Tolsen Grip ground wire

[Bud_Keil]

I am installing a Tolsen CS-8 grip in my RV-4. I have Dynon HDX, intercom, A/P servos, and comm. The new grip has only a single common (ground) wire for all 8 functions. My current grip has the PTT switch grounded through the intercom and the trim HAT switch grounded to a local airframe ground. Should I wire the Tolsen grip common wire through my intercom ground along with the trim hat switch, A/P disconnect, Missed Approach, and Frequency Flip Flop switches or go to a local airframe ground?

 

[Rhino]

I assume you mean Tosten. Use airframe ground for the switch common white wire.

 

[Rhino]

I will qualify that by saying I have no clue what you use for a missed approach switch. Dynon doesn't have one as far as I know. But whatever it connects to, I assume it uses ground. Airframe ground should presumably be fine for that too, but you'll need to confirm that using documentation for whatever it's connected to.

 

[Marc_J._Zeitlin]

I will qualify that by saying I have no clue what you use for a missed approach switch. Dynon doesn't have one as far as I know.

What the OP is calling a "missed approach" switch is normally referred to as a TOGA (Take-Off and Go-Around) switch.

This is usually a momentary double pole switch that has two purposes - it grounds a line to the IFR Navigator (in my case, a Garmin GPS-175) and it grounds a line to the Skyview. The Garmin switches to "missed approach" mode and sequences the navigation to the missed approach. The Skyview changes vertical mode to IAS. So if you're shooting an approach and go missed, you punch the TOGA button (on the stick is nice, but it can be anywhere reachable) and push the throttle in to WOT. The plane will hold the approach speed (in my case, 90 KIAS) and start climbing, while following the navigator along the missed approach course. I can retract the nose gear at my leisure when a climb is established, and then adjust IAS for a cruise climb when safe to do so.

Of course, after becoming established on the approach, long before going missed, I've set the target altitude to the hold altitude for the missed, so the climb will stop there.

 

[Rhino]

Thanks. Contact 2. That should also be fine with airframe ground.

 

[Bud_Keil]

My bad. I meant TOGA. I also have a Garmin GPS 175 installed.

Grounding the PTT to airframe ground will not interfere with my intercom?

 

[Marc_J._Zeitlin]

Grounding the PTT to airframe ground will not interfere with my intercom?

It depends on the rest of the electrical system of your plane, and how you have everything grounded. If you just have ground wires attached to the AL structure of the plane, you may induce ground loops. If you have all your grounds going to one particular ground bus, that's less likely. If you run the ground wire from the stick to the same point that you have your intercom and radios grounded to, you should be fine, but again, it will all depend on the architecture of YOUR electrical system.

 

[Rhino]

As Marc noted, there are so many possible variables that a 100% accurate prediction cannot be made. However, there are no signals going through the stick. So even if the conditions for a ground loop technically existed (a difference of potential between the stick ground and intercom ground), it is extremely unlikely to have any effect. All you're doing is switching ground on and off. There is no audio, no analog, and no digital, so it would be very tough to introduce noise via that route. Not impossible, but very tough. If you look at the references for common ground in the Dynon documentation, you'll see it is always in reference to an audio, sensor or data ground, most often serial data. Tosten tells you to use airframe ground. Even the Dynon interconnect diagrams show disconnect switches using airframe ground. There should be no problems using airframe ground for your stick, but feel free to use something else if you have concerns along those lines. If you already have a ground wire coming from the intercom, and you want to play it really safe, by all means use that. Having the wire already in place gives you options if something doesn't work right.

 

[WorkingWarbirds]

Generally its accepted that grounding to where all the audio grounds terminate will result in the fewest problems. In most cases this is the back of the Audio Panel, but the GPS175 has a fat aluminum ground bus built into the connector shell, I used that on the the RV7a I upgraded for all the grounds including audio. Of course, it was mounted right below the audio panel.

 

[Rhino]

This isn't an audio ground.

 

[WorkingWarbirds]

This isn't an audio ground.

The PTT is, and since all of them use a common ground wire, put it where all the audio grounds and that eliminates any chance of an audio ground loop.

 

[Rhino]

PTT is a system ground. It is not an audio return. Again, you can shield it to be careful if you want, and I recommend it if you already have shielded cable to use. Like we said, strange things sometimes happen with audio. But this is not an audio line. No audio goes to or from your stick, unless you have the strangest stick configuration I've ever seen.

 

[WorkingWarbirds]

PTT is a system ground. It is not an audio return. Again, you can shield it to be careful if you want, and I recommend it if you already have shielded cable to use. Like we said, strange things sometimes happen with audio. But this is not an audio line. No audio goes to or from your stick, unless you have the strangest stick configuration I've ever seen.

Not to beat a dead horse, but shielding won't do anything. Like you said, it's not carrying audio signal. It IS running to either the intercom or the audio panel, and adding a second ground location to that is what you want to avoid. Evidence of that if you look at PS Engineering's installation manuals they run PTT back to the Mic Low input, not the airframe ground like they do the other momentary switches. Its an active ground in the audio panel any time you are transmitting. Having a ground in two difference places for the audio panel is what you want to avoid.

 

[Rhino]

You can't avoid adding a ground location, because the PTT switch is a connection to chassis ground. The rule on audio grounding applies to shielding, because that how most of the audio signals are grounded in an avionics install. That's why I mentioned it. Yes, PS Engineering depicts it that way, because it normally runs within the same cable carrying headset and mic audio. Dynon on the other hand, depicts it going straight to chassis ground, not to the audio panel, with no shielding. My point is that there's a difference between power/system/chassis ground and audio grounds, and the rule is intended to apply to audio/data grounds. Did you run all the power grounds on every box in your avionics install to the ground on the intercom? I'm guessing not. I've never seen anyone else do that, but I learned long ago that people often do strange things. And yet again, go ahead and ground through your cable to the intercom if you want, especially if the wire is already there, and even more so if it's shielded. As Marc noted, and I also acknowledged, there may be something else in your system that's not done correctly, that could indeed bring this ground into play. So sure, go ahead. But the rule is not intended for chassis grounds not related to audio or data signals.

 

[WorkingWarbirds]

The industry has moved on from using shields for the audio low ground. Nobody does that anymore, not Garmin, PS Engineering, Avidyne... nobody. Dynon's wiring does not live up to current industry standards either. Like them not shielding their RS-232 channels, and the extra "optional" ground wire from the chassis of the displays to.... wherever? There are a lot of ways you can do it that will work fine, but if you wire it the way PS-Engineering depicts in their PMA8000 and above install manuals, you have done it correctly. Those guys ONLY do aviation audio and have it down to a T.

 

[Rhino]

Changing standards is a different topic, but definitely a relevant discussion. PS Engineering hasn't moved away from shielding audio low though. This is from the PMA 7000B install manual.

 

[WorkingWarbirds]

While I understand that the PMA7000B is a current product, it was specifically designed to be compatable with the King KMA24. That audio panel traces its linage back into the late 1970's. The PMA8000 series is pin compatible with the GMA340, which was late 90's. The standard has been floating ground shields for over 20 years. Doing it the 1980's way is not what I would be advocating.

 

[Rhino]

The PMA6000 does the same thing. I'm not going to look at all of them because it's not really important. About the only thing that doesn't change is that standards always change. I happen to agree with that one change though. The low line should be within the shield (balanced) rather than being the shield itself (unbalanced). That was discussed in another thread here not long ago, along with the fact that it makes wiring confusing when different manufacturers use different standards. None of that of course changes the fact that a PTT trigger is not an audio line. While it's certainly not a bad idea to shield it or use a common ground, and I recommend doing so, it isn't subject to the same rules as audio grounds. The only direct reason we might treat this one differently is if the wire for PTT travels within the same cabling as audio wiring which is certainly possible after it enters mic jack on. The indirect reason is, we do it as a common practice because doing so can sometimes mitigate wiring deficiencies elsewhere in your system. But being a common practice doesn't make it part of the rule for audio wiring. From the switch to the jack, PTT does not travel with any audio wires, and it never carries audio, low or high. It does sometimes travel with audio wires after the mic jack though. But since this particular one is on a stick, rather than a headset jack, it is unlikely to route within the shield of audio wiring, and quite possibly not even alongside it. Now, to add even more complexity to the issue, if you also route the same PTT connection through the headset jack so you can key from the headset, you just added that circuit to your audio wiring. Yet another reason to follow the common grounding rule, just to be on the safe side. So Bud, ground it to the intercom, and we can stop arguing about this.

 

[Rhino]

This is the other thread where different grounding schemes were discussed.

Audio cable from Dynon to audio panel

Can someone tell me where does the audio wires coming out of Dynon harness connects in my audio panel? I am using a PS Engineering audio panel. all I could see on the Dynon documentation is the guidance of “these audit out cables go to the audio panel” however I could not find on the audio...

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