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EMMG Midi Synth

I’m organizing a MIDI workshop at PumpingStation One sometime in 2024. I decided to try to Work with the garage door up, and share everything as I am doing it. This is not meant to be a full-fleshed finished documentation more splattering my brain on a wall so I can see more clearly.

Constraints

  • < $20 . Initially I was going to make two devices each < $20 but that’s more work and more risk of getting it wrong
  • Can be soldered by beginners in a reasonable amount of time, so the SMDs will be pre populated
  • Can be made by JLCPCB
  • Provide several modalities to interact (touch, rotary)
  • Provide feedback (display or leds)
  • MIDI and USB-MIDI connectivity

Software

Probably going to use CircuitPython because of synthio and other modules that are relatively easy to use for beginners. Only issue is that it is only single core, so for more advanced uses that will be insufficient. Not even sure it can drive display and touch and sound together reliably.

2024-07-13 - I received a few I2S DACs so here is the kind of sounds that thingy is going to be able to do:

A led that changes color slowly next to a tea cup with cute cats on it

Hardware

  • Raspberry Pico a new version is coming soon really excited
  • A PCM5120 I2S board this is a big chunk of the cost but it is also an annoying one to make
  • 8 Potentiometers 10K
  • Analog Multiplexer 74HC4051DRG - SSD1306 display (SPI 4 wire)
  • 1 Switch
  • Cap sensing

This leaves 2 GPIOs out of the PICO which I’ll probably leave free if they want to do their own extensions.

Current files are here: https://github.com/bjonnh/2024_emmg_workshop_midi

Plan 2

2024-07-12 I have sent 5 of them for production to JLCPCB. Current cost is around $25, not including eventual customs. The cost should be a bit lower with more units, but we are still above the expected $20. Some components moved a little bit from the design below but nothing big in the DRC (for once).

Rendering of Plan 2 seen from the front with a Raspberry Pico on the top left, a tiny oled screen on its right a jack on the right of the screen. Below the screen are two jacks that cannot be seen on this render. There are 8 potentiometers vertical. A button and pads arranged in 4x3

	I like this one better, it is smaller, only one layer to solder things on, and overall a better usability.

Plan 1

Front PCB where we can see 12 touch pads agenced in 4 x 3, place for 4 potentiometers on the top, 3 on the right, and one potentiometer and a switch next to a acreen.

Back PCB, we see the midi interface and the emplacement for the audio card

Schematic

This is a fully routed try. I’m not a fan of it. I will put the display above the midi ports to gain some space. Ideally I can save all that space on the right and get all the pads closer together too.

Sources of inspiration

https://www.tindie.com/products/todbot/qtpy_synth/ https://diyelectromusic.com/

FAQ

  1. I want to buy one

    Nope this was only for a workshop with real meat in a real room. if you want something like that, todbot is selling some on Tindie he is the one who inspired that so give it back to him.