A gate-level, hardware-controlled digital traffic light system designed without using any microcontrollers. This project features dynamic cycle acceleration via asynchronous pedestrian requests and hardware-enforced fail-safe mechanisms such as interlocking and conflict resolution.
| Proteus Schematic | Physical Implementation |
|---|---|
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- No Microcontrollers: Fully implemented at the gate level using 74-series logic components and basic semiconductors.
- Synchronous State Machine: Built using an NE555 Timer in astable mode, dual 74HC74 D-Type Flip-Flops, and a 74HC86 XOR gate to generate a 2-bit synchronous counter.
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Dynamic Timing Control: Integrated BC237 NPN transistors and potentiometers to dynamically scale the operating frequency (
$0.133\text{ Hz} - 0.699\text{ Hz}$ ) by altering the RC time constant. - Asynchronous Pedestrian Intervention: A debounced hardware switch prompts an accelerated cycle towards the pedestrian phase safely through combinational state progression without compromising cross-traffic safety.
Unlike software-defined solutions, safety metrics in this system are hardware-impossible to bypass:
- Dual Green Protection (Conflict Resolution): A 74HC00 NAND gate instantly detects if both main and side roads are assigned a GREEN status simultaneously. It immediately triggers an asynchronous reset to a safe initial state (State 0: Main Green, Side Red).
- Dead State Protection (Dark Intersection): A supervisory network utilizing 74HC32 OR gates continuously monitors all lighting channels. If an illegal state occurs where all lights are turned OFF (all outputs LOW) during power-up or operation, the system automatically auto-resets back into the safe initial cycle.
| State (Phase) | Main Road Lights | Side Road Lights | Pedestrian Lights | Description |
|---|---|---|---|---|
| State 0 | GREEN | RED | RED | Traffic flows on the main road. |
| State 1 | YELLOW | RED | RED | Main road prepares to stop. |
| State 2 | RED | GREEN | RED | Right of way is given to the side road. |
| State 3 | RED + YELLOW | RED | GREEN | Safe crossing duration for pedestrians. |
- ICs (Logic & Timing): NE555, 74HC74, 74HC86, 2x 74HC32, 2x 74HC08, 74HC00, 74HC04
- Semiconductors: 2x BC237 NPN Transistors, 4x 1N4148 Fast Switching Diodes
- Display Elements: 3x Green LEDs, 3x Red LEDs, 1x Yellow LED
- Passives: 100kΩ / 50kΩ Potentiometers, 47kΩ, 6x 10kΩ, 7x 330Ω Resistors, 44µF Electrolytic & 3x 100nF Ceramic Capacitors
/Simulation: Contains the Proteus Design Suite schematic file./Documents: Contains the comprehensive academic project report.