Okay, I know there are easier ways but I'm nuts (as will become apparent in a moment). I'm trying to do this in a 99 E430
So I'm trying to tie into the existing mic for an alpine bluetooth kit. Here's what I've pieced together from the forums. Now somewhere I'm doing something wrong but I don't know where.
1. The existing mic terminates at the db25 connector in the trunk (pins 14 & 15).
2. That same db25 connector in the trunk connects to the rj50 in the center console (pin 1 of rj50 = pin 23 of db25 & Pin 7 of rj50 = pin 1 of db25).
What I'm trying to do is to patch the mic into the rj50 connector and then from the rj50 connector to my bluetooth kit mic in. I've used a db25 to ethernet connector and then built a little rj45 connector that loops the mic signal back (i.e. db25 Pin 14 is looped to db25 pin 23).
Now I realize this is as convoluted and nuts as could be and the intelligent answer is just add a new mic and run the cable down the side bolster but I'd really like to use the built in mic if possible.
A stupid question but what you write is you looped the db25 pin 14 but you don't tell what did you do for the db25 pin 15.
Pin 15 is the positive wire for the microphone, it also feeds DC for the pre-amp stage at the microphone. The drive voltage and the signal swing may not match your BT HF kit but it should not harm trying.
If you did loop both wires and applied the correct polarity, I guess you checked that the microphone is present (I guess you did have the full HF kit and then it of course would be present).
I went back and mapped the db25 pins and the post that I grabbed the pinout from was slightly off. Turns out to be pins 3 & 12 that connect to the center console rj50.
A little further testing required but at least I know one error!
Where did you get the pinout info for the rj50 db25? Does the rj50 have +12V and switched +12V from the db25? Hope you'll post a follow-up on how your system is working (mic quality, etc.). Thanks.
Only thing, the OP in that thread may have mistaken the RJ50 plug for a RJ45 plug. If so, when he mapped the RJ50 pins to the DB25 pins, I think he was off by 1. That is, I believe pin 1 on RJ45 would corresponds to pin 2 on RJ50, pin 2 on RJ45 would correspond to pin 3 on RJ50, etc.
But that referenced thread does confirm some of the same info that are in this thread:
- pin 14 on db25 = mic (-)
- pin 15 on db25 = mic (+)
- stock mic may have bias voltage on line for pre-amp (but I guess a decoupling capacitor is expected in any BT kit's mic connection, so this should not cause a problem?)
- however, in the referenced thread, pin 3 on the db25 is chassis ground (vs. 8ball's last post)
I wonder what is the wire guage for the wiring from the db25 to the RJ50. Would it pose any safety concern to run +12V on it? Hmm...probably depends on the power draw of any device that draws power from it?
Only thing, the OP in that thread may have mistaken the RJ50 plug for a RJ45 plug. If so, when he mapped the RJ50 pins to the DB25 pins, I think he was off by 1. That is, I believe pin 1 on RJ45 would corresponds to pin 2 on RJ50, pin 2 on RJ45 would correspond to pin 3 on RJ50, etc.
But that referenced thread does confirm some of the same info that are in this thread:
- pin 14 on db25 = mic (-)
- pin 15 on db25 = mic (+)
- stock mic may have bias voltage on line for pre-amp (but I guess a decoupling capacitor is expected in any BT kit's mic connection, so this should not cause a problem?)
- however, in the referenced thread, pin 3 on the db25 is chassis ground (vs. 8ball's last post)
I wonder what is the wire guage for the wiring from the db25 to the RJ50. Would it pose any safety concern to run +12V on it? Hmm...probably depends on the power draw of any device that draws power from it?
The documents at the link should give the wiring for your car. I was not able to figure out which kit you actually have.
The mic line cannot be decoupled with a capacitor, as I mentioned before, the pre-amplifier at the microphone is powered by the microphone plus wire. The audio signal needs to be AC-connected at the phone control unit.
The wiring is typically 0.32 mm2 which should be enough to power a phone at the cradle anyway.
Okay, several weeks later here's what I know, I know nothing!
In any case I've managed to get the internal mic working but not well. The pins were a little screwy. Pin 14 & 15 on the DB25 are the mic. Pins 2 and 11 do run through to the rj-50. I patched them through and I do get audio out of the mic.
The problem is it sounds like I'm talking about 150 feet away. I'm assuming it's an issue of the pre-amp. I purchased a vellman pre-amp mic kit but frankly I think I screwed up the assembly of the pre-amp because when I plug it in I get nothing but static and buzz.
Any other thoughts on how to get the 'existing?' pre-amp to work?
I went to find an old binder of paper copy schematics. The first point you do not seem to take seriously is the fact that the built-in microphone has a simple FET-amplifier stage that is powered by a phantom voltage at the microphone positive signal wire! The difficult question is the DC-voltage level which easily varies between microphone implementations. This MB microphone seems to use 8V phantom voltage. This is relatively high, equally the mic output is relatively high, in order to avoid interference from the rest of the car wiring.
The first thing I would check is the phantom DC from your Alpine BT kit (what ever it is, you don't seem to give details). If it does not give 8V, which I very much doubt, you would have to build your own phantom voltage supply circuit plus an isolation circuit towards your Alpine kit. If you don't want to do that, just remove the MB microphone and place the Alpine kit mic to that place.
Considering wiring, the link that gave the D25 connector & RJ50 pin assignment, seemed to have an offset of 1 for the RJ50, probably because the person had assumed it was an RJ45 connector with 8 pins only.
If you want to get a clean signal, take care of the shields for each wire harness. Pin 20 on the D25 connector is the shield RJ50 cable. In my Euro kit (this is a DME1-E kit for a W210 for example and for a Nokia 61xx phone, so it may be different on your Motorola kit) the external microphone signal is wired on pin #9 on the RJ50 connector, that is pin 6 on the D25.
Note again that there is no separate pre-amp at the car microphone such that would be driven from an external power feed, you really have to have the correct supply through the mic wire. The impedance of the mic input on the phone kit would need to be approximately correct too but I'm guessing this would not be an issue. Once you get the car mic working, you actually may have a too high input level for your car kit (and you cannot reduce the signal with a resistor divider because it would reduce the power supply voltage too).
Thanks so much for taking the time. I can't tell you how much I appreciate it.
Okay, you were spot on. The alpine unit is only showing 3v.
Suggestions on how to handle the difference. "build your own phantom voltage supply circuit plus an isolation circuit towards your Alpine kit" Could you point me in the right direction to learn how to build one?
Full disclosure - this is my first time trying something like this so my learning curve is steep but I'm game.
"If you want to get a clean signal, take care of the shields for each wire harness." Can you be more explicit? I'm assuming I want to make sure that the sheilds are connected, yes? I see the pin for the rj50 connector sheild - pin 20. I don't see which pin is the sheild for the db25. Again, my apologies I'm a newbie.
Thanks for any help!! This has become one of those little pet projects that while I know I should just move on I'm fascinated and convinced it can work.
Linear Mode
