Project justification: (You can skip to step one if you don't want to know why I am making this project.). I listen to podcasts while commuting to and from work. I store my podcasts on my iPhone (work phone--don't judge!). I drive a 2009 Toyota Corolla and love the fact that it has an AUX jack (it's the first car I have ever owned that had one). So, to make it work for me I had a way too long 1/8" patch cord to connect the iPhone to the AUX jack. Then I saw ASCAS'DIY Bluetooth Speaker Instructable and knew what I had to do. This is the story of what I did.

One feature I knew I really wanted was the ability to not only use Bluetooth audio from a capable device, but also to allow the use of the AUX jack when needed. I really wanted the Bluetooth audio to be disconnected when something was plugged into the 3.5mm AUX jack.

Step 1: Collect Materials

Here are the materials I used:
- USB V2.0 Bluetooth Audio Music Receiver Adapter 3.5mm Stereo for Speaker Phone... ($7.51 shipped) from Newegg
- Reused 12v car phone charger.
- Stereo, 3.5mm, through-connected headphone jack.
- Wires from laying around

Here are the tools I used:
- Screwdrivers
- Pliers
- Soldering iron, solder, etc.
- Wire cutters

Step 2: Prepare the Materials

First, I disassembled the Bluetooth receiver to see what I was working with. The cover was simply pressed together. A small, flat-head screwdriver made opening it quite easy. I initially did not intend on reusing the cover so I was not too careful. I ended up reusing the case anyway but found the damage to be minimal and insignificant.

Removing the cover from the old car charger required a little more force. It was glued at the seam but came apart relatively easily.

find location in car to place newly assembled device, determine power source and where to connect the audio output from receiver.

Step 3: Build the Device

Pulled the AUX jack module out of the car (a 2009 Toyota Corolla). Opened the module up and figured out what was what using the continuity feature on my multimeter. On my module, there are two pins that get shorted together when a plug is plugged into the AUX jack. If these pins are not shorted, the AUX input cannot be selected. So, I simply soldered in a piece of wire, permanently connecting those pins.

Was originally going to put all components into an enclosure and connect the audio lines and power to that module. Once I started trying to figure out how everything was going to go together, I opted to just reuse the receiver's case and heat-shrink other components. This allowed me to put a disconnect between the Bluetooth receiver and the power module. This disconnect was the USB connection that was already on the Bluetooth receiver module.

Connected pieces of wire to the new jack. Had to make sure that I knew which pin went where and used different colored wires to keep them straight. I wrote them down. I recommend drawings and notes whenever there are more than two wires.

Cut the jack end of an old USB extension cable and soldered the red and black wires to the + and -, respectively, outputs.

Now we are ready for the insert and test.

Step 4: Test Final Project.

Time to put it all together...I lucked out big time. There was an unused jack behind the panel where the AUX jack is. And it had 12v on one of the pins! I just pressed the tinned red and black wires into the + and - slots on the connector and saw the power indicator on the charger illuminate. I found that a four pin header would fit quite nicely into the jack connection so after soldering the wires to the pins, everything just fit together.

The AUX jack module fits into the opening in the dash from the front. So, I had to feed the Bluetooth receiver into the opening first and then snap the AUX jack module into place. I could easily access the Bluetooth receiver and positioned it so that it could receive the power connection.

Next was the test. Apply power. Hear the Bluetooth linking sound on the car stereo (with the AUX input selected) the play a podcast. It worked! Took a 3.5mm patch cord and plugged it into the AUX jack and the Bluetooth audio was cut off. Plugged the other end of the patch cord into my phone and the podcast was back! Time to tidy things up.

I used some small wire ties to secure the power connection. Covered up the bear metal parts with some electrical tape. Put the rest of the dash together and finished listening to the podcast.

The real test will be over the next several days and few weeks to make sure everything is road worthy.