HDX and T25 to GMA 245 Comm panel

[Rhino]

I've been asked for assistance with pinouts for the following configuration:

HDX 1100
GMA 245 Comm panel
T25 configured as COM 2

I've come up with the following pinout, but I've never done this setup, and I'm asking for input from anyone who has.

I think it's correct, but I never claim to know all. The only thing I found a bit confusing is the GMA 245 doesn't have a pin for mic/ptt ground from the T25, so I have it tied to the phones ground. All connections on the GMA 245 are made on the J2401 connector, which makes it a bit simpler. COM 1 is an IFD440, but I wasn't asked for help with that. So please, chime in as you see fit folks.

 

[viperpilot]

Thank you, Rhino!

 

[Rhino]

No problem, but I'm still hoping someone experienced with this setup will chime in. Wouldn't be the first time I've missed something.

I've done some more looking, and it appears the GMA 245 does indeed use a shared pin for mic/ptt ground and audio hi, so splicing pins 1 and 9 on the T25 should work.

My comment on the diagram says the GMA 245 is a mono audio panel, but that's only in the context of this installation. Although the 245 does have stereo functions, alert audio is mono only. I'll correct the comment later to make that more clear.

Don't forget to only ground any shielding at one end of any audio cable to minimize the possibility of ground loops. Each unit in your audio distribution system should connect to a common ground, but ground shields on audio wires running between those boxes should only be grounded at one end, unless the shield itself is used as an audio return (LO) connection, such as that seen in unbalanced cables. I recommend using balanced audio wiring, by the way. It is least susceptible to noise interference.

 

[Rhino]

Confirmed. Tying pins 1 and 9 together on the T25 is correct.

 

[viperpilot]

Thank you! I really appreciate your help and the extra research!

 

[Rhino]

You asked another question in the profile post I didn't see before, about muting alert audio. You can route alert audio to one of the NAV inputs on the GMA 245 if you want the ability to mute alerts, assuming you aren't using them for NAV radios. That mutes all alerts when you have that NAV button turned off, but you will always have alerts visually displayed on the EFIS. Alternatively, you can route alert audio to one of the music inputs on the J2402 connector. That will mute your rerouted alert audio in accordance with your audio configuration settings on the GMA 245 (section 2.9 of the install manual).

 

[viperpilot]

Thanks, Rhino for another workaround! I have seen posts on Van's Forums where at least one builder routed the Alert Audio to the AUX inputs on the GMA 245. I'm thinking either option would work. Do you have a preference? I'm leery of suppressing traffic and altitude alerts, so I will probably not reroute, to a switched contact, the Alerts that will come from my IFD440. I might want to keep the music audio for the future (and I think I'd have to cycle the music to the correct music source--something else to mess up!).

 

[Rhino]

You can disable the Alert Mute Music Option function on the GMA 245 (it's enabled by default) to prevent the entertainment (rerouted alert) audio from being muted, so that isn't a concern. However, you may as well use the standard alert audio pins if that's the case, because using that music option setting just makes your audio function the same as the alert input pins do. The only difference would be that the entertainment input gives you stereo alerts as opposed to mono. I'm not sure what advantage that might offer with only one screen, and I wouldn't personally do it that way. I look at it this way. The alert audio pins and the entertainment pins give you essentially the same ability (other than stereo). You really won't see any functional difference between the two. Using a NAV input however, gives you the ability to simply push a button to turn alerts on or off. That gives the easiest inflight reconfiguration option, so that's what I'd do if I didn't have NAV radios. I'm not really familiar with AUX audio on the 245. I imagine it functions similar to music, but I'm not sure.

 

[Rhino]

The NAV 1 and NAV 2 inputs are both on the J2401 connector. To route alert audio to NAV 1, you'd use pins 17 and 18 instead of pins 31 and 32 on the diagram above. For NAV 2, you'd use pins 19 and 20. NAV is mono audio, so pins 13 and 31 on the HDX would remain tied together.

 

[viperpilot]

Thanks Rhino! I like it! I'll wire it that way unless Dynon can tell me they have a fix to "nuisance" audio alerts.
I really appreciate your inputs!

 

[Rhino]

Not sure how ambitious you are, and I don't really want to make things more complicated, but you can make alerts mute for a set period of time with a momentary switch and a timer. It's mentioned in this related thread:

Audio panel connections

Initial installation of D1000 screens to my Garmin245 Audio panel. Each screen has 3 audio wires left right and ground….. i am confused as to where these would go in the audio panel . Comm1 , Aux 1 , alert audio? I am running dual Dynon comms any help appreciated.

forum.flydynon.com

Basically you touch the button, and alerts get silenced for a period of time you set, say 30 seconds or a minute. Prevents you forgetting you turned off alerts. A lot of commercial and military aircraft have that function. Just food for thought. Something like that often doesn't appeal to folks that aren't techno-geeks like me.

 

[Rhino]

This has gotten me curious, and I've ordered one of those relay timers from Amazon to play with. I'm going to hook a momentary switch and run some tests. If it looks promising, I'll devise a pinout and instructions for making it work to temporarily mute alerts from a Skyview. Several people have asked for such a solution.

FYI, the only current reason I know of for stereo on a Skyview is to provide separate alerts for left and right engines on a twin. So if you have a single engine plane, stereo output from a Skyview does nothing for you, and pins 13 and 31 on an HDX will always be tied together.

 

[Rhino]

That particular timer is probably not good for this application. It's normally open rather than normally closed. And since it's a voltage/current relay, it could introduce noise into the equation. I'd need a programmable mixer or switch designed for analog signals (audio) for a final solution. However, this one will work as a proof of concept. And it gives me a new toy to play with.

 

[Rhino]

I put it all in a pdf file.