# AC'97 front panel dongle to IntelHD

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:

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:

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?

• 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. Sep 17, 2012 at 19:44
• 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. Sep 17, 2012 at 19:51
• The CUI SJ-3598 might be the jack you're looking for. I think pins 4 and 5 are the isolated contact. Sep 17, 2012 at 19:54