I am a bit fan of the Pimoroni Dual Expander module for the Raspberry Pi Pico. I've used it quite a lot with my Raspberry Pi Pico MIDI "pack" Interface for example. So I thought it might be nice to place my 3V3 MIDI Module onto a board following the same idea, giving space for a Pico and a prototyping area. This is pretty much an extension to my Raspberry Pi Pico MIDI Module PCB.
Tutorials used in this project:
If you are new to microcontrollers, see the Getting Started pages.
The Circuit
This is simple a standard MIDI 3V3 IN and OUT circuit and the footprint of the Raspberry Pi Pico. I've include two sets of header pins to allow the MIDI interface to link to either UART 0 (GP0/1) or UART 1 (GP4/5), but otherwise there is nothing else really to add.
PCB Design
The main issue with this design was getting the smaller track widths to allow me to route all of the Pico's IO over to the expansion area.
To get an accurate "replay" of the Pico's IO pins for the expansion area, I copied the Pico's footprint and then edited it in the footprint editor, being sure to only save it locally, to mirror it and remove the extra items (like the SWD port and USB pads). It needed a little editing of the labels too, and they don't line up quite so well in mirrored form, but it is pretty close.
I wasn't sure where best to site the header jumpers, but decided I didn't want them beneath the Pico, as I did for my Raspberry Pi Pico MIDI Module PCB, so I opted to have them alongside the Pico between it and the MIDI interface. This conveniently meant there was a bit of space below for some reminder text about how to select the UART.
I toyed with the idea of mounting holes, but in the end, the desire to keep it all fairly minimal won out and I didn't bother.
The MIDI circuit is the simplest H11L1 IN and non-buffered 3V3 OUT I have. I added a GND fill zone on the underside, as I've now taken to doing for my latest designs, but haven't shown that in the above diagram.
But for this one, I've also added a top-side GND fill too. It seemed like a prudent step considering the amount of free space between the tracks.
Closing Thoughts
I think this one could be really useful for experimenting. As I say, I really like the Pimoroni expander, so having one with pre-built MIDI should be really handy. I did toy with the idea of having several expansion "slots", but I've opted for one just for now.
Once again, this is being manufactured courtesy of some of my Seeed Fusion vouchers, so watch this space.
Kevin
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