ARINC to GPS 175 shield?

[Taylorbentz]

I have 2 questions: regarding connecting an ARINC 429 to a Garmin GPS 175 using the below pinout.

1. Garmin calls for a shielded wire, with the shield grounded to the backplate on the GPS 175. Neither Dynon nor Garmin mention what to do with the shield on the Dynon ARINC 419 side. What should I do with the Dynon ARINC 429 side of the shield?

2. The Dynon manual shows a Ground connection on Pin 20 of the ARINC-429. Should this be connected to the same ground bus as the HDX? Or should it be grounded to the shield wire? Or not at all?

This is a C182P.

Anybody's advice would be appreciated!

 

[Rhino]

Ideally all avionics connections would be grounded to the same point. The Third Party Connection and Configuration Guide mentions that several times, though it doesn't specifically mention the 175. Most people in the experimental world use the intercom or audio panel. However, I'm not aware if the certified world allows you to deviate from what's in the 175 manual. It shouldn't be necessary to ground the shield at both ends. In rare circumstances, that can even cause problems. But, if you aren't allowed to deviate from the connection the Garmin manual calls for, I would probably ground it at both ends. Maybe you should ask Dynon to shed some light on that.

 

[Taylorbentz]

Ideally all avionics connections would be grounded to the same point. The Third Party Connection and Configuration Guide mentions that several times, though it doesn't specifically mention the 175. Most people in the experimental world use the intercom or audio panel. However, I'm not aware if the certified world allows you to deviate from what's in the 175 manual. It shouldn't be necessary to ground the shield at both ends. In rate circumstances, that can even cause problems. But, if you aren't allowed to deviate from the connection the Garmin manual calls for, I would probably ground it at both ends. Maybe you should ask Dynon to shed some light on that.

Thanks I appreciate the input. Ground loops seem to be more art than science (art backed by science) so honestly just hearing people's opinions is really helpful. To be clear, when you say "ground at both ends" would you connect the shield on the Dynon side to the Ground pin #20?

 

[Rhino]

Yes. I personally would probably ask Dynon first though. Then you would at least have a written record, which I understand may be important in the certified world (my experience is mainly military and experimental). They may well consider the ARINC lines to not be susceptible to noise, and thus tell you to just ground at the 175 end. That would make things simpler, and I'm a big fan of simpler.

 

[Taylorbentz]

From Dynon:
Shields are typically only grounded on one end with the other left floating or unconnected.
Connecting pin 20 is not necessary. It's there in case the two devices are not using the same battery ground and allows you to ground the arinc module to the navigator so the signals will have a ground path. If they share the same power ground, it's not needed.
I have my GPS175 and Dynon all with power grounds on a common ground bus, so no pin 20 for me, and no connecting the shield to the ARINC 429 module.

Thanks!

 

[Rhino]

Outstanding. Like I said, I'm a big fan of simpler.

 

[GKC Aviation]

From the GPS175 install manual