This board lets you drive up to 32 resistive or inductive loads and 4 servos. It uses 4 ULN2803APG chips (8 channel darlington arrays), each one can be run at a different voltage and sink up to 500mA per channel, up to 2.5 amps in total per chip. I would recommend using this MIDI library for Teensy 4.1
schematic can be found here. NOTE THIS DOES NOT COME WITH THE TEENSY 4.1.