Retro boombox becomes bluetooth speaker

For just a few dollars you can buy a small board that acts as a bluetooth audio device. This board allows you to build your own bluetooth speaker. But why build a new speaker when you still have an old radio in the attic?

The XY-BT-MINI is a bluetooth audio board which you can buy from these popular Chinese webshops. There are two options to power the board: over the micro-USB connector or the ‘BAT’ header. For audio output there are two options as well: a 3.5 mm stereo jack or 3 solder pads (L/GND/R). You can pair it with any device that can stream audio over bluetooth, e.g. your smartphone.

I got my first new radio cassette player from my parents, as a gift. It was a Sharp GF320, which had detachable speakers and an audio input too. I used it for many years until I grew up and switched to more decent audio gear. The Sharp moved to the workshop and played radio for many years. The cassette player eventually gave up, but cassettes became obsolete.

Recently I saw a video of a guy modifying his old boombox using the bluetooth board mentioned above. I absolutely liked the idea and decided to try the same with my old Sharp. Since the cassette player was out of use, I deciced to wire that ‘input’ to the bluetooth board.

To find that input, I had to examine the circuit. Luckely the documentation was available online (some scanned pdf). The block diagram gave me the first clue:

The diagram tells me that there must be some switch labeled SW101, which selects the input (radio or tape). This happened to be a very long switch, engaged by the play-button of the cassette player. I soldered wires on the correct pins to hook up the bluetooth board:

To power the bluetooth board I soldered a 78L05 and a small capacitor on the main board, to obtain 5Vdc from the radio’s 9Vdc power:

Finally I soldered the audio wires and DC to the bluetooth board itself:

I hid the board somewhere in an empty corner of the radio. Now it was ready to play! So I pressed the PLAY button of the cassette player (to power the radio on) and a nice beep sounds through the speakers to tell me the bluetooth module is ready. Then I paired my phone and started streaming audio using the VLC app. Yes…. it rocks!