(still work in progress, not fully tested) A smart MIDI box based on a STM32 "blue pill" microcontroller (STM32F103C8T6). Software is hosted on Github: https://github.com/retro16/MidiBox Uses a HD44780 16x2 LCD screen with the usual I2C converter. The interface is made of 4 push buttons arranged in a directional pad (up, down, left, right). A SD card can be attached for more features. Optional parts -------------- Some parts on the PCB are optional, depending on what you wish to do with the board. * To remove MIDI IN 1, omit R1, R2, D1 and U1. * To remove MIDI OUT 1, omit R3, R4, R5, R6, Q1 and Q2. * To remove MIDI IN 2, omit R7, R8, D2 and U3. * To remove MIDI OUT 2, omit R9, R10, R11, R12, Q3 and Q4. ### Optional SD, LCD and buttons. If you remove the SD card, the LCD screen and buttons, all MIDI messages will be routed to the first MIDI output. It acts like a buffered MIDI merger. MIDI port extenders can be used in that configuration. Building a multiplexed extender ------------------------------- * Build the same PCB as the main board * Omit SD, LCD and buttons as they are unused * Place a jumper on EXT (or link LT and RT pins together). * Set AH and AM to either open or closed to select the 2 MIDI ports it will route (use 0 ohm 0805 resistors or just solder a piece of wire between the pads). Each extender must have a different AH/AM combination. * Connect "EXT TX" of the main board to "EXT RX" of the extender * Connect "EXT TX" of the extender to "EXT RX" of the next extender, and so on and so forth (up to 4 extenders, order is not important) * Connect "EXT TX" of the last extender to "EXT RX" of the main board