# Reuse a microphone (formerly) wired to the digital “General Purpose Input/Output” of a Realtek sound card?

I recently repurposed an old laptop screen (from a Dell XPS L502x) as external monitor, and then made the built-in webcam work without too much fuss.

The camera module also has an embedded microphone, and I'd like to see if I can make that work as well.

I was naively expecting an analogue signal all the way to the sound card. However, the two wires for the microphone seem to be carrying a digital signal, one being DMIC-CLK1/2 and the other GPIO0 / DMIC-1/2. They were connected to pins 46 and 2 respectively on a Realtek ALC665.

I tried to figure out whether there was any recognizable standard for this microphone's signal, but I couldn't make much sense of the docs.

So what is the communication format/standard/protocol of this microphone? Can I turn this microphone into something usable? Convert the signal back to analogue, maybe? Or will it work out of the box if I just make it a jack cable and connect it to my mic in? Would this work with another Realtek "HD Audio Codec" card only?

Here is a picture of the full webcam module:

The back displays the name of the module, "HannStar J QCM20Q-1" but no luck finding documentation online, only offers for used parts.

From left to right the main structures on the front side are:

• a big coil, L3
• a small chip, U2, with "ETF" and some dots written on it
• a partly peeled-off sticker with some product numbers
• the orifice of the microphone
• some metal cover I can't remove
• the webcam lense
• the connector (7 wires, with two mass) above some test points
• a chip with "cFeon F10-100GIP" written on it, apparently this is a memory chip.

Back and front have same top/bottom and opposite left/right, so the microphone is where "PAD L1" is on the back.

Side notes and references, in case it's useful:

My current hardware is a Realtek ALC889 sound card, in a Supermicro X9SCV-Q motherboard that seems to only have two front panel jacks for all audio connectors.
I haven't been able to find schematics for this motherboard.

• Wouldn't it be easier to just swap out the microphone with an analogue one? – Andy aka Feb 12 '16 at 16:59
• Docs for the microphone? I suppose it's a bit late to look at it on a scope, but I suspect it's I2S. – pjc50 Feb 12 '16 at 17:06
• Is the microphone's electret capsule (elecrically) accessible? Maybe you can wirs to the analog leads before the ADC (if it's not built inside the capsule) and save yourself some headaches. Otherwise, if you want your soundcard to accept the mic signal on an analog input, you'll have to build/buy a DAC for whatever protocol it's using (would be far cheaper/easier to buy a new mic, most likely) – Robherc KV5ROB Feb 12 '16 at 17:16
• It's a digital mic, likely MEMS, not electret... – Passerby Feb 12 '16 at 17:49
• I had a look inside again but not much luck finding anything useful (probably why I didn't take any notes before). I've added pictures so you can see for yourself. – Cimbali Feb 12 '16 at 22:30

## 1 Answer

If the signal to the microphone really is digital, then there has to be an IC on the camera module that does the conversion. You need to find that IC and see if there is a datasheet for it. 1) Find all the chips labeled with U designators. 2) Find the datasheet for the chip see if its has anything to do with microphones 3) Figure out how to interface with the microphone IC

The memory chip is probably to identify the camera board.

I see a U3 and U7 on the back of the board, they are located under the EMI shield. I'd place bets that U7 is for the camera and U3 is for the mic.

• That may not be the case. There are microphones (typically MEMS devices) that have a digital output (no A/D required!). – uint128_t Feb 12 '16 at 18:02
• Yep, and the mems device will be housed in an IC. Thats what wee need to know, where the digital lines on the board go to and the datasheet for whatever is on the Camera module pcb – Voltage Spike Feb 12 '16 at 21:47
• This is not an answer. This is a comment. This belongs in the comment section under the question. – Passerby Feb 12 '16 at 22:32