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MIDI Piano Accordion and Stradella Bass

 

MIDI Piano Accordion 

piano_accordion_37note.jpg (8479 bytes)

  

This is a design for a reedless MIDI Piano Accordion. Some of the advantages of such an instrument are instant key changes, via MIDI, and the ability to practice with headphones (silently to the outside world).

 

This keyboard encoder is capable of encoding a number of momentary action, push to make, single pole single throw (SPST), switches for a Stradella Bass 120  and a 41 note piano keyboard (in a 4x12 matrix)  Accordion, utilising a ready built, assembled and tested key-switch interface.

 

The Treble/Melody notes are on MIDI Channel 1. The chord notes are on MIDI Channel 2 and the Bass notes and 3rd notes are on MIDI Channel 3.

    

The Treble/Melody Keyboard encoder is assigned to switches SW0 to SW47 for a 41 key piano keyboard (n a 4x12 matrix (Note that although there are 48 switch inputs only 41 need to be wired).  The switches are arranged as shown in the MIDI Piano Accordion Treble/Melody Mapping.  This schematic diagram also shows the connections for the volume controls VR1, VR2 and VR3 for MIDI Channels 1, 2 and 3, respectively.

 

This arrangement produces MIDI Note numbers 53(F3) to 93(A6), which is the written range for the right-hand manual of a standard 120-bass/41-key piano accordion, three octaves plus a major third.  Actual range can sound one octave lower and one octave higher (F2-A7) depending on the treble and octave Function switch selection.

 

The Bass selection is assigned to a 12x1 matrix and the Chord selection is also assigned to a 12x1 matrix. A circuit schematic of the MIDI Piano Accordion Bass and Chords Mapping

 


 

Function Switch Selection

Note that you should first select the MIDI Channel 1, 2 or 3. Then you can change the Octave or the Sound, via Program Change, on that particular channel.

The Octave switch inputs allow you to change the accordion octave for the Treble, Bass and Chords.

The Program Change switch inputs allow you to change the accordion voices for the Treble, Bass and Chords.

The MIDI Channel switch inputs allow you to select the accordion MIDI Channel for the Treble, Bass and Chords.

 

The Treble, Bass and chords can each be transposed by +/- 1 Octave using two Treble Octave +/- switches, two Bass Octave +/- switches and two Chords Octave +/- switches. 

  

There are four switches for MIDI Program Change -1, +1, -10 and +10 and also two MIDI Channel switches -1 and +1 to select the channel on which the Program Change will take place. 

  

The Octave, Program Change and MIDI Channel switches are shown in the Function switch schematic diagram.

 


  

Other switch arrangements can be assigned if required for keyboard sizes of 26, 30, 34,or 37 notes, and for different note ranges, please email scarff.tom@gmail.com  for details.

 

This unit can be connected to new keyboards switches or it can be used with an older non-MIDI keyboard by using magnetic/reed switches or Hall effect switches.

 

This is a link to the Registers of the Standard Stradella Keyboard.

 

 

MIDI PIANO ACCORDION

ITEM#: MIDIPIANOACC

PRICE:  €75.00


 

*Click to Enlarge*

 

 

 

The MIDI Piano Accordion Encoder Unit consists of:

  • The MIDI channels 1, 2 and 3 are preset, 
  • The piano accordion is preset to MIDI Note numbers 53(F3) to 93(A6), but other ranges can be preset on request,
  • The velocity byte is set to a value of 100, but other values can be preset on request,
  • An assembled  Arduino MEGA, with pre-programmed micrcontroller,
  • A 2.1mm power socket, and associated LED, 
  • USB power or external power choice,
  • A MIDI 5-pin DIN output socket,

 

 

The MIDI Piano Accordion Encoder unit requires:

  • a 9v battery or equivalent DC power source
  • Suitable key-switches or magnetic reed switches or hall effect switches and associated IN4148 diodes,
  • 12 switches and associated IN4148 diodes for the Octave selections, Program Change and MIDI Channel selections.

 

Circuit Schematic:

This unit uses the ATmega Mega microcontroller and can be powered from an external 9 Volt DC power supply/battery or via the USB connection. 

 

 

  

  

Hall Effect Wiring:

Note: Use Unipolar Hall Effect devices and if you use Open Collector devices you will need a Pull-Up resistor for each device.

 

 

  

Videos: 

Here is a video showing how the Root and Major 3rd rods/levers lift one at a time when a button is pressed and here is a video showing when a single bass chord button is pressed 3 rods/levers are mechanically activated simultaneously.

 


 

MIDI Wiring:

The MIDI  OUT connection uses a 5-Pin 180 degree DIN sockets. Note that the MIDI OUT wiring is polarised and the correct pins should be used. 

 


 

Power Supply:

The  Arduino MEGA can be powered via the USB connection or with an external power supply. The power source is selected automatically. 

 

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.

  


 

MIDI Keyboard Wiring:

 

STRADELLA SWITCHES FOR BASS and CHORDS:

Accordions which have had midi units fitted usually have the 12 root note/major 3rd notes served by 12 mechanical switches and the 12 notes which form the  48 chords of the Stradella System are served by another 12 switches only.


The mechanics of the bass system automatically selects the 3 notes/switches of the chord from the 12 available. i.e. the chord is formed mechanically and not digitally.


All 120 bass systems have only 12 bass/3rd  notes and 12 chord notes.

The midi Stradella Bass section is programmed to give, on Midi-Channel 3, 12 fundamental bass (root and major 3rd) notes and on Midi-Channel 2, 12 chord notes. 

 

PIANO ACCORDION TREBLE/MELODY SWITCHES:

 

The Piano Accordion switches are organized in a 12 x 4 matrix (up to 48 switches) arrangement.  Note if less than 48 switches are required, then ONLY the switches required need to be wired.  The switches are wired in a similar manner to the Stradella wiring explained above.

 

For the Treble/Melody switching:

 

Switch SW0 is connected via a diode between pins D14 and D8, giving MIDI Number 53 which is F3,

Switch SW1 is connected via a diode between pins D15 and D8, giving MIDI Number 54 which is F#3,
Switch SW2 is connected via a diode between pins D16 and D8, giving MIDI Number 55 which is G3,
 
etc.

 

PIANO ACCORDION BASS and CHORD SWITCHES:

 

For the Bass and Chord switching:

 
Switch SW0 is connected via a diode between pins D14 and D2, giving MIDI Number 36 which is C2,
Switch SW1 is connected via a diode between pins D15 and D2, giving MIDI Number 37 which is C#2,
Switch SW2 is connected via a diode between pins D16 and D2, giving MIDI Number 38 which is D2,
 
etc.

 

 

PIANO ACCORDION FUNCTION SWITCHES:

  

  

The Octave Function switches are:

 

Treble - Octave is connected via a diode between pins D14 and D4
Treble + Octave is connected via a diode between pins D15 and D4

etc.

 

The Program Change Function switches are:

 

Program Change -1  is connected via a diode between pins D20 and D4

Program Change +1  is connected via a diode between pins D21 and D4

etc.

 

The MIDI Channel Function switches are:

 

MIDI Channel -1  is connected via a diode between pins D24 and D4

MIDI Channel +1  is connected via a diode between pins D25 and D4