Digital Synth VRA8-N for Arduino Uno

Made by ISGK Instruments



  • Monophonic Synthesizer (MIDI Sound Module) for Arduino Uno


  • Serial MIDI In (38.4 kbps), PWM Audio Out (Pin 6, Unipolar), PWM Rate: 62.5 kHz
  • Sampling Rate: 31.25 kHz, Bit Depth: 8 bits

Demo Audio


  • Exhibited in Maker Faire Tokyo 2018

VRA8 Series

Step 1: Wiring

Required Hardware

  • A1: Arduino Uno
  • U1: 3.5 mm Audio Jack
  • R1: 100 ohm Resistor
  • R2: 100 ohm Resistor
  • C1: 100 nF Capacitor
  • Wires


  • See the image

Step 2: Software Installation

  1. Download Source code and extract it.
  2. Download Hairless MIDI<->Serial Bridge and extract it.
  3. Download loopMIDI and install it.

Step 3: Start Synthesizer

Explanation for Windows

  1. Write DigitalSynthVRA8N.ino to Arduino Uno and quit Arduino IDE.
    • CAUTION: We strongly recommend Arduino IDE 1.8.5
      • DigitalSynthVRA8N.ino does not work well with Arduino IDE 1.8.6 or later
  2. Start loopMIDI.
  3. Start hairless-midiserial.exe (Hairless MIDI<->Serial Bridge).
    • Set [File] > [Preferences] > [Baud rate] to 38400 bps.
    • Select Arduino Uno (COM*) on Serial Port.
    • Select loopMIDI Port on MIDI In.
  4. Open vra8-n-ctrl.html (VRA8-N CTRL) with Google Chrome.
    • Select loopMIDI Port on MIDI OUT.
    • Select a MIDI controller on MIDI IN (if you have it).
  5. Click (or touch) the Software Keyboard, and you can hear the sound.


  • Click sounds may occur when you connect the audio out to an amp/a speaker or reset the board
  • Click sounds may occur when you change the controllers
  • Low CUTOFF with high RESONANCE can damage the speakers
  • The Arduino PWM audio output is a unipolar LINE OUT
    • Please connect this to a power amp/a headphone amp (not to a speaker/a headphone directly)



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