Show 'n Tell: Raspberry Pi BLE Midi Bridge Thingy

jebni

Bumping this blast from past to thank @wim for bringing this DIY USB MIDI host to our attention. Great stuff. I had a Pi Zero W lying around, and it was quick work to get up and running.

I did set up the additional Bluetooth MIDI functionality, but while it's very elegant to keep the Pi host's USB connections constant and simply add my iPad via Bluetooth, I think that losing the granularity of AUM's MIDI matrix was a bit sad: I want to be able to choose specific sources and destinations when using an iPad, rather than have them hide behind a single Bluetooth access point.

So instead, I got a USB A/B switch that connects the hub for all my USB MIDI devices to either the Pi or my iPad's USB C hub. Besides making the switch easy, it also supplies constant power to any bus-powered devices connected to it. Unlike the act of unplugging the hub from the Pi and plugging it into my iPad's system, there's no momentary loss of power and annoying reversion to a default patch on instruments like my Microfreak.

The A/B switch also solved another bus-power problem I was having with the Microfreak. The Freak's USB MIDI is by all accounts very temperamental, and connecting it to the Pi without a powered hub made its MIDI OUT behaviour incredibly flaky and impossible to use. But because the A/B switch is also permanently plugged into my iPad's powered USB C hub (whether my iPad is there or not), the Microfreak no longer freaks out when connected to the Raspberry Pi.

So if you're having issues with bus-powered devices connected to a Raspberry Pi, try um, adding more power to the mix. Weird, I know! 🤪 But it's so interesting that it mostly worked. It would have been far easier to grok if the Microfreak simply didn't power on. Instead, the only thing that didn't work was 50% of outgoing MIDI events — incoming events were fine. It was extra infuriating that these problems didn't go away when I plugged in the Microfreak's own 12V AC adapter. Only connecting it to a powerd hub fixed it. If anybody can explain this, I'm all ears!

jebni

(It occurs to me that I only tested adding the AC adapter to the Microfreak once it was up and running on the Pi's USB power. Maybe it doesn't switch on the fly. But in any case, the Microfreak's AC adapter is unusably noisy, so it's a moot point.)

Oh, another thing. I love the idea of @wim's web interface, but because I'm addicted to tinkering, I instead installed this web interface for making/breaking the actual connections that are being automated, which allows you to exercise some finer-grained control if you so desire.

wim

That repository is a good find @jebni. 👍🏼

jebni

@wim said:
That repository is a good find @jebni. 👍🏼

If I find the time to get nerdier, I might try and make the interface a little more intuitive. For me, this usually involves poking things until they break.

@jebni said:
So if you're having issues with bus-powered devices connected to a Raspberry Pi, try um, adding more power to the mix. Weird, I know! 🤪 But it's so interesting that it mostly worked. It would have been far easier to grok if the Microfreak simply didn't power on. Instead, the only thing that didn't work was 50% of outgoing MIDI events — incoming events were fine. It was extra infuriating that these problems didn't go away when I plugged in the Microfreak's own 12V AC adapter. Only connecting it to a powerd hub fixed it. If anybody can explain this, I'm all ears!

I've solved the issue! First, it turns out the powered hub didn't alleviate my Microfreak problem — almost immediately, it started dropping notes again.

I installed a very nice command-line MIDI monitor, confirmed that the Pi was indeed definitely missing half the notes coming in, unlike any other device I put in its place, and then troubleshot it down to the way the Pi manages its OTG USB port, which has been confirmed to spit the dummy with certain USB devices, especially those that are slightly off-spec (so in this perfect storm, it's an issue that also still lies with Arturia's USB implementation).

The workaround: add the term dwc_otg.speed=1 to the Pi's /boot/cmdline.txt configuration file, which reduces it to USB 1.1 speeds, which is more than enough for MIDI, right? Anyway, no dropped notes. If you similarly have a low-bandwidth USB device that's not playing nice with a Raspberry Pi, USB speed settings might be somewhere to look.

(Meanwhile, mucking around with different levels of power to the Microfreak while troubleshooting this was fascinating. Not only does it "sort of work" when underpowered, I hear that some people have reported phantom knob twiddling while bus powered. And at one time, using a powered hub that had no power connected, I managed to boot it into a mode where it only played sine waves and lost all access to its presets. Good times!)

rs2000

Cool!
Adding to that, I've found a repo that now also allows for using the even more (battery) power efficient Pico W as a BT USB MIDI host:
https://github.com/rppicomidi/ble-midi2usbhost

So the recent idea about a wireless pad controller gets fresh food too 😊

Korakios

For automatically accepting BT pairing from any device , I tried the workaround from
https://forums.raspberrypi.com/viewtopic.php?t=324225
which did work for streaming audio to rpi , created BT midi ports on rpi ,but not on iOS
the only solution for a working BT ports on iOS was
bluetoothctl discoverable on && bt-agent -c KeyboardOnly
but it needs logging via ssh and typing the pin

I just found a simple solution , just start from the rpi the following command :
yes | bt-agent
When pairing from an ipad/iphone it will autoconnect , plus (using latest Rasberry OS) midi ports will be created on the iOS device
Hope it is useful

I think it would be much easier if Bluez was providing a BT midi server
Is there a simple way to compile bt-midi.server only , without having to compile the whole Bluez from the old (and unmaintained) repositories ?

wim

@Korakios said:
For automatically accepting BT pairing from any device , I tried the workaround from
https://forums.raspberrypi.com/viewtopic.php?t=324225
which did work for streaming audio to rpi , created BT midi ports on rpi ,but not on iOS
the only solution for a working BT ports on iOS was
bluetoothctl discoverable on && bt-agent -c KeyboardOnly
but it needs logging via ssh and typing the pin

I just found a simple solution , just start from the rpi the following command :
yes | bt-agent
When pairing from an ipad/iphone it will autoconnect , plus (using latest Rasberry OS) midi ports will be created on the iOS device
Hope it is useful

What? That's a great find! So simple.
I'll dig mine out and test, add it to the wiki page ... unless you want to do it.

Korakios

@wim said:

@Korakios said:
For automatically accepting BT pairing from any device , I tried the workaround from
https://forums.raspberrypi.com/viewtopic.php?t=324225
which did work for streaming audio to rpi , created BT midi ports on rpi ,but not on iOS
the only solution for a working BT ports on iOS was
bluetoothctl discoverable on && bt-agent -c KeyboardOnly
but it needs logging via ssh and typing the pin

I just found a simple solution , just start from the rpi the following command :
yes | bt-agent
When pairing from an ipad/iphone it will autoconnect , plus (using latest Rasberry OS) midi ports will be created on the iOS device
Hope it is useful

What? That's a great find! So simple.
I'll dig mine out and test, add it to the wiki page ... unless you want to do it.

Haven't messed with the AB wiki so feel free to add it
To autostart on every reboot (first make sure that the pi is not on read only mode) :
create a simple script named eg btautoaccept
nano btautoaccept

#!/bin/bash
bluetoothctl discoverable on
yes | bt-agent

chmod +x btautoaccept

then add it to rc.local (fortunately it's enabled by default as part of systemd service)

sudo nano /etc/rc.local

and add before exit 0

su korakios /home/korakios/btautoaccept  &

(replace korakios with your pi user name)

If everything goes well , a new iOS device should detect pi BT and by tapping to connect, a pop up will be shown to confirm the pin code (and the pi will accept it automatically). Then BT midi ports will be created automatically.