A 6x6 MIDI Launchpad based on STM32
PluePill has direct USB connection, thus can play as a USB MIDI device.
There has been 2 methods I've considered to use:
- Based on GreatScott!'s Arduino based Launchpad project (YoutTube video here), MIDI commands can be sent over serial line to computer. Then computer side needs a loopback software (e.g. loopMIDI) to create a "virtual MIDI port" where can be then used by a Serial-MIDI Bridge (e.g. Hairless-MIDISerial) to transmit MIDI signals.
- Direct USB MIDI
The 1st scenario does not work well for me as Serial-MIDI bridge software isn't compatible with my macOS (11.1 Big Sur) anymore. Plus, as BluePill already offers USB line natively, why not make it a USB MIDI device which won't require any driver when plugged in. Thus, I went ahead with the 2nd choice and it's being picked up by Garageband directly.
The Launchpad consists of
- 1 piece Generic BluePill (STM32F103C8T6)
- 1 piece 5x7cm prototype board
- 36 pairs of tactile switches and 1N4148 diodes (to cancel ghosting and masking, see details at section 8 here.)
Column: PA5, PA4, PA3, PA2, PA1, PA0
Row: PA6, PA7, PB0, PB1, PB10, PB11
PlatformIO ❌ uses official core stm32duino, which is not compatible with USBComposite for STM32F1 library yet, see here.
As a matter of fact, USBComposite_stm32f1 clearly mentioned in README section that it was based on a 3rd party core Arduino_STM32.
Arduino ✔️ works for me for now. Just follow the instructions of the Arduino_STM32 core installation guide to setup the board. It comes with USBComposite_stm32f1 library where USBMIDI is already available.
As the 36 buttom keypad only requires 12 pins connection if you set it as a matrix as GreatScott! suggested. But you will actually get error like this guy reported here when you are at compiling. Unfortunately, the answer from the author of Arduino_STM32 mentioned that not all official libraries would work with it.
There has been a similar complaint here, but in Chinese. Good thing is, the same person that reported the issue also gave an solution later in the same thread: Don't import Keypad library directly, but re-write it into your code. And the code that's being shared helped me a lot.
I've realized that the keypad only registers 1 keyoress per time. Probably due to the getKey function in the end of the code. Hopefully USBComposite for STM32F1 can be sooner ported to stm32duino so official Keypad library can be directly used.