When I upgraded the stereo of my 2013 Toyota Sienna (although I don't own the car anymore), I found that most of aftermarket receivers are not compatible with the stock hands-free microphone. So, it is usually recommended to give up the stock microphone and install a new one. However, I really wished to re-use the stock microphone and did some research myself. Actually, doing the research, I found that I was not the first who thought about re-using the OEM Mic for the aftermarket receiver. However, to my surprise, none of the precedents seemed to get successful outcomes.
The issue I identified was that, the OEM Mic system uses balanced output, which is generated by an integrated amplifier within the Mic module. On the other hand, the aftermarket Mic system uses unbalanced input. Also, since the aftermarket receiver uses a capacitor Mic, there is phantom power supply to the Mic.
The wiring diagram of Toyota stereo is shown below. We can see the two balanced output terminals MCO+ and MCO- from the Mic module.
|
Pin |
Description |
Test condition |
Test value |
|
MACC |
Microphone power supply |
Ignition switch off |
Below 1V |
|
Ignition switch ACC |
4 to 6V |
||
|
SNS2 (SGND) |
Microphone connection detection |
Always |
Below 1V |
|
MIN+ |
Microphone voice signal |
- |
- |
|
MIN- |
Microphone voice signal |
- |
- |
Another issue I noticed was that the Mic module requires 5V supply, not 12V.
Okay, so to summarize, I needed the following functionalities:
- DC 5V supply
- Balanced to unbalanced conversion
- Phantom power blocking
Parts:
- 1:1 audio transformer
- Note: the transform ratio may need to be adjusted depending on the receivers. In my case, 1:1 transformer turned out working fine. However, for some receivers, it may saturate the AGC amp of the receiver, and distort the sound. Alternatively, a potentiometer can be connected in parallel at the output stage (Mic jack) for volume control.
- LM7805
- Note: if the receiver has a USB port, the 5V supply could be tapped out from the USB port (I haven't tried this though).
- 50uF x 1
- 10uF x 1
- 1uF x 1
- 50k potentiometer x 1
Hi, I only used the LM7805 and my MIC in Tacoma 2014 works! If I add the transformer and capacitors it will sound better? What do the capacitors do on the LM7805 legs? thank you for your diagram!
답글삭제It's great to hear the diagram worked! The transform on the upper part of the diagram is to match signal level between the factory Mic unit and aftermarket head unit. I worried that some aftermarket head unit without protection circuit would be damaged by the high voltage level of the Mic signal from the factory Mic unit, so I added the transformer. The capacity (50 uF) in the upper part is to block DC bias voltage from the aftermarket head unit - some head unit using condenser-type microphone outputs bias voltage from the Mic port, which could damage the factory Mic unit. The capacitors on the LM7805 legs are for noise suppression. The capacitors make the output voltage of 7805 more stable, blocking noise from other electronics of the car.
삭제Thanks for posting this! I used the upper half (plus a standard "buck" voltage converter instead of the bare 7805) to connect the OEM mic in my 2010 Prius to my new head unit. Adding the capacitor to block the DC bias voltage makes a huge difference.
삭제Thanks for the comment. Definitely, buck converter is better than 7805 in terms of the power efficiency. However, I purposely used 7805. Some cheap switched mode power supplies have relatively low switching frequency of around 10 kHz, which is in the audible range. So, they may generate a tone noise mixed with the voice captured at the microphone.
삭제Great to find these instructions! What type of capacitor did you use for the 50 uF? Does polarity matter for this one?
답글삭제Yes, the polarity matters - you can check the polarity of the DC bias voltage at your mic jack using a tester. If you don't want to bother with the polarity issue, you can also use a non-polarized capacitors. In my case, I used an electrolytic capacitor with polarity.
삭제Thanks! I measured the DC bias voltage so that should be fine.
삭제Audio electronics is new to me and I'm unsure about the wiring of the NTE-1 transformer. In your diagram you use a center tap? Did you solder an extra wire? I have the datasheet of the NTE-1 but can't figure it out... Could you add which wire color goes to which connection?
https://asset.conrad.com/media10/add/160267/c1/-/en/000515940DS01/datablad-515940-neutrik-nte1-audiotransformator-impedantie-200-primaire-spanning-12-v-inhoud-1-stuks.pdf
I used a transformer without a center tap, but in case you are using one with center tap, you can leave it unused. For the wire color coding, the signal from the microphone unit goes to the primary side (yellow and white wires - polarity doesn't matter) and the microphone jack is connected to the secondary side (red and black).
삭제Used it with a Pioneer head unit in a 2013 Toyota Auris and works great! Thanks again.
삭제I do seem to hear some more noise/hiss when someone calls me from the car. Any idea what might be causing this?
There are several suspects for the noise. If you hear the noise all the time, it could be the noise from the power source. For example, if you use a cheap buck converter (instead of linear converter like lm7805), the output voltage could be unstable, which appears as noise. You can fix this by using a more stable power source.
삭제On the other hand, if you hear noise only when someone calling you from the car is talking, it could be an input voltage saturation issue. If so, this can be fixed by adjusting the transformer ratio (e.g., 4:1 rather than 1:1), or adjusting the 50k potentiometer.
I used a L7805 but the noise seems to be constant. Could it be the type of condensators I used? I used electrolytic ones (Panasonic) on the feet of the L7805.
삭제I used a L7805 but the noise seems to be constant (although it's not very bad). Could it be the type of capacitors I used? I used electrolytic capacitors (Panasonic) on the feet of the L7805.
삭제It doesn't sound likely as long as the capacitor is not broken. Maybe you can try connecting the output port of the transformer (the second from the top in the diagram) to GND.
삭제would you be interested in selling these, I would be interested in buying one
답글삭제Thanks for your interest. Unfortunately, I don't own a Toyota car any more, so even though I could make one for sale, there is no way for me to test it. Also, as I noted, I only tested it for 2013 Sienna - it seems that the same circuit works for other Toyota cars based on the feedbacks, but I cannot guarantee it 100 percent.
삭제작성자가 댓글을 삭제했습니다.
답글삭제Thank you so much for these instructions!
답글삭제Finally found the time to attempt this on my 2014 Toyota Land Cruiser Prado with a Kenwood DDX920WDABS to replace the terrible microphone that came with the head unit and it worked like a charm – using the OEM microphone sounds so much better.
I didn't use the LM7805 but instead wired up a USB cable and plugged it into a spare USB port on the head unit, and used a 30k Ohm resistor in place of the potentiometer to prevent saturating the amp on the head unit and distorting the audio.
Do you know if a 600 ohm 1:1 transformer would work I searched for the make and model that you used but appart that is difficult to get is somehow expensive. I found some cheap ones on Aliexpress but wondering if they are going to work
답글삭제I guess it would work, as long as it is designed for audio use. But I cannot guarantee it before trying.
삭제