Traffic light simulation 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] as GPIO

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

Agpiozero

Bsys

Ctime

DRPi.GPIO

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'time' instead of the GPIO library.

Using 'gpiozero' which is a different GPIO library.

The RPi.GPIO library is used to control the GPIO pins on a Raspberry Pi for hardware projects like traffic lights.

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.OUT

BGPIO.BCM

CGPIO.BOARD

DGPIO.IN

Attempts:

3 left

💡 Hint

Common Mistakes

Using GPIO.BOARD which refers to physical pin numbers.

Using GPIO.OUT which is for pin direction, not mode.

Setting GPIO mode to GPIO.BCM means we use the Broadcom chip's pin numbering.

3fill in blank

hard

Fix the error in setting up pin 17 as an output.

Raspberry Pi

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

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

A17

B18

CGPIO.OUT

DGPIO.IN

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin 18 instead of 17.

Using GPIO.OUT as pin number.

Pin 17 is the correct GPIO pin number to set as output for the traffic light LED.

4fill in blank

hard

Fill both blanks to turn on the green LED connected to pin 22.

Raspberry Pi

GPIO.output([1], [2])

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

A22

BGPIO.HIGH

CGPIO.LOW

D17

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin 17 instead of 22.

Setting output to GPIO.LOW which turns the LED off.

Pin 22 controls the green LED. Setting output to GPIO.HIGH turns it on.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping LED colors to their GPIO pins.

Raspberry Pi

led_pins = { [1]: [2], [3]: 22 }

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A'red'

B17

C'green'

D'yellow'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'yellow' instead of 'green' as a key.

Mixing up pin numbers.

The dictionary maps 'red' to pin 17 and 'green' to pin 22 for the traffic lights.

Practice

1. What is the main purpose of using GPIO pins in a Raspberry Pi traffic light simulation?

easy

A. To control the LEDs turning on and off

B. To increase the Raspberry Pi processing speed

C. To connect the Raspberry Pi to the internet

D. To store the traffic light timing data

Solution

1. Step 1: Understand GPIO pin function

   GPIO pins on Raspberry Pi are used to send signals to external devices like LEDs.

2. Step 2: Connect GPIO pins to LEDs

   In traffic light simulation, GPIO pins turn LEDs on or off to show red, yellow, or green lights.

3. Final Answer:

   To control the LEDs turning on and off -> Option A

4. Quick Check:

   GPIO pins control LEDs = A [OK]

Hint: GPIO pins control hardware like LEDs in simulations [OK]

Common Mistakes:

• Thinking GPIO speeds up the CPU
• Confusing GPIO with internet connection
• Assuming GPIO stores data

2. Which of the following Python code snippets correctly sets up GPIO pin 17 as an output for the traffic light LED?

easy

A. GPIO.output(17, GPIO.IN)

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

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

D. GPIO.output(17, GPIO.OUT)

Solution

1. Step 1: Identify correct GPIO setup function

   GPIO.setup(pin_number, mode) is used to set pin mode; mode can be GPIO.OUT or GPIO.IN.

2. Step 2: Choose correct mode for LED output

   LEDs need output mode, so GPIO.OUT is correct for pin 17.

3. Final Answer:

   GPIO.setup(17, GPIO.OUT) -> Option B

4. Quick Check:

   Setup pin as output = B [OK]

Hint: Use GPIO.setup(pin, GPIO.OUT) to set output pins [OK]

Common Mistakes:

• Using GPIO.output instead of GPIO.setup to set mode
• Setting pin as GPIO.IN instead of GPIO.OUT
• Confusing setup and output functions

3. What will be the output behavior of this Python code snippet controlling a traffic light LED on GPIO 18?

GPIO.output(18, GPIO.HIGH)
time.sleep(3)
GPIO.output(18, GPIO.LOW)

medium

A. The LED on pin 18 stays off permanently

B. The LED on pin 18 blinks rapidly for 3 seconds

C. The program will cause a syntax error

D. The LED on pin 18 turns on for 3 seconds, then turns off

Solution

1. Step 1: Analyze GPIO.output commands

   GPIO.HIGH turns the LED on; GPIO.LOW turns it off.

2. Step 2: Understand time.sleep effect

   time.sleep(3) pauses the program for 3 seconds while LED stays on.

3. Final Answer:

   The LED on pin 18 turns on for 3 seconds, then turns off -> Option D

4. Quick Check:

   HIGH then sleep then LOW = C [OK]

Hint: HIGH turns LED on, LOW turns it off; sleep pauses timing [OK]

Common Mistakes:

• Thinking LED blinks rapidly without loop
• Assuming syntax error due to time.sleep
• Confusing HIGH with LOW states

4. Identify the error in this traffic light simulation code snippet:

GPIO.setup(22, GPIO.OUT)
GPIO.output(22, HIGH)
time.sleep(2)
GPIO.output(22, LOW)

medium

A. HIGH and LOW should be prefixed with GPIO.

B. GPIO.setup should use GPIO.IN instead of GPIO.OUT

C. time.sleep cannot be used with GPIO.output

D. Pin 22 cannot be used for output

Solution

1. Step 1: Check usage of HIGH and LOW constants

   HIGH and LOW must be written as GPIO.HIGH and GPIO.LOW to be recognized.

2. Step 2: Verify other code parts

   GPIO.setup with GPIO.OUT is correct; time.sleep works fine; pin 22 is valid.

3. Final Answer:

   HIGH and LOW should be prefixed with GPIO. -> Option A

4. Quick Check:

   HIGH/LOW require GPIO. prefix = D [OK]

Hint: Always prefix HIGH/LOW with GPIO. to avoid NameError [OK]

Common Mistakes:

• Omitting GPIO. prefix for HIGH/LOW
• Changing pin mode incorrectly
• Thinking time.sleep causes error

5. You want to simulate a traffic light cycle with red, yellow, and green LEDs connected to GPIO pins 5, 6, and 13 respectively. Which Python code snippet correctly cycles through the lights with 2 seconds red, 1 second yellow, and 3 seconds green, repeating forever?

hard

A. GPIO.output(5, GPIO.HIGH)
GPIO.output(6, GPIO.HIGH)
GPIO.output(13, GPIO.HIGH)
time.sleep(6)
GPIO.output(5, GPIO.LOW)
GPIO.output(6, GPIO.LOW)
GPIO.output(13, GPIO.LOW)

B. for light in [5,6,13]:
GPIO.output(light, GPIO.HIGH)
time.sleep(2)
GPIO.output(light, GPIO.LOW)

C. while True:
GPIO.output(5, GPIO.HIGH)
time.sleep(2)
GPIO.output(5, GPIO.LOW)
GPIO.output(6, GPIO.HIGH)
time.sleep(1)
GPIO.output(6, GPIO.LOW)
GPIO.output(13, GPIO.HIGH)
time.sleep(3)
GPIO.output(13, GPIO.LOW)

D. while True:
GPIO.output(13, GPIO.HIGH)
time.sleep(3)
GPIO.output(13, GPIO.LOW)
GPIO.output(6, GPIO.HIGH)
time.sleep(1)
GPIO.output(6, GPIO.LOW)
GPIO.output(5, GPIO.HIGH)
time.sleep(2)
GPIO.output(5, GPIO.LOW)

Solution

1. Step 1: Check order and timing of lights

   Traffic lights cycle red (2s), yellow (1s), green (3s) in that order repeatedly.

2. Step 2: Verify code matches timing and order

   while True: GPIO.output(5, GPIO.HIGH) time.sleep(2) GPIO.output(5, GPIO.LOW) GPIO.output(6, GPIO.HIGH) time.sleep(1) GPIO.output(6, GPIO.LOW) GPIO.output(13, GPIO.HIGH) time.sleep(3) GPIO.output(13, GPIO.LOW) uses while True loop, turns on red (pin 5) for 2s, then yellow (pin 6) for 1s, then green (pin 13) for 3s, turning off each after delay.

3. Final Answer:

   while True loop with red (2s), yellow (1s), green (3s) -> Option C

4. Quick Check:

   Correct order and timing in loop = A [OK]

Hint: Use while True and sequence GPIO.output with time.sleep [OK]

Common Mistakes:

• Wrong order of lights
• Using for loop without timing per light
• Turning all LEDs on at once