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otto

a standalone battery (and pi) powered USB MIDI host & router

USB MIDI is great but a real pain in the ass when you're away from a computer. This project aims to fix that by providing a cheap and simple way to DIY yourself out of the connection problem.

Otto automatically connects USB MIDI devices to each other while providing its own power. Use it to connect your MIDI controller and groovebox (OP1, Deluge, M8), your grooveboxes to each other (M8 and OP1, anyone?), or as the host to a larger setup. As Otto brings his own battery all you need is the devices and the same cables you'd use to connect them to your computer. Easy peasy.

The preconfigured image provided below should work on any Raspberry Pi capable of running the 32 bit/legacy Raspberry Pi OS.

I have been notified that the Geekworm X306 board has been updated to remove the USB ports and is no longer an option for this project. This will work with any USB/battery hat (or combination thereof) that can be used with a Raspberry Pi so if you find another battery and another USB hub or some combination of those you can still make something like this - just not with the housing I designed.

Parts required:

Assembly:

  1. Mount the heatsink to the Pi by cutting the thermal tape to the size of the SOC and using it to hold the heatsink in place.
  2. Mount the Pi to the X306 board (USB and HDMI ports pointed away from the battery) with the provided screws.
  3. Mount the battery.
  4. Install the X306 board in the housing, if you have decided to give Otto a home.
  5. Prepare the SD card, see card setup below.
    You will need an 8GB or larger microSD card to use the preconfigured image, or 4GB or larger to manually set it up yourself.
  6. Insert the microSD card into your completed Otto and power it on using the button on the front. You're ready to go!

Usage:

Usage is straight forward. Turn the power on, wait ~10-30 seconds (depending on speed of SD card), plug in USB devices you'd like to connect and voila! Turn the device off when done, as you've set the SD to read only there's no need to do a full shut down.

Card Setup:

Preconfigured Image:

Download the latest preconfigured image at this link.

This should work on any Raspberry Pi that can run a 32 Bit Raspberry Pi OS.
It has been tested on a Raspberry Pi Zero 2W as well as a Raspberry Pi 2B.

Extract the .img file from the zip and write it to an 8GB or larger microSD using Rufus or Win32 Disk Imager for Windows, or dd on linux/mac.

Manual Setup:

If you don't want to use the preconfigured image above you can set this up manually.

Steps are taken from this guide for Orange Pi and this guide for Raspberry Pi 3/4:

  1. Download the Raspberry Pi Imager and set up the SD card. Choose the 32bit Bookworm lite image (no desktop is needed). You will need to enter in a username/password, set up wifi, and enable SSH access (on the second tab) in order to finish the setup. Setting the hostname can also be helpful.
  2. Insert the SD in your assembled Otto and boot it up. It will take some time to connect to your WIFI, you can watch your router's DHCP logs to see what IP it pulls or try to ping the hostname you set until you see a response.
  3. Connect to the Pi using SSH
  4. Perform sudo apt update and sudo apt upgrade to update all current packages
  5. Perform sudo apt install git ruby to install required packages
  6. Create and edit the connection script sudo nano /usr/local/bin/connectall.rb
    Paste the following code as the contents:
#!/usr/bin/ruby
#

t = `aconnect -i -l`
ports = []
t.lines.each do |l|
  /client (\d*)\:/=~l
  port = $1
  # we skip empty lines and the "Through" port
  unless $1.nil? || $1 == '0' || /Through/=~l
    ports << port
    #names << name
  end  
end

ports.each do |p1|
  ports.each do |p2|
    unless p1 == p2 # probably not a good idea to connect a port to itself
      system  "aconnect #{p1}:0 #{p2}:0"
    end
  end
end
  1. Save and exit the file (Ctrl+X, then Y, then enter)
  2. Set permissions on the file sudo chmod +x /usr/local/bin/connectall.rb
  3. Connect one or more USB devices to otto and issue connectall.rb to perform a test connection
    Check the results with aconnect -l, it should show connected devices
  4. Create a udev rule to run the script when USB devices are connected sudo nano /etc/udev/rules.d/33-midiusb.rules
    Paste the following as contents:
ACTION=="add|remove", SUBSYSTEM=="usb", DRIVER=="usb", RUN+="/usr/local/bin/connectall.rb"
  1. Restart the udev service to enable sudo udevadm control --reload and sudo service udev restart
  2. Create a systemd service to configure any attached devices at boot sudo nano /lib/systemd/system/midi.service Paste the following as contents:
[Unit]
Description=Initial USB MIDI connect

[Service]
ExecStart=/usr/local/bin/connectall.rb

[Install]
WantedBy=multi-user.target
  1. Reload the systemctl daemon sudo systemctl daemon-reload
  2. Enable sudo systemctl enable midi.service the service.
  3. Reboot the device sudo reboot

At this point USB MIDI routing should be working as expected, you can plug and unplug devices as desired and they should be automatically connected to each other.

In order to prevent SD card corruption you will want to set it up as read-only.

  1. Reconnect to the device via SSH
  2. Clone the rpi-readonly git git clone https://gitlab.com/larsfp/rpi-readonly
  3. Enter the directory cd rpi-readonly and run the setup sudo ./setup.sh

When setup is complete your install will be set to read only mode. You are now ready to make music!

If you want to make changes in the future you can turn read/write mode on with the command rw
When done making changes you can turn read-only mode back on using the command ro