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Digital Circuit Simulator

A powerful Java Swing-based GUI application for designing, simulating, and analyzing digital logic circuits.

Features

  • Visual Circuit Design: Drag-and-drop interface to add components and connections
  • Logic Gates: Support for AND, OR, NOT, XOR, NAND, NOR, XNOR gates
  • Interactive Components:
    • Switches (toggle between open/closed states)
    • LEDs (change color to indicate on/off status)
    • Logic gates with multiple inputs
  • Circuit Validation: Automatic detection of design errors and short circuits
  • Truth Table Generation: Generate complete truth tables for all input combinations
  • Signal Simulation: Real-time signal propagation through the circuit
  • Save & Load: Persist circuits to files for later use
  • Import/Export: Export circuit details as text files

System Requirements

  • Java Development Kit (JDK) 8 or higher
  • Operating System: Windows, Linux, or macOS
  • Screen Resolution: Minimum 1400x900 pixels recommended

Project Structure

oops_prj_trial/
├── src/
│   └── com/circuitsimulator/
│       ├── gui/
│       │   ├── MainWindow.java        # Main application window
│       │   └── CircuitPanel.java      # Drawing canvas for circuits
│       ├── components/
│       │   ├── Component.java          # Abstract base class
│       │   ├── Switch.java             # Interactive switch
│       │   ├── LED.java                # Visual LED display
│       │   ├── LogicGate.java          # Abstract logic gate
│       │   ├── ANDGate.java
│       │   ├── ORGate.java
│       │   ├── NOTGate.java
│       │   ├── XORGate.java
│       │   ├── NANDGate.java
│       │   ├── NORGate.java
│       │   └── XNORGate.java
│       ├── circuit/
│       │   ├── Circuit.java            # Main circuit manager
│       │   ├── Node.java               # Circuit node (pin)
│       │   └── Connection.java         # Connection between nodes
│       ├── validator/
│       │   ├── CircuitValidator.java   # Circuit validation
│       │   └── TruthTableGenerator.java # Truth table generation
│       └── file/
│           └── CircuitFileManager.java # Save/Load functionality
├── bin/                                 # Compiled .class files
├── circuits/                            # Saved circuit files directory
├── build_and_run.bat                   # Windows build and run script
├── build_and_run.sh                    # Linux/Mac build and run script
├── compile.bat                         # Windows compile only script
├── compile.sh                          # Linux/Mac compile only script
└── README.md                           # This file

Compilation & Execution

Windows

Option 1: Build and Run (One Step)

build_and_run.bat

Option 2: Compile Only

compile.bat

Then run manually:

java -cp bin com.circuitsimulator.gui.MainWindow

Linux / macOS

Option 1: Build and Run (One Step)

bash build_and_run.sh

Option 2: Compile Only

bash compile.sh

Then run manually:

java -cp bin com.circuitsimulator.gui.MainWindow

User Guide

Getting Started

  1. Launch the Application

    • Run the build script or execute the Java main class

  2. Creating a New Circuit

    • Go to File → New and enter circuit name
    • Or use the default "New Circuit"

  3. Adding Components

    Using Toolbar:

    • Select component type from dropdown (Switch, LED, AND, OR, NOT, XOR, NAND, NOR, XNOR)
    • Click "Add" button
    • Enter component name
    • Component will appear at mouse position

    Using Menu:

    • Add components through right-click context menu or toolbar

  4. Connecting Components

    • Click "Connect" button
    • Enter first node number (source)
    • Enter second node number (destination)
    • Connection is created and displayed

    Node Numbering Scheme:

    • Use numeric IDs for all nodes (1, 2, 3, etc.)
    • Open LED connections default to GND (LOW)
    • Open switch connections default to VCC (HIGH)

  5. Interactive Simulation

    • Double-click on switches to toggle between open/closed states
    • LEDs automatically update to show current state
    • Red color = HIGH (1)
    • Gray color = LOW (0)

  6. Component Interaction

    • Switches:

      • Green circle = CLOSED (conducting)
      • Red circle = OPEN (non-conducting)
      • Double-click to toggle

    • LEDs:

      • Bright red = ON (receiving HIGH signal)
      • Dark gray = OFF (receiving LOW signal)

    • Logic Gates:

      • Blue rectangles with gate type label
      • Can be dragged to new positions
      • Multiple input support

Circuit Operations

Validation

  • Click "Validate" button or Circuit → Validate
  • Checks for:
    • Incomplete connections
    • Short circuits (0 resistance from HIGH to LOW)
    • Undriven inputs
    • Missing outputs

Simulation

  • Click "Simulate" button or Circuit → Simulate
  • Propagates signals through all components
  • Updates all outputs based on current inputs
  • All LEDs will display the result

Truth Table Generation

  • Click "Truth Table" button or Circuit → Generate Truth Table
  • Automatically tests all possible input combinations
  • Shows output states for each combination
  • Useful for verification and testing

File Operations

Save Circuit

  • File → Save
  • Saves circuit in binary format (.cir)
  • Preserves all components, connections, and settings
  • Default location: circuits/ directory

Load Circuit

  • File → Open
  • Loads previously saved circuit
  • All components and connections restored

Export as Text

  • File → Export as Text
  • Exports circuit information as readable text
  • Lists all components, nodes, and connections
  • Useful for documentation

New Circuit

  • File → New
  • Clears all components and connections
  • Starts fresh with given name

Keyboard Shortcuts

Key Action
Delete Remove selected component
Double-click Toggle switch state
Drag Move component

Menu Reference

File Menu

  • New - Create new circuit
  • Open - Load saved circuit
  • Save - Save current circuit
  • Export as Text - Export to text file
  • Exit - Close application

Edit Menu

  • Clear All - Remove all components
  • Delete Selected - Remove selected component

Circuit Menu

  • Validate - Check circuit for errors
  • Simulate - Run simulation
  • Generate Truth Table - Create truth table

Help Menu

  • About - Application information

Node Numbering System

The circuit uses a number-based connection scheme where each connection point (node) has a unique integer ID.

Rules:

  1. Each node represents a connection point in the circuit
  2. Nodes are identified by unique integer numbers
  3. Multiple components can share the same node
  4. Nodes can carry either HIGH (1) or LOW (0) signals

Defaults:

  • Unconnected LED inputs → Automatically set to GND (LOW / 0)
  • Unconnected switch outputs → Automatically set to VCC (HIGH / 1)

Component Details

Switches (SPST)

  • Type: Input source
  • Function: Provides variable input signal
  • States: OPEN (HIGH/1) or CLOSED (LOW/0)
  • Interaction: Double-click to toggle

LEDs

  • Type: Output indicator
  • Function: Displays output signal status
  • Visual: Color change indicates state
  • Colors: Red (ON/1), Gray (OFF/0)

AND Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: Output HIGH only when ALL inputs are HIGH
  • Truth Table: See truth table generation feature

OR Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: Output HIGH if ANY input is HIGH

NOT Gate (Inverter)

  • Input: 1
  • Output: 1
  • Function: Output is inverse of input

XOR Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: Output HIGH when ODD number of inputs are HIGH

NAND Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: NOT(AND) - Output is LOW when ALL inputs are HIGH

NOR Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: NOT(OR) - Output is LOW when ANY input is HIGH

XNOR Gate

  • Input: 2+ inputs
  • Output: 1
  • Function: NOT(XOR) - Output is HIGH when EVEN number of inputs are HIGH

Features in Detail

Circuit Validation

The validator checks for:

  1. Structural Errors

    • Missing input/output connections
    • Unconnected components

  2. Short Circuit Detection

    • Detects 0-resistance connections from HIGH to LOW
    • Prevents invalid electrical states

  3. Data Flow Issues

    • Identifies undriven inputs
    • Finds potential floating nodes
    • Checks for circular dependencies

Truth Table Generation

  • Generates all 2^n combinations (n = number of switches)
  • Tests each combination automatically
  • Shows outputs for all combinations
  • Formatted table display with borders
  • Useful for verification and debugging

Save/Load System

Binary Format (.cir)

  • Preserves all circuit information
  • Efficient storage
  • Fast load/save operations
  • Version compatible

Text Export (.txt)

  • Human-readable format
  • Component details
  • Connection information
  • Node states

Example Circuits

Example 1: Simple AND Gate Circuit

  1. Add 2 Switches (S1, S2)
  2. Add AND Gate (G1)
  3. Add LED (L1)
  4. Connect:
    • S1 output → AND input 1
    • S2 output → AND input 2
    • AND output → LED input
  5. Double-click switches to test
  6. Generate truth table to verify

Example 2: Half Adder Circuit

  1. Add 2 Switches (A, B)
  2. Add XOR Gate (Sum)
  3. Add AND Gate (Carry)
  4. Add 2 LEDs (SUM, CARRY)
  5. Connect inputs and outputs
  6. Test all 4 combinations

Example 3: Logic Expression Implementation

  1. Implement circuit for: (A AND B) OR (NOT C)
  2. Add 3 Switches, AND Gate, NOT Gate, OR Gate, 1 LED
  3. Build the logic structure
  4. Verify with truth table

Troubleshooting

Application won't start

  • Check Java installation: java -version
  • Ensure JDK is installed (not just JRE)
  • Check PATH environment variable

Compilation errors

  • Ensure all source files are present
  • Use compile scripts in project root
  • Check Java version compatibility

Circuit won't simulate

  • Click "Validate" to check for errors
  • Ensure all inputs are connected
  • Verify node numbers are unique where needed

Short circuit warning

  • Check for conflicting connections
  • Verify node states are appropriate
  • Review circuit logic

Technical Details

Signal Representation

  • HIGH (1): Logic state representing voltage
  • LOW (0): Logic state representing ground

Component Architecture

  • All components inherit from base Component class
  • Each has input and output nodes
  • evaluate() method calculates output from inputs

File Format

  • Circuits saved as serialized Java objects
  • Supports future extensions
  • Backward compatible

Limitations

  • Combinational logic only (no flip-flops, latches)
  • No analog components or voltage simulation
  • Ideal gates (no propagation delays)
  • No bus or multi-bit signals
  • Maximum practical components: ~50 (GUI performance dependent)

Future Enhancements

  • Sequential logic components (Flip-flops, Latches)
  • Timing analysis and delay simulation
  • More detailed gate properties (propagation delay, power)
  • Custom component definitions
  • Circuit library and templates
  • Integrated circuit (IC) support
  • Oscilloscope/waveform display
  • Schematic view (in addition to block diagram)

License & Credits

This is an educational project demonstrating:

  • Object-oriented design principles
  • Swing GUI programming
  • Digital logic simulation
  • Data persistence

Support

For issues, questions, or suggestions:

  1. Check the Troubleshooting section
  2. Review the User Guide
  3. Validate your circuit design
  4. Check error messages in console

Version: 1.0
Last Updated: April 2026
Platform: Java (Cross-platform compatible)

About

Project in Java using Swing GUI implementing Object Oriented Programming principles

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