This page is a draft for the main project page

This project covers the development of MangoTrain's Runaikål, a 12-tone circular instrument utilising electronic synthesis and physical resonance to achieve a Shepard tone effect.

An interactive demo can be found here: [ Demo | Source Code ]

• Signal Path: PWM Output → RC Circuit/TL072 (Sine conversion) → Piezo Buzzers.
• Energy Saving: * The chip enters Sleep Mode immediately after all note tails have faded.
  • Relay Switch: A dedicated “waker” pin triggers a relay to connect the battery to the op-amp only when the chip is active.
• Current Issues: * Volume is insufficient on AA battery power.
  • Potential need for capacitor boosting to increase rounding and volume.

• Shepard Tone: The chip produces three simultaneous sinusoidal frequencies.
  • Higher harmonics decrease in amplitude as the scale ascends.
  • Lower harmonics increase in amplitude as the scale ascends.
  • Result: A “circular” or “donut-like” soundscape.
• Dynamics: * Variable Decay: Sound fades based on contact duration.
  • Muting Simulation: Longer contact increases decay speed to simulate a percussive “mute.”
• Processing: PWM values are processed off-cycle upon a flag to ensure timing delivery is prioritized.

• Perfect 5ths: 6 of the 12 tones are shifted just enough to allow half of the notes to be in perfect 5ths with the other half.
• Timbre: Current sound is described as “Grüüüüm.” Needs further “softening” to move away from a harsh electronic tone toward a more organic “cave” sound.

• Geometry: The design is based on a truncated dodecagon.
• The Gems: 12 symmetrical designs that provide the necessary working surface for play.
• Resonance: Flat surfaces are designed for speakers/piezos to vibrate against to increase volume.
• Portability: The current case design is foldable.

Placeholder for <3D render of the truncated dodecagon case>

An alternative “acoustic-first” approach was considered but deemed extremely difficult:

• Requires modifying the strength of specific partials/overtones physically without changing the whole timbre.
• Velocity must be perfectly controlled across three separate tones to maintain the circular illusion.
• Standard “tongues” (like a tongue drum) do not allow for the necessary overtone division.

Placeholder for <Floral/Spiral tiered design iterations>

• Volume: Solving the “louder for those in the back” requirement.
• Waterproofing: Balancing cheap battery access vs. a sealed/wireless unit.
• Manufacturing: Goal is to refine the design for a limited production run of ~100 units.