For the tinkerer; We’ve released the RaspberryPi image to add MIDI-Host functionality to the RK-004.
RK-004 Raspberry Pi Image
If you want to use the RPiZero as a USB Host or USB midi interface with the RK-004 you can download this image
You can just connect a RPi’s serial port via the top 1 MIDI port on the RK-004 like this, but for you who wants to make it ultimately portable: Connecting the RPiZero inside the RK-004 requires only 4 wires. The RPi Board will be powered from the RK-004. The PiZero will bolt right in with a straight connector but you can also use a flatcable to make the connection. Below is the pinout of the connector (the upper one with serial signals is for the RPi):
(Note that this connector is not just for the RaspBerryPi. Although this is the platform we have released the code for, you can connect any board with serial I/O to it (arduino, etc) and communicate with your music gear.)
To remove the bottom plate of the RK-004 you DON’T turn the plastic studs, you just place something small (preferably non-conductant) between the PCB and bottom acrylic plate and pull the studs out.
Removing the RPi Cutout plate of the RK-004 to make room for the RPiZero needs to be done carefully. Acrylic is very hard can stand quite some beating, but therefore bending it is something which can cause cracks in uncontrollable places.
For RPi’s which are already running a system you can add our repositories like shown in this video. You can connect the RK-004 via the RPi serial port and it will show up like a MIDI port on your system:
curl -sLS https://www.retrokits.com/debian/add.sh | sudo bash
sudo apt-get install rk004d
Our daemon has a built in midi monitor you can view from the terminal with command:
tail -f /tmp/rpirk004midimon