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Discussion Starter #1 (Edited)
As stated in the title, the goal is to be able to use the oem overhead bluetooth microphone with aftermarket headunits. This is for those who prefer not to have a microphone on their dash or steering column.

The primary goal is to get this working with as little modification to the vehicles hardware (harnesses, circuitry, etc...).

It is actually really simple to get the stock Bluetooth mic working. (the following will be avic specific but may be applicable to others)

For the 2.5mm mic input on the new HU,
-TIP is a 5v source
-Sleeve is the mic input

Follow the following diagram carefully. Credit to SVXdc
Code:
   Subaru's pin numbering
  (viewing rear of OEM HU or wires side of car's harness):
   _   ________________   _
  | ---                --- |
  | 8  7  6  5  4  3  2  1 |
  |16 15 14 13 12 11 10  9 |
   ------------------------
   
  Corresponding numbering on PC board:
    2  4  6  8 10 12 14 16
    1  3  5  7  9 11 13 15
   
  PCB   Subaru   Description                  OEM Color
  ---   ------   --------------------------   ------------
  16       1     Mic In (+)                   White/Black
  14       2     Mic Detect A                 Gray
  12       3     Aux In Left +                Yellow
  10       4     Aux In Right +               Blue
   8       5     Subwoofer Amp Turn-On        -
   6       6     Subwoofer Out + (positive)   -
   4       7     Mic Shield                   -
   2       8     NC                           -
   
  15       9     Mic In Ground (-)            Violet/Red
  13      10     Mic Detect B                 Black/Blue
  11      11     Aux Audio Ground             Shield
   9      12     Aux Enable                   Black/Orange
   7      13     Subwoofer Shield             -
   5      14     Subwoofer Out - (inverted)   -
   3      15     NC                           -
   1      16     NC                           -
Connect Pin 1 to the mic input of the HU
Connect Pin 2 to the 5v source
Connect Pin 9 to Ground (either chasis or one of your ground wires)


Since i did not have a nice harness plug, I made do with crimp pins which fit nicely in the cars plug. Those crimp pins were wired up with a 2.5mm jack that was connected to the back of the HU.

The following is just to show the amplifier circuit in the car.

Per the picture below.

Red = Vcc, 5 volts was measured as an output from the stock unit. The Avic MIC out provides 5 volts.
Yellow = Vout (output from amplifier)
Blue = GND

http://img2.imageshack.us/img2/2123/2011imprezamicrophonepc.jpg

Below is the amplifier schematic. All the values are included, except for the capacitors.

 

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Great job! Here's a pic of the factory 16-pin mic/aux harness plug:
Pin 2 should actually be named "MIC B+". It is an output from the OEM HU that supplies +5V power to the OEM mic module's amplifier circuit.

The car's harness connects pin 10, "MIC DET", to ground. The HU uses that to detect that a mic is connected and also to enable the +5V power supply on pin 2. Pin 10 won't be needed when interfacing the factory mic to an aftermarket HU (the pin 10 wire does not go to the OEM mic).

Also, as I mentioned in aacordon's earlier thread, the subwoofer output is not present on HUs in Imprezas. Only in some Foresters.

So you've tried this on an AVIC? People aren't complaining that you sound too loud or distorted? No complaints of excessive wind noise?
 

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Discussion Starter #3 (Edited)
I've primarly tested it on the voice recognition so far, and it has worked out. I need to test it with someone in a controlled environment first. My only attempt at a call was while driving through an area with bad recepetion, so the results were marginal and skewed.

If there is distortion, it could be due to gain as the HU most definately has its own amp within it and it could be clipping the sound.

If gain turns out to be the issue, I can try a simple voltage divider using a pot to determine what the max/min input level to the HU are.
 

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Discussion Starter #5 (Edited)
Results from my test are as follows:

There is alot of Backround noise which muffles my voice. Sound like wind even though the car is at a standstill with windows up.

Echoes are apparent and even worse when echo canceling is turned off.

There may be some clipping if i yell.


I will try and attenuate the mic input tonight and find a good level.

From the circuit, the mic has a gain of 100, centered at 0v.
 

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So here's my question. If I need +5v in order to get the OEM mic to operate I could steal 12v from the map lights and wire in a resistor (messy) or locate a different +5v in the car to tie into and run a fresh cable.

Where are you guys getting your +5v from without the factory HU?
 

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So here's my question. If I need +5v in order to get the OEM mic to operate I could steal 12v from the map lights and wire in a resistor (messy)
[...]
I'd wire in a voltage regulator off the map lights before I tried to use a resistor to drop it to 5v.
 

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I think I was misreading this. What aacordon is saying is that the aftermarket radio supplies you the 5v you need on the tip of the jack and the input from the mic is the shield. Connect the last cable to chassis ground and bam you're in buisness..

I'll have to try this once I get home.
 

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Discussion Starter #10
I think I was misreading this. What aacordon is saying is that the aftermarket radio supplies you the 5v you need on the tip of the jack and the input from the mic is the shield. Connect the last cable to chassis ground and bam you're in buisness..

I'll have to try this once I get home.
Yup thats correct. However the oem mic has a amplifier, and then the aftermarket headunit has its own amplifier. The problem with this is that the overall gain of the mic input is actually the (gain of oem amp)*(gain of internal amp) and clipping occurrs. The mic has to attenuated by 100 before going back to the HU. Or the over head mic will have to be rewired to by pass the amp.

This along with getting pcbs fabricated for the av connectors are on a TO-DO list i have that will have to wait till january when im taking a qtr off from my Masters program.
 

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So in short... I need to bypass the OEM amp. Crap. Well I'll take it out tonight and take a look at it. I've got fairly solid electrical knowledge. Maybe I can figure it out.
 

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Has anybody explored the possibility of just using the stock location to mount the aftermarket mic?

Is there a significant difference in the quality of the microphones? Or is the entire point of this just to avoid running another wire up around the A-pillar to between the map lights there?

I'm assuming that aftermarket head units are designed to work best with the microphones they come with, particularly with regard to background noise, frequency response etc. So what's the big deal about using the stock microphone?
 

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Rocket while I haven't done any direct comparison's this is mainly for ease of use/asthetics. This was supposed to save me manpower but in the end is doing the opposite. You certainly can use an aftermarket mic in the stock location (I suspect you can find better locations).

I'm doing it because I "think" the stock mic is higher quality.
 

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I see the point for aesthetics, but attenuating the signal after it has already been amplified, then amplifying it again isn't going to help with quality. Have you actually pulled out the stock mic and put them side by side? So long as the aftermarket mic fits inside the stock location (so you can't see it more than the stock mic) I bet this would yield the highest quality sound.

Regardless I'm curious to see how this turns out for you - it seems like you're taking all the right steps to do a good job. Perhaps after I finish installing my Z140 we can coordinate calls to a third phone to compare the sound quality of stock mic vs aftermarket.

-Rocket
 

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Sounds like a good plan.
Well I went out and did a bunch of work attempting to bypass the OEM amp. Sadly this netted me zero result. Using the diagram's given I hoped that connecting the white lead to MIC Input and the Black lead straight to ground would work.

However I'm suspecting I'm just grounding out all my signal.


Included are pictures and a link to two videos of me working on this project.







Salvage the OEM Mic.mp4 - YouTube

Salvage the OEM Mic#2.mp4 - YouTube
 

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I did. The pcb that the mic is attached to has a modified built in amplifier. This causes major problems attempting to use the pcb. I believe someone was trying to make a workaround. What I did was desolder the oem mic from the board and hook it straight to the output. The follow the diagram on the first page of this post to complete the wiring.

Honestly neither this fix nor the aftermarket mic work very good in the stock location due to how throaty and bassy the wrx is.
 

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Discussion Starter #18
Finally had time to work on this again.

I just traded in my STI sedan for a STI Hatch. (car was hit and didn't drive the same)

I agree amplifying a signal just to attenuate it again is wasteful and not good for quality, but i dont believe in touching the car's harness at all. So gonna make my best attempt to get this to work.

Since i could not find female harness adapters for the USB cable and the 16-pin aux cable, I removed the connectors from the OEM stereo.

I designed a PCB which takes 5 volts from the USB, or can use 5v from a LDO sourced from the 12v to power the mic amp.

There is a balance line attenuator using (2) 7.5k, and 150 ohm resistors. I included a bypass for testing.


When the board arrives and is populated I will provide the results. Should be in early june.
 

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Discussion Starter #20
I finally got my PCBs in and soldered them. Just need to order a few parts more in order to test the mic line attenuation.

I will test fit it this weekend and see how it will work as is.



 
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