Back in the old days (late '90's-early 2000's), not all phones came with Bluetooth built in. This prompted companies such as Cardo
to build external bluetooth adapters such as the BTA II
. There are others available, but I got one of these for $.99 (used) on eBay. These can be repurposed with a little soldering to send an audio signal to any bluetooth headset, and deliver an audio signal back from the microphone if desired.
First, obtain your BTA II. Got it? Cool. Now use your thumbnail to pop the cover off. You'll see a battery, a circuit board, and the coiled wire that connects to your cell phone. Three wires connect the wire to the circuit board, on mine they were colored white, red and black. The white is +microphone, the red is +speaker, and the black is the common ground. De-solder these wires after carefully noting their orientation.