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First of all, I would like to say that I'm a noob at electronics, so please be merciful :)

I'm trying to convert AC'97 audio front panel dongle on my PC to IntelHD one. The difference is that IntelHD is able to detect the fact someone plugged in headphones or microphone.

Here are some schematics, showing the difference:

schematics

So, when the mic is plugged in, SENSE_SEND(7) and SENSE1_RETURN(6) should get interconnected. Similarly, for headphones its SENSE_SEND(7) and SENSE2_RETURN(10). Seems simple.

Unfortunately, I can't find proper audio jacks anywhere. As you can see, IntelHD requires jacks with normally open switch, while I can only find AC97 jacks, having normally closed switch. So, I need to 'invert' the switch somehow...

I've been thinking about this and came up with the following: SENSE_SEND is probably just a logical '1', so motherboard just detects voltage level on SENSE_RETURN pins. So I came up with this simple NOT-gate:

gate

When the headphones jack is in, and therefore switch is opened (for AC97 jacks), SENSE_SEND gets locked to SENSE2_RETURN via 50k, therefore having logical '1'. When the jack is out, the SENSE2_RETURN is short-circuted to the ground pin (2), therefore having logical '0'.

This is where strange things begin. First of all, SENSE_SEND surprisingly has 2.5V instead of 5V as I expected. So I'm not sure now if the motherboard really measures logical levels on SENSE_RETURN pins. And secondly, whether SENSE2_RETURN is short-circuited to the ground or not doesn't seem to matter! PC detects that headphones are present no matter if I open or close the switch.

I suspect my initial assumption about logical levels is wrong. But then... how it might work inside? Any ideas where I am wrong or how else can I invert the switch?

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  • \$\begingroup\$ Keep in mind that your AC97 jacks don't short the contact to ground, they connect it to one of the audio signal lines. In fact, on the MIC jack, the contact itself is grounded, so that the audio to the computer is muted when nothing is plugged in. \$\endgroup\$ – Dave Tweed Sep 17 '12 at 19:44
  • \$\begingroup\$ Thanks for your comment, Dave. I understand that. However that should not matter in IntelHD case, right? Right now I'm using a usual switch (not from inside the jack) and it doesn't work. \$\endgroup\$ – torvin Sep 17 '12 at 19:51
  • \$\begingroup\$ The CUI SJ-3598 might be the jack you're looking for. I think pins 4 and 5 are the isolated contact. \$\endgroup\$ – Dave Tweed Sep 17 '12 at 19:54
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Rather than futz around trying to change out the existing front panel AC-97 type audio jacks it may make a lot more sense to get a nice drive tray adapter. These are available in an assortment of styles with various features. Here is a basic one that offers the HD Audio (Azailia compatible) (a.k.a. Intel HD Audio) jacks ready to connect into your motherboard. enter image description here

http://www.newegg.com/product/product.aspx?Item=N82E16813999355

Here are three others to consider with additional features like memory card readers, eSATA connectors, fan speed controls and Firewire.

http://www.newegg.com/Product/Product.aspx?Item=N82E16811996043

http://www.newegg.com/Product/Product.aspx?Item=N82E16820162023

http://www.newegg.com/Product/Product.aspx?Item=N82E16811996006

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    \$\begingroup\$ Thanks for the links, Michael! I really have no idea how you've managed to find those. I failed to do the same. The sad part is, newegg.com won't ship to Russia. Anyway, I was hoping making the front panel dongle could be a fun thing to do myself... \$\endgroup\$ – torvin Sep 20 '12 at 20:55

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