Cheap RollUp Piano with MIDI OUT

[jjj]

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.

[Enzo]

Your MIDI device needs a matrixed input control circuit. Your one button per note squeeze box will either have to be rewired or you will need to build an interface circuit to do the conversion.

"The matrix works with 2v7."

Are you sure? Or did you just measure that voltage between open contacts? The matrix is strobed, that means that every 1/400th of a second - or whatever - a pulse turns on each stobe line (column) of contacts. Then the next, then the next ,etc. The other direction in the matrix is the returns (rows), and th computer circuit watches each return line when each strobe pulse is "on." If it sees any strobe pulses on the return lines, then it knows those switches were closed.

There is not usually a steady voltage in these circuits, the momentary pulses average out on your meter.

[jjj]

Greetings Master Enzo, my friend! I still have a bad conscience, for having upset you last time... Nice to meet you and thanks for offering to help.
Your MIDI device needs a matrixed input control circuit. Your one button per note squeeze box will either have to be rewired or you will need to build an interface circuit to do the conversion.
As mentioned, I now know exactly what matrix it needs. The matrix works with 2v7.

Are you sure? Or did you just measure that voltage between open contacts?
Yes you are right, I only measured between open contacts.

The matrix is strobbed, that means that every 1/400th of a second - or whatever - a pulse turns on each strobe line (column) of contacts. Then the next, then the next ,etc. The other direction in the matrix is the returns (rows), and the computer circuit watches each return line when each strobe pulse is "on." If it sees any strobe pulses on the return lines, then it knows those switches were closed.
So, it's far more complicated than I knew/ thought! So, but I think you know exactly what I'm up to.

I won't have a problem connecting the single tunes to my self-made Kbd., but connecting bundles of 3 to 4 chord notes, from which one or two notes cross over to another block, can surely not be controlled with one push-button (from/ on the accordion accompaniment button).
How to do that in an economical way?
Can it be done with diodes alone? (I got a 1000 of them!) I mean, for as long the chord notes are within the same block (of 8 tunes in one block), I can do it with diodes; but what to do when one or two notes cross over to another block??

Beside, don't you think my idea of realizing my dream with this cheap Rollup Piano than with my Synth, is great idea?

[Enzo]

Yes, when 5v is switched off and on about 50% of the time, your meter will think it sees 2.5v.


Does your accordion box still have to do other jobs? Or will it become strictly a MIDI controller? If it will go to MIDI only, then rewire the buttons as a matrix.

If there are no isolation diodes in the matrix of your rollup, how can it recognise chords without getting confused?

I don't know the system you have, so I don;t know how a bunch of diode-ORs would work here, the rollup doesn;t have a common, it has a matrix.

Without a clear Idea, what comes to my mind is programming an 8-bit ROM to decode chord button inputs, or a PIC chip.

[jjj]

Yes, when 5v is switched off and on about 50% of the time, your meter will think it sees 2.5v.
I see!

Does your accordion box still have to do other jobs? Or will it become strictly a MIDI controller? If it will go to MIDI only, then rewire the buttons as a matrix.
Yes, strictly a MIDI controller.

If there are no isolation diodes in the matrix of your rollup, how can it recognise chords without getting confused?
I wondered, too. It must be that they are already in the IC.

I don't know the system you have, so I don;t know how a bunch of diode-ORs would work here, the rollup doesn't have a common, it has a matrix.
Tomorrow I'll draw up a bit of the matrix.

Without a clear Idea, what comes to my mind is programming an 8-bit ROM to decode chord button inputs, or a PIC chip.
It's hopefully simpler than that.

Beside, I remember you once said that you mostly work at nights...

[Enzo]

Isolation diodes are there to prevent to keys pressed at the same time from shorting either strobe or return lines together. I don;t know how they could be inside the chip.

I understand how matrix keyboards work, I don;t know how your buttons would work in one. For chords, if all the notes had a common strobe or return, then simple diode combinations would work, But I'd be betting that won;t be the case, so multiple contacts would be needed, or some sort of translater.

I don;t do PICs or ROMs. but for someone into them, they are really simple. Write a little basic program or whatever you need and a look up table for the keys to translate

[trevorus]

Enzo, is there anything you don't know something about? Amazing advice and insight as always.

[Steve Conner]

Before you ripped it apart, did you check that it was capable of playing chords? Not all matrix keyboards can recognise multiple keys held down at once. The buzzword is "N-key rollover", and N can be anything from 1 in the cheapest, nastiest controllers, to the number of keys on the keyboard.

I just finished making a keyboard controller out of a PIC in my day job, and they do indeed work just like Enzo says. To add diode ORs, you need to figure out which are the drive lines and which the sense lines (I think Enzo refers to these as strobe and return) and whether they're active-high or active-low. Also how many diode drops the sensing circuit can tolerate before it fails to register the keypress.

It would be far easier to wire one accordion button per piano key, and write a small MIDI filter program that converted the single notes to chords, assuming one doesn't exist somewhere already (google it) To me, that's "simpler" than messing around with hundreds of wires and diodes, and you can change it any time.

[jjj]

Hi friends Sir Steve Conner and Master ENZO,

Before you ripped it apart, did you check that it was capable of playing chords? Not all matrix keyboards can recognise multiple keys held down at once. The buzzword is "N-key rollover", and N can be anything from 1 in the cheapest, nastiest controllers, to the number of keys on the keyboard.

Yes, I did... and got both hands full! That was pretty good.

I just finished making a keyboard controller out of a PIC in my day job, and they do indeed work just like Enzo says. To add diode ORs, you need to figure out which are the drive lines and which the sense lines (I think Enzo refers to these as strobe and return) and whether they're active-high or active-low. Also how many diode drops the sensing circuit can tolerate before it fails to register the keypress.
I'm too stupid (or maybe only lazy to learn) to do it with a PIC. It requires programming etc. That's why I thought to use something ready made and cheap.
The diodes must be within the main chip, because the matrix consists has only 2 terminal blocks with 8 contacts each.
Last night I promised Enzo to sent some details of that matrix; here it is:
Block A (one side of SW):
Pin 1 goes to key 1 of each group (of 8 keys); starting with lowest "C".
Pin 2 goes to key 2 of each group (of 8 keys) etc.
Block B (other side of SW):
Pin 8 goes to group1 (of 7 groups + 1 group 5 keys) start lowest octave side.
Pin7 goes to group 2 etc.

It would be far easier to wire one accordion button per piano key, and write a small MIDI filter program that converted the single notes to chords, assuming one doesn't exist somewhere already (google it) To me, that's "simpler" than messing around with hundreds of wires and diodes, and you can change it any time.
I know what you mean. The chord could be ready combined via software and it would only need MIDI triggering. That idea I had too, but I cannot find any Prog suitable for it.

My latest idea/ tick is to "uniformate" the ordinary zebra piano layout!
Because its present irregularity (the sticking out, narrow black keys) is a pain in the proverbial; costing us years of scales and chords practice!!
I want to create a Kbd with very little key (contact) travel. That way the black keys can be almost level with the white ones, making it far easier for my "two left hands" dexterity to maintain the fingering distances. On my Synth Kbd the black keys are about 10mm above the whites, causing my fingers to run against them... while trying to judge the distances in a different scale. I haven't got the problem playing in C-major, because all keys of the scale are white (have no walls!).

[jjj]

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: MIDIgrid 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/mak...p?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 musical dreams. Now it's about time I make it or I have to continue my mission in next life!