This bluetooth adapter. Since this link will probably be dead relatively soon it might pose a problem for those of you trying to do this mod; the item is listed as a generic bluetooth adapter but in the manual it is revealed to be the BTAV101 manufactured by Flaircomm.
A few lengths of thin wire. I harvested my wires from an old parallel cable.
So, let's get on with it.
UPDATE:- After getting it all together and trying it out it turns out that the mini's case doesn't allow the transmitter to work nearly as far as it normally would. Extending the antenna out of the case doesn't help. It works up to about 6 feet when out of my pocket but it starts getting choppy while in my right pocket. Not sure what's causing the interference in my pocket, but the problem disappears while in my left pocket.
Step 1: Breaking It Down
Step 2: Preparing the Boards.
We're going to want to desolder the connections for the battery and for the 3.5mm pigtail. Remember that the red cable matches the solder point labeled "bat". Once everything has been desoldered you should be left with just the board for the adapter. Lucky for us, the adapter and iPod both have 3.7V batteries, making it an easy swap.
The solder points for the iPod Mini are on the top portion on the rear side. Just below the headphone jack. I found it easier to work with this by removing this portion from the rest of the board. There is only one connecter holding this portion to the board. If you gently lift it up from its center it should come away with no problems.
Step 3: Soldering.
I started with the adapter. The pad labeled "bat" on the adapter has to tap into the red wire on the iPod's battery. The "gnd" pad taps into the black wire. I tapped the connections by coating some wire with solder to make it stiffer, I then inserted the wire into the corresponding port on the white battery connector right beside the original wire. Then to prevent these wires from falling out, I covered the connections with Titan brand glue. The reason I use Titan brand is because it is horrible glue. Really. Even a week after "drying" it's still gooey and can be easily pulled off, this is great if you're waiting for a new high capacity battery to arrive from ebay but can't wait to mod your Mini. I can only find Titan in dollar stores and some convenience stores.
The pads on the adapter labeled "R.line", "GN", and "L.line" get soldered onto the corresponding pads on the iPod Mini. Like I said, I found it a lot easier to separate the headphone portion from the rest of the iPod before soldering it. I coated these connections with glue as well just to prevent any shorting if my horrible soldering didn't prevent the cable from coming loose.
Step 4: Pray. Reassemble. Repeat If Necessary.
Now we put everything back together and we're done. The bluetooth adapter fits nicely on top of my CF card and is still shorter than the battery. I used a piece of electrical tape to hold it in while I was putting it back into the case.