Introduction: The Strings Theory

The Strings Theory is a Midi Synth Module based on the Solina String.
The core of the project is the Arduino Nano that handles incoming midi messages (only notes on and off) and then produce sounds.
The DAC converter is very simple and based on a low pass filter that transforms the square wave into a rippling saw signal.
This is a 4 note poly synth.

Watch the video for the first version with keyboard.
The sound module is the same.

Step 1: Bill of Material

  • Arduino Nano (also chinese with CH340 chip)
  • Optocoupler 6N137
  • Resistors: 220, 10K, 2x 1K
  • Capacitors: 100nF
  • Diodes: 1N4148
  • 4 switches Dipswitch (I used the 8 switches ones)
  • Red led diode
  • 6,3mm mono female
  • DC female
  • 5 pin midi female
  • Knobs
  • 1509B Diecast Hammond Case
  • Wires
  • Solder

Step 2: Drill the Enclosures

I planned the position of every components the allow the perfect closing of the module.
Remember that the Arduino is very small so you need only the fit correctly the potentiometers and the audio, midi and dc females.
The file below includes the graphics and the drill image.

Step 3: Arduino Board and Code

I soldered togheter the Arduino Nano and the dipswitch on a small pcb.
I had already midi in circuit reused from an old project, but i advice you to solder evrything on a single board to simplify the circuit and make a better project and easier to close togheter.

Here's the code and I must to thank Jan Ostman (original code) and Dave Morocco (midi mod).


Step 4: Schematic

Here is the schematic to follow and have your sounding module :-)

The 4 switches Dipswitch allows you to select and filter midi channels.
The coding is very simple:

  • 0000: channel 1
  • 0001: channel 2
  • ...
  • 1110: channel 15
  • 1111: channel 16

Step 5: Put All Togheter

Now it's all on your skills.
Grab wires, solder and scissors and step by step you'll be closer to the end.

Step 6: Enjoy :D

Connect your midi keyboard or midi cable from an audio sound card, connect 9v DC power and 6.3 audio mono output.

Play with the knobs and and play your brand new string synth alone or chained with guitar effetcs.

This istructables is running in the Musical Instruments Contest (closing on 27th Jan).
Please vote me :-)
Thanks to everyone.

Instrument Contest

Participated in the
Instrument Contest