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categories music hack tags techniques electronics midi

When making custom midi devices, I used to use the Adafruit MIDI FeatherWing. It is a great little board, but it is quite big, and not always available.

Front view
Back view


This is a small little board, 28x21 mm ish. That can be used to attach MIDI devices (In and Out) to your microcontroller projects. The design is really simple, there is nothing magic about it. It shows the signals going in or out of the board with tiny LEDs.

I made it ready to be ordered on JLCPCB, except the jacks that we have tons of at the local hackerspace (but I think they also have them on LCSC).

When using boards like that, make sure that you know what you are doing. It is hard to destroy a MIDI device and when it happens usually easy to repair, but it is possible to do permanent and painful damage. And this project obviously comes with no warranties.

Schematic and principle

It is pretty simple, both RX and TX parts are separate on the board. And RX and TX both have pads that can be used to change the modes of the MIDI devices, so you can use Type A or B devices. If you don’t know, use Type A as it is now the standard. I’ve explained the differences on a paragraph below.

The schematic of both RX and TX parts of the board

The MIDI standard requires optocouplers on the RX side to avoid ground loops. There are both rising time and voltage requirements for MIDI that make those H11L1 the best optocouplers for the job. I wish there were smaller package size for those, but these never failed me…

The LEDs shouldn’t have any impact on the signal, if you find out they do, they are easy to kick out with a soldering iron.


Designator Footprint Quantity Value JLCPCB Part #
R2 R_0805_2012Metric 1 10 C17415
R6, R3 R_0805_2012Metric 2 2.2K C17520
R1 R_0805_2012Metric 1 33 C17634
D1 D_SOD-323 1 1N4148WS C2128
DR1 LED_0603_1608Metric 1 LED C2286
DT1 LED_0603_1608Metric 1 LED C72038
U1 SMDIP-6_W9.53mm 1 H11L1 C78589
R5 R_0805_2012Metric 1 470 C17710
R4 R_0805_2012Metric 1 220 C17557

Kicad files

Download the Kicad files


A really simple board, but it makes life much much easier to not have to figure out the pins of the Adafruit board or custom make one.

Total cost: $3.5 per board, but I had the jacks already. Adding the jacks will probably bring it close to $5 per board.

MIDI cables reference


    |   |   >
  S   R   T
TRS Type B Type A TRS (MIDI 2.0) Type C TS only
S Shield Shield Sink
R Sink Source Sink
T Source Sink Source
  • Type A (The MIDI norm) Korg, Akai
  • Type B Arturia, Old Novation devices (all new Novation devices like the MK3 series are on Type A)


                       Female plug seen from the pin sides
                                   4 o   o 5 
                                  1 o     o 3
                                   Male plug
                                   5 o   o 4 
                                  3 o     o 1
DIN Function
2 Shield
5 Source
4 Sink


This project, minitopus by Bjonnh is licensed under CC BY-SA 4.0 CC BY SA


  • 2024-06-01 : Creation of the page


  • Adafruit for the MIDI FeatherWing that inspired this project