Build your own MIDI circuits
Frequently Asked Questions.
MIDI & Music
MIDI and Music Information
MIDI Octave Expander


MIDI Octave Expander


The MIDI Octave Expander is used to expand a MIDI note to add an Octave above and/or an Octave below, so as to increase the overall sound. For example it can be used to increase the 'lushness' of a string section or individual string sounds.



*Click to Enlarge*


MIDI Octave Expander


PRICE:  €50.00






The MIDI Octave Expander unit utilizes:


  • An assembled, built and tested Arduino board including a suitable pre-programmed microcontroller,
  • A MIDI IN and OUT board,
  • A 2.1mm power socket, and associated LED, 
  • A MIDI detection LED,
  • A 150mm wired MIDI 5-pin DIN input socket,
  • A 150mm wired MIDI 5-pin DIN output socket, 
  • The complete circuit schematic is available,
  • The MIDI IN/OUT circuit schematic is also available.



The MIDI Octave Expander requires:

  • A 9 Volt battery or equivalent 9 Volt DC external power source, or USB Connector,
  • 2 pushbutton switches.








     *Click to Enlarge*

The MIDI IN and OUT connectors use  5-Pin 180 degree DIN sockets. Note that the MIDI IN/OUT wiring is polarised and the correct pins should be used.






Two push-button switches provide Octave Down and Octave Up functions.  Press the Octave Down push-button switch once and the MIDI note the unit receives, plus an octave below sounds, push it again and it returns to normal, so the octave below no longer sounds. The operation is similar with the Octave Up  button, but with the octave above sounding. So it is possible to have just the original note playing, the original note plus an octave above or below (2 notes), or the original note plus an octave above and an octave below (3 notes).


The unit detects the incoming MIDI data, and all other MIDI commands and data are transferred from the MIDI IN to the MIDI OUT socket unchanged.




Power Supply:

The  Arduino can be powered via the USB connection or with an external power supply. 


External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.


The board can operate on an external supply of 7 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.