Traffic Light Controller — Digital Circuits Project

👥 Authors

• Zahra AlMudaweb (ID: A00749)
• Dana Barhoom (ID: A00200)
• Supervisor: Mr. Herbert Azuela
• University: American University of Bahrain (AUBH)
• Date: 18/04/2024

📄 Project Description

This project implements a traffic light controller for a two-road intersection using VHDL. The system simulates traffic light operations based on sensor input and uses a state machine to control timing and transitions. The design focuses on real-world constraints, such as traffic sensors and road priorities.

🎯 Objectives

• Design a traffic light controller using VHDL and state machines.
• Simulate and test the behavior of the controller using a testbench.
• Understand the functional behavior of intersections with sensor-based traffic flow control.

🔧 Methodology

• Developed block, state, and traffic light diagrams using draw.io.
• Coded the design using VHDL and tested it with a VHDL testbench.
• Verified correctness with waveform simulation and manual testing.

🚦 System Overview

Inputs

• Sa: Sensor on Road A (main road)
• Sb: Sensor on Road B (secondary road)
• clk: System clock

Outputs

• Ga, Ya, Ra: Green, Yellow, Red lights for Road A
• Gb, Yb, Rb: Green, Yellow, Red lights for Road B

Key Logic

• Road A stays green for 60s by default.
• If a car is detected on Road B, and A's 60s cycle has passed, B turns green for 50s.
• If Road A remains empty and B still has vehicles, B's green cycle extends by 10s.
• Transitions are controlled by a state machine with conditions based on sensor input.

📊 Diagrams Included

• Traffic Light Diagram
• Block Diagram
• State Diagram

💻 VHDL Implementation

• traffic_light.vhdl: Main VHDL code for the traffic controller.
• traffic_light_tb.vhdl: Testbench to simulate input cases and verify functionality.

✅ Testing

• Simulation results show correct transitions of lights per sensor input and time constraints.
• Manual and testbench verification validate behavior under different traffic scenarios.

📈 Results

• Waveform outputs and state transitions are consistent with expected traffic control logic.
• Edge cases (e.g., persistent vehicle presence on Road B) are handled correctly.

🔮 Future Work

• Implement pedestrian crossing signals.
• Add timer-based override features.
• Expand to handle 4-way intersections with more sensors.

📌 Work Breakdown

• Zahra AlMudaweb: VHDL Coding, Testbench, Diagram Design
• Dana Barhoom: System Design, Documentation, Testing & Simulation