.

C It disables all GPIO pins to save power.

D It sets pin numbering to use the Broadcom chip's GPIO numbers.

💡 Hint

There are two common ways to number pins: BCM and BOARD.

GPIO.BCM means the program uses the Broadcom chip's GPIO numbering, not the physical pin numbers.

🔧 Debug

advanced

What error will this GPIO LED blink code produce?

Look at this code snippet. What error will it raise when run on a Raspberry Pi?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

GPIO.output(17, GPIO.HIGH)
print("LED ON")
time.sleep(1)

GPIO.cleanup()

GPIO.output(17, GPIO.LOW)
print("LED OFF")

A RuntimeError: GPIO channel already in use

B RuntimeError: You must setup() the GPIO channel first

C RuntimeError: The GPIO channel has been cleaned up and cannot be used

D No error, the code runs fine

💡 Hint

Consider what GPIO.cleanup() does before the last output call.

After calling GPIO.cleanup(), all GPIO channels are reset. Trying to use GPIO.output(17, GPIO.LOW) after cleanup causes a RuntimeError.

📝 Syntax

advanced

Which option fixes the syntax error in this GPIO blink code?

This code has a syntax error. Which option fixes it correctly?

for i in range(3)
    GPIO.output(17, GPIO.HIGH)
    time.sleep(0.5)

Raspberry Pi

for i in range(3)
    GPIO.output(17, GPIO.HIGH)
    time.sleep(0.5)

A Replace range(3) with range[3]

B Add a colon after the for statement: for i in range(3):

C Remove the parentheses from range: for i in range 3

D Indent the for statement by 4 spaces

💡 Hint

Python for loops require a colon at the end of the header line.

The syntax error is missing colon after for i in range(3). Adding the colon fixes it.

🚀 Application

expert

How many times will the LED blink in this code?

Given this Raspberry Pi GPIO code, how many times will the LED turn ON and OFF?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

count = 0
while count < 5:
    GPIO.output(17, GPIO.HIGH)
    time.sleep(0.2)
    GPIO.output(17, GPIO.LOW)
    time.sleep(0.2)
    count += 1

GPIO.cleanup()

A 5 times

B 10 times

C 1 time

D 0 times

💡 Hint

Count how many times the loop runs and what happens each time.

The loop runs 5 times. Each time the LED turns ON once and OFF once, so 5 blinks total.