LogicSim

A digital logic circuit simulator built in C++ with Qt. Drag logic gates and input/output sources onto a canvas, wire them together, and watch signal state propagate through the circuit in real time.

Aim

A practice project intended as a learning platform for young students (future engineers), to learn the basics of electronics and logic gates through hands-on, visual experimentation rather than abstract theory.

Features

• Interactive circuit canvas: drag components from a palette, drop them onto the scene, and connect ports by clicking between them
• Live simulation: component states update and propagate through the circuit automatically whenever a connection or input changes
• Supported components:
  • Inputs: VCC, GND, push button
  • Logic gates: AND, OR, NOT
  • Outputs: LED, buzzer

Architecture

The simulation core is fully decoupled from the UI Core/Circuit contains no Qt dependencies at all, so the logic can be reasoned about (and tested) independently of how it's rendered.

Core/Circuit/
├── Components/       Component, Port, and concrete component types
│                      (gates, inputs, outputs), built via ComponentsFactory
└── Managers/          CircuitManager — owns all components, evaluates
                        circuit state, notifies observers on change

UI/
├── Controllers/        SceneEditor (canvas interaction), MainGuiContainer
├── disp/                Qt widgets, views, and .ui forms
└── Models/              Component metadata for the palette

Common/
└── Observable/IObserver  Generic observer pattern used to notify the UI
                          when circuit state changes

Key design decisions:

• Factory pattern (ComponentsFactory) creates the correct component subclass from an ElementType enum, keeping construction logic in one place.
• Observer pattern (Observable/IObserver) lets SceneEditor react to circuit state changes without CircuitManager knowing anything about the UI.
• Circuit evaluation repeatedly recomputes component outputs until the circuit reaches a stable state (a fixed-point iteration), so it correctly handles circuits where signal changes cascade through multiple components in one update.

Building

Requirements

• CMake 3.16+
• Qt 6 (or Qt 5) with the Widgets and Multimedia components
• A C++17-compatible compiler

Build

mkdir build && cd build
cmake ..
cmake --build .

Or open CMakeLists.txt directly in Qt Creator and build from there.

Project structure

Path	Contents
Core/Circuit/Components/	Component base class, ports, and all concrete component types
Core/Circuit/Managers/	CircuitManager — the simulation engine
Common/	Shared interfaces (Observable, IObserver)
UI/Controllers/	Scene interaction and window composition
UI/disp/	Qt widgets and .ui form files
UI/disp/Widgets/CircuitElement/	Visual representation of each component type on the canvas
Resources/	Icons and images used by the UI

Roadmap

• Unit tests for CircuitManager and component evaluation logic
• Additional logic gates (NAND, NOR, XOR, XNOR)
• Save/load circuits to file