Minimal Pi Most with USB I2S

Hey everyone,

I found this fantastic project while searching for a possibility to get a digital audio interface to the MOST bridge inside my BMW. While I currently don’t have a Pi Most, I was wondering if it could be possible to pair the core parts of the current version with relatively simple components such as the PCM2706C chip (e.g. link) to provide USB (OTG) streaming from any android device without the raspberry base.

This could establish a digital sound bridge to nearly each retrofit Android device that is installed in a car, having MOST if the Pi Most software is supporting it. Overall it could be a huge benefit compared to the current, qualitatively worse AUX solution for a reasonable price.


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Hi David,

Sorry for the late response, I get the need for this. I am currently looking into creating a standalone version using an MCU, likely an ESP32 or similar, that would act as a usb soundcard, or a bluetooth receiver, or even some kind of wifi hotspot streaming device.

I will keep you posted, unfortunately the PiMost in it’s current format can’t work how you are hoping, atleast not without the GPIO being connected to an external device (which is entirely possible)



Hi Rhys,

thanks a lot for the response. On reading over the different topics in the forum, I recently also realized that the onboard OS8104AAQ chip is supplied via the RPI GPIO ports by a different protocol that you support by your framework. In consequence it won’t understand direct i2s data as provided by a PCM2706C. So I understand the consideration for the ESP32 as “translator” and low level controller.

Another easy idea for the current release would probably a RPI Zero as it’s quite small and less power demanding. I played a bit around with the scrcpy framework which allows to transfer audio data from android digitally via USB and it worked out at least on my Linux system with my phone enabeling the debug mode. So in combination with the RPI Zero and the current PiMost head this could be an easy solution for digital android audio streaming until the aforementioned standalone version can be released.



The Pi transmits and receives i2s audio from the os8104, it is a standard i2s format, however the 8104 actually has 4 sinks and 4 sources, one supports spdif. My plans for the standalone board are to have RCA outputs from an audio chip, and also spdif input, however this is still only in design stage!

When you say a digital link, how are hoping to supply the digital signal, Bluetooth, usb etc?

The idea is to make a connection to a android headup display or an android smartphone by connecting their usb port to the RPI usb. As scrcpy allows to pick up the digital audio signal in raw wav format from the android system via the usb connection with low latency and lag, audio data can be transfered loosless to the RPI Zero, then further to the PiMost head and finally into the MOST. I think usb would be the most stable solution and preferable over Bluetooth protocols. One constraint of this option is that the android system must have usb debugging enabled as there needs to be set settings via adb on starting scrcpy and the android system must be at least version 11.

Hey guys, Merry Christmas,

as Rhys was so kind to sell and send me one of the MOST PI, I was able to try out the i2s concept with a Raspberry Pi Zero 2W. Luckily it worked out without big difficulties. My setup is now the following, providing a fully digital sound link:

Andream Android Tablet USB → RPI USB (g_audio soundcard simulation) → Jack2 → CamillaDSP (later for Frequency correction) → MOSTPI → MOSTBus → BMW Amplifier.

I’m planning to document the configuration in a Git repo for further usage.

You can find an example I recorded on YouTube:

The interface I’m exemplary changing the sound volume is CamillaGui running on the RPI.



This is cool! Also great idea about the DSP, I am going to chuck that onto my projects, hadn’t even crossed my mind!

Hey David,

I am looking for the exact same thing you just achieved for years! Could you help me reproduce your setup for my E90? Or do you have a Git set up yet where you have documented your success?

Greetings from Germany :slight_smile: