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TRRS jack (split keyboards)

A 3.5 mm audio jack used as the link between the two halves of a split keyboard: GND, VCC and one or two data lines over a TRRS cable.

What it does#

A TRRS plug has four contacts: Tip, Ring 1, Ring 2, Sleeve. Split keyboards run QMK’s serial link (one data wire) or I²C (two wires) between the halves, plus VCC and GND, over a standard 4-pole audio cable.

Example circuit: Sleeve = GND, Ring 1 = VCC, Tip = the serial data line; Ring 2 unused. Both halves must use the same assignment.
Sleeve = GND, Ring 1 = VCC, Tip = the serial data line; Ring 2 unused. Both halves must use the same assignment. Open the trrs_split example from this page in PCB Canvas: “Insert into my schematic”.

Any assignment works if both halves match; copy the one of the board your firmware config comes from.

Pitfalls#

  • Never plug or unplug while powered. Sliding the plug in drags the tip across every contact: VCC briefly touches the data pin of the other half and can kill a controller. Unplug USB first.
  • TRS (3-pole) cables work for serial (VCC, data, GND) but not for I²C.
  • Footprint orientation: the jack’s opening must face the board edge.

Footprint#

PJ-320A through-hole (C2884926, extended; usually hand-soldered). The SMD PJ-320D footprint is also available.