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====== Runaikål Project Documentation ======

:!: This page is a draft for the main project page :!:

This project covers the development of [[https://github.com/B7th|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: [ [[https://b7th.github.io/runaikal/index.html|Demo]] | [[https://github.com/B7th/b7th.github.io/tree/master/runaikal|Source Code]] ]

[[https://b7th.github.io/runaikal/index.html|{{ :project:runaikal:runaikal-web-tran.png?400 |}}]]

===== Hardware Specifications =====
==== Core Components ====
^ Component ^ Specification ^
| **Microcontroller** | ATMega328 (chosen over ATTiny45 for scaling and pin count) |
| **Power** | 2x AA Rechargeable batteries |
| **Output** | 4x Piezo buzzers (2 per chip) |
| **Amplification** | TL072 Op-amp with RC circuit and relay |
| **Input** | Contact button located in the "Gem" |

==== Circuitry & Power Management ====
  * **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.

===== Software & Sound Logic =====

==== Synthesis Principle ====
  * **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.

==== Tuning Compromise ====
  * **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.

===== Physical Design & Manufacturing =====

==== Case & Aesthetics ====
  * **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>

==== The Physical Shepard Tone Conundrum ====
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>

===== Current Project Concerns =====
  * **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.
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