Making a MIDI controller device with PicoRuby/R2P2 (RubyKaigi 2025 LT)

RubyKaigi 2025 LT https://rubykaigi.org/2025/presentations/lt/ #rubykaigi

Tip: In the demo movie (and the performance after the LTs), Digital Synth PRA32-U2 (with Panel) written in C++ is played by MIDI Controller PRMC-1 (type-0) using PicoRuby/R2P2

URLs in the slides:
- MIDI Controller PRMC-1 (type-0) Demo https://youtu.be/Eq25Ze3kTH4
- MIDI Controller PRMC-1 https://github.com/risgk/midi-controller-prmc-1
- MIDI 1.0 Detailed Specification https://midi.org/midi-1-0-detailed-specification
- MIDI1.0規格書 https://amei.or.jp/midistandardcommittee/MIDIspcj.html
- Ruby x Arduinoでシンセサイザーを作ってみた (浜松Ruby会議01) https://gist.github.com/risgk/0db52ea683530652d933
- PRA32-U2 https://github.com/risgk/digital-synth-pra32-u2
- ラズベリー・パイPico/Pico W攻略本 https://interface.cqpub.co.jp/magazine/2023pico/
- シンセカイリアル (Synthesizer Meeting Real) on April 28th https://x.com/Yasushi_K/status/1910670512419738018
- PicoRuby https://github.com/picoruby/picoruby
- R2P2 https://github.com/picoruby/R2P2
- Want the option to fix timeout on I2C #206 https://github.com/picoruby/picoruby/issues/206

Transcript

1. Making a MIDI controller device with PicoRuby/R2P2 RubyKaigi 2025 LT Ryo Ishigaki
2. MIDI Controller PRMC-1 (type-0) Demo 2/22 https://youtu.be/Eq25Ze3kTH4
3. Thank you for listening! 3/22
4. MIDI controller PRMC-1 (type-0) • PRMC-1 is a MIDI Controller using PicoRuby/R2P2 • https://github.com/risgk/midi-controller- prmc-1 • Made to control synthesizers in electronic music performances • PRMC-1 transmits MIDI messages • Hardware (no soldering) • Raspberry Pi Pico • Grove Shield for Pi Pico • M5Stack Unit 8Angle • M5Stack Unit MIDI • All code is written in Ruby! 4/22
5. MIDI (Musical Instrument Digital Interface) • Examples of MIDI messages • Note On/Off: Turning on/off a note • Control Change: Modifying sounds (or adjusting parameters) • Program Change: Changing tones • Clock: Synchronizing the tempo of devices (24 clocks per quarter note) • Start/Stop: Controlling playback • MIDI receivers and transmitters use UART (Universal Asynchronous Receiver/Transmitter) at 31.25 kbaud • For details, see the specifications • MIDI 1.0 Detailed Specification https://midi.org/midi-1-0-detailed-specification • MIDI1.0規格書 https://amei.or.jp/midistandardcommittee/MIDIspcj.html 5/22
6. Specifications of PRMC-1 (type-0) • Usage • CH1 – CH4 Knob: Root of Step 1 - 4 Chord • CH5 Knob: Arpeggio Pattern, 1 - 6 • CH6 Knob: Brightness • CH7 Knob: Harmonic Content • CH8 Knob: BPM • SW Switch: Start/Stop Sequencer • Simple functions • 4-step chord sequencer for playing chords as arpeggios • Adjusting Brightness (Cutoff) and Harmonic Content (Resonance) • Unit MIDI has a built-in synthesizer chip (SAM2695), so PRMC-1 can also produce sound directly 6/22
7. About me • Ryo Ishigaki (石垣 良) @risgk • Member of Hamamatsu.rb (called “Hamamatsu Ruby”) • Hamamatsu is the physical birthplace of Ruby • Embedded software engineer • Experience: projector, milling machine, audio product, etc. • Making synthesizers for microcontrollers using C/C++ as a hobby 7/22
8. Making synthesizers • Hamamatsu is famous for its musical instrument industry • One of the reasons I started making synthesizers is that I moved to Hamamatsu • About 11 years ago, my first synthesizer VRA8 was prototyped with Ruby and ported it to Arduino Uno • Details: Ruby x Arduinoでシンセサイザーを 作ってみた (浜松Ruby会議01) https://gist.github.com/risgk/0db52ea683 530652d933 8/22
9. Making and playing synthesizers • As ISGK Instruments, I make about one synthesizer a year and exhibit it at Maker Faire and other events • Latest work: PRA32-U2 for Raspberry Pi Pico 2 https://github.com/risgk/digital-synth-pra32-u2 • I wrote articles on synthesizer making for a magazine and a book • Book: ラズベリー・パイPico/Pico W攻略本 https://interface.cqpub.co.jp/magazine/2023pico/ • I am challenging electronic music performance using hardware synthesizer, called “machine live” • I will be at シンセカイリアル (Synthesizer Meeting Real) on April 28th https://x.com/Yasushi_K/status/19106705124197 38018 9/22
10. PicoRuby and R2P2 • PicoRuby is a Ruby implementation for one- chip microcontrollers • https://github.com/picoruby/picoruby • PicoRuby’s VM is mruby/c • R2P2 (Ruby Rapid Portable Platform) is a PicoRuby shell for Raspberry Pi Pico and others • https://github.com/picoruby/R2P2 • Usage of R2P2 1. Drag and drop a release binary into the RPI-RP2 drive of Pi Pico 2. Connect the shell through a serial port with a terminal emulator 3. /home/app.rb is automatically run at startup 10/22
11. Functional Units of M5Stack • Functional Units of M5Stack are compatible with Grove interface • So, most of these should work with Raspberry Pi Pico • However, as far as I have briefly tested, M5Stack Unit 8Encoder did not work well for some reason... 11/22
12. Timeout error in I2C • When accessing M5Stack Unit 8Angle in R2P2 environment, I2C (Inter- Integrated Circuit) timeout errors occurred frequently • Workaround • Use only 1-byte registers • Reduce communication speed to 20 kbps (usually 100 or 400 kbps) • If an error occurred, retry • I would like PicoRuby to have an option to adjust the timeout (like Arduino) • Want the option to fix timeout on I2C #206 https://github.com/picoruby/picoruby/issu es/206 12/22
13. prmc-1-type-0.rb (about 400 lines) require 'i2c' require 'uart' # options MIDI_CHANNEL = 1 … class M5UnitAngle8 … end class MIDI … end class PRMC1Core … end # setup … # loop loop do … end 13/22
14. class M5UnitAngle8 def prepare_to_get_analog_input(ch) @i2c.write(ANGLE8_I2C_ADDR, ANGLE8_ANALOG_INPUT_8B_REG + ch) rescue retry end def get_analog_input @i2c.read(ANGLE8_I2C_ADDR, 1).bytes[0] rescue retry end 14/22
15. class MIDI def send_note_on(note_number, velocity, channel) @uart.write((0x90 + channel - 1).chr + note_number.chr + velocity.chr) end def send_note_off(note_number, velocity, channel) @uart.write((0x80 + channel - 1).chr + note_number.chr + velocity.chr) end … def send_clock @uart.write(0xF8.chr) end 15/22
16. class PRMC1Core (1) def change_parameter(key, value) case key … when 4 arpeggio_pattern = (value * (6 - 1) * 2 + 127) / 254 + 1 case arpeggio_pattern when 1 @arpeggio_intervals_candidate = [1, 3, 5, 7, 1, 3, 5, 7] @step_division_candidate = 8 when 2 @arpeggio_intervals_candidate = [1, 3, 5, 7, 5, 3, 1, 3] @step_division_candidate = 8 16/22
17. class PRMC1Core (2) def process_sequencer if @playing usec = Time.now.usec … receive_midi_clock … end end … def receive_midi_clock @midi.send_clock … @midi.send_note_on(@playing_note, NOTE_ON_VELOCITY, @midi_channel) if @playing_note != -1 … @midi.send_note_off(playing_note_old, NOTE_OFF_VELOCITY, @midi_channel) if playing_note_old != -1 17/22
18. # setup led_builtin = GPIO.new(25, GPIO::OUT) led_builtin.write(1) i2c1 = I2C.new(unit: :RP2040_I2C1, frequency: 20_000, sda_pin: 6, scl_pin: 7) angle8 = M5UnitAngle8.new(i2c: i2c1) uart1 = UART.new(unit: :RP2040_UART1, txd_pin: 4, rxd_pin: 5, baudrate: 31_250) midi = MIDI.new(uart: uart1) prmc_1_core = PRMC1Core.new(midi: midi, midi_channel: MIDI_CHANNEL) current_inputs = [] 18/22
19. # loop (0..7).each do |ch| prmc_1_core.process_sequencer angle8.prepare_to_get_analog_input(ch) prmc_1_core.process_sequencer analog_input = angle8.get_analog_input if current_inputs[ch].nil? || analog_input > current_inputs[ch] + 1 || analog_input < current_inputs[ch] - 1 current_inputs[ch] = analog_input prmc_1_core.change_parameter(ch, 127 - current_inputs[ch] / 2) end end 19/22
20. After this • I will continue to evolve PRMC-1 • Ruby code is easily modified, so PRMC-1 (type-N) may be made for each performance 20/22
21. Would you like to create your own musical device? Enjoy electronics! 21/22
22. Finally... Live performance! 22/22