Serial output to multiple avionics boxes without isolation.

[fmarino1976]

Only "aviation" RS-232 out of the garmins, and yes, only one of the output can be selected to the same format at a time.

[breister]

I think that the solution is contained within Ranier's comments.

Do NOT use a Serial "ground connect" between devices - instead connect ONLY the "+" wire from the transmitting device to the appropriate wire on the receiving devices, and then make sure all interconnected devices are securely grounded to the same ground bus. Then only if nothing else makes it work you can try connecting the second (dedicated ground) wire to the common ground bus - but I would still only try one at a time until it works and remove any unnecessary wires.

The amount of current generated by serial lines is small, and should not cause damage to any other unit provided they all share a common ground. Yes, Ranier and you other engineers - it is technically possible - but unless I hear of a rash of such occurrences I suspect that it is indeed a rare event.

[Neal@F14]

Originally Posted by SteinAir

Except....you can't really do that. Even though there are 4 outputs, you can only configure one of them to provide GPS serial NMEA or Aviation data out at a time. Don't ask me why, but that's the deal...you can use any one of those ports, just not 2 of them for the same thing. Most all of these devices want the same format, and the 430 only lets you use one of those ports to drive all of those devices who crave the same data!

Cheers,
Stein

Wow, that's a bummer. I'm looking at the Garmin 400 series installation manual right now and it does not mention that it's crippled that way at all, in fact it clearly states "change the selectable RS-232 inputs and/of outputs to match that of the equipment installed in the aircraft", then goes on to list a table of supported input and output format types.

Kinda makes you wonder how they passed their FAA approval with inaccurate/misleading data in the installation manual.

[SteinAir]

Indeed...there are multiple outputs selectable in multiple formats, but like almost everything aviation the install manuals and related regs hardly tell the whole story. It's just one of those things you learn to deal with. As others have mentioned, just split off the single wire and you'll be good.

I only mentioned this specific issue because I noticed in your posts that you had/are working with various people on their electrical installations and I hoped you hadn't wired things assuming the multiple outputs would work. You'd have a lot of head scratchin later on!

Cheers,
Stein

[Auburntsts]

Stein,
What's a good (ie recommended) way to split the signal up other than than direct splices? Would it be OK to fashion a terminal strip or mini-bus of some sort for this data stream so that you can add or subtract components that need the data?

[Neal@F14]

Originally Posted by SteinAir

I only mentioned this specific issue because I noticed in your posts that you had/are working with various people on their electrical installations and I hoped you hadn't wired things assuming the multiple outputs would work. You'd have a lot of head scratchin later on!

Actually I had anticipated using multiple RS232 outputs in my current project, an RV-8 panel with a 430, Dynon HS34 D100 and D120 and a TruTrack DigiFlight-II autopilot. I had already wired up the harness to make use of the 430's RS232 OUT 1 & 2, but since all the harness wiring I've made up so far is still sitting all coiled up in a cardboard box, waiting on the panel itself to get painted before any of the wires actually get fixed into place, the timing is perfect to correct this.

On the RV-10 we just finished this summer, the entire Garmin radio stack was prewired before I got involved with the project, and the serial data line incorporated into its harness only connected to the TruTrak ADI Pilot. The radio stack was purchased and assembled before Dynon ever had all the on-screen HSI programming released and working well, I think the HSI display on the D100 was still in its infancy back in that timeframe mid-2006, so the radio harness wasn't even made to accommodate feeding the Dynon. Now that the newest D100 software has a really good working HSI in it, and the RV-10's owners would really like to have it connected to the GPS data, I was really dreading trying to gain access to the back end of the Garmin stack in the RV-10 because it's practically impossible now that everything is bolted into place. I do have much better physical access to the DB connector at the back of the autopilot, so it won't be too terrible to tap into the serial data line back there and run jumper over to the D100 now.

[breister]

Originally Posted by Neal@F14

Actually I had anticipated using multiple RS232 outputs in my current project, an RV-8 panel with a 430, Dynon HS34 D100 and D120 and a TruTrack DigiFlight-II autopilot. I had already wired up the harness to make use of the 430's RS232 OUT 1 & 2, but since all the harness wiring I've made up so far is still sitting all coiled up in a cardboard box, waiting on the panel itself to get painted before any of the wires actually get fixed into place, the timing is perfect to correct this.

The D100 & 120 are actually somewhat superfluous in this example. Wires will go FROM the 430 TO the HS34 and to the TruTrak; and one ARINC or Serial connection may (I'm not familiar with the 430) go from the HS34 to the 430 (to transmit Course information). All other information will be transmitted from the HS34 to both D100 & D120 via the DSAB twisted pairs.

So, your wiring will actually be quite simple. Check out the Dynon Wiki - 430/530 wiring page.