Two channel streaming in the car

2008/12/19 - projects

Some of us can’t afford an iPhone and AT&T’s overpriced and unreliable service plan. I have an alternative. Most networks offer some kind of internet plan, Verizon for example is only an extra $30 per month, no matter what plan type you have. Alltel also offers an all in one package. Here I will discuss an alternative to using Pandora on an iPhone.

The Phone

I am using a Treo 700WX for this example. One of its many features is 2-channel audio output. Stereo jacks are separated into different segments. On most stereo jacks there is a tip, a middle segment, and a ground. On the standard stereo jack the left channel is the tip, and then right channel is the middle segment. On cell phone jacks, it is usually a mini-stereo jack where the tip is left channel, and the middle segment is microphone.

The Treo however supports 2 channel audio; so the jack has 4 segments. The tip is then the right channel, the first segment after that is the left channel, then the microphone, and then ground. So if a 3 segment jack that is not made for the Treo is used, the microphone still uses the right segment.

With the Treo’s unlimited data plan I can stream music from my server using TCPMP. But I still need a way to connect the phone to the car stereo. This task would have been greatly simplified if I had a stereo with an auxiliary input.

The Stereo

The stereo is stock equipment. It has a CD player and a tape deck. Fortunately I had a stereo jack to tape converter lying around. The first modification I made was I removed the mysterious locking device inside the tape converter. There are a series of gears that if turned at a different speed will lock in to place. This was preventing the stereo from using the tape converter properly, and after I removed it, it worked perfectly.

I then unsoldered the 3 mounting points for the standard stereo jack, and soldered on the wire from the ear-buds for my phone. The hard part was actually getting the wire from the phone jack attached to the solder; the wire is very small and is encased is a metallic-looking casing that makes it difficult to tell if it the wire in the middle is actually making contact. I recommend attaching it at an angle from straight above the devices to increase the likelihood of it making contact. Also, using a multi-meter is always a good idea.

The Stream

Video over LAN Media Player (VLC) is very useful when setting up a stream-able connection. It can trans-code any type of audio and output any bit-rate in any format. So, I used an mmsh-asfh stream, which is generally compatible with windows media player. I can load a playlist file and add the --loop option to make the playlist keep repeating. There are many other options, for example making the playlist play in random order. I can then connect to that on my phone using TCPMP.

Finally I have 2-channel stereo audio streaming wherever I go in my car.