First stab at adding bluetooth

I had a go at adding Bluetooth support to the turned speaker I made using an RN-52. It wasn't clear from the datasheet what sort of output I could expect from the RN-52.  All it said was that it was differential.  I tried hooking up one side of the differential pair to the headphone-in of the speaker to get a better understanding.  It worked! (Kinda!)

While audio was playing (with about 12 ohms across the input to ground) it was fine but there were very large pops when sounds started and stopped.  I suspect (but I don't have a scope available to check) the module centres its signal on 1/2Vin but turns off the driver when it's not using it.  That results in a big step signal when it turns its signal on and off, causing a pop.

Thanks to a tip from the AskElectronics subreddit, I now plan to build the headphone out circuit from the datasheet and then find some way to mix that with the existing headphone in, if possible.