GSA 28 wiring issue

[rhrezo]

I had the connectors for my GSA 28 roll servo made at an avionics shop, got it back, and connected it to the servo. There is an extra two wire bundle and a ground wire from the connector. The shop said "connect the wires labeled Hi and Lo (from the bundled wire) to the CAN node. I can't find any useful (think non-avionics guy) assistance with this. Is the "CAN node" another connector that is tied into the other servo? The schematics from Garmin don't help.

[mrj22]

I had the same question when installing my servo. The CAN bus is a commuication link between all the G3X components you have installed. The HI and LOW wires coming out of the servo get spliced into the HI and LOW CAN bus wires. Look at 2.3.1.3 in the install manual. The servo is an LRU. I cut the CAN bus wires and soldered the two ends with the wire coming out of the servo. Garmin support also sent me a diagram that helped.

[Dbro172]

Im no Expert (pun intended) but I think your wires labeled Hi/lo are the node and what they meant to say was to connect them to the CAN Bus. In this photo, the wire that my fingers are pinching is the CAN bus. This is a mockup of my CAN bus from the GEA 24 to the GSU 25 to the GAD 29 with the GAD 29 at the end of the bus. you could also look at this as being the AP servos to the Left and right of my fingers, with the servo to the right of my fingers, at the end of the bus. (someone please correct me if im wrong here) By the way, this is just another example of the service from Stein air, this mockup was provided with my wiring harness for the GAD 29, showing exactly how to tap into the CAN bus.

[g3xpert]

Originally Posted by rhrezo

I had the connectors for my GSA 28 roll servo made at an avionics shop, got it back, and connected it to the servo. There is an extra two wire bundle and a ground wire from the connector. The shop said "connect the wires labeled Hi and Lo (from the bundled wire) to the CAN node. I can't find any useful (think non-avionics guy) assistance with this. Is the "CAN node" another connector that is tied into the other servo? The schematics from Garmin don't help.

Hello Richard,

The other responders have done a great job explaining CAN bus wiring. We also wanted to explain the 3 methods that can be used to connect a device (LRU) to the CAN bus backbone.

As a reminder, the CAN bus backbone is simply a twisted, shielded pair of 22 AWG wires that runs around the aircraft and connects all the G3X devices that communicate over the CAN bus.

As shown in the diagram below, there are 3 methods that customers use to connect devices to the CAN bus.

Method 1 is what Derek has shown above with two ends of the CAN bus going into the connector backshell at the device. Two short 22 AWG wires are spliced (typically soldered and heat shrinked) onto the CAN Hi and CAN Lo wires and two pins are crimped on. This is probably the most popular method of connecting to the CAN bus and works well.

Method 2 is a second method which has the advantage of not having the CAN bus splicing happening inside the backshell. With method 2, the splicing happens a few inches away in the CAN bus backbone, and a single twisted, shielded pair cable goes into the backshell where two pins are crimped on. Since your supplier provided a pre-wired servo connector, this may be the way you want to tie this into the CAN bus backbone, but remember that a CAN node (short run to CAN backbone) can only be a maximum of 1 meter in length.

Method 3 is something everyone will use exactly twice, since the devices connected to the extreme ends of the CAN bus are always connected in this very simple manner where the shielded, twisted pair CAN bus backbone enters the backshell and the shield is terminated there.

Let us know if we can answer any additional questions.

Thanks,
Steve

[rhrezo]

I can't thank everyone enough- I thought it might be some type of module I had to buy from Garmin (like so many other things!).

[rhrezo]

I think I've got this- the blue and white wire coming out of connector to servo are connected with a bridge wire to the other servo in the fuselage. Does it matter which servo I install a CAN Bus termination between pins 3 and 4?

[rhrezo]

[rotary57]

Originally Posted by rhrezo

I think I've got this- the blue and white wire coming out of connector to servo are connected with a bridge wire to the other servo in the fuselage. Does it matter which servo I install a CAN Bus termination between pins 3 and 4?

The terminator must be installed at the END of the bus.

[Mike S]

Richard, welcome to the good ship VAF.

Lots of good info here isn't there??

[rhrezo]

Help me out here- where, in this set of wires, is the "end of the bus"? I very successfully put people to sleep for a living but airplanes are wired differently and I'm frustrated.