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Re: Keyboard Nirvana (AlphSyntauri / Soundchaser interfaces)

Ralph wrote:

I haven't discovered yet if Syntauri and Passport actually worked
together in the early days (1978-1979, or not).
They were clearly separate companies, but they were located within an
hour's drive of each
other in the Bay Area of California.  Their software certainly seems
to be distinct from each other.

I believe both keyboards are diode-matrix type, and I suspect that the
keyboard interfaces
are nearly identical:

My "Theory of Operation" guesses (mostly from
http://retiary.org/ls/writings/aes_alphasyntauri.pdf - page 4)

The CPU acts as the keyboard scanner, writing the key address to a
memory location.  7 bits of address
would allow for 128 keys.

The state of the key is read (perhaps one of:
  00 - not pressed
  01 -switch 1 closed
  10 - switch 2 closed
  11 both switches closed (illegal state))


There is only one switch per key in the non-velocity-sensing keyboards.
The switches are normally open.  They are connected as a matrix, though
I've forgotten the "shape" of the matrix.  ;-(

There is no logic in the keyboard, it's just switches and diodes.  The
controller card presents a bit vector to one side of the matrix with a
single bit turned on, and the other side of the matrix is read to
determine the state of the switches in that "row".


The state of the pedals would also need to be read, unclear if these
read as two additional bits of state,
or if they are treated merely as separate keys.


IIRC, they are treated like extra keys.


The key states are saved to a memory buffer, and compared with the
previous scan results.

The 49-key AlphaSyntauri keyboard was NOT described as being velocity-
sensitive.
The 61-key AlphaSyntauri keyboard WAS described as being velocity-
sensitive.
The 49-key Passport Soundchaser keyboard - UNKNOWN - I haven't taken
apart the Passport
Soundchaser keyboard enough to tell, I'm hoping to find a close-up
photo of the interface card.

It would be WONDERFUL to add aftertouch to the keyboard, I've seen
projects described
on the various Synth-DIY lists and forums that talk about adding a
strip of pressure-sensitive resistors
to the bottom of a row of keys.  It would require an A/D converter to
deal with the change in voltage.


Right.  It would be pretty slow to make the aftertouch specific to
each key.  Perhaps rather large "zones" would be enough.


It would be a good Carte Blanche project to replace the Mountain
Computer Music system
cards.  (as a 3.3v card, I'm not clear it would be a completely
suitable replacement for the keyboard interface,


Not a problem--the keyboard is passive.


although figuring out a way to replace the mountain computer light pen
functionality on a VGA monitor is a priority.)


I'd think that accomodating a mouse for composition and editing
would be much preferred to an awkward light pen.  (Ever try holding
a pen up to a screen for a half hour?  ;-)

Light pens "give good demo" but are hell for more than an occasional
"designation" of a point on a screen.


My dream would be to have a "generic" card which could connect to
EITHER keyboard, and
allow Soundchaser and Syntauri keyboards to be used interchangeably,
and as MIDI keyboards as well.


Quite an adapter.  ;-)  Each adapter was designed independently, with
arbitrary differences in scanning strategies, so a "universal" adapter
would just be three adapters on one board--maybe "soft".  ;-)


Keypress to MIDI should be easiy achievable on the board, using an
Arduino or similar microcontroller chip.
That would allow the card to be used outside of the Apple // entirely,
as needed, with only a DC supply.


It would be just as easy to build a MIDI interface into the keyboard,
making it the equivalent of any $10 thrift store keyboard synth.  ;-)

-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

"The wastebasket is our most important design
tool--and it's seriously underused."