It looks DIY, with a 3.5mm stereo socket (presumably for the BC2), and a lead with a mono 1/4" jack. They're spliced together with a resistor across the join, one lead from a 9V battery connected to one side of the join, and the other lead from the battery apparently going to the third pin of the input socket.
Any thoughts on what this arrangement might be used for...?
I'm interested in putting together an Arduino-based MIDI converter for it, like the MIDI Solutions Breath Controller or Anatek Wind Machine. There are some notes on the BC2 here, though I don't really understand the statement:
....the Tip (red wire) of the stereo plug is ground, the Sleeve (black wire) is +Volts and the Ring (white wire) is the output voltage.
What is "+Volts" here...? Is this what the 9V battery is supplying...?