Cheap In-car Bluetooth Hands-free Kit With Music Streaming (A2DP)

Optional bluetooth car kits can cost lots of $$$ at your dealers but there's a much cheaper way to have wireless hands-free kit in your vehicle that will also play music from your phone on your cars stereo system. This device supports A2DP so you can use it with Google Maps navigation, YouTube, VLC - in fact any game or software of your choice.

This project took some time and some of the steps are optional. I've done those steps because I wanted to preserve OEM look in my car.

What you need:

• Car with audio system that supports stereo aux-in
• Bluetooth A2DP receiver with HFP (hands-free profile) support and built-in microphone
• 3,5mm 3-pin cable, 5 meters
• 12V-to-5V car phone charger

Also I have to give some credit to aka.guf for his tutorial: https://www.instructables.com/id/Adding-Bluetooth-support-to-your-car/

For the Epilog VII contest judges: I would love the laser cutter to make my own mount and adapters. Often I find myself in need for such device when trying to install 3rd-party multimedia devices in cars.

Step 1: Bluetooth Receiver Modification

I decided to fully hide my hands-free system. And that meant that I needed to prepare the device for external controls.

Things done:

1. Disassembled the whole thing.
2. Removed the weight plate from the base.
3. Extended the microphone wire.
4. Added middle button external control wire (other two buttons are volume and track control which are not necessary to have. You can control that from your phone if needed).
5. Extended the blue LED (status indicator) with a 30cm wire.
6. Removed battery and replaced with a 1000μF capacitor. Battery can power the device for several hours and I wanted the device to switch off when I leave the car. Capacitor was necessary for the device to not switch off while using because of the "low battery voltage" trigger.

Step 2: Control

I wanted to keep the OEM look and feel inside my car so I've used empty button in my dome light to control the device.

Bluetooth receiver have 3 buttons, but the middle one is the most important since it controls device power, play/pause, answer/end call. Other two are just volume and next/previous track.

I've made an instructable before about using that button in 2007 Volvo C30, so if you would like to check it, here it is: https://www.instructables.com/id/How-to-activate-em... This step i specific to my car, but I believe that all cars have some empty buttons that you can easily activate and use with 3rd-party devices.

Step 3: Status Indicator

This step is optional and for me that was the hardest thing to do.

Since my car does not have passenger airbag off switch (no ISO-FIX in front seat) I could take the lower part of the dome light indicator (passenger airbag off) and reuse it as bluetooth status indicator.

1. To do so I removed the dome light and pretty much disassembled it to the last part. Some elements are mounted in plastic so I had to melt it to take it apart.
2. I reached the seat belts / air bag indicator and used nitro solvent to remove the paint from it.
3. I designed new graphics using similar font and icon but in my case lower part was "A2DP AUDIO" with a bluetooth icon. Check the EPS project file attached.
4. Took everything to printing company and made a brand new custom indicator.
5. I've placed blue LED behind the indicator. The diode was modified with a nail file to better diffuse the light.
6. Then assembled everything back using hot glue where needed.

Step 4: Audio and Power Lines

Both lines go under the glove compartment, inside the A-pillar and above the windshield. Again - this step is specific to my car but in all cars there's always a way to wire everything nice and clean. Remove dashboard trim and door seals, disassemble few parts (like center console and glove compartment) and you'll find a way.

Audio line is connected to the AUX port. If you car stereo doesn't have audio-in connection you can use Fm transmitter.

Power line is connected to the 12V power socket using an 12V splitter that I made earlier. Thanks to that all wires are hidden under the trim and the 12V socket is empty. Also this power outlet is ignition-hot so when i turn off the engine my bluetooth receiver will shutdown.

Step 5: How to Use It

Only one button control.

Press and hold - turn it on or off.
Single press - play or pause; on incoming call to answer; while calling to end the call.
Double press - redial last number.

LED fading in and out - connected to device
LED flashing quickly - pairing mode
LED flashing slowly - connection lost, searching for the device