USB to USB keyboard protocol converter
======================================
Hardware requirement
--------------------
Arduino Leonardo
http://arduino.cc/en/Main/ArduinoBoardLeonardo
Circuit@Home USB Host Shield 2.0
https://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-2-0-for-arduino-assembled/
Buying Arduino Leonardo and USB Host Shield 2.0(from Circuit@home) will be the easiest way, you won't need even soldering iron.
Arduino's Shield will also work well but I think Sparkfun's needs to be modified.
http://arduino.cc/en/Main/ArduinoUSBHostShield
https://www.sparkfun.com/products/9947
Also Pro Micro 3.3V(not Mini) or Teensy with mini host shield will work with some fixes on signal/power routing.
https://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-for-arduino-pro-mini
https://www.sparkfun.com/products/12587
https://www.pjrc.com/teensy/td_libs_USBHostShield.html
Build firmware
--------------
$ git clone git://github.com/tmk/tmk_keyboard.git
$ cd tmk_keyboard
$ git submodule init
$ git submodule update
$ cd converter/usb_usb
$ make
Program converter. Push reset button on Leonardo before run this command. Serial port name(COM17) depends your system. On Linux I got /dev/ttyACM0.
$ DEV=COM17 make program
or
$ avrdude -patmega32u4 -cavr109 -b57600 -Uflash:w:usb_usb.hex -PCOM17
Limitation
----------
Only supports 'HID Boot protocol'.
Not support keyboard LED yet.
Note that the converter can host only USB "boot protocol" keyboard(6KRO) and not NKRO, it is possible to support NKRO keyboard but you will need to write HID report parser for that. Every NKRO keyboard can have different HID report and it is difficult to support all kind of NKRO keyboards in the market.
Update
------
2014/12/11 Added Hub support(confirmed with HHKB pro2)
Resource
--------
USB Host Sheild 2.0
https://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-2-0-for-arduino
https://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-for-arduino-pro-mini
USB Host Sheild 2.0 source
https://github.com/felis/USB_Host_Shield_2.0
Arduino USB Host Shield(with bootst converter)
http://arduino.cc/en/Main/ArduinoUSBHostShield
Arduino source
https://github.com/arduino/Arduino/hardware/arduino/{cores,variants}
Initial release of TMK USB-USB converter
https://geekhack.org/index.php?topic=33057.msg653549#msg653549
http://deskthority.net/workshop-f7/is-remapping-a-usb-keyboard-using-teensy-possible-t2841-30.html#p74854
Arduino-based hardware keyboard remapper - Colemak forum
http://forum.colemak.com/viewtopic.php?id=1561
Teensy + Host Shield
http://www.pjrc.com/teensy/td_libs_USBHostShield.html
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