1. Overview

This project implements a compact electronic piano mechanism that combines magnetic sensing (Hall effect) with a mechanically responsive key system. The design prioritizes (i) analog sensing of key displacement, (ii) tactile feedback through nonlinear restoring forces, and (iii) modular, repairable construction.

2. Mechanical Structure and Supports

The mechanical system is designed to ensure stable, repeatable key motion while minimizing wobble and misalignment.

• Key Mounting (Rotational Axis):
  Each key is mounted on a shared rod (axle), allowing rotational motion similar to a lever. This enforces a single degree of freedom and ensures consistent pivoting.

• Threaded Inserts and Screws:
  Structural components are assembled using threaded inserts embedded in the base. This provides:

  • Repeatable assembly/disassembly without degrading the material

  • Higher clamping force compared to direct screw insertion into plastic or wood

• Wedge Constraint (Key Leveling):
  A mechanical wedge beneath each key defines the resting position. Its purpose is:

  • Prevent overextension from spring force

  • Ensure all keys return to a uniform height (planar alignment)

  • Provide a hard stop that stabilizes the equilibrium configuration

Overall, the structure behaves as a constrained rotational system with well-defined boundary conditions.

3. Magnet-Based Sensing Mechanism

Each key is instrumented with a permanent magnet attached to its underside, positioned above a Hall effect sensor.

• Operating Principle:
  As the key is pressed, the magnet moves closer to the sensor, changing the local magnetic field. The Hall sensor outputs a voltage proportional to field strength:

  Vout proportional to B(D)

  where D is the magnet–sensor distance.

• Advantages of This Approach:

  • Contactless sensing → no mechanical wear

  • Enables continuous (analog) key position detection rather than binary switching

  • Supports expressive control (velocity or pressure sensitivity)

• Nonlinearity Consideration:
  The magnetic field decays nonlinearly with distance, so the voltage response is inherently nonlinear. This can be:

  • Calibrated in software

  • Or used directly for expressive mapping

4. Key Retraction and Restoring Mechanism

The restoring force is implemented using extension springs attached at the rear of each key.

• Mechanical Behavior:

  • The spring force increases with displacement:

    F=kx

  • Because of lever geometry, the perceived resistance at the finger is non-uniform, typically increasing as the key is pressed further.

• Tactile Outcome:

  • Provides a progressive resistance profile, closer to real piano feel than linear rubber domes

  • Enables more controlled actuation and improved user feedback

• Interaction with Wedge:

  • The wedge ensures that when the spring retracts, it does not overshoot

  • This creates a well-defined equilibrium point and avoids oscillations or uneven resting states

5. Noise Reduction and Material Considerations

Mechanical prototypes introduced audible and tactile noise, addressed through damping strategies:

• Foam Padding:

  • Added at contact points (e.g., wedge interface, base contact)

  • Reduces impact noise and vibration transmission

• Surface Friction Mitigation:

  • Smoothing or lining contact regions reduces scratchy motion artifacts

  • Improves perceived quality of interaction

• Tradeoff:

  • Excess damping can reduce responsiveness

  • Optimal design balances quiet operation with crisp mechanical feedback

6. Electrical and Signal Challenges and Potential Improvements

(a) ADC Stability and Wiring

• Long analog wires introduce:

  • Noise pickup (EM interference)

  • Voltage fluctuations and unstable readings

Mitigation:

• Shorten wire lengths

• Use twisted pairs or shielding where possible

(b) Digital Filtering / Hardware Smoothing

• Adding a capacitor across signal and ground acts as a low-pass filter:

  τ=RC

• This reduces high-frequency noise before ADC sampling

• Complement...