Adding Bluetooth to an old stereo

After updating the stereo in my E34 I had an old JVC casette stereo that was destined for the bin. Having seen others add Bluetooth to old stereos I thought I’d give it a go with the JVC, might give it a lease of life in another project or so…

I odered a Bluetooth module from China on ebay similar to this one https://www.ebay.ie/itm/CSR8645-APT-X-HIFI-Bluetooth-4-012V-Receiver-Board-for-Car-Amplifier-Speaker/233641309859?hash=item36661b76a3:g:I4EAAOSw7iNfAqB1
I chose this one as it has a 12V to 3.5V regulator on board so you don’t have to worry about stepping the voltage down.

Power and ground needs to be supplied to the Bluetooth board. Ground can be taken from any of the ground points on the stereo circuit board and I took power from the ignition signal that goes to the stereo. If taken from constant 12V there will be a very tiny draw on your battery when the car is switched off.
You also need to wire up the audio Left, Right and Centre signals to the stereo circuit board.

On the stereo circuit board you will need to identify where the audio signals run. On mine for example the casette carrier connected back to the board via a 6-pin connector. I soldered the audio signals from the bluetooth board to this point. Note Audio ground is not shown in this photo.

Using this approach, a tape can still be played provided the bluetooth isn’t playing music. Downside is that to play music over the bluetooth you need to fool the stereo into thinking it’s playing a tape. To do this simply pull the magnetic tape out of a casette and use that. You can see it in the video below.

So far I’ve only bench tested this and it seems to work fine. Obviously if you are doing this yourself you would have to find a suitable mount point inside the stereo and ensure that the Bluetooth module is insulated from the case to prevent shorts etc.

Has anyone else experience with this type of work, be great to hear about it.

Nice work! it certainly beats those dodgy 3.5mm audio cassette adapters that fed the signal to the tape head!