Traffic light simulation in Raspberry Pi

Introduction

A traffic light simulation helps us understand how traffic signals change colors to control cars and people safely.

To learn how to control lights using a Raspberry Pi.

To practice programming with hardware like LEDs.

To create a simple model of real-world traffic signals for education.

To test timing and sequence control in electronics projects.

Syntax

Raspberry Pi

import time
import RPi.GPIO as GPIO

# Setup GPIO pins
GPIO.setmode(GPIO.BCM)
RED = 17
YELLOW = 27
GREEN = 22
GPIO.setup(RED, GPIO.OUT)
GPIO.setup(YELLOW, GPIO.OUT)
GPIO.setup(GREEN, GPIO.OUT)

# Function to turn off all lights
def all_off():
    GPIO.output(RED, False)
    GPIO.output(YELLOW, False)
    GPIO.output(GREEN, False)

Use GPIO.setmode(GPIO.BCM) to refer to pins by their Broadcom number.

Set each LED pin as output with GPIO.setup(pin, GPIO.OUT).

Examples

Turn a specific light on or off by setting its pin True or False.

Raspberry Pi

GPIO.output(RED, True)  # Turn red light on
GPIO.output(RED, False) # Turn red light off

Pause the program to keep the light on for some time.

Raspberry Pi

time.sleep(3)  # Wait for 3 seconds

Use a function to switch off all LEDs before changing the light.

Raspberry Pi

all_off()  # Turn all lights off

Sample Program

This program cycles through red, green, and yellow lights using LEDs connected to a Raspberry Pi. It prints which light is on and waits the right amount of time. Press Ctrl+C to stop.

Raspberry Pi

import time
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
RED = 17
YELLOW = 27
GREEN = 22
GPIO.setup(RED, GPIO.OUT)
GPIO.setup(YELLOW, GPIO.OUT)
GPIO.setup(GREEN, GPIO.OUT)

def all_off():
    GPIO.output(RED, False)
    GPIO.output(YELLOW, False)
    GPIO.output(GREEN, False)

try:
    while True:
        # Red light on
        all_off()
        GPIO.output(RED, True)
        print("Red light ON")
        time.sleep(5)

        # Green light on
        all_off()
        GPIO.output(GREEN, True)
        print("Green light ON")
        time.sleep(5)

        # Yellow light on
        all_off()
        GPIO.output(YELLOW, True)
        print("Yellow light ON")
        time.sleep(2)

except KeyboardInterrupt:
    print("Program stopped")
    all_off()
    GPIO.cleanup()

Important Notes

Make sure your LEDs are connected with proper resistors to avoid damage.

Use GPIO.cleanup() to reset pins when the program ends.

Press Ctrl+C in the terminal to stop the program safely.

Summary

Traffic light simulation uses LEDs and timing to mimic real traffic signals.

GPIO pins control the lights by turning them on and off.

Use loops and delays to cycle through the colors in order.

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