Digital output (GPIO.output) in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output state of the LED after running this code?

Consider this Raspberry Pi Python code controlling an LED connected to GPIO pin 18.

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)
state = GPIO.input(18)
print(state)

What will be printed?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)
state = GPIO.input(18)
print(state)

A 1

B 0

C GPIO.HIGH

D None

💡 Hint

GPIO.HIGH sets the pin to ON, so reading it back returns 1.

Setting GPIO.output(18, GPIO.HIGH) turns the pin ON. Reading it with GPIO.input(18) returns 1, which is printed.

🧠 Conceptual

intermediate

Which GPIO.output call will turn OFF the LED connected to pin 23?

You have an LED connected to GPIO pin 23. Which command will turn the LED OFF?

A GPIO.output(23, True)

B GPIO.output(23, GPIO.HIGH)

C GPIO.output(23, 1)

D GPIO.output(23, GPIO.LOW)

💡 Hint

LOW means OFF, HIGH means ON.

GPIO.LOW sets the pin voltage to 0V, turning the LED OFF. GPIO.HIGH or 1 or True sets it ON.

🔧 Debug

advanced

Why does this code raise a RuntimeError?

Look at this code snippet:

import RPi.GPIO as GPIO
GPIO.output(17, GPIO.HIGH)

When run, it raises a RuntimeError: 'You must setup() the GPIO channel first'. Why?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.output(17, GPIO.HIGH)

A Because GPIO.setup(17, GPIO.OUT) was not called before output()

B Because GPIO.setmode() was not called before output()

C Because GPIO.cleanup() was called before output()

D Because GPIO.output() cannot be called with GPIO.HIGH

💡 Hint

You must prepare the pin as output before setting its value.

GPIO.setup(pin, GPIO.OUT) configures the pin as output. Without it, output() raises RuntimeError.

📝 Syntax

advanced

Which option contains a syntax error in using GPIO.output?

Identify the code snippet that will cause a syntax error when trying to set GPIO pin 5 to LOW.

A GPIO.output(5, 0)

B GPIO.output(5 GPIO.LOW)

C GPIO.output(5, GPIO.LOW)

D GPIO.output(5, False)

💡 Hint

Check for missing commas or parentheses.

Option B misses a comma between arguments, causing a syntax error.

🚀 Application

expert

How many times will the LED blink in this code?

Given this code to blink an LED connected to GPIO pin 12:

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)
for i in range(5):
    GPIO.output(12, GPIO.HIGH)
    time.sleep(0.2)
    GPIO.output(12, GPIO.LOW)
    time.sleep(0.2)
GPIO.cleanup()

How many times does the LED turn ON (blink) before the program ends?

Raspberry Pi

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)
for i in range(5):
    GPIO.output(12, GPIO.HIGH)
    time.sleep(0.2)
    GPIO.output(12, GPIO.LOW)
    time.sleep(0.2)
GPIO.cleanup()

A 1

B 10

C 5

D 0

💡 Hint

Each loop cycle turns the LED ON once.

The loop runs 5 times, each time turning the LED ON once, so 5 blinks total.