Adding Bluetooth Support to Your Car




Introduction: Adding Bluetooth Support to Your Car

About: I'm an Electronic Engineer now looking for a new challenge. I've been working with Mecalexo Inc. for the past few years at designing interactive booths for science museum. Almost every project I tackled re...

I just bought a used Toyota Matrix 2011 and it has an AUX port to plug your phone or MP3 player so it plays on the car radio. It's a great feature and I've been using it but the audio wire is annoying and is always in the way. I have decided to add a Bluetooth audio receiver to the car while making sure the AUX port is still available if needed.

Bear with me since this is my first instructable :)

If you think it is worthy, vote for me !

Step 1: Equipment Needed

  1. Step-down DC-DC converter (Fixed 5V output). I bought mine from Banggood for 2.27$ shipping included, #SKU151702.
  2. A2DP Bluetooth receiver with 1/8" analog audio output. I bought mine from Banggood for 8.83$ shipping included, #SKU151813. Note that the input shown on the product's photos is the power input. [EDIT]The module I used in the first place included an internal battery and was not booting correctly all the time. I switched to a USB-powered dongle without internal battery instead and now it works like a charm. You can get those USB-powered A2DP with 1/8" audio output on eBay for around 4$ including shipping. Typically the rectangular black device like shown in the photos is NOT what you want, I tried them and they do not work. Get a dongle that looks like a USB thumb drive with a 3.5mm (1/8") audio output.
  3. 2 position rectangular connector kit. This is going to be used to connect the car +12V to the module once completed. It will ease removal when servicing is required. Molex, Amp, TE are good suppliers of those. I bought mine from a local electronic shop in Montreal (Addison). You could also use a barrel type power connector but since it is not latched, I was afraid it would come loose with the vibrations.
  4. 2 x wire-taps. These connectors are used to "suck" power from a 12V line. The wire in place stays the same, it is just spliced. Google "wire tap connector". Make sure you buy a model that will fit your wire size and that will not require you to cut the wire in place. Got mine from Addison.
  5. Some wire scraps, ideally the same size as the car wiring.
  6. Some heatshrink tubing.
  7. A female 1/8" audio cable. I used a cable that I cut to get the part I needed. I prefer going this route since the head is sealed and strong.
  8. 2 x 1k resistors. I used 909 ohms I had lying around but 1k is more common.
  9. Soldering iron and solder.
  10. Heat gun for the heat shrink tubing.
  11. Multimeter.
  12. A male to male 1/8" audio cable for pin placement investigation.
  13. Tie-wraps to secure everything in place.
  14. You might need double-sided tape to secure some parts. I didn't.

Step 2: Car Wiring - Getting +12V From Cigarette Lighter

Take the keys off the ignition. Remove the plastic panels to get access to your AUX input and the cigarette lighter. In the Matrix, it is just a matter of pulling on the panels, really easy, they pull right off. It might not be as easy with another car. Been there...

Unplug all the wiring while making sure you'll remember where each goes. Use the 2 wire-taps to "extract" 12V from the cigarette lighter wiring. Bring this 12V to one side of the rectangular connector. Make sure the wires going from your taps to the rectangular connector are long enough to allow you to easily remove/replace the plastic panels. I do not have photos of this step.

Step 3: Getting Access to the AUX Connector

In the Matrix, the AUX connector is located inside a small black enclosure. You will have to open this to get to the 1/8" jack. Insert a 1/8" male plug into the jack and, using a multimeter, find the location of tip, ring and sleeve on the connector (see last photo for the Matrix, I've done it for you). In my car, there are 5 pins used: the usual 3 for the audio and 2 acting as a switch. When a plug is inserted, the switch is closed. This is used by the radio to determine if a device is plugged in since AUX and CD share the same input button. To make sure I would never have problems with the selection of the AUX input on the radio, I deliberately shorted the switch on the solder side. The radio then always lets me select between CD or AUX (selection toggles when input button is pressed) whereas it would skip AUX if nothing was plugged in before the mod. This will allow me to use the Bluetooth module even if the AUX port is unoccupied. Otherwise, the radio would not let me select the AUX port.

Step 4: Solder the Resistors and Bring Out Another Audio in Port

Strip the insulation off the female 1/8" jack cable. This jack is where the Bluetooth audio signal will be coming from. Lets call it the "Bluetooth jack". I stripped mine quite a bit because of the way I wanted to use the pins on the rear white connector to serve as a mecanical stress relief. Solder one side of the 1k resistor on the AUX audio jack where the tip is coming in (the location where you found the tip in the previous step). I soldered the resistor on the white connector pins instead of the AUX audio jack ones because I had to bring the cable from the top. I did not have access to the solder side of the PCB because of mechanical constraints. Solder the other side of the resistor to your Bluetooth jack tip wire. Repeat for the ring. Solder both sleeves directly together (this is a common) without the use of resistors.

So, what happens here ? An audio signal is going to be coming from the Bluetooth jack. It will connect to the existing tip and ring through 1k resistors. When nothing is plugged in the AUX jack, the signal coming from the Bluetooth module will pass unobstructed to the radio. However, when an MP3 player is plugged in the AUX jack, more than 99% of the signal received at the radio is going to be attributed to the MP3 player and less than 1% to the Bluetooth receiver. If the Bluetooth receiver is not used at that time (which is almost always the case), it will output 0V anyway. From my experience, even when both devices are competing, the Bluetooth receiver is indiscernible. So, when nothing is plugged in the AUX port, you hear the Bluetooth receiver. When something is plugged in the AUX port, you hear what you just plugged in. This makes sense !

Step 5: Power the Bluetooth Receiver

In the package received with the Bluetooth receiver, there was a USB to barrel connector cable. This is the cable I'm using to charge and power the receiver. Cut the USB head off of the cable and strip it. Cut both ends off of the DC-DC converter and strip the ends. Solder the cable that came with the receiver to the output of the DC-DC receiver such that the DC-DC is powering the receiver. Use some heat shrink tubing on the wires to make a clean and safe job.

[UPDATE] If you went with the Bluetooth receiver without an internal battery, you will have to solder the output of the DC-DC to the power pins of the USB connector on the Bluetooth receiver.

Install the other side of the rectangular connector on the input side of the DC-DC converter. 12V from the car is going to be coming in from this connector.

Step 6: Putting It All Together

Connect the audio output of the Bluetooth receiver to the newly soldered audio input. Connect the output of the DC-DC converter cable to the Bluetooth receiver. Using tie-wraps, make sure all components are secured. This is an important step if you don't want your add-on to rattle while on the road...

Go back to your car and connect the rectangular connectors together. Switch the receiver ON. Put the plastic covers back on and test your new addition.

Some thoughts:

  • The receiver is always ON even when the car is not running. Although the standby time is spec'ed at 230 hours, I am curious on how it will handle the deep discharge. I tried removing the battery inside the receiver but I had trouble getting it to work properly. I think I was getting an error code on the LEDs telling me that battery was dead/absent/etc.
  • I wonder if this will work in the -40C we sometimes get in Canada... The Bluetooth chip is probably rated down to 0C.

[UPDATE 1]: It looks like the device is not powering properly each and every time when the battery has been completely depleted. It is probably the same problem I was seeing when I removed the battery. I am contemplating using another module. A member used the PT-810 module and didn't mention having any boot up problems. However, he said audio was not really good. Any suggestions are welcomed.

[UPDATE 2]: I have changed the A2DP module for a device that is USB-Powered and doesn't have an internal battery. It works a lot better with such a module. See step 1 for more information.

I wanted to add a video to my first instructable but my camera is my phone and I wanted to film it... Not an easy task...

Please tell me how this went for you !



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52 Discussions

This is especially useful if you own a vehicle where the stereo is heavily integrated into the car electronics, which makes swapping head units impractical. If the car doesn't come with an input jack, you can always crack the H/U and connect to the main board.

5 replies

i would love to see how to crack the HU and connect to the main board, right now my only option is to use a cassette tape adapter, since I don't have an input jack

You'd need electronics knowledge and access to an oscilloscope to determine where to tap in. Essentially you would have to locate where the signal feeds into the amplifier's pre-amp and cut the traces. Some wire and an appropriately sized relay and you have added an extra input. It wouldn't surprise me if there are companies that will do it for a fee.

I have read that tapping into the Sirius XM connector can work as well

You are correct that if there is an unused input on the back of the unit, such as for an optional external satellite radio tuner, that would make far more sense than opening up the H/U. You might have to determine how to tell the H/U that there is a source connected to that input.

You are correct that if there is an unused input on the back of the unit, such as for an optional external satellite radio tuner, that would make far more sense than opening up the H/U. You might have to determine how to tell the H/U that there is a source connected to that input.


2 years ago

Looking for help with my Matrix Bluetooth problem. I actually upgraded my stereo from the base model to the premium model with built in Bluetooth (86120-02C50) and I can't for the life of me get it to pair with my phone. I follow the voice prompt directions, and when the computer asks me to press the talk button and give a name for the device, it says it is listening, but can't hear me when I speak. My car appears to have the factory microphone in the courtesy light housing. This step seems unnecessary, why do I have to give a name for the device when I should just be able to scan for it. t won't let me past this point without vocally assigning a name to the phone. HELP!!!

As an alternative, you can just use one of these for $20. It plug right into you aux port. no work required. Lasts 8 hours, or leave it plugged in with an inverter. Supports calling.

Search amazon for:

Mpow Portable Bluetooth 3.0 Audio Music Streaming Receiver Adapter w/ Hands Free Calling and 3.5 Mm Stereo Output

4 replies

Actually, this is a better device by the same manufacturer. I have it and it works very well. The music sound quality is perfect. The handsfree calling sounds really good to the person on the other end with the mic mounted on the dash. It would be a MUCH better starting point for this project.


I got something really similar from Belkin. You can judge the sound quality here:

Yes, good find! This would be much better. Not only is it 12V right to the device, but it supports BT4.0 which includes the AtpX protocol. AtpX is much better then A2PT that was added in BT2.0. It is more battery efficient, sound quality is far superior, plus includes more features. However, only newer devices (phones and such) support it. I know my Samsung S4 does, but older S3's don't. I have BT4.0 headphones and they sound fantastic. I also get almost 2 day of continuous listening at work.

That's nice, but that's not integrated into the unit and it obscures the aux port. It could damage the port and/or it's own plug if it gets bumped into a lot. From the looks of it, his setup would probably allow him to disable the connection on the device end and then let someone plug their device in via the aux port. Much easier switching back and forth if you have a friend or family member and their device doesn't have bluetooth audio support.

So I have a dumb general question. I have a ton of resistors laying around that are 3K or 6K resistors. Would those work in place of the 1K resistors that are commonly used in these projects?

4 replies

There are no dumb questions here, don't worry. Yes, you can use 3K resistors instead of the recommanded 1K, it will work fine. The only drawback is that you will have to crank the volume a bit more on the radio. Look at the schematic I drew on step 4 (last image). You can apply Kirchhoff's law with your 3k resistor and see the resulting effect. The bigger the resistor, the bigger the voltage drop across it and the smaller resulting voltage at the radio. Have fun and thanks for posting !

i know its a bit late but you could use three 3k resistors in parallel to get 1k Ohm

Nice instructable. I really like this. I was considering voting for you but, the problems you've encountered with the battery in the module need to be addressed. Anyway, I will keep following this.


How do you like your matrix, I have a 06 (1st gen) And I am thinking about upgrading(to the 2nd gen).

1 reply

So far so good. Previous car was a Mazda 3 2005 and it was all rusty. Toyotas have a much better track record on this issue, I shouldn't be dissapointed.