Audio transmission through Bluetooth


#1

Hey,
My friends and I want want to use a Bluetooth audio module (example: RN52 or XS3868) instead of RN42 in the tympan design. We learnt that a microcontroller cannot be used for audio streaming. So can we bypass teensy 3.6 and connect the Bluetooth directly to the codec? If yes, which pins do we connect it to?
Thank you.


#2

Hi,

The limit on the Tympan is the bluetooth module (the RN42), not the microprocessor.

It’s the RN42 that doesn’t support any of the bluetooth audio transmission modes. The RN42 supports a basic serial protocol (as well as a bunch of other non-audio modes). The serial protocol mode is too slow for sending digital audio.

So, if you’re interesting in bringing your own bluetooth module for doing the audio transfer, most of audio-capable bluetooth modules have the option of outputting the audio as an analog signal. You can then take the analog signal and feed it into the Tympan’s line-in inputs, either via the pink jack or via the solderable through-holes on the side of the Tympan board.

If you injected the bluetooth audio into the line-in, the audio codec would digitize the signal for processing by the Teensy, which will then be output via the audio codec to the headphone output.

If you don’t care about the fancy audio processing that the Teensy enables, and all you want is simply to get audio out of your Bluetooth module, the Tympan will probably be overkill. In this case, you really just want a headphone amplifier after the analog output of your bluetooth module.

Chip


#3

Okay, so no need to connect Tx & Rx (I am new to this) ?

Thank you.


#4

I, myself, have never tried to do something like what you’re doing, so we’re figuring it out together.

Completely separate from the Tympan/Teensy, I would try to connect to your bluetooth module from your phone (or whatever). If your phone thinks that its playing audio to your module, that is a great first start.

Then, I agree with you that you probably only need to connect the audio output of your bluetooth module to the line-in inputs on the Tympan. You’ll also need to connect the ground of the bluetooth module to the ground of the Tympan.

Finally, you’ll need to tell the Tympan to listen to the line-input instead of the its microphones. If you use the pink microphone jack, most of the Tympan example programs have a line that you can uncomment to use “mic_jack_as_line_in”.

If you upload such a modified program on the Tympan, I would think that you would hear the bluetooth module’s output passing through the Tympan and coming out the Tympan headphone jack.

Good luck!

Chip


#5

@Anagha
You will be happy to know that the next version of the Tympan audio board will have an onboard Bluetooth module that supports audio, the BC127. Our Rev D board is in prototype phase. We have the first round of hardware, and will be reviewing it for bug fixes and feature add-ons before going into production. The design files, etc. will be released soon, so follow us on twitter to know when they hit our github (likely in about a week).