I have a 3.5mm headphone jack attached to a bluetooth module with both right and left channels being occupied (also ground of course). The Li-Po battery that powers the module takes 5v from usb directly to charge it. What I want to do is be able to charge the battery through the headphone jack when the module is turned off. I thought of using a diode between the jack and battery along the batterie's 5v rail to keep the flow from the battery away from whatever channel it was sharing with the module (either right or left), but then power from whatever channel the battery was connected to would flow into the battery. I could already just use a switch to cut the battery of from the port entirely when the module is off, but where is the fun in that, I want it to be automatic!