Make my own bluetooth stereo for my car

[mike1305]

Hey guys! I've mostly been lurking for the last few months, but there is a project idea that's been bouncing around in my head that I just can't shake.

I drive a 2002 Crown Victoria (used cop car, hehe). Unfortunately, the stereo unit is only AM/FM, so currently I'm using an FM adapter to listen to music off my cell phone. Problem is, I haven't been able to find an adapter that isn't clunky as hell. Plus. the headphone jack on my phone is going to shit, so the music quality cuts in and out unless it's in JUST the right angle (drives me insane).

The easy way out is to just install a bluetooth head unit, but
1.) that's boring
2.) I'd like to keep the stock stereo (one less reason for a crackhead to bust into my car)

I'd love to homebrew a way to use bluetooth on my car without purchasing a bluetooth head unit. This would require some way to switch the lines to the speakers - between my stock head unit, and a custom system that connects to my phone.

my FUD on the project:
 - pretty sure the amp is built into the head unit - can I find a bluetooth device with enough power to drive the speakers?
 - There are front and rear speakers (4 total), so I'd need to split the L and R channels to get audio to all the speakers. I don't care about fade/balance not working. But this presumably leads to half the power going to each speaker.

What I'd like to do is purchase a bluetooth audio receiver, install it somewhere under the dash, then tap into the audio wires running out of the stereo. I'd be able to activate bluetooth audio with a switch somewhere, and essentially divert the input to the speakers to my bluetooth receiver. I'd permanently power it with a simple 12V->5V adapter.

Receiver: http://www.newegg.com/Product/Product.aspx?Item=9SIA1KT0T74005

Power adapter: http://www.aliexpress.com/item/DC-Buck-Converter-Step-Down-12V-to-5V-3A-15W-Car-LED-Power-Supply-DC-Step/490202528.html

So why am I here blabbing on to all of you nice people?

One, does anyone have insight to my FUD? Most people aren't dumb enough to do this on their own, so there isn't much guidance out there.

Also, I am having trouble finding a double throw switch that controls multiple inputs/outputs at once. Is this a thing? I can't seem to find the search term to find anything relevant on Google. Basically, one throw that will switch all eight lines at once (+ and - for all four speakers).

Additionally,

Also, does anyone have experience with homebrewed bluetooth stuff? Could this be something that I make myself on one board? The all-in-one device would require bluetooth A2DP, accept 12V power, and have two outputs. Might potentially solve my output drive problem if I can integrate an amp to the design. Might also be able to control the switch itself using a microprocessor or some kind, but I have minimal experience in that area (but always willing to learn).

Sorry that I'm all over the place, I tend to post stream-of-consciousness. Is anyone willing to chip in? Is this a useless project? Do I ask to many questions?

Cheers,

mike

[peter.mitchell]

No way in heck would that module drive your speakers. What you should do is pull apart the headunit and find where the tuner (or even better, the tape deck if it has one) goes into the power amp and connect the output of the bluetooth module there, that way you can use the headunits amp for the speakers.

[cthree]

http://www.rovingnetworks.com/products/RN52

[smashedProton]

If you have an auxiliary input you could hook it up there.  It should be pretty simple.  You can take some of the 12 volt coming in the back to power your module.

[avrnoob]

I myself made several attempts with this.
One of them is published here: http://blog.avrnoob.com/2012/08/diy-car-bluetooth-a2dp.html
This was not so great because this bluetooth module needs about 100mA when receiving and linear regulator was overheating.
Next I tried this thing http://www.aliexpress.com/store/product/Free-Shipping-Wireless-Bluetooth-A2DP-Music-Receiver-For-3-5mm-Speaker-Home-Audio-HiFi-Stereo-System/116779_692228307.html it works ok and has battery, but it does not work when charging.
Next was this module http://www.aliexpress.com/item/Bluetooth-module-krc-86b-v3-audio-speaker-car-amplifier-earphones-diy/792991660.html I added 3.3v switching regulator and it works fine, but sound is a bit overamplified on max volume from the phone, not sure why (it's like too much low freq, clipping). This is maybe because of my diy aux which I've done to the head unit here http://www.flickr.com/photos/29276244@N03/4979869937/# I just took audio lines which goes from cd player to the main chip and now using cd with silence track on loop I get aux in.

[justinjja]

You would need to either take apart the stock head unit and tap into radio output before the amplifier,

Or get a separate amplifier and bypass the stock HU all together,
here is a cheap one: http://www.amazon.com/Audio-R1002-2-Channel-Power-Amplifier/dp/B004S50ZB2/ref=sr_1_3?ie=UTF8&qid=1373007843&sr=8-3&keywords=car+amp

[mike1305]

Thanks so much for all your replies. I'll reply back when I make some progress!

Since it's just an AM/FM stereo, there are no CD/Tape/AUX inputs to steal (or I'd definitely use that). I was pretty sure that I'd need my own amp for this. I know there are a ton of audiophiles out there (of which I am not), so if I go that route of using a separate amp and bypassing the HU altogether, are there any key specs I need to keep an eye on to avoid audio degradation? Doesn't need to be perfect, mind you.

Another thought was to just steal an equivalent stock unit from a junkyard to give me more flexibility. Might go that route if this is more trouble than it's worth.

AVRnoob, thanks for the links to your blog, I'll be investigating this weekend.

Cheers,

Mike

[cthree]

I'm not into car audio stuff but I have installed an amp to boost the output of a weak head unit before and basically you need to convert the stereo 2 channel speaker output into a balanced line level (RCA type) signal (there is a black box audio shops use for this). You then feed that into the amp which does its thing. You reconnect the speakers to the speaker connections of the amp.

I'm sure you can Google around and find schematics, block diagrams and instructions for both the line level converter and a simple 2 channel amp. I'm sure you could build a project which combines all of it and a bluetooth audio module into a single box you hook in series with your speaker wires coming out of the back of pretty much any regular head unit.

You could use the microcontroller in the module or add your own to automatically switch between bluetooth audio and the head unit based whether there is anything playing over bluetooth. The module I referenced outputs for a standard 3.5 mm audio jack so it should be pretty easy to hook up. Adding a 3.5mm auiod jack AUX input would also be trivial so you could hook up an iPod or anything with a headphone output jack.

Let us know how it goes and what info you find out.

[cthree]

Here are some line output converters that car audio shops use http://www.crutchfield.com/S-cNntRzCLSbo/g_721/Line-Output-Converters.html

They are also called high/low converters.