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Thread: MIDI data between two Bluetooth LE enabled MCUs

  1. #1

    MIDI data between two Bluetooth LE enabled MCUs

    I'm attempting to establish a connection between:
    - Teensy 3.6-powered MIDI controller connected via serial to an Adafruit Bluefruit LE UART Friend module (nRF51)
    - Adafruit ItsyBitsy nRF52840 (combo MCU and Bluetooth LE nRF52)

    Initially the problem was, I had two of the BLE "Friend" modules and they cannot establish a connection to each other, they both operate in Peripheral mode. So I got the ItsyBitsy, which can also operate in Central mode (operates as master, pairs with a Peripheral device). But now I'm discovering there aren't any working example sketches of BLE-Midi running in Central mode to start from as I normally would.

    Most assume Peripheral mode is all we need for MIDI controllers as they will sent BLE Midi to a computer or a phone, etc... but I want mine to send it to a dedicated receiver which translates it to serial and USB MIDI.

    Thinking it through again as I've written this post, may be simplest to set up my BLE connection as a serial data pipe to communicate raw data, since I already wrote a bunch of code from scratch that handles sending MIDI data over RFM69 and receiving it on the other end I could adapt.

    Has anyone accomplished this or similar?

  2. #2
    As it turns out, the minimum latency is 7.5ms for BLE MIDI, per the spec. In conjunction with other sources of latency that means 20-50ms, real world. Far too much for my hardware's need. It is outright recommended not to send more than one MIDI message every 20ms in some tutorials, ugh. My earlier RFM69 solution was actually better, I just need to figure out a better sort of antenna (anyone have experience there)?

    Lesson learned, I shouldn't have assumed that because BLE MIDI is somewhat common, it was appropriate for my purposes without researching it thoroughly.

    Thankfully I expect I'll use them on other projects. Not a bad thing to have in my back pocket and I may reserve one to leave onboard my MIDI controller as a secondary method, albeit less than perfect, to connect to devices likes iPads and phones.

    Now if anyone is still reading - anyone accomplished the goal of a robust, high-bandwidth wireless MIDI transmitter that can keep up with the speed of a USB MIDI connection? Using any technology, widely available for use with a Teensy (preferably... but also, for any MCU)?


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