the becoming of the midibox axe

[Wisefire]

hi guys,

again with another MB project this time the midibox axe. dont worry the other projects wont be forgotten.

however the other project (MB chaos specificly) will be needing me to know more about programming mios then

i do now, so i decided to take on a lighter task first..

the midibox axe:

im going to build a midicontroller out of this.. the "piano" keys will control the base note, and the red buttons on the neck will be the interval from that ground note. the yellow buttons wil transpose the piano notes temporarily(keep pressed to transpose) to a half octave up, a whole, 1 1/2 octave and 2. the blue triangular arrowlike buttons will be used to switch synth presets allthough there are four and only 2 will be used for that.. dont yet know what the other pair will do. and finally the green.. the biggest will be modded to be a pot meter for modulating pitch, cutoff, resonance etc. and the other 2 will be used to switch between such selections. the 6 neck buttons have leds under them.. which will be used.. for example to see if you have one of the transpose button pressed or maybe to show what note you are pressing on the "piano" part.. or amount of modulation.

maybe even all of that..

there will not be a LCD. as this is a lowbudget project.. let me rephrase that.. its a no budget project.

ive already hit a few snags.. first off the 6 button parts (the Piano and the red neck buttons) have peculiar

connections..  for example the six red neck buttons dont share one common +5 wire.. instead there are 2 "in" wires and 3 "out" wait ill draw you a picture

can this be incorporated into midibox as is or do i need to modify it? i really dont wanna modify this.. as playing with tact switches is a bitch.. and tracing a new pcb wont be possible soon.. and soldering on traces themselves?

not a very easy job! even more difficult is that the leds have a connection in this aswell.. however that i solvable.

secondly, im affraid i dont have enough space to place the core the din and the dout in there.. but i'll think of a way when the time comes..

unmultiplexed AIN.. possible, right? (havent searched the forum for that yet) i only need one ain for the potmeter

with greets,

wisefire

[stryd_one]

Yeh too easy.

in1->out1=note1

in1->out2=note2

in1->out3=note3

in2->out1=note4

in2->out2=note5

in2->out3=note6

Use 2 DOUT pins for the 2 ins, 3 DIN pins for the three ins, and adapt the scanmatrix code to your needs.

Basically, you'll set the 1st DOUT pin, then scan the 3 DIN's, then clear the 1st DOUT pin, set the 2nd DOUT pin, and scan the three DIN's again. The resulting DIN values will tell you which buttons are pressed.

Make sense?

PS I am at work and haven't had time to think this through so I could be totally wrong ;)

[Wisefire]

*note*

make the preset menu buttons double click for prevention of accidental press

[Wisefire]

i dont quite follow you there stryd_one..

to my limited knowledge.. on the DIN PCB all the +5 lines are connected and it doesnt matter which one you pic.. then i would be stuck with only 3 inputs... hold on... are you saying i can use the dout as supply lines?? thats interesting..that would mean that i can scan in sections.. yeah.. does anyone know if this is possible in TK'z design?

[stryd_one]

... hold on... are you saying i can use the dout as supply lines?? thats interesting..that would mean that i can scan in sections.. yeah.. does anyone know if this is possible in TK'z design?

Exactly :) Check out the example application on the ucapps.de download page, it's called sm_example (actually there are two). The SM stands for Scanning Matrix. Yours is a 2x3 design, the example is setup for 8x8, so it'll need some modification...

FWIW I Hope to test the example out and extend it to larger matrices later on, as I will need it for the vX. Your matrix is 2 DOUTs X 3 DINs, total of 6. The example is 8x8 = 64, but you could run many, many more buttons. Using a whole DOUTx4 and DINx4 module would be 32x32=1024 buttons!! Even I don't need that many! :)

[Wisefire]

very cewl.. first ill have to trick out the guitar with the modules.. and then try to code something :S

edit: i wonder if i can remove the huge capacitor from the core board if im gonna use a stabilized PSU?

wanna make the core as low profile as i can get.. ive got limited space in there..

[NorthernLightX]

very cewl.. first ill have to trick out the guitar with the modules.. and then try to code something :S

edit: i wonder if i can remove the huge capacitor from the core board if im gonna use a stabilized PSU?

wanna make the core as low profile as i can get.. ive got limited space in there..

Hi,

sure, you can remove all the following parts if you supply the Core with regulated 5v: rectifier, 2200uF elco, 330nF kerko, regulator (has to be removed), and if you like the 10uF and 100nF caps can be left out too.

If you want to keep it simple: leave out everything before J2 and remove the regulator.

Cheers,  Alex.

[Wisefire]

hmm.. id like to leave the rectifier.. so i dont have to worry about polarity.. would that be possible?

[NorthernLightX]

hmm.. id like to leave the rectifier.. so i dont have to worry about polarity.. would that be possible?

No problem, but take into acount that the rectifier will eat 0,7V of you input voltage. I don't think it's a good plan, look at the optimized SID psu: it uses Core:J2 to get the power in, and thus omits the rectifier too. If you're really paranoid about swapping the polarity by accident, use plugs and sockets that can only be connected one way. A 3 pin SIL header could also do the trick: mount it in the place of the regulator. Then use a female SIL (also 3 pins) and solder the GND to the middle pin, and +5V to one of the outer pins. Leave the other pin blank. Now, if you reverse the plug by accident, you will apply +5v to the wrong track, but that's no problem because there's nothing mounted there. Get the picture?

Cheers,  Alex.

[Therezin]

That thing is the craziest idea i've ever seen.

I want one.

[Wisefire]

NLX: that would be a good idea, however its not the plug that im worried about.. its the psu itself. it not permanently connected to the wires.. so i could swap polarity there.. and then the plug itself would be backwards..

i dont mind that it eats .7V hmm.. maybe ill just leave the power stuff on there.. nothing could go wrong in that case.. well maybe it wont fit.. but thats a risk im willing to take :D

therezin: try ebay.. or marktplaats.. ive seen 2 of these same guitars on marktplaats (the dutch ebay)

and indeed its crazy :D

[Wilba]

You might want to consider powering it via the two unused pins of the MIDI cable.

That's how Starr Labs' Ztar (MIDI guitar) is powered.

Obviously at the other end of the cable you have to use some kind of adapter and plug in the power there, but the idea of only having one cable attached (and hiding any other power supply components in the adapter, outside the axe) might be worth the effort. (BTW, the Ztar is the inspiration of my own still-yet-to-be-realized MIDI string/fretboard controller.)

[stryd_one]

That's clever! Not meaning to hijack the thread, but as a long-time guitar player I'd love to help with that if you like Wilba. I'll drop you an email about it so we can keep this thread on topic ;)

[NorthernLightX]

This stuff RoXX!  ;D

I have an old acoustic guitar lying around, paid way too much for it as it was damaged beyond playability, maybe give it a second life as a midibox  8)

I like the idea of power-over-midicable, will definitely research such an option!

[stryd_one]

Something just occurred to me... Power and data signals mixed together in the same cable... I mean, obviously it works OK in the ZTar, but even a total electronics n00b like me knows that it's not recommended. (OK I know about this from my IT work. Put CAT6 next to power = network issues) I wonder if there is some kind of special circuitry in a Ztar which attempts to overcome the potential for signal noise? Does it come with it's own MIDI cable? Maybe it's internally shielded?

[Wisefire]

power cables are usually AC.. AC changes direction.. DC does not.. therefore i figure that DC would pose less of a problem for data then AC does.. well.. im guessing that..

[stryd_one]

Right you are :) The change in direction of current flow creates electromagnetic interference which can flow into the data lines and make false 1's and 0's. This, I am sure of... But DC, I don't know about? This is the part where the IT guy (me) asks for advice from someone with more of a clue about electronics :) heheh

[Wisefire]

we can always try it to see if it works..

[RadicalAns]

USB has 5VDC and data all in the same cable. Seems to work fine for that.

-Dave

[Wisefire]

that settles it.. power over midi is entirely possible!

[NorthernLightX]

I would design a power-over-MIDI adapter in the same way power-over-ethernet is done: create a box with a MIDI-in and Power-in, and a Power&MIDI-out. In your MIDIBox case you can take the power right off the pins at the inside of your MIDI plug.

I'd definitely use DC, but I'm not sure what's the best place for the  regulation: I don't know if the regulated voltage signal would deteriorate when transferred over some length of cable. If that's a non-issue: definitely place your regulating circuit in the PoM adapter. Accidentally swapping the wires is not possible this way, I don't recall ever hearing about anyone successfully inserting a 5 pin DIN plug the wrong way  ;D

Cheers,  Alex.

[RadicalAns]

USB has 5VDC and data all in the same cable. Seems to work fine for that.

-Dave

Now that I think of it, the Novation X-Station is powered and does midi via USB.

-Dave

[Wisefire]

NLX: thats what i was thinking of aswell.. also it would help me to prevent my synth from falling of its respective stand..

[stryd_one]

I should start this by saying that I'm 99% sure that this will work... But keep in mind that not all cables are the same, and cable sheilding will play a major role in whether this will work. As I said, I am fairly confident that it would be fine, but still, that is made under the assumption that there is a similarity between USB and MIDI cables, and assumptions are the mother of all f*ckups ;)

[Davo]

I don't see any electrical reason why you couldn't regulate the power before it goes into the midi cable.  I'd prefer to regulate it afterwards for versatility purposes.  For example, you find a wall wart that supplies about or just above the voltage you need and you don't know it's regulated or not.