3V3 MIDI Module PCB – Part 2

Here is the build guide for my 3V3 MIDI Module PCB.

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

These are the key tutorials for the main concepts used in this project:

• PCB Design in KiCad from Arduino Uno Dual Merge MIDI “Shield” – Part 2.
• Ordering your PCB: a Beginners Guide for Manufacturer Options

If you are new to microcontrollers, see the Getting Started pages.

Bill of Materials

• Naturally, you’ll need a 3V3 MIDI Module PCB (GitHub link below).
• Resistors: one each of 220Ω, 470Ω, 10Ω, 33Ω.
• 100nF ceramic capacitor (not 100uF as labelled on the board!).
• 1N914 or 1N4148 diode or similar.
• H11L1 optoisolator.
• 2x 5-pin 180 DIN sockets (see photos for footprint).
• Optional: 6 pin DIP socket.
• 4-way header pins.

The socket is optional but recommended.

Build Steps

The build should be a relatively straightforward through-hole components build.  All components should be placed on the same side of the board, as indicated by the markings.

I recommend the following order:

• Diode and resistors
• 6-way DIP socket (if used).
• Capacitor
• 4 pin header.
• H11L1 if soldered directly.
• 5-way DIN sockets.

Here are some of the build steps in photos.

To use, the following connections are required:

• 3V3 power.
• GND.
• IN connected to a 3V3 microcontroller’s RX.
• OUT connected to a 3V3 microcontroller’s TX.

In the photo at the top of this post, you can see this connected to a Raspberry Pi Pico.

Testing

I recommend performing the general tests described here: PCBs.

PCB Errata

As mentioned above there is an error in the labelling of the capacitor.  It should be 100nF not 100uF.

As I mentioned before, I do NOT recommend using this board with more expensive single board computers such as the Raspberry Pi.  It is designed for simple connections to microcontrollers.  It will probably work fine, when everything else in the circuit is working fine, but if something goes wrong (e.g. you plug in a faulty MIDI lead or device) there is no protection for the pins driving the output circuit and you risk damaging your expensive (and hard to source these days) Raspberry Pi or similar board!

Potential Future Enhancements:

• A future version could include some mounting holes (I did think about it, but then decided not to).
• An output buffer for additional protection.
• A MIDI activity LED might be useful in the future.

You can find the PCB design files on GitHub here: https://github.com/diyelectromusic/sdemp_pcbs/tree/main/MIDIModule3V3

Closing Thoughts

Once again, I used the Seeed Fusion pcb service, spending some of my discount vouchers and I’m very happy to keep doing so.  As far as I’m concerned the boards so far have always come back in good time and have been perfect for what I need.

Also, as always I have a couple of unpopulated pcbs spare if anyone is interested in having one.  Just ping me a message via some suitable route.  Alternatively, all the required design files are on GitHub.

Kevin