DIGITAL LOGIC / CIRCUITS / HARDWARE

Four-Way Traffic Light Controller

A hardware-based digital logic controller that automatically sequences red, yellow, and green signals for a four-way intersection.

AND / OR / NOT GatesJK & D Flip-FlopsCounters555 TimerBreadboardingCircuit Testing

Physical four-way traffic light signal assembly with lit lamps — The physical four-way traffic-light assembly built for the project.

Overview

I designed and assembled a four-way traffic control system using digital logic circuitry. Rather than programming a microcontroller, I implemented the sequencing with combinational logic, sequential components, and clock-generation circuitry, then tested the system with a physical traffic-signal display.

How it works

Logic gates. AND, OR, and NOT gates determine signal outputs based on the controller’s current state.
State storage. JK and D flip-flops track and transition between traffic-signal states.
Timing. A 555 timer and counters drive the sequence and regulate state transitions.
Signal coordination. The circuit cycles through red, yellow, and green phases to coordinate traffic directions.
Debugging and testing. I assembled the control circuit on a breadboard and diagnosed wiring, logic, and timing issues until the signal sequence operated reliably.

Circuit implementation

The controller was constructed from discrete integrated circuits and wiring on a breadboard. The photograph below shows the implemented logic and interconnections.

Breadboard circuit with digital logic ICs and connecting wires — Breadboard implementation of the digital logic and timing circuit.

Results

The circuit successfully coordinated 12 red, yellow, and green LED outputs. I verified the sequence across more than 100 continuous signal cycles to check for consistent timing and operation.

12Signal outputs

100+Continuous cycles tested

Additional view of the completed four-way traffic light system — A second view of the completed physical traffic-signal system.

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