Home brew HD front panel audio, without the hard to find jacks!

Discussion in 'Hardware/Parts' started by JuanLobo, Apr 17, 2014.

  1. JuanLobo

    JuanLobo

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    Apr 17, 2014 at 8:35 PM #1
    JuanLobo

    JuanLobo

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    I was on a quest for weeks to find panel mount jacks that conformed to the Intel HD audio spec. It requires a 3.5mm (1/8") stereo jack with an isolated switch to tell the motherboard a plug has been inserted. These jacks are hard enough to find as circuit board mount, but impossible to find as threaded panel mount. Here is the typical Intel front panel HD audio circuit (Pulled from here)

    HD Audio Circuit.jpg

    After digging into the Intel HD audio spec, I found that all the jack switches do is insert a fixed resistance value between the Sense_Send pin and ground. Each jack is assigned 1 of 4 resistance values, but each manufacturer may use these values for different jacks. Here is the basic idea:

    Jack Detect Circuit.jpg

    So, with this in mind, I came up with an idea to cheat and use TRRS (Tip, Ring, Ring, Sleeve) jacks that are much more common. They are available in threaded panel mount, as well as circuit board mount. The idea is, you figure out what values your mobo uses for pin 6 to ground and pin 10 to ground when no audio cables are plugged in. Unplug the front panel from the mobo, as well as any cables you might have plugged into the rear panel, just to be safe. Then you can measure the resistance with a multimeter to figure out what values to use. They should be one of the 4 values above.

    Now you can use a circuit like this:

    HD Audio Circuit Cheat.jpg

    It should work because regular computer headphones/mics use TRS connectors (just one ring) and when you plug them into a TRRS jack, it will short the first ring to ground along with the sleeve. That puts the resistor into the sense_send circuit and tells the motherboard what jack is now occupied.

    There is a bonus too: If you use a 4 conductor TRRS extension cable plugged into this front panel, it won't tell the mobo you have something plugged in until you plug into the far end of the extension cable. This allows you to have a remote headphone jack!

    The down side is you can't plug TRRS earbuds (like those used on phones) directly into the jack. If you really want to use those, you would need a TRRS to headphone/mic splitter cable.

    ----------------------------
    Ignore the part below unless you are on the prowl for the Intel spec HD audio jacks. I put this here just for those on google hunts for 3.5mm front panel HD audio jack with isolated switch:

    http://www.ab.auone-net.jp/~est/pdf/3.5.pdf (MJ-3335-5)
    http://www.temple-star.com/2.5mm_3.5mm_6.4mm_azalia_hd_audio_SMT_Earphone_Jack.htm (The ones marked "HD")
    http://www.cui.com/product/resource/sj-3506-smt.pdf
     
    vipe155 likes this.
  2. JuanLobo

    JuanLobo

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    Apr 25, 2014 at 3:20 AM #2
    JuanLobo

    JuanLobo

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    Confirmed to work. Audio jack detection working in OSX and windows.

    Multimeter showed pin 6 to ground to be 20K, and pin 10 to ground to be 39.2K. Also found schematic of Gigabyte H61 motherboard that confirmed that is all those pins do is provide a fixed resistance to ground.

    Used these panel mount jacks: http://www.digikey.com/product-detail/en/SJ5-43502PM/CP5-43502PM-ND/1956558
     
  3. vipe155

    vipe155

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    Mar 18, 2018 at 5:37 AM #3
    vipe155

    vipe155

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    Hi everyone,

    Sorry to resurrect an old thread, but with no PMs allowed I don't have much of a choice. I'm interested in this mod for a custom front panel for my desk. Only issue is that I measured the resistance of pin 6 & 10 on my Asus MB, and pin 10 came up with the 39.2K value but pin 6 was 59.2K.

    Is it possible ASUS used a different resistor value? I triple checked that pin, but it doesn't fit the 5.1k/10k/20k/39.2 options listed above. Thanks!
     
  4. JuanLobo

    JuanLobo

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    Mar 23, 2018 at 4:45 PM #4
    JuanLobo

    JuanLobo

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    I guess there is no reason it couldn't be different. The values I showed may have been specific to Intel and Gigabyte. I just assumed everyone used those values. This was with the front panel unplugged, and nothing plugged into the back?
     
  5. vipe155

    vipe155

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    Mar 23, 2018 at 5:18 PM #5
    vipe155

    vipe155

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    Yeah, I actually had the motherboard out and not connected to anything. I was happy when I saw the 39.2 value come up and match your information, but then a little concerned when the 6 pin value was so much higher. 59.2k (exact) value resistors don't seem to be very common, so I figured using a 59k one would be fine.
     
  6. vipe155

    vipe155

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    Mar 26, 2018 at 11:20 PM #6
    vipe155

    vipe155

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    Any chance somehow when I measured pin 6 I was actually getting some kind of addition (20K + 39.2k) and reading 59.2k? I just wired this up, and both jacks work but only are detected as the 39.2K jack. For example, if I plug one jack in it detects, but if I plug in the other it "takes over" the spot of the first one already plugged in, never detecting both individually. Like the motherboard is not correctly seeing the resistance value for pin 6, just pin 10s.

    I'm thinking it's actually the same as yours and I need to put a 20K instead of that 59k.
     
  7. JuanLobo

    JuanLobo

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    Mar 30, 2018 at 2:18 AM #7
    JuanLobo

    JuanLobo

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    Can't hurt to experiment! Might even use a potentiometer or 2 and try the various values. Wish I had more to offer. Ohh, and you aren't trying to plug in earbuds or something that is already TRRS? That would confuse it.
     
  8. vipe155

    vipe155

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    Mar 30, 2018 at 5:59 AM #8
    vipe155

    vipe155

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    No, just regular TRS plugs. I've got some 20K resistors on the way, and I'm hoping it's actually Intel spec standard and the motherboard just uses 39.2k & 20k values.
     
  9. vipe155

    vipe155

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    Apr 2, 2018 at 8:55 PM #9
    vipe155

    vipe155

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    Just wanted to report that the 20K resistor on pin 6 worked perfectly. Don't know what was up with the measurement I got initially, but I appreciate you coming up with this as it was the perfect solution to my custom front panel for my desk.
     

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