Airplay in the Car

Bluetooth is a popular method to wirelessly play music from a phone through a car stereo system. But it's not the only option. You can also use Apple's Airplay. This can be done using an Airport Express. Of course, you could buy a power converter to plug into your car's 12V jack, but what fun is that when you could modify the Airport Express to run off of USB?

*I'm sure Bluetooth is both an easier and cheaper solution, but I've seen this done and wanted to try it out myself.

Materials

1. Airport Express. I bought mine second hand on eBay because I didn't feel like spending $100 on something I was going to hack up
2. 5V to 3.3V Voltage Regulator. Also bought on eBay
3. USB Cable. I'm sure you've got a few of these sitting around
4. Short lengths of wire. I cut a couple inches off the USB cable to use
5. Solder
6. Heat shrink tubing
7. Sugru
8. USB Car Charger. A USB wall charger also comes in handy for testing so you don't have to keep running out to the car but is not required

Tools

1. Computer to set up the Airport Express
2. Knife/Screwdriver to pop off the Airport bottom cover
3. Wire cutters/strippers
4. Soldering Iron
5. T6 and T8 Torx screw drivers
6. Heat gun

Note: this step can be performed after modifying the Airport Express.

Plug the Airport Express and hook up to your computer via Ethernet cable. Open AirPort Utility (standard on Mac, can be downloaded for Windows). Follow the instructions to create a wireless network.

On the Internet tab, under TCP/IP, choose Configure IPv4: Using DHCP. Then under DHCP, the beginning address should be 10.0.1.2 and ending address 10.0.1.200.

On the Music tab, check the "Enable Airplay" box. You can create a password for the airplay system, but this is unnecessary if you created a password for the network.

On the Advanced tab, under IPv6, choose "Link-local only" for the IPv6 mode.

If you want to hide the network SSID so that people nearby can't see it, on the AirPort tab under Wireless, there is a "Wireless Network Options..." button that will give you the option to "Create a closed network". I didn't feel that it was necessary since the network is password protected and there isn't an internet connection.

In order for your phone to connect to the Airplay network AND the internet via your phone carrier, you'll need to change a setting on the phone. If you have an iPhone, connect to the new wireless network and go into the settings for that network. Choose "Static" under the IP address.

Note: When you set up your phone this way, the carrier connection (LTE, 4G, 3G, etc) will display in the status bar even when connected to the Airport Express wifi network. You can tell you are connected to the wifi network in the Settings app.

Note: it should go without saying that the unit should be unplugged before continuing.

The Airport Express takes 120V and steps it down to 3.3V via an internal power supply. We'll need to take that out before we continue. Pry off the bottom cover of the express using a flat blade screwdriver or knife. The power supply is the L-shaped component in the upper right corner in the first picture. It has an aluminum shield on it that I took off first. You can leave this on.

Remove the six T8 screws holding the circuit board in and pry the circuit board out. Do not attempt to remove the power supply yet. The circuit board needs to be removed first and there are two additional screws that need to be removed before the power supply can come out.

Once the circuit board is removed, remove the two T6 screws holding the connector on the power supply down. You can now remove the power supply.

With the power supply removed, you can now put the circuit board back in. There is a long screw toward the front of the Airport Express that previously went through the power supply, I recommend putting some sort of a spacer in to keep the circuit board from getting pulled down if you over tighten the screw. Do NOT reinstall the two side-by-side screws that connected the power supply to the circuit board.

With the circuit board reinstalled, we are ready to install the 3.3V voltage regulator and USB cable.

Note: I used heat shrink tubing to protect from possible shorts. If you do the same, don't forget to put the tubing on the wires before you solder. Common sense, but better a reminder than to have to re-do later.

Cut the end of the USB cable off so you have a cable with one USB A male connector. Typically, the red wire is positive voltage, black is negative voltage, green and white are data. We do not need data, so they can be cut flush with the cable insulation/shielding. Feed the USB cable through the hole for the power connector of the Airport Express before soldering. The red wire will be soldered to the Voltage In (VIN) pin on the voltage regulator and the black wire will be soldered onto the ground terminal of the circuit board.

Solder a small length of wire to the Voltage Out (OUT) pin on the voltage regulator. The other end of this wire is soldered to the power terminal of the circuit board.

Solder another small length of wire to the ground (GND) pin of the voltage regulator. The other end is soldered to the ground terminal of the circuit board along with the black wire of the USB cable. See the attached diagram.

Once everything is soldered, shrink the heat shrink.

*I do not claim to be a soldering expert. It ain't pretty, but it works.

I had some extra Sugru laying around so I decided to use that to add some strain relief to the USB cable and to mount the voltage regulator to the Airport Express chassis. I would have used hot glue to mount the voltage regulator, but I don't have any. I'm not sure how well the Sugru will hold up to the heat given off by the voltage regulator, but since I used the heat shrink, I'm not too worried about it coming loose and shorting something.

Once the Sugru has set, pop the cover back on. At this point, I used a USB wall charger and plugged the Airport Express into the wall to make sure it powered on. Hook up headphones to the Express, connect your phone to the network, choose a song and choose your Airplay network.

If it works, take it out to the car, plug it into a USB car charger (or USB port in your car, if you have one) and enjoy. I recommend plugging it into a plug that turns off with the car, otherwise you may find yourself with a dead battery if you leave it plugged in.

Note: it takes about 37 seconds from the time it receives power to the time you can connect to the network.