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.

Practice

1. What is the main purpose of using Python on a Raspberry Pi?

easy

A. To control hardware like LEDs and sensors easily

B. To create websites only

C. To run Windows applications

D. To edit videos

Solution

1. Step 1: Understand Raspberry Pi's use with Python

   Python on Raspberry Pi is mainly used to control hardware components like LEDs and sensors.

2. Step 2: Compare options with this purpose

   The options describing website creation only, running Windows applications, and video editing do not relate to hardware control, so they are incorrect.

3. Final Answer:

   To control hardware like LEDs and sensors easily -> Option A

4. Quick Check:

   Python on Raspberry Pi = hardware control [OK]

Hint: Think about what Raspberry Pi projects usually do [OK]

Common Mistakes:

• Confusing Raspberry Pi with a general computer
• Thinking Python on Pi is only for web development
• Assuming it runs Windows apps natively

2. Which of the following is the correct way to import the GPIO library in Python on Raspberry Pi?

easy

A. import GPIO.RPi

B. import RPi.GPIO as GPIO

C. from GPIO import RPi

D. import raspberry.GPIO

Solution

1. Step 1: Recall the standard import syntax for GPIO

   The correct import statement is import RPi.GPIO as GPIO to use GPIO functions easily.

2. Step 2: Check other options for syntax errors

   The other options ('import GPIO.RPi', 'from GPIO import RPi', 'import raspberry.GPIO') do not follow Python import syntax or correct module names.

3. Final Answer:

   import RPi.GPIO as GPIO -> Option B

4. Quick Check:

   Standard GPIO import = import RPi.GPIO as GPIO [OK]

Hint: Remember the exact module name: RPi.GPIO [OK]

Common Mistakes:

• Swapping module and package names incorrectly
• Using wrong import syntax
• Assuming 'GPIO' alone is a module

3. What will be the output of this Python code on Raspberry Pi?

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

medium

A. 0

B. HIGH

C. 1

D. Error

Solution

1. Step 1: Understand GPIO setup and output

   Pin 18 is set as output and then set to HIGH, which means voltage is ON (1).

2. Step 2: Check GPIO.input(18) after setting HIGH

   Reading the pin returns 1 because it was set HIGH.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   GPIO.output HIGH means input reads 1 [OK]

Hint: HIGH means 1, LOW means 0 in GPIO [OK]

Common Mistakes:

• Confusing HIGH with string 'HIGH'
• Expecting 0 instead of 1 after setting HIGH
• Thinking GPIO.input returns string values

4. Identify the error in this Raspberry Pi Python code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
GPIO.output(12, HIGH)

medium

A. Missing GPIO prefix before HIGH

B. Wrong pin number for BOARD mode

C. GPIO.setmode should be BCM

D. GPIO.setup should be input, not output

Solution

1. Step 1: Check usage of HIGH constant

   HIGH must be referenced as GPIO.HIGH, not just HIGH alone.

2. Step 2: Verify other code parts

   Pin 12 is valid in BOARD mode, setmode can be BOARD, and output pin can be output.

3. Final Answer:

   Missing GPIO prefix before HIGH -> Option A

4. Quick Check:

   Use GPIO.HIGH, not just HIGH [OK]

Hint: Always prefix constants with GPIO. [OK]

Common Mistakes:

• Using HIGH without GPIO prefix
• Confusing BOARD and BCM pin numbering
• Setting output pin as input by mistake

5. You want to blink an LED connected to pin 17 on Raspberry Pi using Python. Which code snippet correctly blinks the LED once with a 1-second delay?

hard

A. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN)
GPIO.output(17, GPIO.HIGH)
time.sleep(1)
GPIO.output(17, GPIO.LOW)

B. import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, 1)
time.sleep(1)
GPIO.output(17, 0)

C. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, GPIO.HIGH)
time.sleep(1)
GPIO.output(17, GPIO.LOW)

D. import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, GPIO.HIGH)
time.sleep(1)
GPIO.output(17, GPIO.LOW)

Solution

1. Step 1: Check pin numbering and setup

   BCM mode, import time, GPIO.setup(17, GPIO.OUT) are all correct.

2. Step 2: Verify output and delay

   GPIO.output(17, GPIO.HIGH), time.sleep(1), GPIO.output(17, GPIO.LOW) blinks once (on for 1s then off).

3. Step 3: Identify errors in other options

   One lacks import time (NameError on sleep); another uses BOARD mode (pin 17 ≠ BCM pin 17 physically); another sets GPIO.IN (should be OUT).

4. Final Answer:

   import RPi.GPIO as GPIO import time GPIO.setmode(GPIO.BCM) GPIO.setup(17, GPIO.OUT) GPIO.output(17, GPIO.HIGH) time.sleep(1) GPIO.output(17, GPIO.LOW) -> Option D

5. Quick Check:

   Use BCM mode, output pin, and time.sleep for blinking [OK]

Hint: Use GPIO.HIGH/LOW with time.sleep for blinking [OK]

Common Mistakes:

• Mixing BOARD and BCM pin numbers
• Setting pin as input instead of output
• Forgetting to import time module