KN-86 Deckline — Pi Zero Sourcing Guide
Spec hygiene (CLAUDE.md rule 1). This document lists components and suppliers. It does not restate concrete spec values (processor frequencies, memory sizes, current draw, runtime, dimensions, resolution, etc.). Those live in CLAUDE.md’s Canonical Hardware Specification table. The BOM below references part numbers and functional roles; any value a BOM line item carries (capacity, wattage, impedance) is specific to that part, not to the canonical device spec.
1. Pi Zero 2 W Overview
Section titled “1. Pi Zero 2 W Overview”The KN-86 bill of materials is built around the Raspberry Pi Zero 2 W as the compute module, the Elecrow 7” IPS display over HDMI, a QMK-compatible USB HID keyboard controller on a custom mechanical keyboard PCB (per ADR-0018), and a MAX98357A I2S DAC/amplifier — commodity modules wired together, with the keyboard PCB as the only v0.1 custom-fab item. For the canonical hardware identity (processor family, RAM, display resolution, audio chip model, battery capacity, runtime band, case dimensions, ship target), see CLAUDE.md Canonical Hardware Specification.
This guide covers sourcing: where to buy each line item, at what rough unit cost, with what lead time, and which items carry supplier concentration risk. Prices are April 2026 US market benchmarks and will drift; treat them as ballparks, not quotes.
2. Bill of Materials
Section titled “2. Bill of Materials”All prices are US-market benchmarks as of April 2026. Shipping to San Antonio, TX, is the target for lead-time estimates.
Electronics Core
Section titled “Electronics Core”| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 1 | Raspberry Pi Zero 2 W (or Zero 2 WH) | Compute module (primary) | 2 | $15.00 | $30.00 | Adafruit, Pimoroni, Raspberry Pi direct |
| 1b | Raspberry Pi Pico 2 (RP2350) | Realtime I/O coprocessor — YM2149 PSG synthesis + SSD1322 OLED driver per ADR-0017. (Cart-bus responsibility originally on the Pico 2 was removed by ADR-0019; cartridge interface moves to USB-MSC via the bridge IC on line 5d.) | 2 | $5.00 | $10.00 | Adafruit, Pimoroni, Raspberry Pi direct |
| 2 | Elecrow 7” IPS display, HDMI input | Display (primary, already owned at project start) | 1 | $65.00 | $65.00 | Elecrow direct |
| 2b | SSD1322 3.12” OLED, 256×64, yellow, 16-pin SPI | CIPHER-LINE auxiliary display (ADR-0015) | 2 | $18.00 | $36.00 | Waveshare direct, Adafruit (if stocked), AliExpress |
| 3 | microSD card, 32 GB A2 | nOSh OS + cartridge filesystem + A/B slots | 2 | $10.00 | $20.00 | Amazon (SanDisk Extreme, Samsung EVO) |
| 4 | mini-HDMI to full-HDMI adapter or short cable | Pi Zero 2 W → Elecrow primary display | 1 | $6.00 | $6.00 | Adafruit, Amazon |
| 4b | 7-wire Dupont jumper cable set (F-F) | CIPHER-LINE SPI harness for v0.1 bench build | 1 | $4.00 | $4.00 | Amazon (assortment pack), AliExpress |
| 5 | QMK-compatible keyboard controller (Pro Micro ATmega32U4, Sea-Picro / KB2040 RP2040-class, or equivalent) | USB HID keyboard scanner per ADR-0018; exact part chosen at hardware bring-up | 2 | $5–$15 | $10–$30 | SparkFun, Adafruit, Amazon, AliExpress |
| 5b | Custom 30-key keyboard PCB (fabbed per ADR-0018 Option B) | Hot-swap Choc v1 sockets, 1N4148 SMD diodes, controller socket — the one v0.1 custom-fab item | 5 (batch min) | $6–$12 / board | $30–$60 | JLCPCB, OshPark, PCBWay |
| 5c | Internal USB 2.0 hub IC (TUSB2036, FE1.1s, or equivalent) + passives | Fans Pi OTG out to keyboard controller (ADR-0018) + USB-to-SD card reader bridge IC (ADR-0019, the cartridge interface) per ADR-0018 hub topology | 1 | $2.00 | $2.00 | LCSC, Mouser, Digi-Key |
| 5d | USB-to-SD card reader bridge IC (Genesys GL3224 / GL3232, Realtek RTS5129, or equivalent) + passives | Cartridge interface per ADR-0019 — exposes the cartridge SD card to the Pi as USB mass storage. Specific part TBD during breadboard prototype (ADR-0019 Open Q §1). | 1 | $2–$4 | $2–$4 | LCSC, Mouser, Digi-Key, Arrow |
| 5e | Full-size SD push-push surface-mount socket with card-detect switch (Hirose DM1 series, Molex full-size SD push-push family, or equivalent) | Receives the cartridge SD card; mounts on the internal cartridge-interface PCB at the back of the slot per ADR-0019. Specific part TBD during bring-up (ADR-0019 Open Q §2). | 2 | $1–$3 | $2–$6 | Digi-Key, Mouser, LCSC |
| 5f | Custom internal cartridge-interface PCB (mounts the SD socket + bridge IC behind the slot) | Small PCB hosting the SD socket, bridge IC, and pigtail to the internal USB hub. Custom-fab item; design lands as ADR-0019 follow-up CART-01. | 5 (batch min) | $4–$8 / board | $20–$40 | JLCPCB, OshPark, PCBWay |
| 5g | Cartridge SD card (full-size, ≥ TBD GB) for first-party launch carts | The actual storage medium inside the cartridge clamshell shell. Capacity floor TBD per ADR-0019 Open Q §5. Per-cart provisioning is a packaging task, not a v0.1 bench-rig BOM line — listed here as a placeholder so the cartridge-interface BOM is complete. | varies | varies | per cart | SanDisk, Samsung, etc. (Amazon, B&H) |
| 6 | Short USB pigtail for keyboard controller → internal hub | Internal USB routing per ADR-0018 | 1 | $5.00 | $5.00 | Amazon |
| 7 | USB OTG micro-USB → hub wiring | Pi OTG host mode into the internal hub IC | 1 | $5.00 | $5.00 | Adafruit, Amazon |
| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 8 | Kailh Choc v1 low-profile switches (mixed clicky / tactile) | 30-key matrix | 35 | $0.60 | $21.00 | Keebio, Splitkb, Chosfox |
| 9 | MBK blank black keycaps for Choc v1 (1U) | Keycaps (blank for v0.1; legends deferred) | 35 | $0.75 | $26.25 | Little Keyboards, SplitKB, Keycapsss |
| 10 | MBK wide keycap for EVAL (2.75U or 3U) | Special wide keycap | 1 | $3.00 | $3.00 | Custom order / 3D print |
| 11 | 1N4148 switching diodes | Matrix rollover isolation | 40 | $0.05 | $2.00 | Amazon (BOJACK 100-pack), Jameco |
| 12 | Hookup wire (22 AWG, multi-colour) | Matrix wiring harness | 1 | $12.00 | $12.00 | Amazon |
| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 13 | Adafruit MAX98357A I2S DAC/amp breakout | Digital audio → amplified speaker output | 1 | $10.00 | $10.00 | Adafruit direct |
| 14 | 28 mm round speaker, 8 Ω, 2 W | Mono speaker | 2 | $3.00 | $6.00 | Amazon (6-pack), eBay |
| 15 | 3.5 mm TRS PCB-mount switched stereo jack | Headphone jack with speaker cut-off | 2 | $1.00 | $2.00 | Adafruit, Amazon |
| 16 | 3.5 mm TRRS PCB-mount 4-pole jack | Link port (for linked-play between two decks) | 1 | $1.00 | $1.00 | Adafruit |
| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 17 | LiPo pouch cell, 3000 mAh, 3.7 V, with PCM | Battery (see CLAUDE.md for capacity spec) | 1 | $13.00 | $13.00 | Amazon (AKZYTUE, Liter), PiShop.us |
| 18 | TP4056 USB-C LiPo charger module | Charge regulation + cell protection | 2 | $3.50 | $7.00 | Amazon (HiLetgo 3-pack), PMD Way |
| 19 | Adafruit PowerBoost 1000C | 5V boost converter w/ USB passthrough | 1 | $20.00 | $20.00 | Adafruit direct |
| 20 | Latching slide switch, small panel mount | Power switch | 2 | $1.50 | $3.00 | Amazon, Digi-Key |
| 21 | JST-PH connector + hookup wire kit | Power harness | 1 | $14.00 | $14.00 | Amazon (Keszoox or BDHI kit) |
Mechanical / Enclosure
Section titled “Mechanical / Enclosure”| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 22 | Pelican 1170 Protector Case, black | Off-the-shelf hardcase shell (polypropylene, ABS latches, integrated hinge, watertight, includes Pelicanfoam) — see CLAUDE.md for dimensions | 1 | $60.00 | $60.00 | Pelican direct, B&H, Amazon, authorised dealers |
| 23 | PLA or PETG filament, black, 1 kg spool | Inset panels: display bezel, key plate, cartridge-slot retainer, port-cutout plate, interior brackets (material selection TBD during bring-up — both are cheap enough to test) | 1 | $24.00 | $24.00 | Prusa 3D direct, Printed Solid |
| 24 | M2.5 brass heat-set inserts | Screw mounts into printed inset panels | 100 | $0.02 | $2.00 | Prusa 3D 100-pack, Amazon assortment |
| 25 | M2.5 × 6 mm screws, black oxide | Fasteners for inset panels | 100 | $0.10 | $10.00 | Amazon, Fastener Superstore |
| 26 | Clear acrylic sheet, 1 mm (or polycarbonate) | Display window behind the lid bezel panel | 1 | $8.00 | $8.00 | Home Depot, Amazon, AcmePlastics |
Cables & Miscellaneous
Section titled “Cables & Miscellaneous”| # | Component | Role | Qty | Unit Cost | Total | Primary Supplier |
|---|---|---|---|---|---|---|
| 29 | 3.5 mm TRRS cable, 1 m | Linked-play cable (two decks) | 2 | $5.00 | $10.00 | Amazon (Devinal), Monoprice |
| 30 | 100 nF ceramic bypass capacitors, 0603 | Power supply decoupling | 20 | $0.05 | $1.00 | Amazon assortment, LCSC |
| 31 | Red 3 mm diffused LED | Power / charge indicator | 2 | $0.15 | $0.30 | Amazon (EDGELEC 100-pack) |
Totals
Section titled “Totals”| Category | Subtotal |
|---|---|
| Electronics Core | ~$201 |
| Input | ~$64 |
| Audio | ~$19 |
| Power | ~$57 |
| Mechanical / Enclosure | ~$104 |
| Cables & Miscellaneous | ~$11 |
| Grand Total (hardware BOM) | ~$456 |
Notes on the total:
- The Elecrow display is already owned at project start; the $65 line item appears in the BOM for a second-unit build but does not contribute to an already-owned v0.1 unit.
- The CIPHER-LINE SSD1322 auxiliary OLED (line 2b) is new per ADR-0015 and is not already owned. Two units are budgeted — one per deck in a linked-play pair — and the Dupont jumper kit (line 4b) covers the v0.1 bench harness for both.
- A single pair of decks for linked-play testing needs 2× of most items (two Pi Zero 2 W, two keyboard controllers, two key sets, two CIPHER-LINE modules, etc.). The table above shows per-deck quantities except where linked-play is intrinsic (e.g., TRRS cable, keyboard controller spare).
- Keycap legend service (UV printing) is not in this BOM. v0.1 ships with blank MBK keycaps. Legends are budget $65–$170 extra when commissioned.
- The only v0.1 custom-fab items are the keyboard PCB (line 5b, ADR-0018) and the internal cartridge-interface PCB (line 5f, ADR-0019). All other v0.1 interconnects are off-the-shelf modules on an interior plate (see the Build Spec “Assembly plan”).
- For v0.1 bench rigs, cartridges are still microSD-resident filesystem objects on the Pi’s boot SD; the production cartridge format (full-size SD card in a custom two-piece clamshell shell, read via USB mass storage through the line-5d card reader bridge IC) is committed as ADR-0019 and is pulled in during a future bring-up wave (ADR-0019 §“Follow-on work” CART-01 through CART-07). The new BOM lines (5d, 5e, 5f, 5g) are listed here so the cartridge-interface sourcing path is visible from this guide; first-cycle bring-up should order line 5e (a couple of candidate sockets) and 5d (a candidate bridge IC) for the breadboard prototype before committing to a fabbed cartridge-interface PCB.
CIPHER-LINE auxiliary OLED (SSD1322) — candidate parts
Section titled “CIPHER-LINE auxiliary OLED (SSD1322) — candidate parts”Per ADR-0015, the CIPHER-LINE module is a 3.12” OLED, SSD1322 controller, 256×64 pixels, yellow pixel element, 16-pin SPI. Josh’s verbatim spec is: “3.12 inch OLED Display 256x64 OLED LCD Display SSD1322 Module 16pin for Arduino (Yellow)”.
Three candidate sources evaluated:
| Supplier | Part / listing | Typical unit cost | MOQ | Lead time to San Antonio, TX | Notes |
|---|---|---|---|---|---|
| Waveshare (direct from waveshare.com) | “3.12inch OLED (B), 256×64, SSD1322 Driver Chip” | $16–$20 | 1 | 3–10 days (DHL express); 14–21 days (economy) | First-party manufacturer listing with published datasheet, mechanical drawing, and demo code. Most reliable source for v0.1. Yellow-pixel variant sold alongside white-pixel variant — verify yellow is in cart before checkout. |
| Adafruit (if stocked) | Reseller of SSD1322 breakout boards (stock is intermittent) | $20–$28 | 1 | 2–3 days (domestic US) | Adafruit occasionally stocks SSD1322 breakouts; when stocked, their pinout is documented and their support is reliable. Check before ordering; fall back to Waveshare if out of stock. |
| AliExpress (various resellers) | Search: “SSD1322 256x64 OLED yellow 16pin” | $10–$16 | 1 (most listings) | 14–28 days (AliExpress Standard); 30–45 days (free economy) | Lowest unit cost but longest lead time and most variable quality. Acceptable for a spare after the bench-validated Waveshare unit confirms the mechanical and SPI details. Do not build against an AliExpress-only supply chain for v0.1. |
Recommended v0.1 order pattern: 2× from Waveshare direct on Day 1 (one per deck in a linked-play pair, both bench-validated before mechanical install); 1× from AliExpress as a spare on the same day so it arrives later in the build cycle for post-Stage-5 spares stock.
v0.1 sourcing risk: the yellow-pixel SSD1322 variant is less commonly stocked than the white-pixel variant in Adafruit and casual Amazon listings. Waveshare direct is the primary supplier for yellow specifically. Mitigation: confirm yellow pixel element in the product listing before checkout, and accept a white variant only as a stand-in for the bench rig (the mechanical, electrical, and firmware paths are identical — only the visual brand suffers).
3. Supplier Notes
Section titled “3. Supplier Notes”Primary suppliers — consolidate orders to minimise shipping
Section titled “Primary suppliers — consolidate orders to minimise shipping”| Supplier | What to order here | Rationale |
|---|---|---|
| Adafruit Industries | Pi Zero 2 W, MAX98357A, PowerBoost 1000C, 3.5mm jacks, JST-PH kits, heat-set inserts (if not ordering Prusa), small passives | Domestic US, consistent stock, 2–3 day shipping, high-quality breakouts with documented pinouts. |
| Amazon Prime | microSD cards, speakers, TP4056 modules, screws, acrylic sheet, TRRS cables, capacitor assortments, LED assortments, Dupont jumper-wire assortments, battery (from reputable seller only) | Free 2-day shipping, acceptable for commodity parts. Verify LiPo battery seller reputation. |
| Pelican direct / B&H / authorised dealers | Pelican 1170 Protector Case (with Pelicanfoam) | First-party or authorised-dealer channel keeps finish and latch QA consistent. B&H frequently has better pricing than Pelican direct; Amazon listings are hit-or-miss for genuine stock. |
| Prusa 3D (or authorised reseller) | PLA or PETG filament, heat-set inserts | In-house quality control on filament; 100-pack insert sets are the best per-unit price. |
| Keebio / SplitKB / Little Keyboards | Choc v1 switches, MBK keycaps | Keyboard-community suppliers with best stock of the low-profile Choc ecosystem. |
| AliExpress / eBay | Keyboard controller clones (Pro Micro or RP2040-class), bulk 1N4148, SSD1322 3.12” 256×64 spare | Long lead time (2–4 weeks for AliExpress) but best unit cost for commoditised parts with no brand sensitivity. Order these first in the cycle. |
| JLCPCB / OshPark / PCBWay | Custom 30-key keyboard PCB (ADR-0018) | Only v0.1 custom-fab item. JLCPCB is the lead-time + cost winner for 5-board minimums; OshPark is the purple-board option if aesthetics matter. ~2-week cycle design-to-in-hand. |
| Elecrow direct | 7” IPS primary display (if not already owned) | Only place that stocks the exact panel we’ve validated. |
| Waveshare direct | SSD1322 3.12” 256×64 yellow OLED (CIPHER-LINE, ADR-0015) | First-party manufacturer of the exact panel we’re targeting; published datasheet, mechanical drawing, and demo code. Yellow variant is stocked here more reliably than at casual resellers. |
Recommended ordering cadence
Section titled “Recommended ordering cadence”- Day 1: Pelican 1170 from Pelican direct, B&H, or an authorised dealer (typically in-stock, 2–5 day shipping). Order PLA/PETG filament in parallel if not in stock locally.
- Day 1: Waveshare direct order (2× SSD1322 3.12” 256×64 yellow OLED for CIPHER-LINE; ship DHL express for the bench rig, economy for the spare). Order early — Waveshare shipping is slower than Adafruit.
- Day 1–2: Adafruit order (Pi Zero 2 W, MAX98357A, PowerBoost 1000C, jacks).
- Day 1–2: Amazon batch (microSD, speakers, TP4056 3-pack, screws, capacitor assortment, cables, LED pack, Dupont jumper kit for CIPHER-LINE harness, battery). Single large order to amortise shipping.
- Day 2–3: Keyboard supplier (Keebio or SplitKB) for Choc switches and MBK keycaps.
- Day 3+: Home Depot / Lowe’s for acrylic sheet (same-day or 1-day pickup).
- Day 3+ (optional): AliExpress order for spare SSD1322 + keyboard controller clones + bulk 1N4148. Long lead time but builds a spares cache.
- Day 1: JLCPCB (or equivalent) order for 5× custom 30-key keyboard PCB per ADR-0018. ~2-week lead time gates Stage 3 Input bring-up, so queue early.
Vendor consolidation pattern
Section titled “Vendor consolidation pattern”Aim to keep the order count under 10 shipments. A typical v0.1 build closes out at ~$480–$510 BOM across Adafruit, Amazon, Keebio (or equivalent), Prusa, Pelican (or authorised dealer), Waveshare direct (for CIPHER-LINE), JLCPCB (for the ADR-0018 keyboard PCB), and optionally AliExpress for keyboard controller clones / bulk passives / SSD1322 spare. A local run to a hardware store covers the acrylic display window.
4. Cost Summary
Section titled “4. Cost Summary”| Bucket | Cost band |
|---|---|
| v0.1 bench rig (primary display already owned, incl. CIPHER-LINE + Pico 2 coprocessor) | $370–$430 |
| v0.1 bench rig (new primary display, incl. CIPHER-LINE + Pico 2 coprocessor) | $435–$500 |
| Second deck for linked-play testing | Add ~$340 (most items already purchased in spares; CIPHER-LINE is a per-deck item, budgeted in base BOM) |
| Optional: UV-printed keycap legends (31 caps) | +$65–$170 |
| Optional: soldering iron + helping-hands + multimeter (if not already owned) | +$80–$150 |
| Optional: 3D printer consumables + printer time (if printing in-house) | Printer assumed on-hand; only filament appears in BOM |
The archived prior-era sourcing guide at docs/_archive/hardware/KN-86-Sourcing-Guide.md quoted a similar ballpark for the earlier microcontroller-based build with custom PCBs. The Pi Zero 2 W v0.1 build lands in a comparable envelope by spending more on the compute module while saving by deferring custom cartridge PCBs and main-board PCB to a future hardware revision.
5. Sourcing Risks
Section titled “5. Sourcing Risks”High-risk items
Section titled “High-risk items”-
Pelican 1170 Protector Case. The shell is the largest single-part dependency. Pelican stocks the 1170 consistently and multiple authorised dealers carry it, so sustained stock-out is unlikely — but a discontinuation or size refresh would force an inset-panel respin. Mitigation: buy one spare shell with the first unit so the inset panels can be validated and any rework happens against a confirmed interior geometry (268 × 153 × 80 mm). Keep the STEP / PDF drawings archived in
refs/pelican-1170/so the insets can be reproduced if the stock foam cut-out pattern changes. -
Elecrow 7” IPS display. Single-supplier. We’ve locked the mechanical design, boot config, and SDL rendering pipeline to this specific panel’s resolution, which is the canonical display spec (see CLAUDE.md). A discontinuation would force a display-swap ADR and a CAD respin. Mitigation: none beyond monitoring Elecrow’s catalog; buy a spare panel early.
-
Raspberry Pi Zero 2 W. Global supply can spike into shortage during chip crunches, which has happened twice in the past four years. Mitigation: order 2 units up front (one for the rig, one as spare). Authorised resellers (Adafruit, Pimoroni) historically prioritise fulfilling 1–2 unit hobbyist orders over bulk commercial allocations, which helps us.
-
LiPo battery from unreputable sources. Counterfeit cells are a fire risk and appear regularly on low-priced listings. Mitigation: only order from listed primary suppliers (Amazon with brand verification, PiShop.us, LiPo Battery Supply). Reject any cell without a PCM (protection circuit module) and pre-attached JST-PH leads from the factory.
4b. SSD1322 yellow-pixel variant. Per ADR-0015, CIPHER-LINE uses the yellow pixel element — not the more common white variant. Waveshare direct is the primary stock channel for yellow; Adafruit stock is intermittent; Amazon and AliExpress listings frequently default to white even when the listing title reads “yellow.” Mitigation: order from Waveshare direct for the first two decks, with a verified yellow variant in cart before checkout. A white unit is acceptable as a bench-stand-in for mechanical fit-check and SPI validation only — it does not ship in any build Josh signs off on.
Medium-risk items
Section titled “Medium-risk items”-
Kailh Choc Jade switches (if used). Heavy-clicky variant has thin supply; other Choc v1 variants (White, Brown) are widely available. Mitigation: v0.1 build can use Choc White throughout if Jade is out of stock. The spec does not commit to a specific switch variant.
-
MAX98357A breakout. Adafruit is the authoritative source. Clones exist on Amazon/AliExpress but quality varies. Mitigation: order from Adafruit direct for the first two builds; only move to clones after characterising one against an Adafruit reference.
-
Custom keycap legends via UV printing. Single-shop workflow with variable turnaround (7–21 days). Not on the v0.1 critical path since we can ship with blanks. Mitigation: defer to a polish pass; if the chosen shop goes dark, the Etsy MBK-printing community has multiple alternates.
Low-risk items
Section titled “Low-risk items”- Commodity passives, screws, cables, filament. Substitutable across dozens of suppliers with no mechanical or electrical risk.
Tariff risk (macro)
Section titled “Tariff risk (macro)”Q1 2026 US tariffs affected imports from certain manufacturing regions. For this BOM the exposure is in three places: (1) the Pi Zero 2 W itself (bounced across Adafruit, Pimoroni, etc., all of whom absorb the adjustment in their published pricing), (2) AliExpress-sourced keyboard controller clones / bulk passives, and (3) the custom keyboard PCB fabrication per ADR-0018 (JLCPCB-class fabs are tariff-sensitive). The tariff exposure on the keyboard PCB is small at per-board cost but should be re-evaluated if fab volume scales beyond v0.1 bench-rig quantities.
6. References
Section titled “6. References”- CLAUDE.md Canonical Hardware Specification — single source of truth for all concrete hardware values referenced in this BOM.
docs/hardware/KN-86-Pi-Zero-Build-Specification.md— companion document: hardware topology, assembly plan, developer vs. production mode.docs/architecture/adr/ADR-0011-pi-zero-firmware-update-system.md— system image update system, SD partition layout, desktop flasher plan (consumes several BOM lines: microSD size, USB-C port, keyboard controller).docs/architecture/adr/ADR-0018-custom-mechanical-keyboard-build.md— custom mech-keeb construction model (consumes BOM lines 5, 5b, 5c, 6, 7 and the JLCPCB-class fab supplier line).docs/architecture/adr/ADR-0019-cartridge-storage-and-form-factor.md— cartridge storage and physical form factor (full-size SD card in a custom two-piece clamshell sled, read via USB mass storage). Consumes BOM lines 5d (USB-to-SD bridge IC), 5e (SD push-push socket), 5f (cartridge-interface PCB), and 5g (per-cart SD media). Supersedes the earlier ADR-0013 (DMG / MBC5 / CR2032 path), which has no concrete BOM lines in v0.1.docs/architecture/adr/ADR-0015-cipher-line-auxiliary-display.md— CIPHER-LINE auxiliary OLED decision; source for BOM lines 2b and 4b, the Waveshare supplier entry, and the SSD1322 yellow-variant sourcing risk.docs/architecture/adr/ADR-0017-realtime-io-coprocessor.md— Pi Pico 2 (RP2350) realtime I/O coprocessor; source for BOM line 1b. Suppliers are the same channels as the Pi Zero 2 W (Adafruit, Pimoroni, Raspberry Pi direct); no separate supplier note needed.docs/ui-design/KN-86-Input-System-Architecture.md— 30-key layout and matrix wiring (consumes BOM lines 8–12).docs/_archive/hardware/KN-86-Sourcing-Guide.md— archived prior-era sourcing guide (superseded by this document; retained for historical context only, do not edit).