Smart Traffic Light System

COE411 – Embedded and Cyber Physical Systems | Milestone 2

Name	ID
Youssef Hussien	94899
Youssef Abdellatife	94622
Seif Hussien	97215

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Project Overview

An intelligent intersection controller built on the ESP32 using FreeRTOS. Simulated entirely in Wokwi via VS Code + PlatformIO. No physical hardware required.

Features

• Standard Green → Yellow → Red traffic cycle
• Pedestrian crossing via push button (forces red immediately)
• Vehicle detection via HC-SR04 ultrasonic sensor (extends green by 5 s, max 3×)
• PWM buzzer alerts via LEDC driver
• FreeRTOS Rate-Monotonic scheduling with binary semaphores and queue

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GPIO Pin Mapping

Component	ESP32 Pin	Purpose
RGB LED – Red	GPIO 25	Red traffic light
RGB LED – Yellow	GPIO 26	Yellow traffic light
RGB LED – Green	GPIO 27	Green traffic light
Buzzer	GPIO 32	PWM alert (LEDC)
Push Button	GPIO 19	Pedestrian crossing request
HC-SR04 TRIG	GPIO 5	Ultrasonic pulse trigger
HC-SR04 ECHO	GPIO 18	Echo return

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FreeRTOS Task Summary

Task	Priority	Period	Purpose
Pedestrian Task	4 (highest)	Aperiodic	Button press → force red
Traffic Cycle Task	3	1000–10000 ms	Green/Yellow/Red sequence
Ultrasonic Task	2	100 ms	Distance sensing
Buzzer Task	1 (lowest)	Queue-driven	PWM tone generation

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Project Structure

smart_traffic_light/
├── src/
│   └── main.c          ← All firmware code (tasks, ISR, drivers)
├── diagram.json        ← Wokwi circuit diagram
├── wokwi.toml          ← Wokwi + PlatformIO integration config
├── platformio.ini      ← PlatformIO build configuration
└── README.md

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How to Run (Wokwi Simulation)

Prerequisites

• VS Code
• PlatformIO IDE extension
• Wokwi for VS Code extension
• Wokwi licence (free for students)

Steps

1. Clone / open the project folder in VS Code.

2. Build the firmware:

   PlatformIO: Build   (Ctrl+Alt+B)
   

3. Start the Wokwi simulation:

   • Open diagram.json
   • Click the ▶ Start Simulation button in VS Code (or press F1 → Wokwi: Start Simulator)

4. Interact with the simulation:

   • Watch the RGB LED cycle Green → Yellow → Red.
   • Click the green push button to trigger a pedestrian crossing (LED goes red, buzzer beeps).
   • In the Wokwi panel, set the HC-SR04 distance slider to < 20 cm while green is active to trigger a green extension.

5. View serial output in the PlatformIO Serial Monitor for real-time task logs.

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Timing Constants (adjustable in main.c)

Constant	Default	Description
GREEN_PHASE_MS	5000 ms	Normal green duration
YELLOW_PHASE_MS	2000 ms	Yellow transition
RED_PHASE_MS	4000 ms	Normal red duration
PEDESTRIAN_CROSSING_MS	5000 ms	Extra red for safe crossing
GREEN_EXTENSION_MS	5000 ms	Green extension per detection
MAX_EXTENSIONS	3	Max consecutive extensions
ULTRA_DETECT_CM	20 cm	Detection threshold

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Inter-Task Communication

[Pedestrian Task] ──xSemPedestrian──►[Traffic Cycle Task]
[Ultrasonic Task] ──xSemExtension───►[Traffic Cycle Task]
[Pedestrian Task] ──xQueueBuzzer────►[Buzzer Task]
[Traffic Cycle Task]──xQueueBuzzer──►[Buzzer Task]