[Joonas] became frustrated with cheap but crappy MIDI to USB converters, and the better commercial ones were beyond his budget. He used a Teensy LC to build one for himself and it did the job ...

Take a 5-pin DIN cable and connect your MIDI keyboard’s MIDI Out to the MIDI In on your interface. Note that, unlike USB MIDI devices, 5-pin DIN cables are not power cables as well as data ...