Hardware: L-shaped board outline with LiPo battery notch
L-shape opens toward bottom-left; the two long outer edges carry the jack rows (CV top, MIDI right, ~52 mm each), USB-C on the short left edge beside the battery. Top arm = all CV analog + switching converters (noise kept far from radio); right arm = digital + MIDI + RM2 at the bottom-right corner for best antenna keepout. Target 2000 mAh cell -> ~70x58 mm bounding box, 50x35 mm notch. Renumbered build order.
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# Hardware Plan — flexible MIDI router (v1)
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Status: draft 2026-08-21. Custom all-in-one PCB, desktop, USB-powered, **bipolar
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±10 V CV** via onboard ±12 V rails, 3.5 mm TRS MIDI, 4× stereo CV, 64×32 OLED +
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tact buttons (no encoder, low profile).
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Status: draft 2026-08-21. Custom all-in-one PCB, **L-shaped with a LiPo
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battery notch** (~70×58 mm bounding box, 2000 mAh target), desktop, USB or
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battery powered, **bipolar ±10 V CV** via onboard ±12 V rails, 3.5 mm TRS MIDI
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(1 in + 3 mirror out), 4× stereo CV, 64×32 OLED + tact buttons (no encoder,
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low profile).
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**MCU target:** develop/test on **RP2040** (Pico W dev board — the firmware
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already runs on it), product on **RP2350**. The RM2 radio module is compatible
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@@ -218,15 +220,18 @@ Host PCB responsibilities (from the RM2 datasheet):
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## 10. Build order (hardware)
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1. Schematic (this doc is the spec).
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2. RM2 module footprint + antenna keepout.
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3. RP2040 + flash + USB + SWD.
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4. Power (BQ24075 power-path + LiPo, 3.3 V buck-boost, +12 V boost,
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2. Board outline: L-shape, ~70×58 mm bounding box, bottom-left battery
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notch (50×35 mm for 2000 mAh cell). RM2 antenna keepout at bottom-right
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corner; USB-C left, CV top, MIDI right (§12).
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3. RM2 module footprint + antenna keepout.
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4. RP2040 + flash + USB + SWD.
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5. Power (BQ24075 power-path + LiPo, 3.3 V buck-boost, +12 V boost,
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−12 V inverter, 4.096 V + 2.048 V refs, MAX17048 fuel gauge).
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5. CV analog (DAC + difference-amp + offset + trim + bidir protection + TRS).
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6. MIDI TRS circuit.
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7. OLED + buttons.
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8. Keypad header (the Pimoroni keypad connects via a header or is integrated).
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9. PCB layout, DRC, review, fab.
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6. CV analog (DAC + difference-amp + offset + trim + bidir protection + TRS).
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7. MIDI TRS circuit.
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8. OLED + buttons.
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9. Keypad header (the Pimoroni keypad connects via a header or is integrated).
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10. PCB layout, DRC, review, fab.
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## 11. Connection table (netlist source of truth)
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@@ -377,3 +382,62 @@ Keypad header J11 (Pimoroni RGB Keypad):
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U1.GPIO16, GPIO22, GPIO26, GPIO27, GPIO28 ── unassigned (status LEDs / analog in / future)
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```
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## 12. Board outline (L-shape, battery notch)
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The LiPo cell is the single largest item, so the PCB is **L-shaped** — the
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55-ish mm connector square with the **bottom-left quadrant notched out** for
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the battery. The two *long* outer edges of the L carry the two jack rows
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(each needs ~52 mm for 4 jacks); USB-C sits on the short left edge, right
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beside the battery — which is where BQ24075, MAX17048 and the cell pigtail
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want to be anyway.
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```
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═══════════════════════════════════════════
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║ CV CV CV CV ║ top arm → CV analog
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║ J7 J8 J9 J10 DAC·refs·opa·±12V ║ (DAC8568, REF3040/2040,
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║ ║ 2× OPA4192, boost+inverter, LC)
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║ USB-C ║
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╚═══╗ ║
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║ ║
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B ║ MIDI MIDI MIDI MIDI ║ right arm → digital + MIDI
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A ║ J6 J5 J4 J3 ║ (6N138, UART, RP2040, flash,
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T ║ MCU · flash · RM2 ▼ keepout ║ RM2, SWD, keypad, OLED, btns)
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║ SWD · keypad · OLED · SW1-4 ║
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╚═══════════════════════════════════════╝
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↑ battery notch (bottom-left, off-board cell)
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```
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**Sizing (battery drives the notch):**
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| Cell | Pouch size | Notch | Bounding box |
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|-------------|-------------|------------|--------------|
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| 1500 mAh | ~36 × 30 mm | 36 × 30 mm | ~56 × 55 mm |
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| 2000 mAh (target) | ~50 × 35 mm | 50 × 35 mm | **~70 × 58 mm** |
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Both long arms clear the 52 mm the jacks need (top arm = full width, right
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arm = full height). USB-C (~9 mm) fits the short left edge either way.
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Target the **2000 mAh / ~70 × 58 mm** outline; a 1500 mAh cell just shrinks
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the notch.
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**Edge assignment:**
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- **Top edge:** 4× CV jacks (J7–J10), full width.
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- **Right edge:** 4× MIDI jacks (J3 in + J4/J5/J6 mirror out), full height.
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- **Left edge (short, top-arm left end):** USB-C (J1).
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- **Bottom edge (short, right-arm bottom end):** SWD header (J2), keypad
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header (J11), battery pigtail — accessible, non-user-facing.
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**Region assignment (the split is functional, not just compact):**
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- **Top arm = all analog/CV + the two switching converters.** Keeps the ±12 V
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boost/inverter noise up near the CV op-amps and far from the radio/MCU.
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Inductors + LC against the top edge; DAC8568, REF3040, REF2040, 2× OPA4192
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follow.
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- **Right arm = digital + MIDI + radio.** RP2040 + flash + RM2 + 6N138 + UART.
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**RM2 at the bottom-right outer corner** of the right arm — the point
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farthest from the battery, jacks, and switching converters — with its
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antenna keepout extending off the corner (best RF spot on an L-board).
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- **Battery + charger (bottom-left notch area):** short USB-C → BQ24075 →
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cell traces, MAX17048 fuel gauge beside them.
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- **Inner L corner (top-right inside):** quietest spot on the board — put the
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DAC→op-amp routing and the reference/analog star-ground here, sandwiched
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between the analog and digital arms but off both edges.
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