Open-KeyPrec

Open-Sourced Electric Keyboard Percussion Instrument

Code   Build   Usage   License

About

Open-KeyPrec is an open-sourced, pressure-sensitive electric keyboard percussion (mallet) MIDI instrument. It has 61 keys, spanning 5 octaves of playing range from C2 to C7 like a standard Marimba. It also has a MIDI control panel with 16 buttons, 12 knobs (8 × 280° potentiometers and 4 × 360° rotary encoders).

The sensors are controlled by a development board, and the output is converted into a standard MIDI device. You can use audio workstation softwares like GarageBand or Reaper (or open-source alternatives like LMMS, Zrythm, or Ardour) to simulate the sounds of all kinds of different instruments.

Code

Source code structure

• /src - PC driver written in Rust
• /firmware - Development board firmware written in C++
• /circuits - Printed circuit boards
• /models - 3D-printable models

Toolchains & Environments Used

• EasyEDA: Web-editor for creating circuit boards
• FreeCAD: Software for designing mechanical 3D models
• CLion: IDE for Rust & C++
• PlatformIO: Firmware development toolkit

Pin Configuration

Pins	I/O	Description
4	O	Mux Select for C2-B6
5	IA	Mux Input for C2-B6
1	IA	Input for C7
8	I	(Panel) Input for 4 rotary encoders
3	O	Mux Select for buttons and potentiometers
2	I	Mux Input for buttons
1	IA	Mux Input for potentiometers
3	O	RGB LED Control

Total ADC channels required: 7 Total GPIO required: 23

Build

Materials Required

!!!!!!!!!! TODO !!!!!!!!!!

Tools Required

• FDM 3D Printer (~$300 Ender 3 is fine)
• Soldering kit (iron, solder, flux)
• Wood Saw
• A computer

1. Order PCBs

I ordered my PCBs from JLC, but any PCB service would work. They should accept the exported Gerber zip files in circuits/Exports folder.

I created two circuit boards for this keyboard, one is the multiplexer (Mux v2.zip) which uses the CD74HC4067 1:16 multiplexer ic to convert the 61 separate analog inputs requirement into only 5 analog inputs and 4 digital switch outputs. It also haso diodes and resistors for voltage protection. The other pcb (OKP-Panel-SMT.zip) is for the MIDI control panel containing the buttons and knobs.

1. Go to jlcpcb.com (Or jlc.com if you read Chinese)
2. Upload the Gerber file
3. Set parameters: FR-4, 2 Layers, Color, leave default for other options

PCB Assembly (SMT)

If you're not comfortable soldering small SMD components, you can order PCB Assembly from JLC. You can also select which parts you would like to SMT based on your soldering abilities. For example, in the Mux pcb, I ordered SMT for only the 0603 Zener diodes and the CD74HC4067 ic, and hand-soldered everything else.

1. Order "PCB Assembly" (SMT) and click confirm
2. In the SMT menu, upload the BOM and CPL (PickAndPlace) files
3. After uploading, remove the parts you want to manually solder (they're pretty expensive, since someone in the factory still have to manually solder them for you)
4. Order manually-soldered parts somewhere else (e.g. szlcsc.com)

Usage

Flash Firmware

1. Install PlatformIO Core (Guide)
2. Open the firmware directory
3. In your preferred IDE, edit src/config.h with your pin configuration.
4. Edit platformio.ini to match your dev board.
5. Connect dev board, build and upload firmware using platformio run --target upload

Setup MIDI Device

!!!!!!!!!! TODO !!!!!!!!!!

Setup Audio Softwares

A MIDI keyboard doesn't make sound on its own. To actually play an instrument, you would need an audio workstation software and some VST sound sources.

Notation: 🍎 - macOS, 🪟 - Windows, 🐧 - Linux

Free Mallet Sound Sources

Built-in Sources

• GarageBand comes with marimba, vibraphone, and glockenspiel sound sources. It's free but macOS only and does not have VST support.
• LMMS comes with several mallet instruments.

External Plugins

Name & Link	Author	Platforms	Formats
Alto Glockenspiel	Steinberg	🍎 🪟	VST, AU
Marimbaphonic	Alan Vista	🍎 🪟	VST, AU
VibroMaster	Alan Vista	🍎 🪟	VST, AU
DSK Virtuoso (Celesta, Glockenspiel, ...)	DSK Music	🪟	VST

Unfortunately there aren't any free VSTs supporting linux that I can find. You have to use Windows for this one if you don't have a mac/hackintosh. If you found any additional VSTs, feel free to make a PR!

Other free VST Plugins: https://github.com/webprofusion/OpenAudio