Adding Bluetooth Support to Your Car

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 !

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.

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.

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.

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 !

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.

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 !