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 Forum index » DIY Hardware and Software » Musical Interfaces
Monome-like button matrix
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MathHat



Joined: May 29, 2008
Posts: 13
Location: SLC

PostPosted: Sat Jun 21, 2008 9:10 am    Post subject: Monome-like button matrix Reply with quote  Mark this post and the followings unread

Okay, after my last failed idea, I thought I'd try something a bit more realistic. SparkFun has a nice kit now for building 4x4 arrays of tactile RGB-backlit buttons. I can imagine that having 7 colors per button means many more possible interfaces, but what about 16 million? The Ardiuno and Wiring boards both have PWM outputs, but only 6 of them, whereas the PCB in the kit has 3 inputs per row. Thus, a few questions:

Can I use mux IC's on PWM outputs safely (i.e. without major signal loss)?
-or-
Could I cut the PCB in half?
-or-
Are there other (cheap) kits or chips that have 12 or more PWMs?

Otherwise, I'll either do something funky like interface between two WiringMinis, or be satisfied with 7 colors.

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blue hell
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PostPosted: Sat Jun 21, 2008 9:24 am    Post subject: Reply with quote  Mark this post and the followings unread

You could use regular outputs driven from a timer interrupt and do your own pwm in software (although 16 mega colors might be a bit over the edge you still could have a lot). Multiplexing pwm seems to be not so easy to get it synced up correctly, otoh when it's nearly synced it might work ok as well.

Would the processor have any other tasks?

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Kassen
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PostPosted: Sat Jun 21, 2008 10:00 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure I'd dare trying that. The Arduino's timing facilities seem quite primitive. There's a function to get the ms that have passed since boot-up as a int. Maybe I'm spoiled with ChucK which has no problem at all talking about a millionth of a a sample but come on.... ms is at least a order of magnitude too coarse.
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blue hell
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PostPosted: Sat Jun 21, 2008 10:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Kassen wrote:
The Arduino's timing facilities seem quite primitive.


Looked it up, you'd have to write a library for it or so it seems to do something with timer interrupts in assembly. Maybe best to get rid of that OS thingie altogether then Shocked the processor is not the problem.

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MathHat



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PostPosted: Sat Jun 21, 2008 1:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
You could use regular outputs driven from a timer interrupt and do your own pwm in software (although 16 mega colors might be a bit over the edge you still could have a lot). Multiplexing pwm seems to be not so easy to get it synced up correctly, otoh when it's nearly synced it might work ok as well.


I suppose I could just get a few muxes and try it.

Blue Hell wrote:
Would the processor have any other tasks?


Well, if it were the stupidest possible interface, it would be scanning the buttons and using USB for sending push events and handling color-change events.

In a different direction, are there any existing controller chips that do what I want? I'm not well-worded in part numbers.

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PostPosted: Sat Jun 21, 2008 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

MathHat wrote:
In a different direction, are there any existing controller chips that do what I want?


Not that I know, it seems like a typical processor job to me. Scan a couple of keys, debounce those, do some user feedback & talk with another computer. It always boils down to just that Laughing

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MathHat



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PostPosted: Sun Jun 22, 2008 8:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I was talking about the LEDs; the buttons are no problem. I found a few threads elsewhere of projects that used the MAX7221 for 7 color matrices, so I'd want a chip like that, but with PWM on the DIG outputs. This seems to have something like what I'm looking for...

EDIT: Yep, the TLC5940 looks like it will do fine. I can use one for each color and power two rows of an 8x8 at a time.

EDIT2: Not that this is much of a surprise, but it looks like someone else did the same thing (but with digital potentiometers).

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MathHat



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PostPosted: Sun Jul 06, 2008 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, I've been studying crazy keyboard layouts like the one by Bosanquet or the "Harmonic Table" on the C-Axis, and I think I want to make it a hexagonal lattice instead. I've found some buttons that should do nicely, spaced out approximately as wide as accordion buttons. The rest of it stays the same.

This new arrangement also made me think of a possibly insidious name for the project: Honeybuttons.

Yeah, I know it's almost the same as a Microzone at this point, but it's cheaper and has fancy lights!

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MusicScienceGuy



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PostPosted: Mon Jul 07, 2008 5:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

MathHat wrote:
OK, I've been studying crazy keyboard layouts like the one by Bosanquet or the "Harmonic Table" on the C-Axis, and I think I want to make it a hexagonal lattice instead. I've found some buttons that should do nicely, spaced out approximately as wide as accordion buttons. The rest of it stays the same....


Great idea. Here's some relevant, I hope, cross-post info from the DYIKeyboard site:
1) Key touch (usually called touchweight: see link, with sub components Downweight and Upweight) is critical to good playing. On my home-build jammers I had a trouble playing eighth-notes, while I could play them on the piano. I traced, I hope, the problem to the pressure needed on the keys.
The downtouch on my keys was too high - middle two rows were 65-90 grams, and the other rows even higher at 120 gm and upwards.

This is not surprising, as I hacked off the end of the white keys to make them the same length as the black keys. At the time of construction, I was happy to have a working keyboard, so did not worry about the weights. Now, I'm refining the design, and tracing down issues, so I'm learning about key touch. On a piano, downweight should be 60-40 grams, and upweight should be ~20 gm. The difference is due to friction.

I found that the heavier down-pressure on the keys actually made them "slower", and more tiring.
Slower seems counter-intuitive - one would think that the key would move down faster and spring back faster with more spring pressure. Not so - the key is so light (>15 gms) that the downweight is not a factor. The
limiting factor must instead be the muscle force "ramp-up/turn-off" speed of the finger muscles.

65 grams is, I think, about the upward limit for electronic keyboard keys - it can be heavier than on a piano, because a piano has 20-30 grams of
friction + 10 grams of inertia. Still, more downweight does not get one anything. I would aim for 40-50 gms and about 5 mm of movement.

2) I recommend the jammer/Thummer/wicki-Hayden layout. The c-thru layout is really hard to explain to people. The jammer is fairly easy. I also feel the jammer layout has many things going for it.
Also, there's little point making a competitor for the forthcoming mini C-Thru unit, and cutting into their sales.

If C-thru comes out with a $500 unit I'll buy that too, as an adjunct to my learning, and morph it into a jammer if I don't like it. Laughing

Ken/MusicScienceGuy

Last edited by MusicScienceGuy on Thu Jul 10, 2008 6:10 pm; edited 2 times in total
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MathHat



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PostPosted: Tue Jul 08, 2008 7:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for this useful info! I had been wondering about speed-limiting factors, reading threads like this and watching videos of accordian and keyboard players. This makes a lot of sense. Of course, I'm not too agile-fingered in the first place, so the key action will only need to be good enough.

The buttons I've chosen are intended for arcade machines, which are notorious for encouraging hi-speed button mashing and other abuse. From machines I've played, they tend to have a pretty short travel, and I'm not sure about the downweight, but I'm guessing that they aren't any worse than a typical PC keyboard. They might make glissandos a tad difficult in comparison to the Microzone, though, because of the bezel around the buttons that would space them apart. On the other hand, I'd love to know where I could find short-travel, fast-action hexagonal keys without a bezel or "sheath" and that can be backlit by a 5mm LED. Wink

Also, because I'll be backlighting every button and adding the logic myself, I'll be able to program many isomorphic layouts that I can flip through for comparison. I've heard good things about Wicki, but I'm not about to throw the other options out the door if I can experiment with them this easily. Very Happy

And don't worry, I don't intend to make a business around this. I might upload schematics/code, but this is for me. Smile

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MusicScienceGuy



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PostPosted: Tue Jul 08, 2008 11:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Consider joining the DIYKeyBoard.org group.
We need your input.
Ken.
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