[sdiy] Keyboard scanner

[Andre Majorel]

On 2009-07-28 20:58 +0100, Neil Johnson wrote:

> As part of my Siel Opera 6 project I am designing a 61-key keyboard  
> scanner module, based on an Atmel ATmega8.  It scans all 61 keys via an 
> external 74LS154 decoder and diode matrix (already present on the  
> existing contacts board), measures the time-of-flight, and works out  
> note-on velocity and note-off velocity.  It also handles pitch-bend  
> wheel, modulation wheel, expression pedal and sustain pedal analogue  
> inputs.  The intention is that it will talk to a master processor via  
> SPI (100kbps should be fast enough).
>
> If this board were to be used for other projects it would be useful if 
> the 74LS154 was also on the scanner PCB, together with a suitably larger 
> connector (probably 26-pin IDC header).  This would necessitate a larger 
> board than a dedicated one for my project.
>
> I figure this project might also be useful to others, perhaps those  
> building their own keyboards.  How much interest would there be?

Thanks for asking. I have two DX7 keyboards here waiting to be
turned into a two-manual controller. Each keyboard is a 12 x 5
matrix (actually 13 x 1 for the first octave). Each key is an SPDT
with the anode of an 1SS133 diode connected to the SP. 34-way HE10
connector of which 13 + 5 + 5 = 23 pins are used.

There will be a pedal board, at least two octaves with velocity,
more if possible (probably will be round switches on a hex grid).

The analogue controls will be somewhat unconventional, with two or
three bend levers per keyboard (one per zone), no mod wheels and a
whole row of pedals.

If your scanner PCB can handle a DX7 keyboard and enough analogue
inputs, I guess three of them would do the job. The analogue
inputs might be handled separately anyway because if they're going
to be routed to analogue outputs, no need to ADC-DAC them (and clog
the 100 kbps link).

For the brain, I was thinking a PC motherboard running some free
Unix because that's what I know. But PCs don't speak SPI, do they ?

> If you would find such a board useful then please email me
> off-list and if there is enough interest I'll extend the design
> accordingly.

Whoops ! I always forget about that off-list part. :-)

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>