Digital input (GPIO.input) in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read the state of a GPIO pin.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN)
state = GPIO.[1](17)
print(state)

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

Ainput

Boutput

Cinput_read

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.output() instead of GPIO.input()

Trying to read a pin not set as input

The GPIO.input() function reads the digital state of a pin set as input.

2fill in blank

medium

Complete the code to check if the button connected to pin 22 is pressed (assuming active low).

Raspberry Pi

GPIO.setup(22, GPIO.IN, pull_up_down=GPIO.PUD_UP)
if GPIO.[1](22) == GPIO.LOW:
    print("Button pressed")

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

Aoutput

Binput

Cinput_read

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.output() instead of GPIO.input()

Not setting pull-up resistor for active low button

Use GPIO.input() to read the pin state and compare it to GPIO.LOW for active low buttons.

3fill in blank

hard

Fix the error in the code to correctly read a pin state.

Raspberry Pi

GPIO.setup(5, GPIO.IN)
pin_state = GPIO.[1](5)
if pin_state == 1:
    print("Pin is HIGH")

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

Aread

Binput_read

Cinput

Doutput

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.output() or GPIO.read() which do not exist

Confusing pin setup with reading

The correct function to read a pin is GPIO.input(). Other options cause errors.

4fill in blank

hard

Fill both blanks to create a dictionary of pin states for pins 10 and 11.

Raspberry Pi

pins = [10, 11]
states = {pin: GPIO.[1](pin) for pin in pins if GPIO.[2](pin) == GPIO.HIGH}

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

Ainput

Boutput

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.output() to read pin state

Mixing input and output functions

Use GPIO.input() to read pin states. Both blanks require the same function.

5fill in blank

hard

Fill all three blanks to create a dictionary of pin states for pins 7, 8, and 9 where the state is HIGH.

Raspberry Pi

pins = [7, 8, 9]
high_pins = {pin: GPIO.[1](pin) for pin in pins if GPIO.[2](pin) == GPIO.[3]

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

Ainput

CHIGH

DLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.output() instead of GPIO.input()

Comparing to GPIO.LOW instead of GPIO.HIGH

Use GPIO.input() to read pins and compare to GPIO.HIGH to filter pins that are on.

Practice

1. What does GPIO.input(pin) do in Raspberry Pi programming?

easy

A. Resets the pin to default state

B. Sets the pin mode to output

C. Writes a value to the pin

D. Reads the current digital state (True/False) of the specified pin

Solution

1. Step 1: Understand GPIO.input function

   GPIO.input(pin) reads the current digital signal on the given pin, returning True if the pin is HIGH and False if LOW.

2. Step 2: Differentiate from other GPIO functions

   Functions like GPIO.setup set pin modes, and GPIO.output writes values. Only GPIO.input reads the pin state.

3. Final Answer:

   Reads the current digital state (True/False) of the specified pin -> Option D

4. Quick Check:

   GPIO.input reads pin state = A [OK]

Hint: Remember: input reads pin state, output writes to pin [OK]

Common Mistakes:

• Confusing GPIO.input with GPIO.output
• Thinking GPIO.input sets pin mode
• Assuming GPIO.input writes values

2. Which of the following is the correct way to set up GPIO pin 17 as an input pin?

easy

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

B. GPIO.input(17, GPIO.IN)

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

D. GPIO.input(17)

Solution

1. Step 1: Identify the correct function to set pin mode

   Use GPIO.setup(pin, mode) to set pin mode. Here, mode should be GPIO.IN for input.

2. Step 2: Check each option

   GPIO.setup(17, GPIO.OUT) sets pin as output, wrong mode. GPIO.input(17, GPIO.IN) uses GPIO.input incorrectly with two arguments. GPIO.input(17) calls GPIO.input without setup. Only GPIO.setup(17, GPIO.IN) correctly sets pin 17 as input.

3. Final Answer:

   GPIO.setup(17, GPIO.IN) -> Option C

4. Quick Check:

   Setup input pin = B [OK]

Hint: Use GPIO.setup(pin, GPIO.IN) to prepare input pins [OK]

Common Mistakes:

• Using GPIO.input to set pin mode
• Setting pin as output instead of input
• Calling GPIO.input before setup

3. What will be the output of this code snippet if the button connected to pin 22 is pressed (assuming pressed means HIGH)?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.IN)
state = GPIO.input(22)
print(state)

medium

A. True

B. 22

C. False

D. Error

Solution

1. Step 1: Understand pin setup and input reading

   Pin 22 is set as input. When the button is pressed, the pin reads HIGH, so GPIO.input(22) returns True.

2. Step 2: Check the print output

   The variable state holds True, so print(state) outputs True.

3. Final Answer:

   True -> Option A

4. Quick Check:

   Pressed button = True output [OK]

Hint: Pressed button means pin HIGH, so GPIO.input returns True [OK]

Common Mistakes:

• Assuming pressed means False
• Confusing pin number with state
• Expecting numeric output instead of boolean

4. Identify the error in this code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.input(18)
GPIO.setup(18, GPIO.IN)

medium

A. GPIO.input called before GPIO.setup

B. GPIO.setup uses wrong pin number

C. GPIO.setmode is missing

D. No error, code is correct

Solution

1. Step 1: Check order of GPIO calls

   GPIO pins must be set up before reading input. Here, GPIO.input(18) is called before GPIO.setup(18, GPIO.IN), which is incorrect.

2. Step 2: Verify other parts

   Pin number 18 is consistent, and GPIO.setmode(GPIO.BCM) is present. So no error there.

3. Final Answer:

   GPIO.input called before GPIO.setup -> Option A

4. Quick Check:

   GPIO.input called before GPIO.setup = D [OK]

Hint: Always setup pins before reading input [OK]

Common Mistakes:

• Calling GPIO.input before GPIO.setup
• Ignoring pin mode setup
• Assuming code runs without setup

5. You want to detect if a motion sensor connected to pin 27 is active (HIGH) and print "Motion detected" only once when it changes from LOW to HIGH. Which code snippet correctly implements this behavior?

hard

A. GPIO.setup(27, GPIO.OUT)
while True:
if GPIO.input(27):
print("Motion detected")

B. GPIO.setup(27, GPIO.IN)
prev_state = False
while True:
current_state = GPIO.input(27)
if current_state and not prev_state:
print("Motion detected")
prev_state = current_state

C. GPIO.setup(27, GPIO.IN)
while True:
if GPIO.input(27):
print("Motion detected")

D. GPIO.setup(27, GPIO.IN)
prev_state = True
while True:
current_state = GPIO.input(27)
if current_state and not prev_state:
print("Motion detected")
prev_state = current_state

Solution

1. Step 1: Setup pin as input and track previous state

   Pin 27 must be set as input. To detect change from LOW to HIGH, store previous state starting as False (LOW).

2. Step 2: Detect rising edge and print once

   Inside the loop, read current state. If current is True and previous is False, print message once. Then update previous state.

3. Step 3: Analyze options

   GPIO.setup(27, GPIO.IN) prev_state = False while True: current_state = GPIO.input(27) if current_state and not prev_state: print("Motion detected") prev_state = current_state correctly implements this logic. GPIO.setup(27, GPIO.OUT) while True: if GPIO.input(27): print("Motion detected") sets pin as output, wrong. GPIO.setup(27, GPIO.IN) while True: if GPIO.input(27): print("Motion detected") prints repeatedly while HIGH, not once. GPIO.setup(27, GPIO.IN) prev_state = True while True: current_state = GPIO.input(27) if current_state and not prev_state: print("Motion detected") prev_state = current_state starts prev_state as True, so first detection missed.

4. Final Answer:

   GPIO.setup(27, GPIO.IN), prev_state = False (rising edge detection) -> Option B

5. Quick Check:

   Detect rising edge with prev_state = False first [OK]

Hint: Track previous state to detect change from LOW to HIGH [OK]

Common Mistakes:

• Setting pin as output instead of input
• Printing repeatedly instead of once
• Initializing previous state incorrectly