Setting pin mode (IN, OUT) in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this GPIO pin mode setup code?

Consider this Python code using the RPi.GPIO library to set a pin mode and read its state:

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

What will this code print if the pin 18 is connected to ground?

Raspberry Pi

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

A 0

B Raises RuntimeError

C GPIO.IN

D 1

💡 Hint

Remember, when a pin is set as input and connected to ground, its state reads as low.

The pin 18 is set as input. When connected to ground, the input reads low, which is 0.

❓ Predict Output

intermediate

What happens when you set a pin as output and write HIGH?

Given this code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(23, GPIO.OUT)
GPIO.output(23, GPIO.HIGH)
print(GPIO.input(23))

What will be printed?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(23, GPIO.OUT)
GPIO.output(23, GPIO.HIGH)
print(GPIO.input(23))

A 0

B Raises RuntimeError

C 1

D GPIO.HIGH

💡 Hint

Output pins reflect the value you set on them.

Pin 23 is set as output and set to HIGH, so reading it returns 1.

🔧 Debug

advanced

Identify the error in this pin setup code

Look at this code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, 1)
GPIO.setup(17, GPIO.IN)
print(GPIO.input(17))

What error will this code cause when run?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, 1)
GPIO.setup(17, GPIO.IN)
print(GPIO.input(17))

A No error, prints 0 or 1 depending on pin state

B RuntimeWarning: Channel already in use

C RuntimeError: You must setup GPIO before using it

D TypeError: invalid argument type

💡 Hint

Think about setting up the same pin twice without cleanup.

Setting up the same pin twice without cleanup causes a RuntimeWarning about channel already in use.

🧠 Conceptual

advanced

Which statement about GPIO pin modes is true?

Choose the correct statement about setting GPIO pin modes on Raspberry Pi:

A Pins set as output automatically detect input voltage

B Pins set as output can read external voltage levels

C Pins set as input can drive voltage to external devices

D Pins set as input can only read voltage levels, not drive voltage

💡 Hint

Think about the difference between input and output pins.

Input pins read voltage levels but do not drive voltage. Output pins drive voltage but reading them depends on the hardware.

❓ Predict Output

expert

What is the output of this GPIO pin toggle code?

Consider this code that toggles a pin state:

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(27, GPIO.OUT)
GPIO.output(27, GPIO.LOW)
time.sleep(0.1)
GPIO.output(27, not GPIO.input(27))
print(GPIO.input(27))

What will be printed?

Raspberry Pi

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(27, GPIO.OUT)
GPIO.output(27, GPIO.LOW)
time.sleep(0.1)
GPIO.output(27, not GPIO.input(27))
print(GPIO.input(27))

A 1

B 0

C Raises RuntimeError

D Raises TypeError

💡 Hint

Think about toggling the pin state from LOW to HIGH.

The pin starts LOW (0). The code sets it to the opposite of current state, which is HIGH (1). Then it prints 1.