Converter

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A converter is a small device which translates the signals between two other devices. In the keyboard world, this is mostly used to get older keyboards to work on a computer which only accepts USB keyboards. Please note that a converter is not the same as an adapter! Converters contain computer chips and need to be powered (mostly through the USB port), while an adapter is simply a passive component adapting one cable/port to another.

Adapters may be freely used in conjunction with all converters, but care must be taken not to use an exact duplicate of another converter on the same USB circuit when connecting multiple keyboards. If two converters have the same PCB ID (i.e., identical chip sets), the USB will only recognize one of them for purposes of key switch reassignments. Buy your converters from different manufacturers, and you should be okay.

Commercial PC/XT, PC/AT, and PS/2 to USB converters

Several converters exist to make PC/XT, PC/AT, PS/2, and/or Mac ADB keyboards work on newer USB computers. Note that these are “convertors,” not cheap and simple “adaptors.” Here's a short overview of the most popular and reliable converters:

Belkin USB Dual PS/2 Converter
The Belkin F5U119 series is a three-plug converter with ports for both a mouse (green) and a keyboard (purple), although a second keyboard will sometimes work on the green mouse port as well. Works with virtually all PS/2 keyboards. Belkin have sold this product under a large number of similar model numbers, and the various models ship with different controller chips. As of 2023 this converter appeared to be out of stock and presumably out of production, although a few can occasionally be found on eBay. Some of the controller chips used are notorious for resetting periodically: the keyboard will cease responding, followed by the green lock LEDs flashing as the keyboard re-initialises.
Hagstrom Electronics, Inc. Model KE-XTUSB Converter
Higher end converter for XT, AT, PS/2 keyboards, and perhaps a few others. US-made in Strasburg, Virginia. PCB enclosed in plastic box has jumper settings for six different protocols to accommodate almost any hard-to-find keyboard (including Leading Edge 2014). Comes with USB-B to USB-C cable. Priced circa US$55 and readily available with reputation for excellent customer service as of 2023.
tinkerBOY Converters for IBM Model F/XT & Model M/AT to USB; also Mac ADB to USB
Major player in the keyboard converter business. Merchandise made largely or entirely in Baguio City, Philippines. Also sells converters of other kinds. Can be purchased on eBay for circa US$34, but shipping from the antipodes takes 10 days/2 weeks. QMK firmware supports both Via and Vial protocols, plug and play, and NKRO.
Retro Fuzion Converter
This Australian company sells their own converters for PC/XT and PC/AT to USB computers. Price including shipping to USA was circa US$57 as of 2023. No support for Apple ADB at that time.
"Blue Cube" converter.
"Blue Cube" Converter
Converter with a single female PS/2 port and USB male port. Works for most keyboards. Once ubiquitous, as of 2023 they are apparently out of production and very hard to find. Known to work with keyboards that need more power, such as the IBM Model M, where cheaper converters fail. They never appear to have been sold under a brand name, but most known Blue Cubes contain the same Cypress chip and decent firmware.
ID Innovations Inc. Converter
Jeffrey Zimmerman with ID Innovations Inc. advises that this converter has been permanently discontinued as of 2023, although it may occasionally be found on eBay.

Commercial USB to PS/2 converters

These are designed to allow modern USB keyboards and mice to be connected to a PS/2 KVM switch, or a USB KVM switch to be connected to a server with PS/2 keyboard and mouse ports.

tinkerBOY Converters for PS/2 computers to use USB keyboards
Major player in the keyboard converter business. Merchandise made largely or entirely in Baguio City, Philippines. Can be found on eBay, but shipping from the antipodes takes 10 days/2 weeks. QMK firmware supports both Via and Vial protocols, plug and play, and NKRO. Good quality.
Adder KMU2P
StarTech PS22USB — PS/2 to USB Keyboard and Mouse Adapter
This converter, now discontinued, allowed a USB keyboard and mouse to be connected to the PS/2 ports on a computer.
TRIPP LITE 0DT60002 "Minicom"
Vetra USB-327 MegaMatch™, USB to PS/2 Converter
Apparently no longer trading (archived snapshot available thanks to the Wayback Machine)

Commercial ADB to USB converters

Griffin iMate
The Griffin Technology iMate was once the most common and best-known ADB to USB-A converter. As of 2023 it is out of production and no longer appears on Griffin Technology’s web site, although one can occasionally be found on eBay.
Big Mess o'Wires Wombat
The Wombat is a converter on a small, unenclosed PCB with three jumperred settings. ADB to USB-A only. Circa $39 USA.

Commercial Classic Commodore Computer keyboard to USB converters

Vesalia Keyrah 2
The Keyrah V2 made by Vesalia fits inside the case of C64, VIC-20, Amiga 1200 and other classic Commodore computers and makes it possible to use their internal keyboard and connected joysticks with modern computers over a USB connection. The PCB contains flat connectors for various internal keyboards and two classic Commodore joystick/mouse connectors.

DIY converters

It is possible to make a custom converter using a small microcontroller. These converters have a few benefits in that they allow to transform the input and output, e.g. to make your own macro keys or Fn layer.

The easiest way is to use a development board with an Atmel controller like the Teensy board for example.

Soarer's XT/AT/PS2 converter

Main article: Soarer's Converter

A general-purpose converter with handy tools to customize the keymapping of the provided binary file. Only the source of the tools is available. The documentation can be found on Geekhack. See this forum thread on DT for more info.

NOTE: a Teensy should be sufficient for the firmware and some basic config files. If you want to do a lot of advanced stuff like macros and Fn layers, try the the Teensy++. Check the documentation for more info.

Hasu's USB Controller/converter projects

Main article: TMK

These projects are only available as source code on GitHub. It is specially written for the Teensy development boards and keymapping must be done in the source files themselves.

A short overview of sub-projects:

HaaTa's Kiibohd Controller/converter projects

Main article: Kiibohd controller

Only available as source code on GitHub. It has a number of modules that can be re-compiled to support various obscure keyboard protocols. Designed to work as a converter or as a replacement controller depending on how the configurations are setup. Keyboard layouts and macros are configured on their one layer independent of the input scan module and output module. The framework is designed to support multiple output protocols, but currently only a basic 6KRO USB module is working.

Current list of supported protocols:

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