A few months ago my Motorola S9-HD Bluetooth headphones died. They had a good run but the speakers started to go bad. The electronics inside, however, were completely fine. These headphones have a good battery life of about 5-6 hours and a decent range so I figured they would work great with an upcoming project I have in mind. I decided to strip them apart and see if I could make a small adapter instead of buying a new one. The main functionality that I wanted to keep was the power, volume up, and volume down. The headset can also answer calls, skip forward/backwards, and pause music but I didn't worry about these functions since the final application would not utilize them.
I started out dissembling the headphones to the core components. I desoldered the faulty speakers and soldered on some probe wires to the PCB that controlled the controls I was interested in. I attached the control pad to the side with the volume up/down buttons and used a multimeter, with continuity monitoring, to figure out which wires carried the signals I needed. Once I got the pin outs, I ziptied the wire bundles together and prepared a case.
I had a small enclosure laying around and I cut an access holes for the USB and audio out cable. I salvaged this audio out plug from an old pair of headphones. I then drilled 12 small holes to mount my three pushbutton switches on the top cover. I hot glued the switches in place and wired all of the ground wires together. I then wired the adapter to the controls and audio out using the schematic attached.
I organized all of the wires inside the enclosure and attached some labels for the buttons and pairing instructions. The unit works great and I'm excited to utilize it for my next project!