Simple way to play midi on a stepper motor.

There are a lot of projects that make Musik with Arduino and a Stepper motor.

• https://www.instructables.com/Make-Music-With-Stepper-Motors/
• https://projecthub.arduino.cc/JonJonKayne/arduino-midi-stepper-synth-162864 (this one even controls multiple motors)
• https://github.com/jzkmath/Arduino-MIDI-Stepper-Motor-Instrument

But somehow they all use some roundabout way of getting MIDI to the Microcontroller (or so I felt). I wanted a CLI based approach on a linux PC which would allow me play any MIDI file to the Microcontroller. So I did some digging...

• ESP32 or similar
• A4988 stepper motor driver
• stepper motor
• power supply for stepper motor

Check e.g. the following resourced for a minimal HW setup:

• https://www.engineersgarage.com/nodemcu-esp8266-stepper-motor-interfacing/
• https://www.pololu.com/picture/view/0J3360

The ESP32 is using the Midi library to listen to Midi data coming in through the serial port (i.e. USB connected to your PC) It will then drive the stepper motor to produce the note required by the Midi data.

• Logs on to your wifi and produces some debugging output on telnet port (since serial is occupied with MIDI data)
• Calculates a lookup table for intervals needed to play a certain note on the fly at setup
• Accepts Midi files streamed from your PC
• blinks LED

There is only one channel supported. If you have a midi file with multiple channel, you need to filter out the channel beforehand and stream that to the ESP. If you have a midi with multiple channels the playback will sound strange. In part this is due to the extremely rudimentary and blocking implementation of playing the notes. This could be handled much more elegantly, possibly even by simply using this library: https://github.com/daniel-centore/arduino-tone-library

This uses the excellent arduino_midi_library: https://github.com/FortySevenEffects/arduino_midi_library Using the USB serial to transfer the Midi Data, you need to set the Baud Rate to 115200 (that’s what ttymidi uses as default). We are using callbacks which start/stop the playing of notes once a note starts/ends.

You can use timidity to quieten unwanted tracks and output the result to a file timidity -OmM -o imperialmarch_trumpet.mid -Q 1,2,3,4,6,7,8,9,10,11,12,13,14 Downloads/imperialmarch.mid

• Download ttymidi from https://code.launchpad.net/~ttymidi-team/ttymidi/trunk (using bzr)
• build it (just “make” in the directory)

Use ttymidi to create an ALSA port which is bound to a Serial Device /dev/ttyUSB0

./ttymidi -v -s /dev/ttyUSB0 -n myweirdcontroller

Use pmidi to play the MIDI file via the serial port.

Check which ports are available to play to

    pmidi -l
     Port     Client name                       Port name
     14:0     Midi Through                      Midi Through Port-0
    128:1     myweirdcontroller                 MIDI in

Use pmidi to play a midi file to that ALSA port (decisive pointer on that gem. It’s about using timidity as ALSA input. Just substitute with ttymidi as above)

pmidi -p128:1 imperialmarch_trumpet.mid