Controlling GPIO through web interface in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the GPIO library.

Raspberry Pi

import [1] as GPIO

Drag options to blanks, or click blank then click option'

Agpiozero

Bos

CRPi.GPIO

Dflask

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'gpiozero' instead of 'RPi.GPIO' when using low-level GPIO control.

Importing unrelated libraries like 'os' or 'flask'.

The RPi.GPIO library is used to control GPIO pins on Raspberry Pi.

2fill in blank

medium

Complete the code to set the GPIO mode to BCM numbering.

Raspberry Pi

GPIO.setmode([1])

Drag options to blanks, or click blank then click option'

AGPIO.BCM

BGPIO.BOARD

CGPIO.OUT

DGPIO.IN

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.BOARD when BCM numbering is required.

Confusing pin modes with numbering modes.

Using GPIO.BCM sets the pin numbering to Broadcom SOC channel numbers.

3fill in blank

hard

Fix the error in setting up pin 18 as output.

Raspberry Pi

GPIO.setup(18, [1])

Drag options to blanks, or click blank then click option'

AGPIO.OUT

BGPIO.IN

CGPIO.PWM

DGPIO.INPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.IN instead of GPIO.OUT for output pins.

Using invalid constants like GPIO.PWM or GPIO.INPUT.

To control an LED or output device, the pin must be set as GPIO.OUT.

4fill in blank

hard

Fill both blanks to create a Flask route that turns the LED on.

Raspberry Pi

from flask import Flask, [1]
app = Flask(__name__)

@app.route('/led/on')
def led_on():
    GPIO.output(18, [2])
    return 'LED is ON'

Drag options to blanks, or click blank then click option'

Arequest

BGPIO.HIGH

CGPIO.LOW

Drender_template

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.LOW to turn LED on (it turns it off).

Not importing 'request' when needed in Flask.

The Flask request module is commonly imported for routes, and GPIO.HIGH turns the LED on.

5fill in blank

hard

Fill all three blanks to complete the Flask app that controls the LED state based on URL parameter.

Raspberry Pi

from flask import Flask, request
app = Flask(__name__)

@app.route('/led/<state>')
def led_control(state):
    if state == '[1]':
        GPIO.output(18, [2])
    else:
        GPIO.output(18, [3])
    return f'LED turned {state}'

Drag options to blanks, or click blank then click option'

Aon

BGPIO.HIGH

CGPIO.LOW

Doff

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'on' and 'off' strings in the condition.

Using GPIO.LOW to turn LED on.

The URL parameter state is checked for 'on' to set the pin HIGH; otherwise, it sets LOW to turn off the LED.

Practice

1. What is the main purpose of using a web interface to control Raspberry Pi GPIO pins?

easy

A. To control hardware remotely using a web page

B. To increase the Raspberry Pi processing speed

C. To install new software on the Raspberry Pi

D. To connect the Raspberry Pi to a printer

Solution

1. Step 1: Understand the role of GPIO pins

   GPIO pins allow Raspberry Pi to interact with hardware like LEDs or motors.

2. Step 2: Recognize the benefit of a web interface

   A web interface lets users control these pins from any device with a browser, remotely and easily.

3. Final Answer:

   To control hardware remotely using a web page -> Option A

4. Quick Check:

   Web interface = remote GPIO control [OK]

Hint: Web interface means remote control via browser [OK]

Common Mistakes:

• Confusing GPIO control with software installation
• Thinking it speeds up the Raspberry Pi
• Assuming it connects to printers

2. Which Python library is commonly used to create a web server for controlling GPIO pins on Raspberry Pi?

easy

A. NumPy

B. Pandas

C. Flask

D. Matplotlib

Solution

1. Step 1: Identify web server libraries

   Flask is a lightweight Python web framework used to build web servers.

2. Step 2: Match Flask with GPIO control

   Flask can handle web requests to turn GPIO pins on or off via buttons on a webpage.

3. Final Answer:

   Flask -> Option C

4. Quick Check:

   Flask = web server for GPIO control [OK]

Hint: Flask is the simple web server for Python GPIO control [OK]

Common Mistakes:

• Choosing data libraries like NumPy or Pandas
• Confusing plotting library Matplotlib with web server

3. Given this Flask route code snippet controlling GPIO pin 17:

from flask import Flask, request
import RPi.GPIO as GPIO

app = Flask(__name__)
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)

@app.route('/pin17/<state>')
def pin17(state):
    if state == 'on':
        GPIO.output(17, GPIO.HIGH)
        return 'Pin 17 is ON'
    elif state == 'off':
        GPIO.output(17, GPIO.LOW)
        return 'Pin 17 is OFF'
    else:
        return 'Invalid state'

What will be the output if you visit /pin17/on in the browser?

medium

A. Invalid state

B. Pin 17 is ON

C. Pin 17 is OFF

D. 404 Not Found

Solution

1. Step 1: Analyze the URL parameter

   The URL /pin17/on passes 'on' as the state argument to the function.

2. Step 2: Check the condition for 'on'

   The code checks if state == 'on', then sets GPIO pin 17 HIGH and returns 'Pin 17 is ON'.

3. Final Answer:

   Pin 17 is ON -> Option B

4. Quick Check:

   URL /pin17/on = Pin 17 ON [OK]

Hint: Match URL state to if-condition for output [OK]

Common Mistakes:

• Confusing 'on' with 'off' states
• Expecting an error for valid URL
• Ignoring the return string

4. This Flask code snippet is intended to turn GPIO pin 18 ON or OFF via web requests:

from flask import Flask
import RPi.GPIO as GPIO

app = Flask(__name__)
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

@app.route('/pin18/<state>')
def control_pin(state):
    if state = 'on':
        GPIO.output(18, GPIO.HIGH)
        return 'Pin 18 ON'
    elif state == 'off':
        GPIO.output(18, GPIO.LOW)
        return 'Pin 18 OFF'
    else:
        return 'Invalid'

What is the error in this code?

medium

A. Using '=' instead of '==' in the if condition

B. Missing GPIO.setup for pin 18

C. Flask app is not created

D. No return statement in the function

Solution

1. Step 1: Check the if condition syntax

   The line if state = 'on': uses '=' which is assignment, not comparison.

2. Step 2: Identify correct comparison operator

   It should be if state == 'on': to compare values properly.

3. Final Answer:

   Using '=' instead of '==' in the if condition -> Option A

4. Quick Check:

   Use '==' for comparison, not '=' [OK]

Hint: Use '==' to compare, '=' assigns value [OK]

Common Mistakes:

• Confusing assignment '=' with comparison '=='
• Ignoring syntax errors in if statements
• Assuming GPIO setup is missing

5. You want to create a web page with two buttons to turn an LED on GPIO pin 22 ON and OFF. Which Flask route and HTML snippet correctly implement this control?

@app.route('/led/<state>')
def led_control(state):
    if state == 'on':
        GPIO.output(22, GPIO.HIGH)
    elif state == 'off':
        GPIO.output(22, GPIO.LOW)
    return f'LED is {state}'

Choose the correct HTML buttons to send the commands:

hard

A. Turn ONTurn OFF

B. Toggle

C. ONOFF

D.

Solution

1. Step 1: Understand Flask route expects URL with state

   The route '/led/<state>' expects 'on' or 'off' in the URL path.

2. Step 2: Check HTML methods to send GET requests

   Forms with action URLs send GET requests correctly when submitted, matching the route.

3. Step 3: Compare options

   <form action='/led/on'><input type='submit' value='ON'></form><form action='/led/off'><input type='submit' value='OFF'></form> uses forms with action '/led/on' and '/led/off', which matches the Flask route and triggers the function properly.

4. Final Answer:

   <form action='/led/on'><input type='submit' value='ON'></form><form action='/led/off'><input type='submit' value='OFF'></form> -> Option D

5. Quick Check:

   Forms with correct action URLs = proper GPIO control [OK]

Hint: Use forms with action URLs matching Flask route [OK]

Common Mistakes:

• Using fetch without handling promises
• Using buttons without URL or form action
• Using incorrect URLs that don't match Flask route