Button press detection in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Detecting a button press with GPIO input

What will be the output of this Raspberry Pi Python code when the button connected to GPIO pin 17 is pressed?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_UP)

try:
    while True:
        if GPIO.input(17) == GPIO.LOW:
            print("Button pressed")
            break
        time.sleep(0.1)
finally:
    GPIO.cleanup()

A No output, program runs forever

B GPIO.setup error

C Button pressed

D RuntimeError due to missing cleanup

💡 Hint

Remember that the button is connected with a pull-up resistor, so pressing it pulls the pin LOW.

The code sets up GPIO 17 as input with an internal pull-up resistor. When the button is pressed, the input reads LOW, triggering the print statement and breaking the loop.

❓ Predict Output

intermediate

Detecting button release event

What will this code print when the button connected to GPIO pin 22 is released after being pressed?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

try:
    while True:
        if GPIO.input(22) == GPIO.HIGH:
            print("Button released")
            break
        time.sleep(0.1)
finally:
    GPIO.cleanup()

A RuntimeError due to wrong pull_up_down setting

B Button released

C No output, program runs forever

D Button pressed

💡 Hint

Check the pull-down resistor and what HIGH means for the button state.

The button is set with a pull-down resistor, so when released, the input reads HIGH, triggering the print statement.

🔧 Debug

advanced

Why does this button press detection code not print anything?

Consider this code snippet intended to detect a button press on GPIO pin 5. Why does it never print "Pressed"?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

while True:
    if GPIO.input(5) == GPIO.LOW:
        print("Pressed")
        break
    time.sleep(0.1)

A The button pin lacks a pull-up or pull-down resistor, so input is floating

B GPIO.setup should use GPIO.OUT for button input

C The code needs GPIO.cleanup() before the loop

D time.sleep(0.1) is too short to detect the press

💡 Hint

Think about what happens if the input pin is not stabilized with a resistor.

Without a pull-up or pull-down resistor, the input pin floats and may never read LOW reliably, so the condition never triggers.

📝 Syntax

advanced

Identify the syntax error in this button detection code

Which option correctly fixes the syntax error in this Raspberry Pi button detection code?

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.IN, pull_up_down=GPIO.PUD_UP)

if GPIO.input(18) == GPIO.LOW
    print("Button pressed")

A Add a colon at the end of the if statement line

B Change GPIO.LOW to GPIO.HIGH

C Remove the parentheses from GPIO.input

D Indent the print statement at the same level as if

💡 Hint

Check the syntax of the if statement in Python.

Python requires a colon at the end of the if statement line to mark the start of the block.

🚀 Application

expert

How many times will the message print if button bounces?

This code detects button presses on GPIO pin 23 and prints "Pressed" each time the input reads LOW. The button is known to bounce (rapidly change state) when pressed. How many times will "Pressed" print if the button is pressed once?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_UP)

for _ in range(10):
    if GPIO.input(23) == GPIO.LOW:
        print("Pressed")
    time.sleep(0.01)

A Only once, because time.sleep(0.01) filters out bounces

B Exactly once, because the loop runs 10 times but only one LOW reading occurs

C Never, because the pull_up_down setting is incorrect

D Multiple times, due to button bouncing causing repeated LOW readings

💡 Hint

Think about how button bouncing affects the input signal during rapid reads.

Button bouncing causes the input to rapidly switch between LOW and HIGH, so the code may print "Pressed" multiple times during the loop.