Most LX instruments — Era, LX 10K, the iris line and their accessories — connect to each other over a CAN bus on an RJ45 connector that carries data and power. It is a deliberately simple system, and almost every fault we see with it comes from one of five installation mistakes. This article is the practical wiring reference; the theory behind it is in the LX Academy article on the CAN bus.
What the CAN port is and is not
- The RJ45 CAN port is not an Ethernet port. It looks identical and it is not. Never patch it into a network switch, a router or a PoE injector.
- The RJ12 ports (USER, INPUTS, FLARM) are also not interchangeable with each other, even though they look the same.
- The CAN cable carries both power and data, which is why an accessory needs one cable rather than two.
The two rules that matter most
1. Two terminators. Exactly two.
A CAN bus must be terminated with 120 Ω at each physical end of the cable run — two resistors, never one, never three.
With only one terminator the bus still works on the bench, and on a warm day, and during the first flight. Then it develops the classic symptom every avionics shop knows: an intermittent fault that appears only in turbulence, only in the cold, or only after two hours. The signal edges reflect off the unterminated end, the receiver misreads frames, the frames get retransmitted, and eventually a device drops out and comes back.
If a system behaves perfectly on the ground and misbehaves in flight, check the termination before you check anything else.
2. Chain, do not star.
Devices hang off the bus; they do not sit in line with it in separate branches. Long stubs — a metre of cable out to an accessory in the wing root — turn each branch into a small antenna and a small reflector. Keep stubs to a few centimetres. If a device is far away, extend the bus itself to it rather than running a long spur.
Power on the bus
Every device on the chain draws its current through the same conductors, and the resistance of those conductors turns that current into a voltage drop. The device furthest from the feed feels it most.
Practical consequences:
- Feed the bus near its electrical middle, not at one end.
- Keep the run as short as the airframe allows.
- Do not hang a genuinely hungry load off the end of a thin shared cable just because the connector fits.
- Fuse every supply run at the battery end, sized for the wire and not for the instrument.
- Measure the bus voltage at the last device, during a radio transmit, at the end of a flying day. That is the honest measurement; the one at the battery terminals is not.
Typical accessory chains
Era with accessories. The AHRS module, the LX Joy joystick and a flaps sensor all connect over the same CAN bus. Connect the AHRS and the artificial-horizon page appears — no configuration and no additional wiring.
LX 10K. One CAN bus runs between the main unit and the vario indicator. The indicator is fed and driven through that single cable.
iris. CAN links iris devices to each other and to the rest of the panel; Gen 1 instruments are configured over the CAN2WiFi adapter, while Gen 2 has WiFi in the instrument itself.
Both the Era and the LX 10K ship with a 40 cm CAN-BUS cable in the box. Longer cables are available from your dealer; make one up yourself only if you are confident about the pinout and the crimp quality, because this is the connector that vibration works on.
Cable and connector practice
- Use a proper twisted pair for the two signal wires, all the way, including through connectors.
- Use quality RJ45 plugs and a good crimp tool. A conductor that is merely touching will conduct on the ground and stop conducting in the cold at altitude.
- Strain-relieve every connector and support the cable every 30 cm, so vibration works on the tie and not on the crimp.
- Give every instrument enough service loop to be pulled forward without disconnecting it.
- Keep the CAN run away from transmitting antenna cables where you can.
- One clean ground reference for the whole panel. Two devices grounded at two points with current flowing between them do not agree on what zero volts means.
Five faults, in the order we see them
| Fault | Symptom |
|---|---|
| Missing or single terminator | Intermittent dropouts, worse in turbulence and in cold |
| Long stubs / star topology | Same, and harder to find |
| Power fed at one end of a long chain | The far device browns out first; often blamed on the device |
| A crimp that passed the tug test | Works on the ground, fails at altitude |
| Two grounds, one current | Odd behaviour on several devices at once |
Before the first flight
- 120 Ω at both physical ends of the bus
- Devices chained, stubs short
- Feed near the middle of the chain
- Every connector strain-relieved and supported
- Supply fused at the battery end
- Bus voltage measured at the last device during a transmit
- A spare CAN cable of the right length in the trailer — the failure that strands you is mechanical, not electronic
When the bus is not the right answer
CAN is built to move small, urgent messages with guaranteed priority: an airspeed, a flap position, a warning. It was never built to move a moving map, a camera feed or a firmware image at speed. That is why the NAVIA platform moves to gigabit Ethernet with Power over Ethernet — one CAT 6 cable per device, a hub at the centre instead of a chain, and no solder joints in the installation. The virtue survives the change: one cable per box.
Where to go next
- Wiring diagrams and installation manuals for your device: the LX download center.
- The theory: the LX Academy articles on the CAN bus and on cockpit power systems.
- Anything that does not match this article: your dealer first, then LX support.