# Design Decisions

## Build Approach

Wooden case with salvaged laptop lid (screen + hinge) as the canopy. Approximate briefcase dimensions, with the display panel setting minimum width and depth.

## Salvage Exclusions

- **Webcam:** Scrapped. Proprietary pinout, not worth reverse engineering.
- **Keyboard/trackpad:** Proprietary connectors, not reusable.
- **RAM:** DDR3L soldered, wrong generation.
- **SSD:** Owner repurposed.
- **WiFi card:** Intel 7265NGW — OPi3B has built-in WiFi+BT, no external card needed.

## Case Orientation & Nomenclature

User sits at the **stern**, facing the **bow**. Hinge axis runs port-to-starboard along the bow edge.

### Base (wooden enclosure)

| Term | Surface | Notes |
|------|---------|-------|
| **Deck** | Top | Keyboard, controls, SBC access |
| **Keel** | Bottom | Sits on table |
| **Bow** | Back edge (spine side) | Power input, heat exhaust, farthest from user |
| **Stern** | Front edge (lip side) | User-facing, keyboard near here |
| **Port** | Left (facing bow) | |
| **Starboard** | Right (facing bow) | |

### Canopy (laptop lid + screen)

| Term | Surface |
|------|---------|
| **Canopy dorsal** | Outside of lid |
| **Canopy ventral** | Screen side |

### Bow Wall Functions

- Power input (5V USB-C for charging)
- Exhaust fans blowing away from user
- Heat management surface

## Carry Handle

Stern edge (lip). Screen is lightweight, hinge is rigid, and a lid latch is planned — so the canopy-open-under-gravity concern is handled. Keeps the bow wall dedicated to power input and exhaust.

## Power System

IP5389 power bank board (preliminary). All-in-one: charging, BMS, USB-C PD output. See [power-system.md](power-system.md) for details.

## Display Connection

**Chosen path:** HDMI → eDP-to-HDMI controller board → Innolux N156HGE-EAB panel.

The Orange Pi 3B has a native eDP port and a MIPI DSI port, but neither is used. Here's why:

### eDP Port — Investigated, Ruled Out

The 30-pin eDP ZIF connector on the OPi3B underside could theoretically drive the salvaged laptop panel directly. In practice, eDP pinouts vary between manufacturers for the power and backlight signals despite VESA's standard for the data lanes. A panel expecting 12V on a pin the SBC sends 3.3V won't light. Send 12V where 3.3V is expected and you get smoke.

Orange Pi does not publish schematic-level documentation for the eDP connector pinout. Tracing it manually (multimeter + RK3566 datasheet) is possible but finicky, and the salvaged panel's exact pinout would need cross-referencing too. The $35 controller board was the right call — it's the proven approach the entire laptop-reuse community uses.

### MIPI DSI Port — Investigated, Ruled Out

The 3B has a 2-lane MIPI DSI port on the back edge (15-pin FFC, Raspberry Pi-compatible form factor). Supported panels include several 5" and 7" Pi-style DSI touchscreens, enabled via the `raspi-7inch-touchscreen` overlay in `/boot/orangepiEnv.txt`. However:

- Enabling DSI **disables HDMI** — the RK3566 can't drive both simultaneously under Linux on the OPi3B (confirmed by community testing and manufacturer)
- The 15.6" salvaged panel is eDP, not DSI — a different interface entirely
- No practical path to use it for the primary display

### Result

The salvaged panel connects via its matched eDP-to-HDMI controller board. The OPi3B's HDMI output drives the controller board. The MIPI DSI and eDP ports remain unused and unpopulated internally.

## Video Output

Mechanical HDMI A/B switch (passive, no power). Routes OPi3B's single HDMI to either the internal display (via eDP or eDP-to-HDMI controller) or a panel-mount HDMI jack on the starboard side. DisplayLink doesn't work on ARM — no drivers exist. Dual simultaneous display is not possible on the OPi3B (single HDMI output).

## Input Device

ThinkPad TrackPoint keyboard (specific model TBD based on availability). Chosen for built-in TrackPoint pointer and 15.6" deck space compatibility.

## Carry Handle

Stern edge (lip). Screen is lightweight, hinge is rigid, and a lid latch is planned — so the canopy-open-under-gravity concern is handled. Keeps the bow wall dedicated to power input and exhaust.