WSTYPE-4106: A Standard Pinout for I²C over GX16-4 (4-pin 'aviation') Connectors


I have since decided that, to prevent devices expecting lower voltage from being plugged into higher-voltage ports and getting fried, it's better to use GX12-4 connectors (slightly smaller sibling of GX16-4) for 3.3V connections and GX16 for 5V connections, which could be USB or connections to I²C devices that expect 5V.


I want to wire up some I²C devices using GX16-4 connectors, also known as 'aviation connectors'. Which pins should go to which I²C wires? If possible I would like to follow existing wiring / pinout conventions.

Suggested Standard

(Which I am calling "WSTYPE-4106", which is short for urn:oid:

WSTYPE-4106 pinout
PinColorI²C role

Looking at the front of the male GX16-4 connector, pins are numbered counterclockwise starting from the bump, 1, 2, 3, 4, corresponding to +, SCL, SDA, and -, respectively.

Warning! As noted by the unicycle charging port page, The numbering order on GX16-X connectors is different from that of GX12-X ones (they are mirrored from left to right). If you adapt this standard to GX12-4s, make sure to use the GX12-4 pin number to position mapping. i.e. pin 1 should still be + and so on, but the wiring will be mirrored from the GX16 version.

Male GX16-4 connector with I²C wires attached


Pin 1 should definitely be positive, as that is common across all uses of GX16 connectors that I have found. Leaning towards pin 4 being ground to match with the USB-over-GX16 convention, and SCL and SDA being pins 2 and 3, respectively (because SCL and SDA tend to be listed in that order).

Existing conventions

I²C pinouts

None of these use aviation connectors.

USB Keyboards

Some people like to use GX12-4 or GX16-4 for USB keyboards. They seem to have standardized on the following pinout:

Conventional USB-over-GX16-4 pinout
PinColorUSB role

This matches the pinout (by number) of regular USB connectors.

Electric Unicycle Chargers

These are a thing, and apparently use GX16-3 connectors with pin 1 carrying the positive voltage, and pin 2 the negative (maybe the third pin is used for ground?). See this electricunicycle forum post or this page about charger customization.