Introduction

The GAL20V8A-15LNC is a programmable logic device (PLD) that offers a flexible way to implement combinational and sequential logic without the need for a microcontroller. It is particularly useful in DIY electronics projects where custom logic gates, state machines, or decoders are required. In this project, we will design and build a Custom Logic Controller using the GAL20V8A-15LNC to manage a simple traffic light control system.

This project focuses on the hardware setup and practical application of the GAL20V8A-15LNC without diving into programming or exhaustive design theory.

Project Overview

The traffic light control system will:

1. Control three sets of LEDs to simulate traffic lights.

2. Operate based on predefined logic sequences.

3. Be modular and expandable for more complex traffic scenarios.

This system serves as an excellent demonstration of the GAL20V8A’s capability to implement complex logic operations in a compact form factor.

Key Features

1. Custom Logic Implementation: Define specific logic functions for traffic light control using the GAL20V8A.

2. Sequential Timing Control: Use external timing circuits to manage transitions between states.

3. LED Visualization: Clearly display the logic states through red, yellow, and green LEDs.

4. Scalability: Easily expand the system for additional traffic lights or pedestrian crossings.

Components Needed

1. GAL20V8A-15LNC - The programmable logic IC for implementing custom logic.

2. 74LS193 4-Bit Binary Counter - For timing and state progression.

3. 555 Timer IC - Generates a clock signal for the counter.

4. LEDs (Red, Yellow, Green) - Visualize traffic light states.

5. Resistors - For current limiting (330Ω for LEDs, 10 kΩ for pull-up/pull-down).

6. Capacitors - For decoupling and timing (0.1 µF and 10 µF).

7. Push-button Switches - For manual state transitions or reset.

8. Breadboard and Wires - For prototyping.

9. Power Supply - +5V regulated power source.

Understanding the GAL20V8A-15LNC

The GAL20V8A is a high-performance PLD with the following key features:

1. 20 Inputs/Outputs: Configurable as inputs, outputs, or bidirectional.

2. Programmable Logic: Enables complex combinational and sequential logic designs.

3. High Speed: Propagation delays of 15ns make it suitable for real-time applications.

The programmable logic inside the GAL20V8A will define the traffic light control logic, including state transitions and timing signals.

Traffic Light Logic Design

State Diagram

The system operates in the following states:

1. State 1 (Green): Green LED ON, others OFF.

2. State 2 (Yellow): Yellow LED ON, others OFF.

3. State 3 (Red): Red LED ON, others OFF.

The logic will be:

1) Transition from Green → Yellow → Red → Green.

2) Timing intervals managed externally using a binary counter and a 555 timer.

Circuit Design

Block Diagram

1. Clock Generator:

A 555 timer generates clock pulses for state transitions.

2. State Counter:

A 4-bit counter (74LS193) determines the current state.

3. GAL20V8A Logic Controller:

Implements the traffic light logic to control LED outputs.

4. LED Driver Section:

LEDs visualize the output for each state.

Step-by-Step Implementation

1. Clock Generator

1. Configure a 555 timer in astable mode to generate clock pulses.

1) Use a 10 kΩ resistor, a 1 kΩ resistor, and a 100 µF capacitor for a frequency of approximately 1 Hz.

2. Connect the output of the 555 timer to the clock input of the 74LS193 counter.

2. State Counter

1. Connect the output of the 555 timer to the counter's clock input.

2. Use the 4 output bits of the 74LS193 (Q0–Q3) as inputs to the GAL20V8A.

3. GAL20V8A Logic Controller

1. Configure the GAL20V8A to process the counter inputs and generate the required logic for the LEDs.

2. Assign:

1) Q0 (LSB) and Q1 to control timing transitions.

2) Q2 and Q3 for optional future expansion (e.g., pedestrian signals).

4. LED Driver Section

1. Connect the output pins of the GAL20V8A to current-limiting resistors (330Ω) and then to the LEDs.

1．Pin assignments:

1) Green LED: Output pin 1

2) Yellow LED: Output pin 2

3) Red LED: Output pin 3

2. Ensure the LEDs are powered by the +5V supply with appropriate ground connections.

System Operation

1. Initialization

1. Power on the circuit.

2. The 555 timer starts generating clock pulses, triggering the counter.

2. State Transition

1. The counter increments with each clock pulse, cycling through binary states.

2. The GAL20V8A processes the counter outputs and generates the appropriate control signals for the LEDs.

1．For example:

1) State 0 (Binary 00): Green LED ON, others OFF.

2) State 1 (Binary 01): Yellow LED ON, others OFF.

3) State 2 (Binary 10): Red LED ON, others OFF.

3. Visual Output

1. Observe the LEDs transitioning through the traffic light sequence:

Green → Yellow → Red → Green.

Testing and Debugging

1. Clock Signal Testing:

Use an oscilloscope or multimeter to verify the 555 timer’s output frequency.

2. Counter Functionality:

Confirm the 74LS193 cycles through binary states.

3. GAL20V8A Logic Verification:

Check the output logic against the expected traffic light sequence.

4. LED Testing:

Ensure each LED lights up correctly in its designated state.

Applications and Extensions

1. Pedestrian Crossing Integration:

1) Add additional states and outputs for pedestrian signals.

2) Use extra pins on the GAL20V8A for control logic.

2. Sensor-Based Control:

Interface the system with IR sensors or buttons for real-world traffic management.

3. Complex Traffic Scenarios:

Expand the logic to control multiple intersections.

4. Educational Use:

Demonstrate programmable logic in an intuitive, visual format.

Conclusion

This Custom Logic Controller for Traffic Lights using the GAL20V8A-15LNC is an excellent DIY project for understanding the principles of programmable logic devices. It combines hardware design, logic implementation, and real-world application in a single project. Once built, the system is scalable and can serve as a platform for more advanced traffic management designs or educational demonstrations.