Cheap RollUp Piano with MIDI OUT

Discussion in 'General Electronics Chat' started by jjj, Nov 16, 2008.

  1. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    My musical mission goes on... :)

    I bought a cheap RollUp Piano with MIDI OUT, which works 6VDC.
    I ripped the silicon/vinyl Kbd apart to trace the circuit and contacts. It has the usual 8x8 matrix circuit without visible diodes.

    Now I would like to connect an old 120-button accordion bass box onto it. Each button has only one contact.

    At first I thought of just using signal diodes to bundle the 3 to 4 tune chords, but I soon realized that the moment a tune goes into another block of 8, one switch won't do the job.
    The matrix works with 2V7

    Q: How else could make it work with one switch the most economical way?

    Thx in advance for the good advice.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You could wire it with a rotary switch. The switch would have multiple disks, with multiple poles going to one of two positions. This lets you use the same row selection for all 120 switches, but switches the column action from one section to another.

    These multidisk rotary switches are not as common, but Mouser has one that could work. 3 poles per disk and three disks. It's part # 690-C4D0904N-A @ $23.11. You would want a knob to go with it. All of this is in pg 1644 of the current Mouser catalog.
     
  3. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    Thx beenthere,

    I think we misunderstood each other... because I need to play the chords like an accordion bass.

    I want to connect this cheap Rollup MIDI OUT piano to Janko Kbd. layout (I made myself). That's no problem, because there goes only one tune (or 2V7) to each key on the Kbd.
    The problem is that I want to bundle several tunes for chords; i.e. for instance the button G7 chord:
    F, G and B from one block (of 8 in a block) and D from the next block (to make up the 4 note G7 chord: F G B D).
    Each button of the 120-button accordion bass has only one contact.
    So, how to make one PB-switch switch 4 notes, whereby one is from another
    block of 8 (of that 8 x 8 matrix) ??
    I don't think that can be done with diodes alone, unless the tunes come from the same block (of 8).
    There I could use diodes; for instance Cmaj Chord: C E G
    C --->I----
    E --->I---- Then these 3 go to the C-Button SW ___/.____ and to the same block (in the 8 x 8 matrix).
    G --->I----
    But the moment another block is involved a different switching arrangement will be necessary. Maybe 4066 or AND gates???

    Maybe this explanation is still not good enough? Than I have to draw part of the 8 x 8 matrix...
     
    Last edited: Nov 16, 2008
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you can play chords on the keyboard, then you should be able to duplicate them with the accordion buttons and diodes.

    Do you know how octaves are decoded? As you say, that's going to be critical. I have worked on an organ with a multiplexed keyboard. I would think if you duplicated a closure, it would work whatever the octave that key was in. From your example, it would take as many buttons as there are Cmaj chords to play (1 per octave?).

    I would get a few diodes - 1N4148 are about $.05 each - and experiment. Closing a keyswitch should bring a signal line low. Run a wire out from several keyswitches and see if grounding through an external switch and diodes will cause all those notes to sound as a chord. The action of the keyswitches should be easy to measure with a meter. Look for the voltage change rather than the contact resistance.

    If it works, buy lots of 1N4148's and get busy.

    And yes, I did miss what you want to do at first.
     
  5. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    If you can play chords on the keyboard, then you should be able to duplicate them with the accordion buttons and diodes.
    Yes, that sounds good, but in that case are 3-4 switches activated!

    I would get a few diodes - 1N4148 are about $.05 each - and experiment. I got over a 1000 of them and I also don't think I can damage anything, because they all are merely switching; I only will get right/ wrong tunes. Besides, the PS and the speaker can be plugged in; so, I can hear the result!

    Well, I'm almost sure that it will only be possible to do bundle the chord notes within the group (of 8) with diodes and those chords, with notes from the adjacent group will have to be switched via a 4016, AND-gates etc.
    Regards, jjj from Chile
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Some friends of mine recently left a roll up keyboard in South America for use there.
    This wouldn't be the same keyboard would it?
     
  7. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    You're not joking, aren't you? :)
    I bought mine on eBay $US77, incl. shipping from HK...(Chinatown)
    Its sounds are awful, but I only wanted MIDI OUT and that's as good as any Kbd. Controller can get.
    It offers the advantage to allow building and trying out various Kbd. layouts, such as Janko or C-system.
    I also want to build an ordinary "zebra" piano layout, but with buttons and the black keys equal-leveled with the white keys. That'll be easier on my two "left hand dexterity".
    I.e. my Synth's black keys stick out over the white ones and that makes my fingers run against them, when I try to mach the same distances in other scales. (Not sure if you follow me?)
    My theory is, that if all keys are equal-leveled or "uniform", then this problem won't exist! I leave you with some food for thought... :)
     
  8. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    Anyone remember that Star Trek episode when Cap'n Picard brings home a roll up piano from another planet? Who would've guessed we'd have the real thing so soon. ")
     
  9. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    The last couple days I was searching for some kind of midi filter, where the chords are already bundled or can be bundled and then called up with one button... but I seem not to find such a thing.
    It's much more complicated to wire up chords than just one MIDI trigger.
     
  10. jjj

    Thread Starter Senior Member

    Feb 25, 2007
    111
    0
    I think I found, what I'm after, here:
    http://midigrid.fullpitcher.co.uk/moreaboutmg.html

    Incidentally, it's very much what I had in mind. Something like a page with single, triggerable chords in it.

    I wrote MIDIgrid and explained my needs. Not sure if it really works for my purpose? It should, but I don't know how to wire the buttons for MIDI...
    MIDIgrid or "MIDIgreed" merely wrote: It allows the user to create a virtual instrument that plays only the notes or chords required in a particular improvisation session. These can then be played with a mouse or triggered from an external MIDI device.
    As the bottom of this page ( http://www.drakemusicproject.org/makepage.asp?page=4cPS-MG ) shows, if I use MIDI control I have to buy another rollup piano and wire it to the 120- button of the accordion accompaniment (and set it on another MIDI channel), because it's impossible triggering MIDIgrid chords from the same rollup Kbd I play the melody. Or is there another way?
    For decades I try to realize my dreams. Now it's about time I make it or I have to continue my mission in next life! :)
    Regards, Young pensioner (67) from Chile
     
    Last edited: Nov 19, 2008
Loading...