The goal is to build a keyboard filter — something that sits in between the keyboard and the main computer, and provides macro capabilities.

There's also the goal of building a USB Rubber Ducky, but that's for another day, for more malicious purposes. The keyboard-filter is useful for benign purposes of macros. It could also be used as a keylogger, but again, this page is for more benign goals.

Keyboards that have macro programming built-in

These macros must be BUILT-IN via firmware, inside the keyboard, since many of the computing environments I work in don't allow installing ANY software, which excludes nice options like AutoHotkey. The upside to this is that they work in any OS, not just Windows or MacOS.

• The most well-known is the QMK firmware (newbie intro). There are spinoffs and alternate projects:
  • Via is a closed-source configurator for QMK keyboards
  • KMK firmware, which runs on anything that runs CircuitPython
  • ZMK firmware
    • unlike QMK, this works just fine with Bluetooth
  • more
  • more
• Ultimate Hacking Keyboard [more]

Arduino

• Use as a USB-peripheral keyboard is supported in the native library.
• There are many YouTube / Instructable / etc writeups on how to make a macro-keyboard-thingy from an Arduino. (for example)
• The Arduino natively only supports one USB port. How do you get two?
  • There used to be a USB Host shield, but it has been retired.
  • It looks like the latest active work on USB-Host for Arduino is in this software package, which links to several hardware solutions.

Raspberry Pi

• There are many different varieties of RPi, but use as a USB-peripheral keyboard is supported in:
  • Raspberry Pi Zero and later
  • Raspberry Pi 4 and later
• Key search terms are "dwc2", which is the module needed to do OTG. Also "g_hid", which is the brand of USB that's needed to implement keyboard and mice.
• How to setup the Raspberry Pi 4 for use as a USB OTG / USB gadget: [1] [2]
• As of January 2022, my preferred setup is the RPi 4, in a case that contains a small display (to display current status of the macro processing).
• Sidenote: As of January 2022, it's almost impossible to find an RPi in stores, due to global chip shortages among other things. The only option is to buy one on EBay for twice the price.
• How to setup a RPi Zero + Arduino Pro Micro, working together to form a keylogger
• Actually, the Raspberry Pi 400 would be perfect.
  • Some code to forward all USB keypresses and mouse movements out the USB-C port.
  • This sweet angled connector allows you to install a small display on the keyboard (display sold separately from the connector)
  • Advice: buy a faster/larger microSD card