I have a range of Ready-Made MIDI Modules but all of my 3V3 ready ones tend to be DIY MIDI Interfaces, so I thought I’d capture the now largely ubiquitous 3V3 MIDI circuit that I keep using into a single module.
Note: This is recommended for use with cheap microcontrollers, NOT more expensive single board computers such as the Raspberry Pi.
Update:
- Find the Build Guide here: 3V3 MIDI Module PCB – Part 2
Tutorials used in this project:
- MIDI In for 3.3V Microcontrollers
- MIDI, MicroPython and the Raspberry Pi Pico
- Notes on KiCad for PCB design: Arduino Uno Dual Merge MIDI “Shield” – Part 2
If you are new to microcontrollers, see the Getting Started pages.
The Circuit
This is my now-standard microcontroller 3V3 MIDI IN circuit, based on the H11L1, and the 3V3 compatible MIDI OUT. There is no buffering, it is all left pretty simple, so the microcontroller isn’t as protected as it might be. For this reason, I recommend only using this board with a microcontroller, not more expensive single-board computers (such as the “full” Raspberry Pi).
For a discussion of the current issues around driving MIDI OUT directly like this, see: MIDI, MicroPython and the Raspberry Pi Pico.
The module will be powered just from 3.3V and provides a RX/TX link and GND. It gives single MIDI IN and MIDI OUT ports, but I’ve tried to keep it as compact as possible.
There isn’t a lot more to be said about it!
Note: There is an error in the schematic and PCB labelling. That capacitor is a 100nF not a 100uF capacitor.
PCB Design
I’ve gone with a relatively simple layout, all using through-hole components. The link back to a microcontroller will be via jumper header pins.
I decided to label the pins IN and OUT rather than attempt to solve the “RX to RX or RX to TX?” issues I have with some of my other off-the-shelf modules!
Even this isn’t totally clear of course, as one might interpret it as “OUT” from the module has to go to “IN” (RX) on the microcontroller… but I went for OUT being the MIDI OUT circuit and IN being the MIDI IN circuit. This means IN should connect to RX and OUT should connect to TX. It was the thing that made the most sense to me at the time…
You can see from the footprints that once again I’ve used the slightly tailored version of the MIDI sockets, with rectangular pins, but other than that I think everything else was fairly straightforward in layout.
And as I say that capacitor value is wrong. It’s a 100nF ceramic capacitor.
Closing Thoughts
Whilst I’m still spending my Seeed Fusion coupons, this one went in the basket too.
Some enhancements for the future could include:
- MIDI activity LEDs for each port.
- A switch to temporarily disable the MIDI link if required.
- An output buffer to make it a little more robust and universal.
- Mounting holes. I did toy with the idea, but then decided I don’t tend to use modules like this in mounting-type situations, so didn’t bother.
Kevin
Simple DIY Electronic Music Projects 