2 layers42.4 × 22.4 mm Osborne 2732 to 2764, the printed circuit board in 3D

Osborne 2732 to 2764

Osborne 1 related stuff

Size: 42.4 × 22.4 mm
Copper layers: 2
Thickness: 1.6 mm
Parts: 4
Nets: 26
Pads: 56
Tracks, vias: 38, 0
Pours: 1
Routed: Yes
KiCad: KiCad 9.0 (file 20241229)
Created: 15 Aug 2024
Updated: 21 Apr 2025

Overview

Osborne 2732 to 2764 is an open-source printed circuit board by BrettHallen, from the BrettHallen/Osborne_1 repository on GitHub. It is a 2-layer board of 42.4 × 22.4 mm with 4 parts on 26 nets, routed with 38 tracks and 0 vias.

Its parts include 3 connectors and 1 resistor.

README

README.md

Osborne Model 1

ROMs

[2732] Original Osborne BIOS vers. 1.40 (from my Osborne)
[2732] Original Osborne BIOS vers. 1.43
[2732] Original Osborne BIOS vers. 1.44 (latest)
[2732] 3rd party Micro Management OZROM 1E (thanks to user nelgin on VCFED Forums)
OZROM manual (cleaned up version thanks to VCFED user booboo)
[2764] Combined OCC v1.44 & OZROM (requires daughterboard below)
[2716] Original Osborne character generator ROM (from my Osborne)
[2716] Original Osborne Screen Pac BIOS Rev. A

Differences between ROM v1.4 and v1.44 include:

text

; CBOOT - added seek 10 tracks and home drive
; GKEY - fixed bell bug
; SENDEN - changed the number of retrys to NRETRY
; PSEKC - added disk head settle delay
; SELDRV - changed start up delay to 500 ms

OCC v1.4 ROM

Image of OCC v1.40 ROM

OCC Character Generator ROM

Image of OCC character ROM

Micro Management OZROM

Image of OZROM

Daughterboard

[29-Aug-2024: tested successfully]
ROM daughterboard to accomodate 28-pin 2764 (8KByte) EPROM in the Osborne's 24-pin 2732 (4KByte) BIOS socket. Idea is to allow switching between the official Osborne ROM and the 3rd party OZROM.

Address pin A12 is pulled high by the 10KΩ resistor (so default is upper ROM address range 0x1000 to 0x1FFF) or can be switched to ground via a strapping or switch connected to the A12 pin header (so lower ROM address range 0x0000 to 0x0FFF).

3D image of daughterboard

Assembled daughterboard

Installed in Osborne

Using A Gotek

Big thanks to Dave Dunfield for the original ImageDisk-format (IMD) disk images.

How to tell if an Osborne 1 disk image is single density (SD) or double density (DD)?

Both disk formats have 40 tracks:

SD disks have ten 256 byte sectors per track (2560 bytes/track) -> 92KByte formatted capacity
DD disks have five 1024 byte sectors per track (5120 bytes/track) -> 184KByte formatted capacity

Example output of fsed.cpm info command on an IMG disk image:

text

              Sector length: 1024
           Number of tracks: 40
          Sectors per track: 5

EXMON Video Output

Photos of the EXMON video output shunt.

Sullins MP-0100-10-DS-4 card edge connector
Hyko K688-DI - this appears to combine horizontal & vertical sync with the video output, powered by +12V

Pinout of EXMON

Double Density Upgrade

Photos of the original Osborne DD upgrade board and details of a modern reproduction board.

Screen Pac Upgrade

Photos of the Screen Pac board.

Project files

Show this board on your page

https://pcbkit.io/boards/BrettHallen/Osborne_1

The board's own page, for a message or a post.

Source

Repository: BrettHallen/Osborne_1
Board file: 2732-to-2764/RevA/Osborne_2732_to_2764.kicad_pcb
Commit: 5aa5f2b
Licence: Not stated

Parts

Qty	Value	Footprint	References
1	10KΩ	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P2.54mm_Vertical	R1
1	2732_ROM_Socket	Open2327RomAdapter:DIP-24_W15.24mm-Notch	J1
1	2764	Package_DIP:DIP-28_W15.24mm_Socket	J2
1	A12	Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical	J3

Similar boards

2 layers18.5 × 26 mm
24g2usb rp2350zero
joypad-ai/joypad-os
Universal controller firmware for building adapters, dongles, and custom controllers.
4 parts1.7kApache-2.0
2 layers116 × 33 mm
966595-1 and 963356-1
rusefi/rusefi
rusefi - GPL internal combustion engine control unit
4 parts1.2k
2 layers19 × 18 mm
Daughter board
hackclub/OnBoard
💡 Join 1,000 teenagers and make your first PCB with a $100 grant!
4 parts915
2 layers24.8 × 24.8 mm
Nrf24 breakout
tardate/LittleArduinoProjects
a collection of "Little Electronic & Arduino Projects", most involving electronics or an Arduino in one way or another!
4 parts803MIT
2 layers26 × 20 mm
Cap chain
drandyhaas/KiCadRoutingTools
A set of Python/Rust tools to aid routing in KiCad
4 parts744MIT
2 layers34.7 × 20 mm
XG Station Power MSI
osy/XG_Mobile_Station
Open source eGPU dock for ROG Ally and ROG Flow
4 parts712CC-BY-4.0
2 layers20.3 × 24.5 mm
Jack power input
Luos-io/luos_engine
Open-source and real-time orchestrator for cyber-physical-systems, to easily design, test and deploy embedded applications and digital twins.
4 parts546MIT
2 layers35.1 × 92.1 mm
SDEX2M2 MicroSD Express to M.2 NVMe Adapter for Switch 2 WIP
NVNTLabs/switch2-SDEX2M2
Micro SD Express to M.2 NVME Adapter for Nintendo Switch 2
4 parts542GPL-3.0

Questions

How big is the Osborne 2732 to 2764 PCB?

It measures 42.4 × 22.4 mm and has 2 copper layers, 1.6 mm thick.

What parts does the Osborne 2732 to 2764 use?

4 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Where can I download the Osborne 2732 to 2764 KiCad files?

From the BrettHallen/Osborne_1 repository on GitHub, at the commit this page was made from: the board is 2732-to-2764/RevA/Osborne_2732_to_2764.kicad_pcb and its schematic 2732-to-2764/RevA/Osborne_2732_to_2764.kicad_sch. PCBKit opens the board in the browser, with nothing to install.

Can I use the Osborne 2732 to 2764 design in my own project?

Its repository states no licence, so its author keeps all rights: ask BrettHallen before reusing the design.