ARAVIND SUNDARARAJAN

Project Overview

9-Key Macro Board is a custom-designed mechanical keyboard PCB that provides programmable macro functionality through a compact, professional-grade circuit design. The project demonstrates advanced PCB design skills using KiCad, incorporating mechanical switches, AVR microcontroller programming, and robust circuit architecture for reliable keyboard operation.

The board features a 3x3 grid of mechanical switches arranged in a matrix configuration, with each key capable of being programmed for custom macro functions. The design includes proper debouncing, power management, and programming interfaces, making it suitable for both personal use and as a foundation for larger keyboard projects.

This project showcases comprehensive hardware development skills, from schematic design and PCB layout to component selection and firmware integration. The modular design approach allows for easy customization and expansion, while the professional-grade components ensure reliable operation in demanding environments.

PCB Design & Layout

Detailed PCB layout showing the 3x3 key matrix, AVR microcontroller, and supporting circuitry

Layout Architecture

The PCB design follows professional layout principles with clear separation of functional areas:

• Key Matrix Section - Left two-thirds of the board containing the 3x3 mechanical switch array
• Control Circuitry - Right one-third housing the AVR microcontroller and supporting components
• Programming Interface - AVR ISP connector for firmware updates and debugging
• Power Management - Decoupling capacitors and voltage regulation circuitry

Key Matrix Design

The 9-key matrix is implemented using a 3x3 grid configuration:

• Switch Footprints - Compatible with MX-style mechanical switches and Alps switches
• Diode Protection - Each switch includes a protection diode for proper matrix scanning
• Routing Optimization - Efficient trace routing to minimize PCB layers and manufacturing complexity
• Silkscreen Markings - Clear component placement indicators and reference designators

Component Selection

Component Specifications

Microcontroller: AVR ATmega32U4 or similar
Switch Type: MX/Alps compatible mechanical switches
Diodes: SOD123 package, 1N4148 or equivalent
Crystal: 16MHz SMD crystal oscillator
Capacitors: 0805 SMD package, 0.1μF and 4.7μF
Resistors: 0805 SMD package, 10kΩ pull-ups
Programming: AVR ISP 6-pin connector
PCB Layers: 2-layer design with ground plane

Circuit Design

Key Matrix Circuit

The key matrix implements a 3x3 scanning configuration with proper diode protection:

• Row Scanning - Three row lines (Mrow0, Mrow1, Mrow2) for key detection
• Column Sensing - Three column lines (Mcol0, Mcol1, Mcol2) for key identification
• Diode Protection - Each switch includes a protection diode (D0-D8) for proper matrix operation
• Pull-up Resistors - External pull-ups ensure reliable signal levels

Power Management

Robust power distribution and filtering for stable operation:

• Decoupling Network - Multiple 0.1μF capacitors distributed across the board
• Bulk Capacitance - 4.7μF capacitor for power supply stability
• Ground Plane - Comprehensive ground plane for noise reduction
• Voltage Regulation - Proper voltage levels for microcontroller and switches

Programming Interface

Complete programming and debugging capabilities:

• AVR ISP Connector - 6-pin programming interface (RST, SCK, MOSI, MISO, VCC, GND)
• Reset Circuit - Manual reset switch with proper debouncing
• Clock Circuit - 16MHz crystal with 22pF load capacitors
• USB Interface - For communication and power from host computer

Key Features

Technical Specifications

• PCB Dimensions - Optimized for 3x3 key layout with control circuitry
• Layer Count - 2-layer design with ground plane
• Component Density - Efficient use of board space
• Manufacturing - Standard SMD components for cost-effective production
• Compatibility - Works with standard mechanical keyboard switches
• Programming - Standard AVR programming tools and protocols

Development Process

Design Workflow

The project followed a systematic hardware development approach:

• Schematic Design - Created comprehensive schematics using KiCad
• Component Selection - Researched and selected appropriate components
• PCB Layout - Designed professional-grade PCB layout
• Design Review - Verified circuit functionality and manufacturability
• Prototyping - Built and tested initial prototypes
• Iteration - Refined design based on testing results

KiCad Implementation

Professional PCB design using industry-standard tools:

• Schematic Capture - Multi-sheet schematic with proper hierarchy
• Component Libraries - Custom and standard component footprints
• PCB Layout - Manual routing with design rule checking
• Design Rules - Manufacturing-friendly design constraints
• Documentation - Comprehensive design documentation

Technical Challenges

Several challenges were addressed during development:

• Matrix Scanning - Implementing proper key matrix with diode protection
• Power Distribution - Ensuring stable power across all components
• Signal Integrity - Maintaining clean signals in compact layout
• Manufacturability - Designing for cost-effective PCB production
• Component Compatibility - Ensuring compatibility with standard switches

Applications & Use Cases

The 9-key macro board serves various practical applications:

Productivity Enhancement

• Software Shortcuts - Program common software commands and shortcuts
• Text Macros - Insert frequently used text or code snippets
• Workflow Automation - Streamline repetitive tasks in various applications
• Gaming - Custom gaming macros and hotkeys

Professional Applications

• CAD/CAM Operations - Quick access to common design commands
• Video Editing - Timeline and editing shortcuts
• Audio Production - DAW control and mixing shortcuts
• Programming - Code snippets and development tools

Educational Value

• PCB Design Learning - Demonstrates professional PCB design principles
• Embedded Systems - Shows microcontroller integration and programming
• Hardware Development - Complete hardware development workflow
• Open Source Hardware - Contributes to open hardware community

Project Significance

The 9-key macro board represents a significant achievement in hardware development and demonstrates several important skills:

• Professional PCB Design - Industry-standard design using KiCad
• Component Integration - Successful integration of multiple component types
• Circuit Architecture - Well-designed circuit with proper power and signal management
• Manufacturing Considerations - Design optimized for cost-effective production
• Documentation - Comprehensive design documentation and schematics

This project showcases the ability to design and implement complex hardware systems from concept to production-ready design. The modular approach and professional-grade components demonstrate understanding of both technical requirements and practical manufacturing considerations.

Future Development

The 9-key macro board design provides a foundation for future hardware projects:

• Expanded Keyboards - Scale to larger keyboard layouts (60%, TKL, full-size)
• Advanced Features - Add RGB lighting, OLED displays, or wireless connectivity
• Custom Firmware - Develop advanced macro programming and configuration
• Commercial Products - Potential for small-batch production or customization
• Educational Resources - Create tutorials and documentation for the community

The modular design approach allows for easy expansion and modification, making this project a valuable foundation for future hardware development work.