USB bridge A

Routes and merges midi data between two USB devices and one TRS midi device

USB Bridge A features two midi USB hosts and conventional TRS midi input and output.
Midi data is routed between the connected devices and merged if necessary.

Data received from a USB device will be send to the other USB device and to the TRS output.
Data received on the TRS input will be sent to the two USB devices.
Depending on the kind of data it will be merged, see below.

You can use this to:

Connect one or two midi USB midi controllers/keyboards to a conventional midi device
Connect a keyboard to a module with only USB device capability
Connect a cheap USB midi interface and get more conventional midi IOs
Use your phone to control your Eurorack or as a synthesizer

Merging and routing

If all three midi inputs are used (2xUSB, 1x midi TRS), it is necessary to route and merge midi data.
Here, USB Bridge A differentiates between several types of midi data:
Note and controller data

These are all the midi messages that can be merged without any issues. If two devices send midi at the same time, data will be interleaved and sent to the receiving device.
Clock Data

Clock data can not be merged, only one midi clock stream can be used at a time. When USB bridge A receives clock data, it will lock the receiver to this clock source. Once you press stop, the receiver is freed and clock data can be received from an other device.
Sysex data

Sysex data is even trickier to handle than clock data, because sysex messages can have an arbitrary length. if multiple sysex streams are received simultaneously, USB bridge A buffers the data and will forward it to the receiver as soon as possible. This way sysex messages are merged as well.

LED indication

LEDs show the status of USB and midi:
NO USB device connected: off
USB device connected successfully: green
Receiving midi: flashes yellow
USB device connected, but not compatible: red
Overcurrent detected: blinks red

TRS midi LED:
Module is powered: LED green
Receiving midi: flashes yellow

Voltage converter

USB bridge A includes an optional DC/DC converter to convert 12V to 5V. This means eurorack cases without a 5V supply are also supported. A jumper on the back selects between 5V or 12V input. The DC/DC converter topology means current draw is less on the 12V supply. For example: If your USB device draws 500mA, USB bridge A will only draw about 220mA from 12V.

https://tubbutec.de/usb-bridge-a/