Electrical Specification

Unless stated otherwise, all IO pins use 3.3V.

IO pins are driven from a microcontroller, so expect them to sink/source about 10mA. You can power a LED from them, but don’t expect them to drive a servo.


The keyboard provides three potential power sources to the card.


This is the main supply for digital logic. It is always available. The keyboard has to convert the 5V provided from USB into 3V3, so anything drawing very large amounts of current should use the 5V rail instead.

Keyboards are expected to supply about 500mA on the 3V3 rail.


Used to supply power-hungry components, like RGB LEDs. It is available on both sides of a split keyboard.

The 5V supply must be protected by an overcurrent fuse on the keyboard. As with any USB device, expect it to supply about 500mA.

Controller modules are not required to supply 5V to the keyboard: the keyboard is required to operate with only 3V3.


Direct power from the USB connector, used for things like battery charging.

A module can passively measure the voltage on the two CC pins to determine roughly how much power can be drawn. The highest voltage determines the maximum current allowed:

Voltage  Allowed current
< 0.2V None, USB disconnected
0.2V - 0.66V 500 mA
0.66V - 1.23V 1500 mA
> 1.23V 2000 mA

A module may never draw more than 2000 mA, as that is the absolute limit of the connector.

USB PD communication is explicitly forbidden. The module may only measure the voltage present on the CC pins.

On split keyboards, raw power is only available on the primary half.


Ground pins have been distributed along the connector. Connect ground pins close to high-speed connections for better signal integrity.

All ground pins are connected on the keyboard, feel free to leave some disconnected when not needed.

Reserved pins

For compatibility with future revisions, all reserved pins must be left floating.