Home automation with relay modules in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the GPIO library for Raspberry Pi.

Raspberry Pi

import [1]

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

ARPi.GPIO

Bgpiozero

Cwiringpi

Dserial

Attempts:

3 left

💡 Hint

Common Mistakes

Using gpiozero instead of RPi.GPIO for low-level pin control.

RPi.GPIO is the standard library to control GPIO pins on Raspberry Pi.

2fill in blank

medium

Complete the code to set GPIO pin 17 as an output.

Raspberry Pi

GPIO.setup([1], GPIO.OUT)

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

A18

B22

C27

D17

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing input pins instead of output pins.

Pin 17 is commonly used for relay control and must be set as output.

3fill in blank

hard

Fix the error in the code to turn the relay ON by setting the pin LOW.

Raspberry Pi

GPIO.output(17, [1])

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

AGPIO.HIGH

BTrue

CGPIO.LOW

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.HIGH to turn the relay ON, which actually turns it OFF.

For many relay modules, setting the pin LOW activates the relay (turns it ON).

4fill in blank

hard

Complete the code to create a dictionary mapping relay names to their GPIO pins.

Raspberry Pi

relays = {[1]: pin for {{BLANK_3}} in ['relay1', 'relay2', 'relay3']}

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

A{

Bpin

Crelay

D}

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect dictionary syntax or variable names.

The dictionary starts with '{' and maps relay names to pin numbers stored in 'pin'.

5fill in blank

hard

Fill all three blanks to turn all relays OFF by setting their pins HIGH.

Raspberry Pi

for pin in relays.values():
    GPIO.output([1], [2])
print([3])

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

Apin

BGPIO.HIGH

C"All relays are OFF"

DGPIO.LOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.LOW to turn relays OFF, which actually turns them ON.

We loop over each pin, set it HIGH to turn relay OFF, then print a confirmation message.

Practice

1. What is the main purpose of using a relay module with a Raspberry Pi in home automation?

easy

A. To increase the Raspberry Pi's processing speed

B. To safely control high-power devices using low-power GPIO signals

C. To store data from sensors

D. To provide internet connectivity

Solution

1. Step 1: Understand relay module function

   A relay module acts as a switch controlled by the Raspberry Pi's GPIO pins to turn devices ON or OFF safely.

2. Step 2: Identify the purpose in home automation

   It allows the Pi to control high-power devices without directly handling high voltage or current.

3. Final Answer:

   To safely control high-power devices using low-power GPIO signals -> Option B

4. Quick Check:

   Relay modules = safe device control [OK]

Hint: Relays switch big power with small signals [OK]

Common Mistakes:

• Thinking relay speeds up the Pi
• Confusing relay with data storage
• Assuming relay provides network access

2. Which of the following Python code snippets correctly sets GPIO pin 17 as output and turns the relay ON (assuming active LOW)?

easy

A. GPIO.setup(17, GPIO.OUT)
GPIO.output(17, GPIO.LOW)

B. GPIO.setup(17, GPIO.OUT)
GPIO.output(17, GPIO.HIGH)

C. GPIO.setup(17, GPIO.IN)
GPIO.output(17, GPIO.LOW)

D. GPIO.setup(17, GPIO.IN)
GPIO.output(17, GPIO.HIGH)

Solution

1. Step 1: Set GPIO pin mode

   Pin 17 must be set as output to control the relay, so GPIO.setup(17, GPIO.OUT) is correct.

2. Step 2: Turn relay ON with active LOW

   For active LOW relay, sending GPIO.LOW activates the relay, so GPIO.output(17, GPIO.LOW) is correct.

3. Final Answer:

   GPIO.setup(17, GPIO.OUT) followed by GPIO.output(17, GPIO.LOW) -> Option A

4. Quick Check:

   Active LOW means LOW signal turns relay ON [OK]

Hint: Active LOW relay ON means output LOW [OK]

Common Mistakes:

• Setting pin as input instead of output
• Using HIGH to turn ON active LOW relay
• Confusing pin numbers

3. What will be the output of this Python code controlling a relay on GPIO pin 22?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.OUT)
GPIO.output(22, GPIO.LOW)
print(GPIO.input(22))
GPIO.cleanup()

medium

A. 1

B. Error: GPIO.input() not allowed on output pin

C. 0

D. GPIO.LOW

Solution

1. Step 1: Setup and output LOW on pin 22

   The code sets pin 22 as output and writes LOW (0) to it.

2. Step 2: Read pin state with GPIO.input(22)

   GPIO.input returns the current pin state; since output is LOW, it returns 0.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   Output LOW means input reads 0 [OK]

Hint: GPIO.input reads output pin state correctly [OK]

Common Mistakes:

• Expecting 1 instead of 0 after output LOW
• Thinking GPIO.input causes error on output pins
• Confusing GPIO.BCM with GPIO.BOARD numbering

4. Identify the error in this relay control code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.LOW)
GPIO.cleanup()
GPIO.output(18, GPIO.HIGH)

medium

A. Calling GPIO.output after GPIO.cleanup causes an error

B. GPIO.setup should be called after GPIO.cleanup

C. GPIO.setmode must be called twice

D. GPIO.output cannot use GPIO.HIGH

Solution

1. Step 1: Understand GPIO.cleanup() effect

   GPIO.cleanup() resets all GPIO pins, releasing resources and resetting pin states.

2. Step 2: Check GPIO.output after cleanup

   Calling GPIO.output after cleanup without re-setup causes a runtime error because pin 18 is no longer configured.

3. Final Answer:

   Calling GPIO.output after GPIO.cleanup causes an error -> Option A

4. Quick Check:

   Use GPIO.setup after cleanup before output [OK]

Hint: Don't use GPIO.output after cleanup without setup [OK]

Common Mistakes:

• Thinking cleanup only clears pin states but allows output
• Believing setup order is flexible
• Assuming GPIO.HIGH is invalid

5. You want to control two relays connected to GPIO pins 5 and 6 to turn ON a fan and a light respectively. The relays are active LOW. Which Python code correctly turns ON the fan and turns OFF the light?

hard

A. GPIO.setup(5, GPIO.OUT)
GPIO.setup(6, GPIO.OUT)
GPIO.output(5, GPIO.HIGH)
GPIO.output(6, GPIO.HIGH)

B. GPIO.setup(5, GPIO.OUT)
GPIO.setup(6, GPIO.OUT)
GPIO.output(5, GPIO.HIGH)
GPIO.output(6, GPIO.LOW)

C. GPIO.setup(5, GPIO.IN)
GPIO.setup(6, GPIO.IN)
GPIO.output(5, GPIO.LOW)
GPIO.output(6, GPIO.HIGH)

D. GPIO.setup(5, GPIO.OUT)
GPIO.setup(6, GPIO.OUT)
GPIO.output(5, GPIO.LOW)
GPIO.output(6, GPIO.HIGH)

Solution

1. Step 1: Setup pins 5 and 6 as outputs

   Both pins must be outputs to control relays: GPIO.setup(5, GPIO.OUT) and GPIO.setup(6, GPIO.OUT).

2. Step 2: Apply active LOW logic for relays

   To turn ON the fan (pin 5), output LOW; to turn OFF the light (pin 6), output HIGH.

3. Final Answer:

   Setup pins as output, output LOW on 5, HIGH on 6 -> Option D

4. Quick Check:

   Active LOW ON = LOW, OFF = HIGH [OK]

Hint: Active LOW ON means output LOW, OFF means HIGH [OK]

Common Mistakes:

• Setting pins as input instead of output
• Reversing HIGH and LOW for active LOW relay
• Turning both devices ON or OFF incorrectly