Raspberry Pi Zero MIDI PCB

This is a MIDI interface for a Raspberry Pi Zero. It is designed to be stackable so it can be used with my RPi Zero MiniDexed IO Board PCB.

Here is the Raspberry Pi Zero MIDI PCB Build Guide.

Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers and single board computers, see the Getting Started pages.

The Circuit

This is the fully buffered MIDI IN/OUT/THRU circuit I’ve used several times before, loosely based on the design used in the Clumsy MIDI board. This provides IN and OUT linked to the RPi’s RX/TX pins whilst also including a hardware MIDI THRU hanging straight off the RX pin too.

It is 3V3 compatible for use with the Raspberry Pi but the 74HCT14 acts as both a buffer and level shifter so that the MIDI OUT and THRU portions of the circuit present a 5V MIDI design to the outside world. This means that the HCT variant of the 74HCT14 is required, not the HC version. It also means that the H11L1 is powered from 3V3 and the 74HCT14 from 5V.

The schematic itself allows for the use of either TRS (Type A) or DIN MIDI sockets.

This only uses the following RPi GPIO pins:

GPIO14 (TX)
GPIO15 (RX)
5V
3V3
GND

PCB Design

I’ve just managed to get everything into the footprint of a Pi Zero board as long as I only use MIDI TRS sockets.

I did consider the idea of detachable MIDI DIN sockets too (the schematic includes both) but in the end opted for simplicity and went just with TRS. That option is reserved for a future edition should I wish.

It can’t be seen in the PCB view above, but there is actually a missing link that I’ve missed off when routing the board (the perils of have silkscreen overlaps and elements in your schematic unused in the PCB is not probably paying attention to the DRC…). The 74HCT14 should have pins 2 and 3 tied together, but no link was included. A simple solder bridge should suffice.

Closing Thoughts

I’m annoyed about that missing link, but thankfully it is a pretty easy fix.

Apart from that, I’m pleased with how this has come out. As I say a future edition might include detachable MIDI DIN socket connections too.

Kevin