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ADB to USB keyboard converter

This firmware converts Apple ADB keyboard protocol to USB, you can use it to plug old ADB keyboard into modern computer. It works on TMK ADB-USB Converter, PJRC Teensy2.0 and other USB AVR MCU(ATMega32U4, AT90USB64/128 or etc) and needs more than 10KB flash at least.

Discuss here:

You can buy a TMK converter here:


Also check these when you are in trouble.


Connect ADB pins to controller just by 3 lines(Vcc, GND, Data). By default Data line uses port PD0.

ADB female socket from the front:

 / o4 3o \      1: DATA
| o2   1o |     2: Power SW
 -  ===  -      3: VCC
  `-___-'       4: GND

This converter uses AVR's internal pull-up, but it seems to be too weak, in particular when you want to use a long or coiled cable. The external pull-up resistor(1K-10K Ohm) on Data is strongly recommended.(It is almost must!)

Pull-up resister:

Keyboard       Conveter
5V------+------|VCC   |
        |      |      |
       [R]     |      |
        |      |      |
Signal--+------|PD0   |
               |      |
GND------------|GND   |
R: 1K Ohm resistor

Define following macros for ADB connection in config.h if you use other than port PD0.


Build firmware and Program microcontroller

See doc/

To build firmware and program TMK Converter run these commands:

$ make -f Makefile clean
$ make -f Makefile [KEYMAP=(plain|ansi|iso|hasu)]
$ make -f Makefile [KEYMAP=(plain|ansi|iso|hasu)] dfu

You can select keymap with optional KEYMAP= (plain is default). Push button on the converter before running dfu target.

Use Makefile.rev1 for old TMK Converter rev.1 and Makefile.teensy for Teensy2.0 instead of Makefile. For TMK Converter rev.2 just use Makefile.

To program Teensy you can use teensy target:

$ make -f Makefile.teensy [KEYMAP=(plain|ansi|iso|hasu)] teensy


You can change a keymap by editing code of keymap_[plain|ansi|iso|hasu|yours].c. How to define the keymap is probably obvious. You can find key symbols in common/keycode.h. And see doc/ for more detail.

Magic command

To get help press h holding Magic key. Magic key is Power key.

Locking CapsLock

Many of old ADB keyboards have mechanical push-lock switch for Capslock key and this converter supports the locking Capslock key by default. See README in top directory for more detail about this feature.

Also you may want to remove locking pin from the push-lock switch to use capslock as a normal momentary switch.

Mouse support

ADB mouse support was added by @mek-apelsin on Apr,2015. It supports only one button as of now.


Not-extended ADB keyboards have no discrimination between right modifier and left one, you will always see left control even if you press right control key. Apple Extended Keyboard and Apple Extended Keyboard II can discriminate both side modifiers except for GUI key(Windows/Command).

And most ADB keyboard has no diodes in its matrix so they are not NKRO, though ADB protocol itself supports it. See protocol/adb.c for more info.

If keyboard has ISO layout you may have swapped keys problem, see this for the detail.