Traffic Lights

In this project extends P001: Light a Flag Outside to use 3 LEDs, and simulate the traffic lights, including basic timed control, and perdestrain request button. Goals:

Understand the basic usage of an LED
Enhance the digital output concept, use digital output on both Micro:bit and Arduino
Conditional logic using if-else
Simple state machine with 2 states
Motivate serious thinking for satefy-critical products

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Story 1: "Set the Traffic Lights"

Story 2: "The Basic Timed Loop"

Micro:bit Codes

Arduino Codes

Story 3: "The Pedestrian Request Interrupt"

The "Idle" State Concept

Story 1: "Set the Traffic Lights"

Connect the external 3 LEDs, understand physical wiring in practice

Story 2: "The Basic Timed Loop"

Use digitalWrite to output a digital (0 or 1) signal

The Swedish Traffic Light Sequence

Red: Stop.
Red + Yellow: "Get ready." The light is about to turn green. You should prepare to move but not cross the line yet.
Green: Go.
Yellow: Stop! (Unless you are so close to the intersection that stopping would be dangerous).
Red: Stop.
Repeat from step 1

Micro:bit Codes

# The "Setup"

RED = DigitalPin.P0

YELLOW = DigitalPin.P1

GREEN = DigitalPin.P2

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 0)

def on_forever():

# 1. RED ONLY (Explicitly turn others off)

pins.digital_write_pin(RED, 1)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 0)

basic.pause(3000)

# 2. RED + YELLOW (Swedish "Prepare")

pins.digital_write_pin(RED, 1)

pins.digital_write_pin(YELLOW, 1)

pins.digital_write_pin(GREEN, 0)

basic.pause(1000)

# 3. GREEN ONLY

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 1)

basic.pause(3000)

# 4. YELLOW ONLY (Clear intersection)

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 1)

pins.digital_write_pin(GREEN, 0)

basic.pause(1200)

basic.forever(on_forever)

Arduino Codes

const int RED = 2;

const int YELLOW = 3;

const int GREEN = 4;

void setup() {

pinMode(RED, OUTPUT);

pinMode(YELLOW, OUTPUT);

pinMode(GREEN, OUTPUT);

// Explicitly force all LEDs to OFF at startup

digitalWrite(RED, LOW);

digitalWrite(YELLOW, LOW);

digitalWrite(GREEN, LOW);

}

void loop() {

// 1. RED ONLY

digitalWrite(RED, HIGH);

digitalWrite(YELLOW, LOW);

digitalWrite(GREEN, LOW);

delay(3000);

// 2. RED + YELLOW

digitalWrite(RED, HIGH);

digitalWrite(YELLOW, HIGH);

digitalWrite(GREEN, LOW);

delay(1000);

// 3. GREEN ONLY

digitalWrite(RED, LOW);

digitalWrite(YELLOW, LOW);

digitalWrite(GREEN, HIGH);

delay(3000);

// 4. YELLOW ONLY

digitalWrite(RED, LOW);

digitalWrite(YELLOW, HIGH);

digitalWrite(GREEN, LOW);

delay(1200);

}

Story 3: "The Pedestrian Request Interrupt"

Challenging fun task, motivating using looping and function

The "Idle" State Concept

In the previous story, the traffic light was always changing. Now, the traffic light has a "Default" or "Idle" state: Green. It will stay Green forever unless a pedestrian interrupts it by asking to cross.

HW Setup Upgrade

Micro:bit: Keep as is, use internal button A or B
Arduino: Upgrade with a button

Micro:bit Codes

# Setup pins

RED = DigitalPin.P0

YELLOW = DigitalPin.P1

GREEN = DigitalPin.P2

# Initialization: Start in the "Idle" state (Cars Go)

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 1)

def on_forever():

# Check if the pedestrian pressed Button A

if input.button_is_pressed(Button.A):

# 1. YELLOW: Warn cars to stop

pins.digital_write_pin(GREEN, 0)

pins.digital_write_pin(YELLOW, 1)

basic.pause(2000)

# 2. RED: Cars stop, pedestrians cross

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(RED, 1)

basic.pause(5000)

# Give them 5 seconds to cross

# 3. RED + YELLOW (Swedish rule: Prepare cars to go)

pins.digital_write_pin(YELLOW, 1)

basic.pause(1000)

# 4. GREEN: Back to idle state

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 1)

# Anti-Spam: Force a 5-second wait before the button works again

basic.pause(5000)

else:

# If button is NOT pressed, explicitly ensure Green is ON

pins.digital_write_pin(RED, 0)

pins.digital_write_pin(YELLOW, 0)

pins.digital_write_pin(GREEN, 1)

basic.forever(on_forever)

Arduino Codes

const int RED = 2;

const int YELLOW = 3;

const int GREEN = 4;

const int BUTTON = 12; // Pedestrian button

void setup() {

pinMode(RED, OUTPUT);

pinMode(YELLOW, OUTPUT);

pinMode(GREEN, OUTPUT);

// CRITICAL: Use INPUT_PULLUP to prevent the pin from floating

// This means the button reads HIGH when NOT pressed, and LOW when pressed.

pinMode(BUTTON, INPUT_PULLUP);

// Initialization: Start with Green ON

digitalWrite(RED, LOW);

digitalWrite(YELLOW, LOW);

digitalWrite(GREEN, HIGH);

}

void loop() {

// Check if button is pressed (Reads LOW because of INPUT_PULLUP)

if (digitalRead(BUTTON) == HIGH) {

// Optional: Add a 1-second delay so the light doesn't change instantly

delay(1000);

// 1. YELLOW (Warn cars)

digitalWrite(GREEN, LOW);

digitalWrite(YELLOW, HIGH);

delay(2000);

// 2. RED (Pedestrians cross)

digitalWrite(YELLOW, LOW);

digitalWrite(RED, HIGH);

delay(5000); // 5 seconds to cross

// 3. RED + YELLOW (Swedish rule: Prepare to go)

digitalWrite(YELLOW, HIGH);

delay(1000);

// 4. GREEN (Back to idle)

digitalWrite(RED, LOW);

digitalWrite(YELLOW, LOW);

digitalWrite(GREEN, HIGH);

// ANTI-SPAM: Give cars at least 5 seconds to drive

// before allowing another pedestrian to trigger the light

delay(5000);

}

// No "else" statement needed here because the loop will just repeat

// and the LEDs will stay in the state they were last left (Green ON).

}

Test and Fix

Do they work? Any risk of ocassional or corner case faults? How to fix

Knowledge Check

Enhance basic knowledge understanding, reflect and summarize what we have learnt

Do you dare to cross the street controlled by the traffic lights system built by you?
What to consider to make a safety-critical program like traffic lights?
What could cause faults or unstability?
- Electrical noise?
- Perdestrains spaming pressing?

Traffic Lights

In this project extends P001: Light a Flag Outside to use 3 LEDs, and simulate the traffic lights, including basic timed control, and perdestrain request button. Goals:

Understand the basic usage of an LED

Enhance the digital output concept, use digital output on both Micro:bit and Arduino

Conditional logic using if-else

Simple state machine with 2 states

Motivate serious thinking for satefy-critical products

Story 1: "Set the Traffic Lights"

Story 2: "The Basic Timed Loop"

Micro:bit Codes

Arduino Codes

Story 3: "The Pedestrian Request Interrupt"

The "Idle" State Concept

HW Setup Upgrade

Micro:bit Codes

Arduino Codes

Test and Fix

Knowledge Check