Bluetooth speaker

Radio Enclosure with Bluetooth circuit

I had two broken things lying around in the house: an Auvio PBT 200 Bluetooth speaker and a FM/AM radio in old-style wooden case. The plastic of the bluetooth speaker was sticky from exposure to light and the battery did not last that long anymore.

The AM/FM radio was probably built around the Sony CXA1191 AM/FM integrated circuit, which appeared on the market at the end of the 80s. The battery holder was broken and so where the controls. I radio looked cute, but I really don’t have a need for an FM/AM receiver, so I decided the transplant the innards of the Bluetooth speaker into the radio.

Enclosure with replacement circuit (for test)The first step was to dismantle the Auvio speaker, which was far from easy, as this device was designed to be easily opened. Inside there were three boards, the main one with all the connectors, a smaller one with the four control buttons and the microphone connected to it, and a third mini-board with the two status LEDs. These were connected using thin ribbon cable that would plug on connectors on the boards. The two speakers were connected using color coded connectors. The battery had a cable with a connector that would plug on two pins on the main board.

While prying it open, I damaged the cable that ran from the control board to the main board. Thankfully the pins of that connection are annotated on the main board, and I figured out that the various controls (forward, backward, bluetooth connect, volume up, volume down) where activated by pulling the relevant line to +1.8 V provided on the same connector. So I decided to leave the control board with its microphone around, but run wires to activate the volume control from the enclosure.

Enclosure with Auvio speakers mountedThe second step was to empty the radio, which was reasonably easy, the only tricky part was the fabric in the front which was glued to some cardboard. The two controls would screw directly into potentiometers on the circuit board, the third one on a metal part that would a switch. I now had to solve two issues, the radio board was inserted vertically in the radio, but I wanted the Bluetooth board to have all connectors accessible in the back, so I had to drill some rails and cut the rear board a bit to let them out. The two speakers could be fixed easily on the front panel, I just had to cut another cardboard shaped to fix the fabric on.

The front had a window that displayed a disk with the various frequencies, I blocked it with backing paper to get a brown, diffuse, feeling and mounted the mini daughter-board with the status LEDs behind it. I had to built a small wooden structure to hold it in place, but nothing overly complex.

Back with control and connectors exposedThe other problem was connecting the rotary controls to push controls, or at least keep them from falling out. I solved this by soldering the control rods to some thick copper cable which, with the help of a washer, would keep the rotary controls in place. For the volume button, the copper cable would press on two micro-switches which would trigger the volume-up and volume down controls. I need to do something similar for the forward and backwards controls, maybe also the Bluetooth connect control.

While this project could be improved, it is functional, the radio works as an external Bluetooth speaker, in theory it should also work as a microphone, but I cannot get any sound it, possibly because the microphone is still connected to the daughter-board with the damaged ribbon cable – I could solder it to the main board. What would be more useful would be to connect the forward / backward controls to another rotary switch and also the connect control, but for the time being I’m pretty happy with the result, having turned two broken device into a cute dieselpunk looking, functional one.

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