Smart Pedestrian Traffic Light

A robust, real-world traffic light system for vehicles and pedestrians, implemented in both Arduino (.ino) and bare-metal AVR-C (.c) for ATmega328P. This project demonstrates advanced embedded design, sensor integration, and state machine logic.

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Features

• Ultrasonic pedestrian detection (HC-SR04)
• 5-state finite state machine for safe, realistic traffic control
• Non-blocking timing (custom millis in C, Arduino millis in .ino)
• False trigger prevention (median filter in Arduino, hysteresis in C)
• Precise echo timing (hardware interrupt in C, pulseIn in Arduino)
• Explicit LED control in every state
• Portable pin mappings (same for both versions)

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Hardware Connections

Signal	Arduino Pin	AVR Port/Bit	Description
TRIG	D6	PD6	Ultrasonic trigger
ECHO	D7 (Arduino)	D2 (C, INT0)	Ultrasonic echo (INT0 in C)
CAR_RED	D8	PB0	Car red LED
CAR_YELLOW	D9	PB1	Car yellow LED
CAR_GREEN	D10	PB2	Car green LED
PED_GREEN	D11	PB3	Pedestrian green LED
PED_RED	D12	PB4	Pedestrian red LED

Note: In the C version, ECHO must be on D2 (PD2, INT0) for hardware interrupt operation.

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How It Works

• Pedestrian detection:
  • Arduino: 3-sample median filter, blocking pulseIn
  • C: Hardware interrupt (INT0), non-blocking, hysteresis
• State machine:
  • VEHICLE_GREEN → VEHICLE_YELLOW → VEHICLE_RED → PEDESTRIAN_GREEN → VEHICLE_PRE_GREEN → VEHICLE_GREEN
  • Ensures minimum green/red times, safe transitions, and no flicker
• Timing:
  • Arduino: Uses built-in millis()
  • C: Custom millis() via Timer0 overflow ISR

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Build & Flash

Arduino (.ino)

1. Open TrafficLight.ino in Arduino IDE or VS Code with Arduino extension
2. Select board and port
3. Upload

Bare-metal AVR-C (.c)

avr-gcc -mmcu=atmega328p -DF_CPU=16000000UL -Os -std=c99 -o TrafficLight.elf TrafficLight.c
avr-objcopy -O ihex TrafficLight.elf TrafficLight.hex
avrdude -c arduino -p m328p -P COM3 -b 115200 -U flash:w:TrafficLight.hex

Adjust -P COM3 as needed.

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Key Differences: Arduino vs. C

Aspect	Arduino (.ino)	Bare-metal C (.c)
Pin control	pinMode/digitalWrite	Direct register (PORTx)
Timing	millis()	Custom millis (Timer0 ISR)
Echo timing	pulseIn (blocking)	INT0 interrupt (non-block)
False trigger filter	Median filter	Hysteresis
Portability	Any Arduino board	ATmega328P (AVR) only
Code style	High-level, easy	Low-level, efficient

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Tips for Success

1. INT0 Pin: ECHO must use D2 (PD2) in C for hardware interrupts.
2. Debouncing: Hysteresis (C) and median filter (Arduino) prevent false triggers.
3. Timing: All delays are non-blocking; system remains responsive.
4. Pin Mapping: Both versions use the same pinout for easy hardware reuse.

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License

MIT License

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Project originally coded with Claude Sonnet 4.6, reviewed and improved for clarity and robustness. Contributions welcome!

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Photos

Below are photos of the working system for reference:

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These images show the real hardware setup and operation of the smart pedestrian traffic light.