🎹 Piano Player – Mechatronics Design Project

🎯 Project Objective

Design and build a full‑range electromechanical piano‑playing system capable of actuating all 88 keys of a standard acoustic piano using MIDI performance data.

The project began as a fully remote collaboration, with mechanical, electrical, and firmware development performed in Taiwan. Over time, it evolved into a long‑term embedded systems and real‑time control R&D platform, serving as a vehicle for learning, architectural experimentation, and scalable mechatronic design.

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🧩 System Overview

The system is built around a modular actuator architecture consisting of two identical 44‑key subsystems, each responsible for half of the keyboard. This modularity supports:

• Incremental mechanical assembly
• Independent subsystem testing
• Easier debugging and refinement
• Remote collaboration and partial builds

The architecture cleanly separates:

• Real‑time actuator control (embedded controller)
• High‑level sequencing, playback, and user interaction (host system)

This separation ensures direct actuation while enabling flexible external control, observability, and experimentation.

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🧩 Early Design Constraints & Rationale

Initial design discussions established several constraints that shaped the first prototype:

• The system needed to use an Arduino‑class microcontroller for accessibility and ease of replacement and institutional knowledge at the partner’s request.
• Hobby servos were selected for availability, simplicity, and low‑cost experimentation.
• The system had to be modular and serviceable, supporting partial builds and rapid iteration.
• Musical performance data would be supplied via standard MIDI, originating from a PC or Raspberry Pi.
• The mechanical structure needed to be low‑cost, easy to fabricate, and modifiable without specialized tools.

These constraints strongly influenced the early mechanical layout, electronics partitioning, and firmware structure.

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⚙️ Mechanical Design

Mechanical design was carried out in Autodesk Fusion 360, with emphasis on:

• Rapid iteration
• Low‑cost fabrication
• Easy disassembly and modification

Due to limited workshop access and budget constraints, the prototype frame was built from laser‑cut plywood and perspex, assembled using mechanical fasteners rather than adhesives. This allowed fast design revisions and mechanical experimentation during early testing.

Design artifacts:

• Assembly Photos
• Sketches and Renders
• Mechanical Drawings

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⚡ Electronics

Original Architecture (Arduino‑Based)

The first-generation system required independent control of 88 servo motors, one per piano key. To support this:

• Two Arduino Mega boards were used, each controlling 44 keys
• A hardware selector switch assigned each board to its note range
• A custom interface PCB handled:
  • Servo signal routing
  • Power distribution
  • External MIDI input
  • Board‑to‑board interconnects and test access

All schematics and PCB layouts were created in KiCad, with fabrication performed by JLCPCB.

PCB documentation:

• Controller PCB Design
• Controller PCB Top Layer
• Controller PCB Bottom Layer
• Populated PCB – View 1
• Populated PCB – View 2

While functional, this architecture revealed limitations:

• Servo timing jitter due to MCU timer constraints
• Power distribution challenges during dense chord play
• Increasing firmware complexity as features grew
• Difficulty scaling beyond the monolithic control loop

These limitations motivated a full system redesign.

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💾 Embedded Software

Initial Firmware (Arduino)

The original firmware:

• Parsed standard MIDI input
• Mapped MIDI notes to actuators
• Controlled servo position and motion timing
• Coordinated multi‑key actuation for chords
• Included diagnostic and test modes

Although successful, the monolithic structure struggled with timing problems as the Arduino was severely underpowered for the job.

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🔧 System Redesign & Modern Architecture

The system is now being re‑architected as a modern embedded control platform focused on determinism, scalability, and robustness.

Hardware & Control Evolution

• Migration from direct MCU‑driven servo outputs to I²C‑based PWM driver boards (PCA9685‑class)
• Improved electrical load distribution and power‑domain separation
• Cleaner signal routing and reduced ISR load

Firmware Architecture (Zephyr RTOS)

The embedded control layer has been ported to Zephyr RTOS running on an STM32WB55, introducing:

• A multi‑threaded architecture separating:
  • MIDI input parsing
  • Event scheduling
  • Actuator motion execution
• Explicit timing determinism and task prioritization
• Robust inter‑thread communication
• Improved fault isolation and system resilience

This architecture cleanly decouples real‑time actuation from non‑deterministic external inputs.

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🌐 Host Control & Web Interface

To support remote testing and flexible playback, a host‑side control layer provides:

• MIDI file browsing and selection
• Playlist management
• Playback control (play, pause, stop, next)
• Real‑time system observation

Evolution of the Host System

The webserver originally ran on a Raspberry Pi 2B, but under heavy load (multiple clients, large MIDI files, real‑time updates) the Pi became CPU‑bound. To improve responsiveness and reliability, the system was migrated to a more powerful openSUSE Linux workstation, resulting in:

• Faster page loads
• Lower latency in control commands
• More stable long‑duration playback sessions
• Headroom for future features (e.g., video streaming, analytics)

This migration reflects the system’s evolution from a simple test interface to a robust orchestration layer.

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📸 Media

Arduino Prototype

• 44‑Servo Test
• Playing “The Greatest” – Sia
• MacGyver Theme Demo

STM32 / Zephyr Prototype (Current)

Note: Only one 44‑key subsystem is shown. The second subsystem was provided to a collaborator for independent testing, and the architecture is validated on a half‑keyboard before full 88‑key reintegration.

• Calibration Demonstration
• “River Flows in You” – Yiruma

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🚧 Current Status & Next Steps

Completed

• Modular mechanical and electrical platform
• Reliable 44‑key real‑time actuation
• MIDI‑driven embedded control
• Host‑based playback and monitoring interface
• Migration of host system from RPi2B to openSUSE workstation

In Progress

• BLE‑MIDI transport integration
• Debugging and performance improvements
• Refinement of actuator motion profiles

Planned Enhancements

• Mechanical completion of the full 88‑key system
• Per‑actuator temperature monitoring and protection
• Power‑aware scheduling for dense chord passages
• Further optimization of real‑time control algorithms

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