BarnacleBoy e53c928e44 document display architecture research and settled design decisions

- eDP direct connection ruled out: undocumented pinouts, voltage mismatch risk,
  community consensus favors controller boards
- MIPI DSI ruled out: 2-lane 15-pin, can't dual-display with HDMI on Linux,
  and the salvaged panel is eDP
- Chosen path: HDMI -> eDP-to-HDMI controller board -> salvaged panel
- Mechanical HDMI A/B switch retained as fallback for external display

2026-05-27 01:12:00 +00:00

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Port Layout

Overview

10 accessible ports + SD reader + Kensington lock, split across four case surfaces. Built-in WiFi+BT eliminates need for USB dongles.

Port Side (Left, Facing Bow)

Data connections. "Plug and unplug frequently" zone.

Port	Count	Source	Notes
USB-A 3.0	4	Powered hub	Flash drives, peripherals, hardware
USB-C (data)	1	Powered hub	Modern peripherals, data transfer
USB-C PD out	1	IP5389 board	Phone charging, 5V/??W

Starboard Side (Right, Facing Bow)

Networking + AV. "Plug in and leave" zone.

Port	Count	Source	Notes
Ethernet RJ45	1	OPi3B native	Gigabit, panel-mount extension
HDMI out	1	HDMI A/B switch	External display, switched from internal
3.5mm audio out	1	OPi3B native	Headphones, speakers, line-out

Bow Wall (Back Edge, Spine Side)

Power and cooling. No data ports.

Feature	Notes
USB-C power input	For IP5389 board charging (5V/3A)
Fan exhaust grilles	Blowing away from user

Stern Edge (Front Edge, Lip)

User-facing. Clean for typing.

Feature	Notes
Carry handle	Stern-mounted per design decision
SD card reader	Panel-mount, for camera cards / quick imaging
Kensington lock slot	Physical security

Internal Components

Component	Connection
Powered USB hub (10-port)	Decased, wired internally. Feeds all USB-A and USB-C data ports.
HDMI A/B switch (mechanical)	Passive toggle. OPi3B HDMI in, two outputs (internal display + starboard panel jack).
	eDP-to-HDMI controller

Constraints

OPi3B has one HDMI output. The A/B switch selects internal or external — not both simultaneously.
The internal display uses an eDP-to-HDMI controller board (matched to the salvaged panel). The native eDP port on the OPi3B is unused — direct connection was investigated but ruled out due to undocumented pinouts and voltage mismatch risk.
DisplayLink USB graphics adapters do not work on ARM Linux (no drivers). Not a viable path for dual display.
Dual simultaneous display would require a dual-HDMI SBC.
Built-in WiFi 5 + BT 5.0 on the OPi3B — no USB dongles needed for wireless connectivity.
Two native USB 3.0 ports available for direct connections (keyboard, mouse) without hub contention.

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