Sunday, May 2, 2010

Bluetooth for the car

When I bought my car, I had them install the iPod integration (it was a dealer-installed option). Well, it turns out that the stupid thing emulates a CD changer, so you get no track names, you only get forward-back control, it can only deal with 6 playlists... It was substandard in every way imaginable.

Meanwhile, I was pretty happy with XM anyway. But XM is really expensive, and it's been annoying in various ways lately, so it's time for a change.

Well, I've discovered Pandora. The Pandora app works far, far better than the XM streaming app (which they charge $3 extra per month for), and has the advantage that if you don't like the song playing you can thumb it down and move to the next one immediately.

So, XM is fired.

Now, how to get Pandora everywhere I want...

Well, for the alarm clock, it's pretty easy. Just use osascript to launch the URL of the channel displayed on the channel's page. But it is a little silly using a laptop as an alarm clock. But it turns out that the Chumby supports Pandora, and it's an alarm clock. Done.

Next, the car. Well, I took my car to the local car stereo place and got them to change out the iPod integration gizmo for one that has a aux input jack. It turns out that the new gizmo also emulates a CD changer, so it's really not any better than it used to be, but with the aux input, and a Bluetooth A2DP receiver, it doesn't really matter.

For this application, the best A2DP receiver is actually the Belkin Bluetooth Music Receiver. It's a good choice because it doesn't require any button pushes to turn on. As long as it is powered from the accessory bus of the car, there's nothing to do to get it working other than tell the phone to connect to it. Finally, this device supports A2DP only - it doesn't support the handsfree or headset profile, so in principle, you can still use a headset to take any phone calls that come in while still listening to music through the car.

The only problem now is that the Belkin device is designed for home audio. So it comes with a AC power supply. Even if it had a car cord available, plugging that into the power port in the dash would be ugly. I had the car stereo folks wire in a set of Anderson PowerPole connectors in the glove box where the new Aux input plug was. So now, I just needed to go from 12 volts to 5 with the tiny coaxial power connector that mates with the jack on the device.

Radio Shack actually came through for me. The had the correct connector set up to mate with a universal power supply jack, and the related universal power supply jack on the end of a pigtail, ready to be wired to your own power supply! They also had an LM7805 5 volt regulator, and I also bought a small electrolytic capacitor to put on the input to smooth the power.

To house the whole thing, I bought a small tin of Altoids, cut a couple of slots in each end for the power input and output wires (using some electrical tape as a makeshift grommet), and a hole in the bottom to screw down the regulator (making the whole tin into a heatsink). I soldered all of the leads together and closed the tin on the wires (with knots tied in them as a strain relief) and taped it shut with electrical tape. After verifying that it worked on the bench, I installed it in the glove box. With everything hooked up, turning the volume on the stereo almost all the way up results in a little bit of alternator whine and some other distortion, but playing music at that volume would be way, way too loud. At normal volume levels, you can't hear anything bad.

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