Saturday, January 2, 2010

Mysteries of push-to-talk (PTT)

I've been wiring up the headphone and microphone jacks for the pilot and co-pilot positions via my PS Engineering 1000II for the last few weeks (yes, I said weeks. It's -14 today.). Now I'm thinking I've been confused into doing it wrong. Yes, I used passive voice there.

Here's why.

I'm using the PS Engineering wiring harness tutorial, which you can find here, if you have Powerpoint.

Here's one of the slides.



It appears to tell me to connect one push-to-talk wire to the tip and one to Audio Lo, the barrel... ground, as I understand it. OK, fine.

Another slide shows this schematic:



So far so good? Good.

Notice that it says connect PTT to tip. Now look at this slide:



Notice the difference? In the first two schematics, it has the PTT wire on the top, indicating that it's the "tip." On the last schematic it identifies the tip as the middle.



Based on the last two images, it suggests one wire comes off the same pole as the ground (Audio LO) and the other comes off the same pole as the audio (AUDIO HI). It appears to me that the schematics in one indicate that audio_hi is the tip and on the other it seems to indicate audio_hi is the ring. In effect -- if you compare image #1 with image #3, it appears to identify a location as a "tip" in one schematic, and then as the "ring" in the other.

Or am I reading it incorrectly?

So, which is it? Let's look to Bob Nuckols of Aeroelectric Connection for help (click for larger image).



To me, that shows the AUDIO-HI wire attaching to the jack without any other wire. Which is too bad because, of course, that's not the way I did it. It's interesting to note that this particular schematic also connects at shield at the jack, which PS Engineering's tutorial says is a no-no. But that's another story for another day.

Update 7:39 p.m. - Armed with the knowledge that there are no electrical symbols here, only a physical reference, I went out to the hangar and got the jacks rewired properly. The -3 temperatures be damned.

8 comments:

  1. I would use you meter on continuity to decide for yourself which terminals are connected.

    I don't believe that the diagrams are intended to show the physical layout of the plug, but rather the logical layout.

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  2. It's not confusing to me where the terminals ARE connected; it's confusing to me where they're SUPPOSED to be connected. One schematic says a wire should go on the tip, the other suggests it goes on the ring. Which is it?

    In schmatic lingo, which of those symbols indicates a tip -^ or -V?

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  3. I am not really following you.

    The ^ or V represent the spring clips that actually engage the plug when it is inserted, they are not any specific lingo. In all the images I see the PTT to the tip (i.e. furthest from the barrell).

    In all three of those diagrams imagine the plug being inserted from the right side.

    Hope this helps.

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  4. I see, so in schematics of jacks, it's not the symbol that is interpreted, it's the position?

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  5. well, I don't think I would call this a schematic. It's a diagram showing the terminals, and how they translate to the plug.

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  6. See, this is the problem for we non-engineers trying to learn the things that we're supposed to learn in building an airplane. You get to the electrical system and now some symbols are important to understand, and you learn how to look at a wiring diagram and figure out a symbol for, say, a fuse, or a resistor, or a ground. We don't know that other symbols you're supposed to ignore.

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  7. A couple links which might be useful for schematics and symbology: http://www.aaroncake.net/electronics/schem.html
    http://library.thinkquest.org/10784/circuit_symbols.html

    FWIW (wiring audio systems is part of my "day job") the symbols used in the diagrams you posted are the standard schematics for these types of jacks. The sleeve (aka barrel) is represented by the rectangular bit, and tip and/or ring contacts are represented by the V-bits. The determination of which is what is, as you note, made by the *position* in relation to the sleeve indication (rectangle). The second diagram could be more easily confused, as the tip and ring are of very similar length...but all the diagrams do show the same connections.

    On the photo of the jack, that's the normal config, but it can also vary depending on the manufacturer of the jack...check with a meter to be sure.

    Best wishes ~
    -JDW

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  8. Many thanks to all. There's a reason this is year 9 of the build, as you can see.

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