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Retro USB

Retro USB is an input converter for USB and ADB keyboards and mice. It works in two directions, connecting modern USB peripherals to a classic ADB-based Macintosh or Apple IIgs computer, or ADB peripherals to a USB-based computer running Windows, OSX, or Linux. The foreign keyboards and mice behave exactly like native peripherals, requiring no special software or drivers – just plug it in and go.


Now you can finally use an optical mouse with your vintage Macintosh, or amaze your coworkers with an antique Apple Extended Keyboard on your work machine. Retro USB is an indispensable tool for Apple collectors and enthusiasts.

Retro USB comes fully assembled and tested.

Retro USB  Retro USB Input Converter, $49
Intelligent USB -> ADB and ADB -> USB conversion for keyboards and mice. Requires an ADB cable for connections to classic Apple computers.
  More Info  Out of Stock

Optional accessories for your Retro USB:

ADB Cable, 3 ft  ADB cable 3 ft, $5
When using USB peripherals on a classic Apple computer, an ADB cable is needed. Standard male-to-male S-video cables from eBay work too.
  More Info  

  Find more items in the BMOW store

Retro USB is great for breathing new life into your vintage Apple hardware collection. If you love old Macs, you know ADB keyboards are expensive and hard to find, and ADB mice are sticky and trouble-prone. With Retro USB, you can substitute modern USB input peripherals instead. Or if you swear by your old Apple Extended Keyboard, you can use it with your modern daily driver computer. Visitors are sure to smile when they see you running 1980s Apple input peripherals on your 2017 machine.

  • No external power source needed
  • On-board power key for Apple computers
  • Upgradable firmware
  • Works with your favorite mice and keyboards

Retro USB was developed by Steve Chamberlin, here at Big Mess o’ Wires. See the blog archive for technical details on its software and hardware.


The Retro USB hardware is compatible with all Apple computers, keyboards, and mice using a mini DIN 4-pin ADB connector, including most early Macintosh computers and the Apple IIgs. It is also compatible with standard USB keyboards and mice with a USB-A connector. When in ADB-to-USB conversion mode, it works under Windows, OSX, Linux, or any other operating system that supports USB HID input peripherals.


USB keyboards and mice with a classic ADB-based Macintosh or Apple IIgs. Set the jumpers as shown on the Retro USB board’s diagram to select USB-to-ADB conversion mode. Use an ADB cable to connect the board’s ADB port to the computer’s ADB port.

A single USB peripheral can be connected directly to the Retro USB board’s USB-A port, or a standard USB hub can be used to connect multiple peripherals at once. When in this mode, Retro USB supports one USB keyboard and one USB mouse, as well as any number of ADB keyboards and mice, all used simultaneously.

Standard bus-powered USB hubs are recommended. Externally powered USB hubs (with their own independent power supply) are not recommended, because they can backfeed power into Retro USB even when it’s off, causing problems.

Power Key

Original ADB keyboards had a power key – a square or rectangular key with a triangle logo that could be used to turn on some later models of Macintosh computers. Retro USB has two substitutes for the power key. There’s a small button on the board that will function as the power key, even when the board is off. And when Retro USB is provided standby power from an auxiliary source, the PRINT SCREEN key or F13 key on a USB keyboard will also function as the power key. To provide standby power, connect the Retro USB board’s USB-B port to a standard USB charger.


ADB keyboards and mice with a modern USB-based computer. Set the jumpers as shown on the Retro USB board’s diagram to select ADB-to-USB conversion mode. Use a USB-B-Mini cable to connect the board’s USB-B port to the computer’s USB port.

A single ADB peripheral can be connected directly to the Retro USB board’s ADB port, or multiple peripherals can be daisy-chained, using the ADB pass-through connector found on all Apple ADB keyboards. When in this mode, Retro USB supports one ADB keyboard and one ADB mouse, as well as any number of USB keyboards and mice, all used simultaneously.

The ADB peripherals will appear as standard HID input devices to modern Windows, OSX, and Linux computers. No special drivers or other software are needed.

Firmware Updates

Retro USB firmware can be updated to fix bugs and add new features. Disconnect all power from the board, and set the board’s jumpers to select USB-to-ADB mode. Download the firmware.hex file from the Retro USB web page, and copy the file to a USB flash drive. Plug the flash drive directly into the board’s USB-A port – do not use a hub. Hold the board’s power key button while you connect the power and turn on the board. Continue to hold the button for a few seconds, until the A and B status LEDs begin blinking rapidly. The update process takes about 10 seconds. When finished, the LEDs will blink slowly together, once per second. You can now press the power button a second time to exit the firmware update and return to normal input conversion mode.

LED Status Codes

The A and B LEDs on the Retro USB board display status and error information. (The A LED is labeled RUN on some boards). During normal use, the A LED will turn on when Retro USB has a working data connection (ADB or USB) to the host computer. The B LED will blink whenever there’s keyboard or mouse activity.

During a firmware update, both LEDs are used to indicate update status:

slow alternating blinks of A, then B (1 blink/sec) – bootloader is searching for a firmware file
fast alternating blinks of A, then B (8 blinks/sec) – bootloader is updating the firmware
slow synchronized blinks of A and B together (1 blink/sec) – bootloader finished successfully

If B blinks several times while A remains off, it indicates a bootloader error:

2 blinks – no valid firmware exists on chip, can’t start main Retro USB program
3 blinks – no firmware files found on USB drive
4 blinks – error in firmware file (checksum mismatch or illegal data)
5 blinks – error while updating firmware in chip memory

Help Commands

You can interact directly with Retro USB by typing help commands on an attached ADB or USB keyboard. Open an empty text document or command prompt on your computer. Retro USB will “type” its responses to your commands, so they appear on the screen.

Control-Shift-Capslock-V – Displays the firmware version number

Control-Shift-Capslock-C – Enters keydump mode. While in this mode, the USB key code is displayed for each key that you press, along with the corresponding ADB key code it’s mapped to (or vice-versa). This can be helpful for troubleshooting key mapping problems.

Control-Shift-Capslock-D – Exits keydump mode.

What are ADB and USB?

ADB connector

From 1986 through 1998, ADB (Apple Desktop Bus) was the standard system for connecting peripherals like keyboards and mice to Apple computers. It was used by the Apple IIgs, as well as all early Macintosh models except the Mac Plus, 512K, and 128K. The ADB connector is a round mini DIN 4-pin, and is physically identical to the S-Video connector.

USB-A connector

USB (Universal Serial Bus) is the dominant standard today for connecting keyboards, mice, and other peripherals to a computer. Nearly everyone will recognize the familiar rectangular USB-A connector that’s used to plug a device into a host machine. USB replaced a variety of earlier standards like Firewire, ADB, and PS/2. Every Apple computer since 1998 has used USB for its input peripherals.

Converting between the two systems involves more than just a physical plug adapter. ADB and USB high-level protocols are fundamentally very different, and also have different signal speeds, signal formats, and voltages. ADB and USB input peripherals have different communication behaviors too. ADB keyboards and mice use event-based reporting, and only communicate when something has changed, whereas USB keyboards and mice communicate their full current state whenever asked.



Retro USB latest firmware version: retro-usb-0.1.5



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Check out Retro USB at the BMOW Store.

1 comment 

1 Comment so far

  1. Steve May 23rd, 2017 1:41 pm

    If Retro USB is out of stock, please check back again in a few days. I’m assembling more as needed.

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