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.

Practice

1. What is the main purpose of the GPIO.setup(pin, GPIO.OUT) command in a Raspberry Pi LED blink program?

easy

A. It cleans up the GPIO pins after use.

B. It reads the input from the LED.

C. It turns the LED on immediately.

D. It sets the specified pin as an output to control the LED.

Solution

1. Step 1: Understand GPIO pin modes

   The Raspberry Pi GPIO pins can be set as input or output. To control an LED, the pin must send signals, so it needs to be an output.

2. Step 2: Role of GPIO.setup

   The command GPIO.setup(pin, GPIO.OUT) configures the pin as an output pin, allowing the program to turn the LED on or off.

3. Final Answer:

   It sets the specified pin as an output to control the LED. -> Option D

4. Quick Check:

   GPIO.setup with GPIO.OUT means output pin [OK]

Hint: Remember: setup with GPIO.OUT means output pin [OK]

Common Mistakes:

• Confusing input and output pin setup
• Thinking setup turns LED on
• Mixing cleanup with setup

2. Which of the following is the correct way to import the GPIO library and set the pin numbering mode for a Raspberry Pi LED blink program?

easy

A. import RPi.GPIO as GPIO\nGPIO.setupmode(GPIO.BCM)

B. import RPi.GPIO as GPIO\nGPIO.setmode(GPIO.BOARD)

C. import RPi.GPIO as GPIO\nGPIO.setmode(GPIO.OUT)

D. import gpiozero\ngpiozero.setmode(GPIO.BCM)

Solution

1. Step 1: Importing the GPIO library

   The standard library to control GPIO pins on Raspberry Pi is RPi.GPIO, imported as GPIO.

2. Step 2: Setting pin numbering mode

   We use GPIO.setmode() to choose pin numbering style. GPIO.BOARD uses physical pin numbers, which is common for beginners.

3. Final Answer:

   import RPi.GPIO as GPIO\nGPIO.setmode(GPIO.BOARD) -> Option B

4. Quick Check:

   Import RPi.GPIO and setmode BOARD [OK]

Hint: Use 'import RPi.GPIO as GPIO' and 'GPIO.setmode(GPIO.BOARD)' [OK]

Common Mistakes:

• Using gpiozero instead of RPi.GPIO
• Wrong method names like setupmode
• Setting mode to GPIO.OUT instead of BOARD or BCM

3. What will be the output behavior of this code snippet controlling an LED on pin 11?

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.OUT)
for i in range(3):
    GPIO.output(11, GPIO.HIGH)
    time.sleep(1)
    GPIO.output(11, GPIO.LOW)
    time.sleep(1)
GPIO.cleanup()

medium

A. The LED will blink on and off 3 times with 1 second intervals.

B. The LED will stay on continuously for 3 seconds.

C. The LED will blink rapidly without delay.

D. The program will raise an error due to missing setup.

Solution

1. Step 1: Analyze the loop and GPIO output commands

   The loop runs 3 times. Each time, the LED pin is set HIGH (on), waits 1 second, then set LOW (off), waits 1 second.

2. Step 2: Understand the LED blinking pattern

   This means the LED turns on for 1 second, off for 1 second, repeated 3 times, resulting in 3 blinks.

3. Final Answer:

   The LED will blink on and off 3 times with 1 second intervals. -> Option A

4. Quick Check:

   Loop with sleep controls blink count and duration [OK]

Hint: Loop with sleep(1) toggles LED on/off 3 times [OK]

Common Mistakes:

• Thinking LED stays on continuously
• Ignoring sleep delays causing rapid blinking
• Assuming missing setup causes error here

4. Identify the error in this Raspberry Pi LED blink code:

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)
time.sleep(1)
GPIO.output(18, GPIO.LOW)
GPIO.cleanup()

medium

A. Pin 18 is not set up as output before use.

B. Missing import of time module.

C. GPIO.setmode(GPIO.BCM) conflicts with pin numbering 18 if BOARD mode expected.

D. GPIO.cleanup() should be called before output commands.

Solution

1. Step 1: Check pin numbering mode and pin number

   The code uses GPIO.setmode(GPIO.BCM), which means pin numbers refer to Broadcom chip pins. Pin 18 is valid in BCM mode, but if the user expects physical pin numbering (BOARD), this causes confusion.

2. Step 2: Understand the mismatch impact

   If the user wired the LED to physical pin 18 (BOARD), but code uses BCM mode, the LED won't work as expected. This is a common error mixing modes and pin numbers.

3. Final Answer:

   GPIO.setmode(GPIO.BCM) conflicts with pin numbering 18 if BOARD mode expected. -> Option C

4. Quick Check:

   Pin numbering mode must match wiring [OK]

Hint: Match setmode with pin numbering used [OK]

Common Mistakes:

• Confusing BOARD and BCM pin numbers
• Calling cleanup too early
• Forgetting to import time module

5. You want to blink two LEDs connected to pins 7 and 11 alternately for 5 cycles using Raspberry Pi GPIO. Which code snippet correctly implements this behavior?

hard

A. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.OUT)
GPIO.setup(11, GPIO.OUT)
for _ in range(5):
GPIO.output(7, GPIO.HIGH)
GPIO.output(11, GPIO.LOW)
time.sleep(0.5)
GPIO.output(7, GPIO.LOW)
GPIO.output(11, GPIO.HIGH)
time.sleep(0.5)
GPIO.cleanup()

B. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.OUT)
for _ in range(5):
GPIO.output(7, GPIO.HIGH)
GPIO.output(11, GPIO.LOW)
time.sleep(1)
GPIO.cleanup()

C. import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.OUT)
GPIO.setup(11, GPIO.OUT)
GPIO.output(7, GPIO.HIGH)
GPIO.output(11, GPIO.HIGH)
GPIO.cleanup()

D. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.IN)
GPIO.setup(11, GPIO.IN)
for _ in range(5):
GPIO.output(7, GPIO.HIGH)
GPIO.output(11, GPIO.LOW)
time.sleep(0.5)
GPIO.cleanup()

Solution

1. Step 1: Setup pins as output and initialize GPIO

   Both pins 7 and 11 are set as outputs using GPIO.setup(pin, GPIO.OUT). The mode is set to BOARD to match physical pin numbers.

2. Step 2: Alternate LEDs in a loop with delays

   The loop runs 5 times. Inside each cycle, pin 7 is turned on and pin 11 off, then after 0.5 seconds, pin 7 is off and pin 11 on, creating alternate blinking.

3. Step 3: Cleanup GPIO pins after use

   Calling GPIO.cleanup() resets the pins safely after blinking finishes.

4. Final Answer:

   Code in option A correctly blinks two LEDs alternately for 5 cycles. -> Option A

5. Quick Check:

   Alternate output with sleep and cleanup [OK]

Hint: Use two outputs toggled alternately with sleep [OK]

Common Mistakes:

• Setting pins as input instead of output
• Not toggling both pins alternately
• Missing time delays causing no visible blink