2026-10-20 YBO bus connector: M8 4-pin

• status: proposed (draft for the family; adopted on Air Hub, Air Hub Pro and Air Hub Mini)
• date: 2026-10-20
• sunset: 2027-03-31
• deviates from: nothing yet. It closes open item 3 of bizplan/governance/product-plan.md (YBO internal bus connector: M8 / RJ45 / Micro-C, due at M3) ahead of the M3 gate for the Air Hub family only, until the owner accepts it for the whole family.
• relatedTask: 20261020-1000-air-hub-commercial-enclosure

Context

The YBO bus is Classical CAN 2.0B at 500 kbit/s with the supply on the same harness: V+, GND, CAN-H and CAN-L. NMEA 2000 runs at 250 kbit/s on M12 Micro-C. On 2026-10-20 the owner moved Air Hub to commercial grade:

• IP54 with conformal coating;
• no sealed M12 / DT connectors;
• USB-C as the primary power input, with PD.

The owner chose an M8 4-pin connector for the harness. The other candidates were rejected:

• N2K-like Micro-C: a YBO node plugged into an NMEA 2000 backbone, or an N2K device plugged into the YBO bus, would join two networks running different bit rates.
• RJ45: it is unsealed and is easily mistaken for Ethernet.

Decision

• Connector: the YBO bus connector is an M8 4-pin, A-coded connector. The device side is a panel socket on the housing wall, sealed by its own O-ring, with flying leads to a board header (JST XH 4-pin on the Air Hub boards). Use the variant rated 60 V; the 30 V parts do not cover the 9–36 V range.

• Pin assignment (proposed, frozen with the harness drawing under Air Hub AIR-O-04):

  M8 pin	Wire	Signal
  1	brown	V+
  3	blue	GND
  4	black	CAN-H
  2	white	CAN-L

• Air Hub: the harness is the secondary supply. USB-C with PD has priority, and while USB-C is valid the M8 V+ does not supply the board.

Consequences

Easier:

• An M8 cannot mate with an N2K Micro-C, so the two buses cannot be cross-connected.
• The part is small enough for the side wall of a commercial housing.
• The panel socket with leads keeps the board free of sealed parts.
• The harness pinout and the housing cut-out can be frozen now.

Harder:

• An M8 contact carries about 3–4 A, which limits how much a branch can feed Key panels (SW-O-03).
• Core and Key are not yet bound to this choice.

At the sunset date, either the family adopts M8 in product-plan.md and the Core and Key specs, or Air Hub follows the family decision taken at M3.