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231 lines
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<title>MIDI Breadboard Instrument (Desk Rave & 16-Track Symphony) — Projects — Ertunç Özbay</title>
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<meta name="description" content="Project notes for the MIDI Breadboard Instrument (Desk Rave & 16-Track Symphony Controller) by Ertunç Özbay: Dual-Core ESP32 synthesizer in ESP-IDF v5.2.2 with RLE Python MIDI-to-C compiler, 30 FPS SPI OLED visualizer, rotary encoder, and triple-buzzer acoustic stage.">
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Ertunç Özbay
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<span class="badge badge-experimental">Status: Active Breadboard Prototype</span>
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<span>Project 03 // ESP32, ESP-IDF C99, FreeRTOS & Python RLE Tooling</span>
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</div>
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<h1>MIDI Breadboard Instrument — Desk Rave & 16-Track Symphony Controller</h1>
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<p class="hero-lead">
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A standalone, dual-core ESP32 MIDI synthesizer, drum sequencer, and 30 FPS SPI OLED visualizer written in ESP-IDF v5.2.2 (C99 / FreeRTOS), powered by a custom Run-Length Encoding (RLE) Python MIDI-to-C compiler.
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</p>
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<p class="reading-width">
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What started as making a passive piezo buzzer squeak evolved into a full 16-track embedded music box with live kick/hi-hat drum transients, hardware PCNT quadrature rotary controls for real-time tempo and volume scaling, and dual-core FreeRTOS task isolation.
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<a class="btn btn-primary" href="https://github.com/ertunc-ozbay/midi-breadboard-instrument" rel="noopener noreferrer">View GitHub Repository</a>
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<a class="btn btn-secondary" href="index.html">All Projects</a>
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<a class="btn btn-secondary" href="../lab.html">See Lab Experiments</a>
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</header>
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<figure class="schematic-frame" aria-label="MIDI Breadboard Instrument Component Diagram">
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<img src="../assets/images/midi-breadboard-layout.svg" alt="Block diagram of the MIDI Breadboard Instrument showing the MIDI conversion script producing C code for the breadboard system, connected to two active buzzers, one passive buzzer, a 1.3-inch SPI OLED screen, one rotary encoder, two buttons, and two LEDs." width="760" height="320">
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<figcaption class="schematic-caption">
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Software-to-hardware pipeline: Python RLE MIDI compiler (<code>midi_to_c.py</code>) generating flash-resident <code>SequenceStep</code> struct arrays for the dual-core ESP32 breadboard synthesizer.
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</figcaption>
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</figure>
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<section class="section-block" aria-labelledby="p3-gallery">
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<span class="section-label">01 // Hardware Build Gallery</span>
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<h2 id="p3-gallery">Breadboard Prototype Photos</h2>
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<div class="card-grid">
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<figure class="card" style="margin:0;">
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<img src="../assets/images/MIDI_FIRST.jpg" alt="Full dual-breadboard overview of the ESP32 MIDI Breadboard Instrument" style="width:100%; height:auto; border-radius:6px; margin-bottom:0.75rem;">
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<figcaption>
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<strong>Full Breadboard Layout:</strong> Dual-breadboard build featuring the ESP32 DevKit, 1.3" 7-pin SPI OLED display, KY-040 rotary encoder, tactile buttons, passive melody piezo, and dual active drum buzzers.
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</figcaption>
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</figure>
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<figure class="card" style="margin:0;">
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<img src="../assets/images/MIDI_SECOND.jpg" alt="Active 1.3-inch SPI OLED visualizer running at 30 FPS on the breadboard" style="width:100%; height:auto; border-radius:6px; margin-bottom:0.75rem;">
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<figcaption>
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<strong>30 FPS Live OLED Visualizer:</strong> Custom 5×7 font renderer displaying track code (<code>WHISP</code>), rotary mode (<code>SPD</code> / <code>VOL</code>), kick/hi-hat drum boxes, and dynamic frequency bars.
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</figcaption>
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</figure>
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<figure class="card" style="margin:0;">
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<img src="../assets/images/MIDI_THIRD.jpg" alt="Close-up of the rotary encoder, tactile buttons, LEDs, and three buzzers" style="width:100%; height:auto; border-radius:6px; margin-bottom:0.75rem;">
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<figcaption>
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<strong>Controls & Acoustic Stage:</strong> Close-up of the rotary encoder, Play/Pause and Next Track buttons, green/red drum LEDs, and the 3-buzzer audio stage.
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</figcaption>
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</figure>
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</div>
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</section>
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<section class="section-block reading-width" aria-labelledby="p3-overview">
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<span class="section-label">02 // Engineering Challenges Solved</span>
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<h2 id="p3-overview">From a Squeaking Buzzer to a Dual-Core Synthesizer</h2>
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<p>
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Pushing a bare-metal breadboard setup to play recognizable, energetic multi-track music required solving several real embedded systems challenges:
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</p>
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<ul>
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<li><strong>The Strobe-Light Bug & RLE Compression (<code>midi_to_c.py</code>):</strong> Raw MIDI files often slice sustained notes into microscopic fragments, causing the LEDs and OLED UI to strobe at 30+ Hz while wasting flash memory. We built a custom Python Run-Length Encoding (RLE) compressor using <code>mido</code> that merges contiguous identical pitch/drum states into solid <code>SequenceStep</code> blocks and routes bass/percussion channels to dedicated drum triggers.</li>
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<li><strong>Acoustic Hardware Limits (+2 Octave Transposition):</strong> Passive piezo buzzers physically struggle to resonate at low bass frequencies. Tracks with deep basslines like <em>Seven Nation Army</em> were transposed up two full octaves so the piezo disc resonates clearly while the active buzzers carry the rhythmic punch.</li>
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<li><strong>Dual-Core FreeRTOS Lockless IPC:</strong> Core 0 runs <code>oled_visualizer_task</code> (30 FPS SPI DMA framebuffer engine) and <code>button_task</code> (debounced input polling), while Core 1 exclusively runs <code>buzzer_sequence_task</code> for microsecond-accurate LEDC PWM pitch generation and hardware PCNT rotary encoder scaling.</li>
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</ul>
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</section>
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<section class="section-block reading-width" aria-labelledby="p3-components">
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<span class="section-label">03 // Confirmed Hardware & Pinout</span>
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<h2 id="p3-components">ESP32 Pinout & Architecture Specifications</h2>
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<table class="spec-table">
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<thead>
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<tr>
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<th scope="col">Component / Peripheral</th>
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<th scope="col">ESP32 Pin / Interface</th>
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<th scope="col">Function</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><strong>Microcontroller</strong></td>
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<td>ESP32 (Dual-Core Xtensa @ 160 MHz)</td>
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<td>ESP-IDF v5.2.2 + FreeRTOS dual-core execution</td>
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</tr>
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<tr>
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<td><strong>Rotary Encoder CLK / DT</strong></td>
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<td><code>GPIO 32</code> / <code>GPIO 33</code></td>
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<td>Hardware PCNT quadrature tracking (1000 ns glitch filter)</td>
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</tr>
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<tr>
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<td><strong>Rotary Encoder SW</strong></td>
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<td><code>GPIO 16</code> (Active Low)</td>
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<td>Toggles knob & OLED HUD between Speed (<code>0.2x–3.0x</code>) and Volume (<code>0%–100%</code>)</td>
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</tr>
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<tr>
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<td><strong>Pause / Next Buttons</strong></td>
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<td><code>GPIO 13</code> / <code>GPIO 14</code> (Active Low)</td>
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<td>Play/Pause toggle and 16-track playlist cycling</td>
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</tr>
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<tr>
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<td><strong>Passive Buzzer (Melody)</strong></td>
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<td><code>GPIO 25</code> (LEDC 13-bit PWM)</td>
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<td>Main melody synthesizer driven by hardware LEDC Timer 0</td>
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</tr>
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<tr>
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<td><strong>Active Buzzer 1 & 2 (Drums)</strong></td>
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<td><code>GPIO 26</code> (Kick) / <code>GPIO 27</code> (Hi-Hat)</td>
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<td>Physical percussion transients on drum steps</td>
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</tr>
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<tr>
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<td><strong>Kick & Hi-Hat LEDs</strong></td>
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<td><code>GPIO 21</code> (Kick) / <code>GPIO 22</code> (Hi-Hat)</td>
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<td>Visual beat indicators synchronized to drum hits</td>
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</tr>
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<tr>
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<td><strong>1.3" 7-Pin SPI OLED</strong></td>
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<td><code>CS: 5, DC: 2, RES: 4, MOSI: 23, SCK: 18</code></td>
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<td>10 MHz SPI2 display running custom 30 FPS visualizer on Core 0</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section class="section-block reading-width" aria-labelledby="p3-playlist">
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<span class="section-label">04 // Flash Memory Playlist</span>
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<h2 id="p3-playlist">The 16-Track Symphony</h2>
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<p>
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All 16 tracks are stored in ESP32 flash memory as <code>SequenceStep</code> arrays featuring <code>frequency</code>, <code>duration</code>, <code>kick_drum</code>, and <code>hi_hat</code> triggers:
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</p>
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<ol>
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<li><strong>Careless Whisper</strong> (Extended Club Edit)</li>
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<li><strong>Take On Me</strong> (EDM Build-up Edition)</li>
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<li><strong>Never Gonna Give You Up / Rickroll</strong> (Double Chorus)</li>
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<li><strong>Can't Help Falling In Love</strong> (Wedding Mix)</li>
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<li><strong>Gimme! Gimme! Gimme!</strong> (Midnight Rave)</li>
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<li><strong>Für Elise</strong> (Beethoven Trance)</li>
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<li><strong>Symphony No. 40</strong> (Mozart Intense Strings)</li>
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<li><strong>Super Mario Bros.</strong> (Main Theme)</li>
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<li><strong>Pirates of the Caribbean 1</strong> (He's a Pirate)</li>
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<li><strong>Pirates of the Caribbean 2</strong> (The Black Pearl)</li>
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<li><strong>Rondo Alla Turca</strong> (Mozart)</li>
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<li><strong>Tetris</strong> (Korobeiniki)</li>
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<li><strong>Sonic the Hedgehog</strong> (Green Hill Zone)</li>
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<li><strong>Castlevania</strong> (Vampire Killer)</li>
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<li><strong>Seven Nation Army</strong> (Transposed +2 Octaves for piezo resonance)</li>
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<li><strong>Mega Man 2</strong> (Dr. Wily Stage)</li>
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</ol>
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</section>
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<section class="section-block reading-width" aria-labelledby="p3-learning">
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<span class="section-label">05 // Workshop Notes & Next Steps</span>
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<h2 id="p3-learning">Current State & Roadmap</h2>
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<div class="callout-box">
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<span class="callout-title">Current State</span>
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<p>
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The firmware is rock-solid on the breadboard: the rotary encoder dynamically scales volume and tempo via lockless IPC variables, all 16 tracks play from flash memory, and the 1.3" SPI OLED renders real-time frequency bars and drum hits at 30 FPS.
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</p>
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<span class="callout-title">Next Steps</span>
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<p style="margin-bottom:0;">
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Migrating the dual-breadboard circuit onto a soldered perfboard or custom KiCad PCB, and optionally re-integrating a WS2812B addressable RGB strip when expanding the enclosure.
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</p>
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</div>
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