Python on Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

GPIO Pin Setup and Output

What is the output of this code when run on a Raspberry Pi with an LED connected to GPIO pin 18?

Raspberry Pi

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)
print("LED toggled")
GPIO.cleanup()

A LED toggled

B RuntimeError: No access to GPIO

C SyntaxError: invalid syntax

D LED toggled twice

💡 Hint

Focus on what the print statement outputs after toggling the LED.

The code sets GPIO pin 18 as output, turns the LED on, waits 1 second, turns it off, then prints 'LED toggled'. No errors occur if run with proper permissions.

❓ Predict Output

intermediate

Reading a Button Press

What will be printed if the button connected to GPIO pin 23 is pressed when this code runs?

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

if GPIO.input(23) == GPIO.LOW:
    print("Button Pressed")
else:
    print("Button Not Pressed")

GPIO.cleanup()

A SyntaxError: invalid indentation

B Button Not Pressed

C RuntimeError: GPIO not set

D Button Pressed

💡 Hint

Remember that the button pulls the pin LOW when pressed due to pull-up resistor.

The code reads GPIO 23 input with pull-up resistor enabled. When pressed, the pin reads LOW, so it prints 'Button Pressed'.

🔧 Debug

advanced

Fix the PWM Frequency Error

This code is intended to make an LED connected to GPIO 12 fade in and out using PWM. What error will it raise?

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)

pwm = GPIO.PWM(12, 1000)
pwm.start(0)

try:
    for dc in range(0, 101, 5):
        pwm.ChangeDutyCycle(dc)
        time.sleep(0.05)
    for dc in range(100, -1, -5):
        pwm.ChangeDutyCycle(dc)
        time.sleep(0.05)
finally:
    pwm.stop()
    GPIO.cleanup()

A No error, LED fades in and out

B RuntimeError: PWM not supported on this pin

C TypeError: PWM frequency must be a number, not str

D SyntaxError: invalid syntax in for loop

💡 Hint

Check the data type of the frequency argument in GPIO.PWM.

The frequency argument is given as a string '1000' instead of a number 1000, causing a TypeError.

❓ Predict Output

advanced

I2C Sensor Data Reading

What will this code print if the I2C device at address 0x48 returns the byte 0x1A when reading register 0x00?

Raspberry Pi

import smbus

bus = smbus.SMBus(1)
address = 0x48
register = 0x00

value = bus.read_byte_data(address, register)
print(f"Sensor value: {value}")

A IOError: No such device

B Sensor value: 26

C Sensor value: 0x1A

D TypeError: unsupported operand

💡 Hint

Remember that 0x1A in hexadecimal equals 26 in decimal.

The read_byte_data returns an integer. 0x1A hex is 26 decimal, so the print shows 'Sensor value: 26'.

🧠 Conceptual

expert

Understanding Raspberry Pi GPIO Pull-up and Pull-down

Which statement correctly explains the difference between pull-up and pull-down resistors in Raspberry Pi GPIO input pins?

A Pull-up resistors connect the pin to 3.3V to ensure a default HIGH state; pull-down resistors connect the pin to ground to ensure a default LOW state.

B Pull-up resistors connect the pin to ground to ensure a default LOW state; pull-down resistors connect the pin to 3.3V to ensure a default HIGH state.

C Pull-up resistors increase the voltage beyond 3.3V; pull-down resistors decrease voltage below 0V.

D Pull-up and pull-down resistors are used to amplify the input signal on GPIO pins.

💡 Hint

Think about how to keep a GPIO pin at a known voltage level when no button is pressed.

Pull-up resistors connect the pin to 3.3V to keep it HIGH by default; pull-down resistors connect to ground to keep it LOW by default. This prevents floating inputs.