Audio on the go

I’ll save you the long back story, but I recently came across a pretty amazing module, the USR-S12.

usrs12

This module seems to be built for integration in other devices, and has an impressive list of features.  The key ones (to me) are:

  • WiFi base station or bridge
  • Airplay

This website has a pretty good breakout of what the interface looks like.

I ordered mine directly from china, for about $35 – but it took about 2 weeks to arrive.  Sparkfun also carries them with a break-out board (including rj45 ethernet) but they want a bit of coin for it.

With module in hand I set about wiring it into my car.  My goal was to stream audio from my iPhone as my car didn’t support the proper bluetooth codecs to play music.  With airplay i could stream podcasts and pandora with a higher sound quality than bluetooth would give me anyways.

My Audi has an interesting interface (AMI) which supports different cables for iphone aux etc.  The ipod cable was interesting to me as it supported analog left/right, data (not used for this application) and power.  I was fortunate to find a wiring diagram for the audi connector on a blog (thanks w.ashcroft!).

audioConnector

The only other sticky-wicket on the Audi part is that there is a small resistor inside the connector housing that tells the car if you have the ipod or the aux cord connected.  I wanted it to think the aux cord was connected so it wouldn’t try to talk via the data lines.  There is a 18.7k resistor in the iPOD cable, and i had to swap that out for a 1k to emulate the AUX cable.

After a quick snip-snip with the wire-cutter the 30-pin ipod connector was removed and I was able to identify which wires were which with a the help of the multi-meter (diode test for the win!).  Soldered power, ground and analog to the USR-S12 and was pretty much ready to go.

20141204_032154925_iOS 20141204_032203288_iOS

Plugged it in and thankfully everything worked as expected.  Iphone joined the new WiFi hotspot in my glove compartment, and airplay sounded awesome!  I made a few small changes through the web interface (10.10.10.254), changing the network/ssid name.  This also changed the name of the airplay host.

Final change is to edit the network properties on the wireless network on your iPhone.  When joined to this hotspot you want to set a static IP (such as 10.10.10.200) and NO default gateway.  This way your phone will still use the cellular network to get to the internet instead of trying to use the hotspot.  This is critical if you want to stream content like Pandora.

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