My Bluefruit EZ-link finally arrived from NZ yesterday (I couldn't find anywhere here in Oz that carried it and the shipping cost from NYC is horrendous). I've hooked it up to one of my NavSpark-Raws and it works with RtkGps, an Android port of RTKLIB (or at least rtknavi).
(please excuse the bad soldering)
The Bluefruit EZ-link has an optional JST Li-ion battery connector on the back that you can solder on. I did. I found that two of the pads in the 2*3 cluster were connected to the battery connector. So I wired them straight to the NavSpark, along with the TXD1->RX connection. This way each board is using its own regulator straight from the battery voltage. I thought it was simpler this way.
Then it was out to the backyard to test it out. I used the side panel of an unused computer case as a ground plane. It seemed to get a pretty accurate fix. The screenshots show the result after about 15 minutes. The "map" view shows me a bit too close to the house though, but that may just be bad image alignment. For most purposes it probably doesn't matter if the aerial imagery is a metre or two off.
One caveat: For some reason Android's SPP implementation is limited to only 9600 baud. Or it defaults to 9600 baud and most apps don't change the speed. Or something like that. So make sure to set the NavSpark "COM port" settings to this speed. The BlueFruit EZ-link automatically detects the speed of the incoming data.
The next step is to put this gear in a box and use an SMA connector for the antenna connection.
What's everyone else doing with their NavSparks? Post some pics and share with the community!