First, Build a Shed

[PapuaPilot]

Congrats Carl. That is a big day when you get to turn on the avionics for the first time. I remember it clearly. Keeping the smoke in makes it a really great day.

Configuration does take some time, but it isn't that hard with the G3X. Doing the compass swing was so easy, I've never done one so quickly.

[PaulSS]

Plugging in the final unit in the chain, the Magnetometer, corrupts the Bus Data. Same at the other extreme of the Bus. Plugging in the final Engine Monitor corrupts the Bus Data.

Does the Garmin CAN bus have a resistor at each end and are yours present, if required? I was just thinking that the MGL harnesses have a 120 Ohm resistor at the start and end and it's just strange that it is your first and last units causing a problem.

I've attached a diagram of my system to both bore people and illustrate what I mean about the positioning of the resistors. You can see one near the SP6 Magnetometer and one near the RDAC.

[David47]

Exciting time Carl .... doing the electrics. Congratulations on making great progress. Routing the wires and bundling them together I guess takes a bit of head scratching. Go well.

[PapuaPilot]

The Garmin CAN bus does have a resistor in each end of the bus. It is built into a special termination plug that goes in series onto the components at each end of the bus. Carl, are you sure you have installed the CAN terminations installed properly?

The magnetometer isn't on the CAN bus, so the issue could be that you haven't assigned the RS232 channels.

Here is a copy of my CAN bus and GSU (AD-AHRS) wiring diagrams, maybe they can help.

[Cherrybark]

Paul,

Yes, the Garmin CAN Bus has the traditional, terminating resistors across the Signal High and Low at the ends of the chain. A "Bus Termination" plug is include with most devices. This is typically a 9-pin, male/female plug with a built in terminating resistor. One of the diagnostic tests is to resistance between Hi & Lo resistance with the terminating plugs installed and that passed.

There are units, such as the ADAHRS, that have an external LED indicating network status. With the terminator plugs at each end of the Bus, the LED blinks a "healthy network" and the diagnostic display shows 0% network failure. Add the Magnetometer, with the terminator plug, and the network goes to 100% failure rate. Same situation at the other end of the Bus. Everything works well with the termination plug installed. Add the Engine Analyzer and the network locks up. I've unplugged all of the devices along the chain and used a VOM to check if the High and Low signal wires were shorted along the path. After shutting down for the evening, I realized that doesn't verify I don't have the High and Low pins swapped along the way. The concrete floor were cold and I was tired of the problem. Today I'll unplug all of the units and start checking pins and doing continuity test along the paths. Really don't want to start cutting away the pretty shrink tubing to visually check the connections.

[Cherrybark]

Paul,

Thank you so much for going to all of the trouble of posting that diagram and explanation. SteinAir delivered my system with the new GMU-11 magnetometer that does communicate on the CAN Bus. I have it powered from the AHRS. Can't tell you how many times I have verified the four simple pin assignments at the device.

There is a voltage drop with such a long run of 20 awg and I thought that might be a problem. But, even without the battery float charger, the unit is getting just over 12V and is spec'ed to run on 9V.

[Cherrybark]

While playing with connector at the Magnetometer (GMU 11) end of the Bus, I caught a change on the status display. Slowly moving the shielded 4-wire cable around caused the unit to alternately join then drop from the network. Cut the connector off the cable, used a pin extractor (5 for cheap on Amazon or eBay), made a fresh 4-pin + ground end, and rebuilt the connector. Plugged it in and all is well, at least on that end of the Bus. Still haven't figured out the EIS end. But, with Christmas just a couple of weeks away, there are cookies to bake and gift tins to assemble for friends. That's a lot more important than spending too many hours debugging wires.

[efwd]

Nice job Carl. Enjoy the Holidays.