Friday, August 10, 2012

DIY Car Bluetooth A2DP

Does not have bluetooth in your car? No problem, let's do it yourself.
I had a spare iPod / iPhone dock Bluetooth A2DP receiver, never used. So I decided to open it up and fit into car 12v plug with aux out.
Here what it looks like when new:

When opened there is one pcb with OVC3860 Bluetooth chip. Actually it sounds better than ISIS chips. That why I decided to use it.
I desoldered 30 pin ipod connector with heat soldering gun.
Backside has some testpoins, maybe useful to easy solder wires for aux and power.
I traced 30 pin connector pads to testpoints and found out that this thing needs 5v power and has left, right, audio ground and 5v in and power ground on testpoints.
I've opened 12 car plug, removed guts and tried to fit this pcb in, no fit =( But with desoldered 30 pin connector there is much unused space on pcb, so I cut it to fir nicely.
Soldered 5v linear regulator and put heatshrink over it later.
Wired power and AUX out to 3.5mm female socket with screw mount and it is done.
Forget to take picture of it when closed, but there is nothing special, just plug hole visible. Sounds nice, but becomes hot almost instantly. This thing eats 100mA when receiving sound and 60mA when idle. So linear regulator works on the edge, it is rated for 100mA. But chip itself gets hot too, not sure why. Anyway I connect car AUX to this plug and have Bluetooth now.

9 comments:

  1. I did this same thing with a very similar unit, but I found the audio output to be terribly noisy, which was disappointing.

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    Replies
    1. Yea I had one with CSR cbluetooth chip and it was low volume and noisy. But with this one with OVC3860 chip it sounds nice. And if you don't have audio isolation transformers on your aux line noise can come from power lines.

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  2. Hi there,

    I'm considering using this thing: http://www.elecfreaks.com/store/audio-bluetooth-speaker-moduleovc3860-p-436.html
    in a DIY bluetooth car powered module and it is also OVC3860 based as well.

    I was just wondering if your unit has pop/crackle suppression built into the circuit as I hear this is a common issue among lower cost bluetooth units.

    Also is the general frequency response and sound clarity pretty good? I tried out a bluetooth unit from Griffin Tech previously and the sound was pretty fuzzy and there was also no bass whatsoever.

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    1. It does not pop when I turn it on/off, but maybe it's because I use audio transformers on aux line. Response is good to me =) Your Griffin possibly was made with ISIS chip, which is much worse =)

      I thought about that module yeara ago, but cost was an issue. Now there is more devices available like this box, but with battery inside and 3mm jack line out, even easier to hack.

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    2. I've done essentially the same thing, only I pull the board out of charger and epoxy it to the BT receiver's housing. Tuck it up behind the dash and wire into Acc (not hot when key is off). I agree that the OVC sounds better than ISIS or the BT v1-2 CSR's, but the CSR8600 BT v4 sets an entirely new standard, I honestly cannot discern a difference vs wired (lossless on Android).

      I got one called wavejamr (there may be others that use the 8600 now) and it's solid, been using for about 5 months now. I also use their USB auto charger to power it, the PCB is small, and it uses a breaker instead of a fuse (key off for 10 secs to reset). Both always cool to the touch, and the wavejamr has a 3.5mm line out jack (likely the one Anton mentioned) so very easy to connect, and disconnect, should you ever need to.

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    3. On paper, Isn't the OVC3860 only supporting SBC codec? Wouldn't the CBR BC5 which also support AAC and MP3 sound better because of the lack of transcoding (if the transmitter support such passthrough codecs). Or is it because of a bad reference design? I think the CSR8600 also support apt-X that's why it may sound compared to the low complexity SBC codec.

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    4. My complain is more related to the interference noise than actual decoding quality, and this can be because of bad design.
      Also I think you have to pay royaltes to use mp3/apt-x/aac decoder in your product, so I guess that generic modules does not have these codecs enabled.

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  3. Did you check to see if it is possible to connect some push-buttons to this board in order to have Play/Pause/Rev/FWD ability?

    Since i also want something to integrate into the car but would like to have such buttons for controls.

    I bought this http://www.aliexpress.com/item/Free-Shipping-1pc-BC8645-4-0-low-power-Bluetooth-audio-speaker-module-support-APTx-high-quality/1503241412.html
    but it has some sort of noise (not even connected to the car yet, was testing it with normal power) also there is an audio feedback when you turn it on and off and seek back or forward but it is in Chinese i think, and also annoying to hear the sound after each push of a button!

    And i was hoping that i will be able to reprogram it but CSR doesn't provide the tools for free ($3K or more for the dev kit)

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    Replies
    1. Hi. With this particular receiver you can send AVRCP commands like play/pause with microcontroller (emulating apple 30pin serial interface), but it's not easy way.
      With another receiver module (take a look my another post http://blog.avrnoob.com/2013/11/lets-make-wireless-speaker.html ) you can add play/pause/next/prev buttons easy by connecting several wires with buttons. And it does not have any sound when connecting. Also I will soon review a new version of that module which has the same design but with BT 4.0 also built on CSR chip.
      I recently made a cool hack with cheap bt serial modules built on csr chips, and yea, their software devkit is not easy to get and it's a pain.

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