Possible mutable product idea? usb midi expander

how difficult would it be to program a device that did something similar to this

http://store.keithmcmillen.com/MIDI-Expander/ ?

this is a really useful product but its so big in comparison to some of the small usb devices around…is it possible to make something like this small enough that it was actually more similar to a cable?

I don’t think so… It is not only a matter of having USB on one side and MIDI on the other - you also need to fit in a power supply and a power connector in there!

There is this one too. http://www.kentonuk.com/products/items/utilities/usb-host.shtml

I am using a raspberry pi for this! Waaaay cheaper.

really? how? I was looking in the internet if somebody has some info on using the pi for this but couldn’t find any.

whats a raspberry pi? @herrprof

It’s a £30 ARM board with a great community.

its simple, just make a linux shell script using aconnect:


I have it run a script at startup that:
Patches my qunexus to a thru port
Patches the through port to a hardware usb midi out
launches my midi application which sends midi to the thru port as well, alsa soft merges the output.

Used this page to determine the aconnect values:

The best part is that this is all with the stock raspbian distro, and no advanced installs or configs are required.

do you have pics —?

does it power the qunexus as well? the goal here being to not use a computer in the chain

i have a powered usb hub powering everything (including the pi). Its not much to look at as everything is buried in my gear box. I have a todo to document the whole process for the piggytracker wiki, but havent had the time.

does is it smaller or larger than the mcmillan box?

bigger. The pi itself is the size of an iphone-ish/pack of smokes and if you just do midi you dont need a hub, but the expander is pretty small… maybe half the size of the pi. The mcmillian box isnt a usb midi device and only works with the kmi products… the pi is about the size of the kenton device and is smaller than the iconnectmidi.

So bare mimimal parts for this:
optional pi enclosire
power cable
usb midi device
usb midi interface ( i use the Edirol um-1 ex)

Minus the midi stuff itll probably cost like like $50 to get the pi up and going. Youll need to setup everything once but once the script is configured to autorun at boot you can run everything headless.

Here is a short instragram of my me playing my modded shruthi-1 via the raspberry pi midi brdige described above:


I know it’s an old discussion, but, herrprof, are you still running your RasPi midi bridge ?
How long does your RasPi needs to boot ?
Would it be possible to have a look at your startup script ?

I’d like to do this to control my Elektrons and Shruthis with my QuNexus, but am too broke to even buy a Kenton USB Host to MIDI interface (and see no point in the McMillen device which only works with their interfaces)… But I still have a spare RasPi B somewhere.
Was thinking about using Arch linux instead of Raspbian for faster boot times in headless…

The Pi uses so little power you could leave it switched on all the time.

Not sure if it would be any quicker, but there is a RiscOS image for it too.

It’s now also possible to do this with the new MIDIbox Core Module:

RiscOS might be nice for its graphical interface, but not as efficient as a bare bones linux distribution (like ArchLinux) in a headless setup…

stuartm, rather, it’s possible to do this with a stm32 microcontroller, I don’t think it has much to do with the MIDIbox Core Module.
The stm32f4 mc specified in the link you posted, might actually be a good idea if you’re on a tight budget and have good DIY skills and no RasPi at hand, as it seem quite cheap, maybe even cheaper than a RasPi.
It won’t help in my situation, in which I already have the RasPi B, a compatible USB hub and the USB to MIDI IN & OUT cable, missing only the script to setup the USB to MIDI routing.
Which I could find myself (I’ve been using linux for 20 years) but I haven’t practiced linux for a solid year and I’m a little rusty in computing matters, so herrprof’s script would give me a welcome kickstart :slight_smile: