B31DD Mini-Project Report

Traffic Light Display System with Servo Control and Serial Monitoring

1. Project Introduction

The Traffic Light Display System is an embedded project designed to simulate a real-world traffic light controller using an AVR microcontroller. This system manages traffic flow by controlling red, yellow, and green LEDs, incorporates a servo motor to represent mechanical signaling (e.g., pedestrian crossing), displays countdown timers on an LCD, and logs traffic light changes via serial communication. Additionally, it features an interrupt-driven button allowing pedestrians to request crossing, thereby altering the normal traffic sequence.

Key Techniques Used:

• Input/Output
• Timer
• Interrupt
• PWM and Servo Control
• Serial Communication
• LCD Display

2. Functionalities

• Traffic Light Control: Manages red, yellow, and green LEDs to simulate traffic signals.
• Servo Motor Integration: Adjusts the servo position based on the active traffic light (0° for red, 90° for green).
• LCD Display: Shows the current traffic light status and a countdown timer.
• Serial Communication: Logs traffic light changes to a serial monitor for monitoring and debugging.
• Interrupt-Driven Pedestrian Button: Allows pedestrians to request crossing, triggering a modified traffic sequence.

3. Hardware Components and Schematics

3.1 Components Used

• Microcontroller: AVR (e.g., ATmega328P)
• LEDs: Red, Yellow, Green
• Servo Motor: Standard hobby servo
• LCD Display: 16x2 character LCD
• Button: Momentary push-button
• Resistors: Current-limiting resistors for LEDs
• Power Supply: 5V regulated supply
• Miscellaneous: Breadboard, jumper wires, USB-to-Serial adapter

3.2 Connection Overview

• LEDs:
  • Red LED: Connected to PORTB3 through a current-limiting resistor.
  • Yellow LED: Connected to PORTB4 through a current-limiting resistor.
  • Green LED: Connected to PORTB5 through a current-limiting resistor.
• Servo Motor:
  • Control Pin: Connected to PORTB2 (OC1B).
  • Power: Connected to an external 5V supply with a common ground.
• LCD Display:
  • Data Lines (D4-D7): Connected to PORTD4-PORTD7.
  • Control Lines (RS, EN): Connected to PORTB0 and PORTB1.
• Button:
  • One Terminal: Connected to PORTD3.
  • Other Terminal: Connected to GND with an internal pull-up resistor enabled.
• Serial Communication:
  • TX Pin (PD1): Connected to RX of USB-to-Serial adapter.
  • Common Ground: Ensured between microcontroller and adapter.

4. Techniques and Methodologies

4.1 LED Control

• Utilized PORTB pins to control red, yellow, and green LEDs.
• Employed bitwise operations to set and clear specific LED states without affecting others.

4.2 Servo Motor Control

• Implemented PWM (Pulse Width Modulation) using Timer1 in Fast PWM mode.
• Mapped specific angles (0° and 90°) to corresponding pulse widths to position the servo accurately.
• Configured the servo to reset to 0° during red light and move to 90° during green light.

4.3 LCD Display

• Initialized the LCD in 4-bit mode for efficient data transmission.
• Displayed the current traffic light status and a countdown timer on two lines.
• Utilized sprintf for formatting countdown strings.

4.4 Serial Communication

• Configured USART for serial communication at 9600 baud rate.
• Implemented functions to initialize USART, transmit single characters, and send strings.
• Logged every traffic light change with appropriate messages for monitoring.

4.5 Interrupt Handling

• Configured an external interrupt (INT1) on PORTD3 to detect button presses.
• Employed a sequence in the ISR, when the button is pressed, to display the yellow light for 3 seconds and then the green light for 5 seconds for pedestrians crossing the road.

5. Demo Results

5.1 Normal Traffic Sequence

1. Red Light:

   • LED: Red LED on.
   • Servo: Positioned at 0°.
   • LCD: Displays “RED LIGHT” with an 8-second countdown.
   • Serial: Logs “RED LIGHT”.
     

2. Green Light:

   • LED: Green LED on.
   • Servo: Positioned at 90°.
   • LCD: Displays “GREEN LIGHT” with a 4-second countdown.
   • Serial: Logs “GREEN LIGHT”.
     

3. Yellow Light:

   • LED: Yellow LED on.
   • LCD: Displays “YELLOW LIGHT” with a 2-second countdown.
   • Serial: Logs “YELLOW LIGHT”.
     (Repeat cycle)
     

5.2 Pedestrian Request Sequence

• Button Press Detected: Triggers the ISR to execute the special sequence.
  

1. Yellow Light:

   • LED: Yellow LED on.
   • LCD: Displays “Pedestrians” with a 3-second countdown.
   • Serial: Logs “YELLOW LIGHT”.

2. Green Light:

   • LED: Green LED on.
   • Servo: Positioned at 90°.
   • LCD: Displays “GREEN LIGHT” with a 5-second countdown.
   • Serial: Logs “GREEN LIGHT”.

3. Return to Normal Sequence:

   • Servo: Resets to 0°.
   • Resumes Normal Traffic Cycle.

6. Performance Evaluation

• Timing Accuracy: _delay_ms() provided sufficient timing for demonstration purposes, but hardware timers are recommended for higher precision.
• Interrupt Responsiveness: The system detected button presses and executed pedestrian requests promptly.
• Servo Control: Smooth and accurate transitions between designated angles.
• Serial Logging: Reliable logging of traffic light changes for monitoring.
• LCD Display: Consistently displayed accurate statuses and countdowns.

Areas for Improvement:

• Implement software or hardware debouncing for the button.
• Extend servo angle functionality for versatile signaling.
• Replace _delay_ms() with timer-based delays for concurrent tasks.
• Add error handling for USART transmission and routine interruptions.

7. Conclusion

The Traffic Light Display System integrates various embedded system components controlled by an AVR microcontroller. Interrupt-driven button handling adds interactivity and realism, showcasing practical applications of PWM, serial communication, and user interfaces.

8. References

• AVR Microcontroller Datasheet
• Arduino Documentation
• LCD Display Lab3 Tutorials
• Servo Motor Control course material
• Serial Communication course material