[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s) - MTCB Hardware Development

Specific to KGL
I've had the KGL variant for a couple of weeks. Since I've had my share of Chinese Android devices of all sorts - I kind of knew what to expect in terms of software.. so I wasn't really disappointed BUT... the hands free in this unit was simply unusable... After getting my wife totally upset and my friends pissed at me for calling them using the unit I knew something had to be done.
So I took it apart.
Being that I'm skilled in electronics and pretty much hands-on, I figured out the problem pretty fast. Or should I say "problems" in plural?
Let me start by saying that if you have the KGL variant and suffer from extreme noise bleeding into the mic - there is no software workaround. You either need to send it back and get something else or open and modify it like I did.
Second - the hardware in this thing is of such low quality, and the design is so bad, it makes me cry. I estimate the production cost of this unit is under $50. Pretty pretty low... even for Chinese stuff.
So.. what's the story with the mic noise, you ask? very simple. The mic signal from the front panel is routed unshielded from a small PCB attached to the panel, via 3 PCBs and 2 ribbon cables, for over 15" until it arrives at the Bluetooth module MIC input. On the way, it picks up so much electrical noise and interference it's almost a miracle that you hear anything but static noise. When an external mic is plugged it, the front panel mic is NOT disconnected. Both are electrically connected in parallel which is unheard of (very bad practice). The Bluetooth module is thus responsible for MIC bias and preamp. The BT module is of unknown source and it's hard to tell what quality to expect there (not much, as we all know). Noise cancellation? echo cancellation? forget it!
Now - we know android needs an audio input - we can have some voice activation on the unit, right? so how is it done? simple! the signal from the BT mic input line is run back to the front panel and into a Wolfson CODEC. Just like that... so that the Android audio in would also suffer from the above issues.
This also explains the exact nature of the unit's BT implementation - the handsfree is not done by the Android - it's completely handled by the BT module. BT module has MIC in, AUDIO out (that goes to the BD37534 audio mixer chip) and RS232 control signals that communicate with the Android BT application for User Interface (probably via AT commands).
When you run an Android app that uses audio input - it comes from the Wolfson CODEC but it's essentialy the same lousy MIC signal that the BT also gets.
BUT!!!
I've made some modifications and lo and behold - I can make a good quality phone conversation now! and the google apps have somewhat better performance too... but it did require me to completely mess up the internal wiring and obviously void the priceless warranty
So after I've figured it out - I decided I needed to do the following:
- Give up the option to work with two mics at the same time and opt for the external mic only for voice calls
- Cut and bypass the original traces since they pick up so much noise
- Add a separate input jack for the external microphone since it was not feasible to cut the lines going into the original one
I started by installing the extra jack on the rear panel. Then I removed a jumper 0ohm resistor at the MIC input to the BT module, disconnecting the MIC input from the circuit. I ran a piece of shielded wire from the new jack to the MIC input signal pin ON the BT board. That completed the hands-free modification.
In order for the Android to have some audio input, I then moved to the front panel, and first installed a 0Ohm jumper that was missing by the WM8731 CODEC. This resistor connects the MIC BIAS pin to the MIC input - it is required when using an electret microphone. I then made a cut in the trace from the front panel microphone to the small PCB connector, and ran a piece of shielded wire from the mic terminals to the WM8731 MIC input.
Now the front mic is only for Android (voice commands etc) and the external mic serves hands free.. I could have probably added some smarter electronics but I don't think it would have added anything to the usage experience.
Let me know if anyone is interested in some pictures I've taken and I will upload.
Crappy piece of equipment but at least now it works.
All the best,
Nir

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Moderation note form dark alex:
these are pictures which belong to dnts' tutorial and research

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harlequin69 said:
Great work and thank you for sharing. I can follow most of what you did there except for adding the jumper to the CODEC due to electret mic use, do you have any pics of this? also why did you choose to use both mics in the end? would it not be better to use the external mic for both BT and android?
Click to expand...
Click to collapse
Regarding external mic for both BT and Android - here is the catch - you need to add a buffer (amplifier circuit) to the mic signal before sending it to two destinations (BT and CODEC) otherwise you will get that awful noise back. The microphones have a high output impedance which makes them prone to electrical noise. Even if you run them using shielded wire to two locations - you will be picking up noise via the ground signal due to the high impedance.
So to keep things simple (for now) I opted for separate mics, with the higher quality one for calls.
As for the required jumper, I attached a pic. The red circle around the empty pads shows where you need to put a short. The green line shows where you would connect the internal mic. Either pad works (they are shorted on the PCB).
Nir

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Specific for KGL
From the top of my head.. sorry for that.. Please use pics in my previous posts.
1. Remove unit. Remove screws holding front panel to the chassis (this varies from one car model to another - mine is KIA Sportage).
2. Carefully lay down front panel. Take notice of the two ribbon cables and don't pull them
3. Remove chassis top cover (2 side screws and one screw on the back).
4. Remove optical drive - 4 screws hold it in place. Carefully disconnect ribbon cable.
5. Install 3.5mm mono jack on the rear panel - 2 holes are available for that (those reserved for DTV antenna). Wire a piece of shielded conductor to the jack, shield going to the part touching the chassis (sleeve) and internal conductor going to the "tip" contact.
6. Locate BT module. It will be at the right side of the chassis (eyeing from front), close to the front end of the PCB.
7. Near the BT module, on the main PCB, locate the component marked "C32". It should be marked "0". Remove it. This is a jumper connecting the BT MIC input to the microphones.
8. Connect the other end of the shielded conductor to the BT module to the pin labeled "MIC+". Do if from the back size of the module. Secure the shielded wire in several places so it doesn't loose up over time.
At this point, the external mic will be the only source for BT audio in. It should (obviously) connected to the new jack we installed.
9. Locate the PCB holding the microphone to the front panel. Locate the PCB trace from the lower microphone terminal (the other terminal is connected to the ground plane of the PCB). make a cut to that trace.
10. Prepare another shielded conductor. connect shied to the mic terminal that is grounded (top one) and the internal conductor to the terminal connected to the trace we just cut. (please see picture titled "front mic").
11. Locate WM8731 CODEC chip. Identify missing "R45" pads (only vacant pads near the WM8731 chip). Make a jumper using some solder and a piece of wire. This calls for delicate soldering.
12. Connect other end of mic conductor to the pad of R42 and R45 further away from WM8731 (please see picture titled "CODEC connection")
13. Put everything back together - start with ribbon for the optical drive, 4 screws for the drive, top cover of chassis and front panel. Make sure, before securing the front panel, that the two ribbon cables are well connected and have not moved or shifted inside their connectors.
14. Cross fingers and connect back to power.
You're done.
Nir

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Relax, don't do it!
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Specific for JY
tomc99 said:
I did find a capacitor linking the BT module on my JY unit, but removing it didn't give me the results I needed, so that's when I moved to cutting the leg on the BT module.
I seem to get some bias at the microphone socket - maybe a little low, from memory around 1.7 volts, but no audio whatsoever.
A little bit of a mystery to me is that after cutting the leg on the module the internal mic is now virtually clear of all buzzing that was evident beforehand.
I may spend a few hours this weekend and set it up on my bench power supply and have a better play with it.
Tom.
Sent from my GT-N5100 using XDA Free mobile app
Click to expand...
Click to collapse
I have a G2110 model( which is a Joyous JY) that suffered with bad buzzing and echoing when using hands free. In stock form testing internal MIC with sound recorder there was no issue. Recording was clear. When I made hand-free call buzzing and reverb sound occurred. I read over and over about the external mic modification and decided to try it. Opened up HU and located C32 which was actually located toward the front center of the unit. I removed it and tested and same issues occurred. I then reconnect C32 as it was apparent that this was not the correct one on this board. I then took advise of previous posts that the cap should be located somewhere near the Bluetooth module so did continuity checks from the + of internal MIC to the caps near the Bluetooth module. I found C102(located seemed to connect to internal MIC on one side and the Bluetooth Mic + on the other. I decided to remove that and test. After removal internal MIC still functioned but hands-free was dead. I am assuming that this was the correct cap that needed to be removed. I did not do anything to the legs of the actual module. I did add an external jack to the backside of the module per the previous posts on how to add external MIC. After I completed the task I tested and the two appear to be separated and the hand-free external seems to function. I still get a little reverb noise but nothing like it was. I am not an electrical guru so I'm not sure if what I did is correct but it seems to have helped somewhat. I took some pics.

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Ok...I need to do this as got that horrible Mike thing going with Bluetooth..
I still need to get my head around the best way to do it..
Best way is going to have to print this thread and work out a plan of attack..
At the moment I have not plugged in the mike at back but been using the front Mike for Bluetooth calls..and of course no one can hear me..
As for Bluetooth coming out to speaks..that all works fine..
Sent from my SM-G900F using Tapatalk

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dgcruzing said:
Ok...I need to do this as got that horrible Mike thing going with Bluetooth..
I still need to get my head around the best way to do it..
Best way is going to have to print this thread and work out a plan of attack..
At the moment I have not plugged in the mike at back but been using the front Mike for Bluetooth calls..and of course no one can hear me..
As for Bluetooth coming out to speaks..that all works fine..
Sent from my SM-G900F using Tapatalk
Click to expand...
Click to collapse
I'm with you pal. This is pretty confusing, especially when you take into account the different models of the head units. I want to improve my mic, but I don't want to mess up and make it worse.
If anyone with a joying unit wants to put together an idiots guide to this mod, I would send a huge thank you your way. [emoji106]
Sent from my iPhone using Tapatalk

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tdopko said:
Specific for JY
I have a G2110 model( which is a Joyous JY) that suffered with bad buzzing and echoing when using hands free. In stock form testing internal MIC with sound recorder there was no issue. Recording was clear. When I made hand-free call buzzing and reverb sound occurred. I read over and over about the external mic modification and decided to try it. Opened up HU and located C32 which was actually located toward the front center of the unit. I removed it and tested and same issues occurred. I then reconnect C32 as it was apparent that this was not the correct one on this board. I then took advise of previous posts that the cap should be located somewhere near the Bluetooth module so did continuity checks from the + of internal MIC to the caps near the Bluetooth module. I found C102(located seemed to connect to internal MIC on one side and the Bluetooth Mic + on the other. I decided to remove that and test. After removal internal MIC still functioned but hands-free was dead. I am assuming that this was the correct cap that needed to be removed. I did not do anything to the legs of the actual module. I did add an external jack to the backside of the module per the previous posts on how to add external MIC. After I completed the task I tested and the two appear to be separated and the hand-free external seems to function. I still get a little reverb noise but nothing like it was. I am not an electrical guru so I'm not sure if what I did is correct but it seems to have helped somewhat. I took some pics.
Click to expand...
Click to collapse
Hi,
I did my soldering too. I found that my microphone is on pin connection infront of BT module and it is connected through c102 jumper. So i cut that microphone and solder it on back of BT module on mic+ and mic-. Problem is that when I call the internal mic is on and external is not working or is off. I am not sure if the external mic was ever on and I did talk thorough internal mic. Can you just tell me what did you solder to what?
Thank you

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dsa8310 said:
I have followed the microphone recipe in post #3964, and here is my experience:
Separation between the Android internal mic and the hands-free external mic is definitely a great solution. With the external mic connected directly to the BT module (and capacitor C32 removed) people tell me that they cannot say that I am using hands-free - the call quality has become that good.
Connecting the internal mic directly to the CODEC chip - not a good idea, unless you have proper tools and you know what you are doing. In fact, Skype and Google Search, both work beautifully with no need for any further change.
Beware, the image in post #3971 , detailing where to connect the mic IS WRONG! The mic should be connected where the strap between the two empty pads is made (in order to have the mic powered with chip's bias voltage). Only the pad at the left end of the green line is OK for mic connection.
I had to redo the soldering, after looking up the chip's pin-out, and this was the end of my empty pads... (overheating with improper tools). With no bias voltage, I could no longer connect the mic directly.
And since I had already cut the mic trace on board, I couldn't reconnect my internal mic, other than using a shielded wire which went outside the unit and into the available external mic socket. Thanks Huifei for your thoughtful design!
And now, my internal mic, even wired through the external mic socket, works perfectly for Android. I got lucky...
So, my advice, stick to the first part of the recipe, it's a must for phone quality hands-free calls, but relax, don't do it - the second part calls for trouble and seems unnecessary, really.
Click to expand...
Click to collapse
Thank you all for the very useful information that you give us every day,
I am owner of a KLD. Specifically a Witson A7047.
I ask you please to be able to summarize in detail the operations to be done in order to make the modification of the microphone.
As I understand, I should find the capacitor C32 and remove it.
I miss, however, the passage for connecting external microphone.
Excuse my trivial question, but understand little of electronics and I have to carry the equipment by the technician. Obviously I will have to explain what to do.
Thanks for the answer

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hello, i'm also using a joying head unit and i have the same problems with my mic. Until now i only used the unit internal mic and the external one is not even connected. Has any of you managed to do any mod (not requiring too much of electronics skills since i dont have any)

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Aender84 said:
hello, i'm also using a joying head unit and i have the same problems with my mic. Until now i only used the unit internal mic and the external one is not even connected. Has any of you managed to do any mod (not requiring too much of electronics skills since i dont have any)
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Click to collapse
The external mic is better than the internal, but it is still not great. It makes a lot of electrical noise on the other end if the phone call. There are some instructions for mic mod here, but I have also read that the joying units are a little different than those details here. I haven't tried it yet, so I can't help any more than that.
Sent from my iPhone using Tapatalk

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But is there any way to still use the car existing mic? My car already had a stock Bluetooth installed so I also heve the mic for it

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Aender84 said:
But is there any way to still use the car existing mic? My car already had a stock Bluetooth installed so I also heve the mic for it
Click to expand...
Click to collapse
Not that I am aware of. It would have to be routed through the Android unit somehow. Otherwise it wouldn't switch automatically when you receive a call. That is if it can even be done at all. I suspect that the Bluetooth module was in the stock radio unit.
Sent from my iPhone using Tapatalk

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I believe is a matter of wiring. The Bluetooth unit was not embedded in the original headunit, so probably there is a way to do it.

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Aender84 said:
I believe is a matter of wiring. The Bluetooth unit was not embedded in the original headunit, so probably there is a way to do it.
Click to expand...
Click to collapse
Are you sure about that? Maybe yours is different than mine. I have the jbl, non-nav unit. I can't access anything to do with the Bluetooth now that I've removed the head unit.
If you're only saying that he can wire the original microphone into the Android unit, that may be possible. It's the same as wiring any external microphone I guess.
Sent from my iPhone using Tapatalk

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I have not possibility to hardware mod.
No software mod can help me?if i buy a bt mic?or bt handfree kit?
Inviato dal mio SM-G920F utilizzando Tapatalk