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Serial output splitting.

Postby Jkoonce128 » Mon Feb 20, 2017 8:28 pm

This is a somewhat generic question, but this seems to be the best place to post. My hangar is finally warm enough to work again, with spring getting here.
I have a 430W that is current for ADS B out. I wired it to my 12" Hxr display with the proper ADSb+ format and it works fine, on the Hxr. I then outputted the serial out from the Hxr to my Trig 22 for GPS info. The format doesn't transfer, so my Trig doesn't see it as legal for an ADS B source. As I understand, I need a direct feed from the 430W to the Trig GPS input.
My question is, can I just split the current 430W serial out feed, and send a wire to the Trig 22 as well as the Hxr? That is, can the 430W serial output drive two inputs? I really would prefer they would be separate, but the 430W wiring at the back of the mounting tray is very busy, and somewhat fixed, so I would prefer not to get into that plug if possible. The Hxr plug with the serial data is readily assessable, so a splice there and then routing a serial wire back to the Trig 22 would be much simpler. The 430W serial feed is data and not a load, so it would seem that it should work, but advice would be appreciated.

Thanks in advance
John Koonce
N78MU
Jkoonce128
 
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Re: Serial output splitting.

Postby Bobturner » Mon Feb 20, 2017 10:00 pm

The answer is yes. Splice a wire into the existing wire out of the GPS, connect it to pin 5 on the Trig or adaptor (which just feeds it thru).
The ADSB approval documents require a direct connection between the GPS and transponder, to make sure no intermediate (like an EFIS) can introduce any extra delay between GPS signal reception, and data reception by the transponder.
There is a limit to how many inputs can be driven by one output, but it's more than two.
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Re: Serial output splitting.

Postby Jkoonce128 » Mon Feb 20, 2017 10:48 pm

Thanks for the quick answer. Also thanks for the answer I wanted to hear! I was dreading getting into the plug at the 430W tray. It is close to the sub panel and no space at all.

John Koonce
RV10
N78MU
Jkoonce128
 
Posts: 9
Joined: Thu Apr 18, 2013 12:37 am

Re: Serial output splitting.

Postby Bobturner » Mon Feb 20, 2017 11:05 pm

Having just recently done this, for the same reason, it isn't as bad as you think to access the 430W connector. Pull the 430, then use a long screw driver from the cockpit side to reach into the tray and unscrew the connectors. Cut cable ties as needed to get the plug to hang down to where you can get at it. Reverse to re-assemble. Hardest part is disassembling the clam shell and putting it back together. I really wish I had had three hands. Of course you also need high density pins, not the standard ones, and a good crimper.
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Re: Serial output splitting.

Postby GRT_Jeff » Tue Feb 21, 2017 3:20 am

The HXr can't read the Garmin-proprietary ADS-B+ format so there's no reason to send it to the HXr. You need the "Aviation" format to the HXr for position and flight plan data, and the ADS-B+ format to the TT22 for ADS-B out. The standard for splitting RS232 is two inputs. I think most of our hardware will work with 3+ inputs.
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