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Lesson 29: Traffic Light Module

In this lesson, you will learn to create a traffic light system using the Raspberry Pi Pico W. You’ll program the Pico W to control three LEDs – red, yellow, and green – mimicking a real traffic light. This project offers a practical introduction to using Pulse Width Modulation (PWM) for LED brightness control and basic control structures in MicroPython. It’s ideal for beginners looking to explore digital signal processing and gain confidence in coding on the Raspberry Pi Pico W platform.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
Raspberry Pi Pico W	BUY
Traffic Light Module	BUY
Breadboard	BUY

Wiring

../_images/Lesson_29_Traffic_Light_Module_pico_bb.png

Code

from machine import Pin, PWM
import time

# Initialize pins for LEDs
red = PWM(Pin(26), freq=1000)  #  red LED
yellow = PWM(Pin(27), freq=1000)  #  yellow LED
green = PWM(Pin(28), freq=1000)  # green LED


# Function to set the brightness of an LED (0-100%)
def set_brightness(led, brightness):
    if brightness < 0 or brightness > 100:
        raise ValueError("Brightness should be between 0 and 100")
    led.duty_u16(int(brightness / 100 * 65535))


try:
    # Example sequence
    while True:

        # Green light for 5 seconds
        set_brightness(green, 100)
        time.sleep(5)
        set_brightness(green, 0)

        # Blink Yellow light
        set_brightness(yellow, 100)
        time.sleep(0.5)
        set_brightness(yellow, 0)
        time.sleep(0.5)
        set_brightness(yellow, 100)
        time.sleep(0.5)
        set_brightness(yellow, 0)
        time.sleep(0.5)
        set_brightness(yellow, 100)
        time.sleep(0.5)
        set_brightness(yellow, 0)
        time.sleep(0.5)

        # Red light for 5 seconds
        set_brightness(red, 100)
        time.sleep(5)
        set_brightness(red, 0)

except KeyboardInterrupt:
    # Turn off RGB LED on interrupt
    set_brightness(red, 0)
    set_brightness(yellow, 0)
    set_brightness(green, 0)

Code Analysis

Importing Libraries

The machine library is used for controlling hardware components, and time is used for creating delays.
```
from machine import Pin, PWM
import time
```

Initializing LED Pins

Here, we initialize the pins connected to the LEDs. PWM is used to control the brightness of the LEDs.

red = PWM(Pin(26), freq=1000)  #  red LED
yellow = PWM(Pin(27), freq=1000)  #  yellow LED
green = PWM(Pin(28), freq=1000)  # green LED

Defining the Set Brightness Function

Note

Due to the fact that the pins of Raspberry Pi Pico can only output a maximum voltage of 3.3V, the green LED will appear dim.

This function sets the brightness of the LEDs. It takes two parameters: the LED and the desired brightness level (0-100%). The duty_u16 method is used to set the PWM duty cycle.
```
def set_brightness(led, brightness):
    if brightness < 0 or brightness > 100:
        raise ValueError("Brightness should be between 0 and 100")
    led.duty_u16(int(brightness / 100 * 65535))
```

Main Loop and Traffic Light Sequence

The while True loop makes the code run continuously. It controls the sequence of the traffic light: green, yellow (blinking), and red.

try:
    while True:
        # Green light for 5 seconds
        set_brightness(green, 100)
        time.sleep(5)
        set_brightness(green, 0)
        ...

Handling Keyboard Interrupt

The except KeyboardInterrupt block is used to handle a manual interruption (like Ctrl+C). It turns off all LEDs when the script is interrupted.
```
except KeyboardInterrupt:
    set_brightness(red, 0)
    set_brightness(yellow, 0)
    set_brightness(green, 0)
```