Whilst on the topic of MIDI modules with built-in expansion capabilities, I also wanted a prototyping shield for an Arduino Uno that has the MIDI circuitry pre-built, so this is the next project.
Tutorials used in this project:
If you are new to microcontrollers, see the Getting Started pages.
The Circuit
This is the very common 5V ready MIDI IN and OUT circuits, utilising a 6N138 for the IN. I've linked up a second set of header pins, as I wanted the first rows of the prototyping area to be linked to the Arduino's IO pins.
But I've also included jumpers that allow for the MIDI interface to be disconnected from RX/TX if required.
PCB Design
The prototyping area was created by adding a single through-hole, setting the grid to 2.54mm and then cutting and pasting many more of them into the space.
There are three columns for 3V3, 5V and GND. These were created by assigning those holes to the correct nets in KiCad and then joining them up. I did create a cut-out in the GND fill zone on the underside of the board around the GND column and then joined them up by hand, otherwise there was a bit of a weird cross-hatching pattern going on between the holes due to the automatic filling algorithm. A single strip I thought was probably more sensible.
As none of these holes appear on the schematic, I get a lot of warnings about pcb and schematic miss-matching when I run the design rules checker. There is probably a correct way to handle that, but I'm afraid I've just ignored them!
Also whilst the 3D view shows rows of pin headers, I've only used them here for the footprint really. I don't anticipate populating them when in use. I just wanted a way to link the Arduino standard headers to the prototyping area.
Closing Thoughts
As I started with the standard MIDI circuits, as used in my design for the Arduino Uno Dual Merge MIDI "Shield", I'd copied over the mistake from that board - the footprint for the 6N138 was too wide (again). Thankfully this time I spotted it when I printed out the design on paper!
This shield would have been so, so handy for some of my early projects, but I can still foresee plenty of uses, assuming it turns out ok, so I still think it is well worth doing.
And yes, I'm still on my spending spree with Seeed Fusion vouchers with this one too - they go a long way when your pcbs are all within the cheapest 100x100mm footprint and you're combining postage!
Kevin
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