Throwing myself under the CAN BUS

NEEDED TO DO A LITTLE PLANNING

This work session started many, many days ago. When I first set out to generically pull some wires for my ZipTips and autopilot servo, I naively thought I could “just pull some wires.” It took less than a minute of reading to learn more and more about the Garmin G3X Touch wiring system and that it has special implications on some wiring systems. The one that took me the most reading to grasp was the concept of a CAN BUS. The good news is that the Garmin G3X Touch Manual is really well written and offers a great deal of assistance. In short, the CAN BUS is a daisy-chained network of LRUs (line replaceable units) within the avionics system. For example, the autopilot servos, the EFIS displays, magnetometer, and IFR Navigator are all linked on this network (and many more). This network must be connected with shielded wire, and these shields must all be grounded on the chain as well. Confused yet? Don’t worry – it really is pretty understandable. Here is what I decided upon:

1. My terminal points on the CAN BUS would be located at GSA 28 autopilot servos. These are going to be the furthest distance from the vast majority of other avionics and also have onboard resistors that make terminating at these locations super easy.
2. Stein has an excellent backshell kit to make the wiring easy. I picked up a kit here.
3. Stein also has a great selection of wire to accomplish the job. I will be using the two conductor, 22AWG, shielded wire. This will help with bookkeeping down the road as well. For example, the CAN BUS has two pins adjacent to each other. These will come from the same two conductor wire.
4. I’ll make the shield ground connections using solder sleeves. You’ll NEVER guess where I picked these up at…

MAKING THE CONNECTIONS

I started with a picture here to illustrate some of the CAN BUS connections. The best resource to learn about these is from the Garmin YouTube video series. It is titled “Garmin G3X Wiring Fundamentals Series.” It is a ten part series, each part is no more than two or three minutes long. They actively demonstrate everything I describe here.

As a result of having watched the clips, my work is shown above. The solder sleeves worked incredibly well. Next is to attach pins and create the backshell. Because I have some pretty excellent wiring tools, this next step was a joy.

One sticky item for me was identifying the method by which to terminate the CAN BUS at a GSA 28 LRU. Therefore, I reached out to Garmin directly and clarified real quick, which is always a good idea. In the image above, you’ll notice that pins 3 and 4 have a jumper between them. This measure is all that is required to terminate the CAN BUS at this location. Impressive.

Overall, doing my homework on the overall avionics wiring was helpful. As a result, I was able to better understand what was happening not only at the right wing, but all throughout the aircraft down the line. I’m getting excited to button up this wing and move on!