Reaction time game in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this reaction time measurement snippet?

Consider this Python code snippet for a reaction time game on Raspberry Pi. What will it print after the user presses Enter?

Raspberry Pi

import time
start = time.time()
input('Press Enter as fast as you can!')
end = time.time()
print(f'Reaction time: {end - start:.3f} seconds')

A Reaction time: 1.234 seconds

B Reaction time: 0.123 seconds

C Reaction time: 0.000 seconds

D SyntaxError

💡 Hint

The printed time is the difference between when the prompt appears and when Enter is pressed.

The code measures the time before and after the user presses Enter, then prints the difference as reaction time. The exact number depends on user speed, but it will be a positive float, not zero or a syntax error.

🧠 Conceptual

intermediate

Which Raspberry Pi component is best for detecting a physical button press in a reaction time game?

You want to measure reaction time using a physical button connected to your Raspberry Pi. Which component should you use to detect the button press?

A SPI communication bus

B I2C communication bus

C GPIO pin configured as input with pull-up resistor

D PWM output pin

💡 Hint

Think about how to read a simple on/off signal from a button.

GPIO pins configured as inputs with pull-up or pull-down resistors are used to detect button presses. PWM, I2C, and SPI are for other purposes.

🔧 Debug

advanced

Why does this reaction time game code never detect the button press?

This code is supposed to detect a button press on GPIO pin 17 and print reaction time, but it never prints anything. What is the problem?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

start = time.time()
while True:
    if GPIO.input(17) == GPIO.HIGH:
        end = time.time()
        print(f'Reaction time: {end - start:.3f} seconds')
        break

A The loop needs a sleep() call to detect input.

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

C time.time() returns a string, causing a TypeError.

D The button is wired to pull the pin LOW when pressed, so checking for HIGH never triggers.

💡 Hint

Check how the button wiring affects the signal level when pressed.

If the button connects the pin to ground when pressed, the input reads LOW, so checking for HIGH never detects the press.

📝 Syntax

advanced

Which option fixes the syntax error in this Raspberry Pi reaction time code?

This code snippet has a syntax error. Choose the corrected version.

Raspberry Pi

import time
start = time.time()
input('Press Enter')
end = time.time()
print(f'Reaction time: {end - start:.3f seconds')

A print(f'Reaction time: {end - start:.3f} seconds')

B print(f'Reaction time: {end - start:.3f seconds}')

C print('Reaction time: {end - start:.3f} seconds')

D )'}sdnoces f3.:trats - dne{ :emit noitcaeR'f(tnirp

💡 Hint

Check the placement of the closing brace and parentheses in the f-string.

The original code misses a closing brace '}' before ' seconds'. Option A correctly closes the expression inside the braces.

🚀 Application

expert

How to implement a non-blocking reaction time game loop on Raspberry Pi?

You want to create a reaction time game that waits a random time, then lights an LED and measures how fast the user presses a button. The program should not freeze while waiting. Which approach is best?

A Use input() to wait for the button press after lighting the LED.

B Use a loop that checks time.time() and GPIO input repeatedly with a small sleep delay.

C Use time.sleep(random_delay) then input() to wait for button press.

D Use a blocking infinite loop without any delay or input.

💡 Hint

Think about how to keep the program responsive while waiting.

Using a loop that checks the current time and button state repeatedly with short sleeps allows the program to stay responsive and measure reaction time accurately.