Looking to build a minimal midi keyboard... advice/tips/assistance needed

[krautrock]

Hi all - new to this site, so ... hello!

Ok, I've decided to build a ludicrous and minimal midi keyboard, a la :

I don't need drum pads, I don't need sliders. I want a pitch and a mod wheel, 3 or 4 knobs. 49 keys. Octave up/down. Oh, and I'd like the wheels to be lit, that'd be nice.

That's it!

So - what's the best way to go about this? Is it to rehouse a midi keyboard, and move the knobs and wheels to where I want them...?
But which keyboard will do all I need here?
The options out there either have the elements I need - but with a ton of added stuff - or the don't have pitch/mod wheels.
Something like the Akai Miniak is almost perfect (3 wheels which are backlit, minimal knobs) except it doesn't have 49 keys. And it's not a (dedicated) midi keyboard.

Or should I take something like a Novation Launchkey, and remove sliders/pads when building the housing :



Or even obtain parts and build that way? (Honestly, that option would be something I'd not have a clue on, so would need a dummies guide).
Any suggestions...?

 

[PaulStoffregen]

I know this is a long-shot, but any keyboard with a schematic available would save you a lot of trouble in reverse engineering.

 

[Nantonos]

If you want to explore the naked keybed route, pretty much your only option is keybeds made by the Italian manufacturer Fatar. (Those are used on several well-known midrange to high-end synths and organs). They don't sell direct but some are sold as spare parts for Doepfer synthesizers and you can order through a shop that stocks them.

http://www.fatar.com/Pages/Intro_production.htm

I bought one (a TP/8O waterfall keyboard) from ModularSquare in France. You should pick somewhere close to where you live, obviously. For example this 49-key TP9.

The keybeds come without cables or a controller. You can buy the Doepfer ones if that suits you, or you can make your own with a Teensy. The cables are TE CONNECTIVITY / AMP - 1483356-3 - MICROMATCH, 16WAY, 250MM and the pins are on 1.27mm (1/20") spacing so you would need to make a PCB to break out those signals and route them to the Teensy pins.

Fatar hide the schematic behind a registered-customer wall but Doepfer have the schematic available, see here. The usual row, column matrix method is used (8 rows and 8 columns reads up to 64 keys) except that there are two sets of columns; one for the normally closed switches at the top of the travel, which break as you start to press a key, and a second set for the normally open switches near the end of key travel. Measuring the time between the first and second switch gives you the key-on velocity. (Measuring again te opposite way for key release gives you the key-off velocity, which MIDI supports but most synths don't, so you may choose not to bother measuring it).

A Teensy++ 2.0 has sufficient input/output pins to write on 8 rows and read on two sets of 8 columns without having to use port expanders.

For rotary knobs, you can use rotary encoders and count the pulses, or you can use analog potentiometers and read the position from measuring the analog voltage using teensy analog-to-digital converters (ADC). Doepfer make a handy pair of sprung wheels (mod wheel and pitchbend wheel) which you can use here.

For the actual MIDI output you have two choices, both of which can be done by Teensy. One is the native, class-compliant MIDI over USB (there is a standard library to provide that functionality) and one is the traditional (and much slower) MIDI over DIN. Or you can choose to provide both. The advantage of MIDI over DIN is that you can directly connect a MIDIkeyboard to a MIDI hardware synthesizer without needing a computer between them to act as a host. On the other hand if you are recording intoa DAW using softsynths then USB MIDI is probably better.

Well, hopefully that gives you a start if you consider that option

 

[krautrock]

Hi -

thanks for the info, really appreciate it. Yeah, I figured Fatar is probably the only option for that route. I think my skills wouldn't be up to it as far as going that route though! Unless I could obtain the parts, and have someone construct the basic skeleton for me.

So - I think my next question here is :

An Akai MPK49 has lit-up wheels, 49 keys, usb midi, control knobs :




Ok, so if I purchase (cheap and easily obtainable) MPK49 and use only the parts I need, could I just "ignore" the pads, sliders, etc? (Is it possible to disconnect those parts, or should I simply hide them under the synth casing, and remove the rubber pads, buttons, etc?) If I did that, would that cause me any short circuiting problems or anything? Could I detach the pads board, the sliders board from the main board without killing everything else?

 

[Dan]

Hello Paul,

I am doing a similar project.
I have a FATAR 76 Keys Keyboard with 2 connectors.
The schematic is here : http://www.doepfer.de/DIY/Matrix_76.gif

I am using the Teensy 2++ because I can plug all the keyboard pins to the Teensy without any external components.

I inspired myself from the Keypad example, because it seems to be the same matrix thing
https://www.pjrc.com/teensy/td_libs_Keypad.html



I have some timing problems.
To get the velocity of the key, I need to measure the time difference between the 2 switch of the key become ON.


What is the best way to measure, with the most possible accuracy, a very small time (less than 1 ms)

And in the same time, scanning the whole matrix, that need (i think) to set some lines ON and OFF to read the columns, like a keypad. input_pullup

Actually, my velocity response sometimes reacts strange. It seems that if the first switch is set ON, and then I continue to read the whole keyboard, before coming back to read the second switch is adding time.



I don't think it is an easy task, because many cheap keyboards have bad velocity response


I want to have the fresh guidance of Paul on this subject

Thank you very much !