MIDIbox Hardware Platform, MIDI_IO Module

MBHP_MIDI_IO is a MIDI breakout board for the MBHP_CORE_STM32F4 module.

It consists of two MIDI IN/OUT pairs and MIDI Activity LEDs which are connected to monoflops.

The input socket J1 has to be connected to J11E of the MBHP_CORE_STM32F4 module. J1 of a second MBHP_MIDI_IO can be connected to J2 in order to get 4 MIDI INs/OUTs in total. More modules can't be chained (4 IN/OUT ports maximum).

This approach has the advantage, that the builder can decide by himself, if - and how many - MIDI IOs he wants to add to his MIDIbox.

Note that the MIDI activity indicators are only an optional feature. The circuit will also work without the circuit around the 74HC00 ICs (see schematic).


Module Schematic Layout Data Quick-view
MBHP_MIDI_IO_V1 mbhp_midi_io.pdf to be published mbhp_midi_io_0.jpg
Additional informations
File Size Description
mbhp_midi_io_orderlist.txt 1k Reichelt orderlist

Available Ports

Following interfaces are provided by the MBHP_MIDI_IO module:

Name No. of pins Description
J1 10 Connection to J11E of the MBHP_CORE_STM32F4 module, resp. to J2 of a second MBHP_MIDI_IO module (to get 4 MIDI IN/OUT ports)
J2 10 Connection to J2 of the first MBHP_MIDI_IO module in the chain to get 4 MIDI IN/OUT ports in total.
J3-J6 2 Optional MIDI Activity LEDs

Soldering Guide

It's always a good idea to start with the smallest components to simplify mounting.
So, start with the resistors and diodes:
  • R1, R3, R5, R6, R8, R10, R11, R13, R15, R17 = 220 Ohm
  • R4, R9 = 1k
  • R2, R7 = 4.7k
  • R12, R14, R16, R18, R19, R20 = 100k
  • D1, D2 = 1N4148
Continue with caps and LEDs:
  • C1, C2 = 100 nF
  • C3, C4, C5, C6 = 10 uF (El.Caps - polarity! Plus leg show to border)
  • the 4 LEDs at J3..J6 don't need sockets.
    Take care for the polarity! Anode (the long leg) shows to the right side!
Mount the IC sockets
And then the DIL Headers and MIDI Sockets
And finally put the ICs into the sockets:
  • IC1, IC2 = 6N138
  • IC3, IC4 = 74HC00

Two MBHP_MIDI_IO modules connected to J11E of the MBHP_CORE_STM32F4 module in a chain.

Board Modification for 3.3V based MIDI outputs

If you are planning to use this module for a microcontroller which outputs MIDI OUT at 3.3V level (such as the MBHP_CORE_LPC17 module), please change the R3, R5, R8 and R10 resistor values to 47 Ohm, and connect J1:Vd to 3.3V instead of 5V!
This measure is not required for microcontrollers which output 5V, or where MIDI output (Tx) pins can be configured in open drain mode.


Thanks to Tim aka. SmashTV for the great idea to chain two MBHP_MIDI_IO modules by using a special J1/J2 pin encoding. He also created the PCB layout. PCBs and kits are available in his MIDIbox Shop.

Last update: 2017-02-26

Copyright 1998-2017, Thorsten Klose. All rights reserved.