flying faders, was [sdiy] keyboard resources

[Byron G. Jacquot]

>This probably isn't that difficult, just rather tedious. I would imagine
>a small micro, (or even a PIC?) to control a number of faders for
>common synth operations would be cool. You would have to implement
>some sort of switching control under the micro as well in order to "store"
>all patch settings too... I think this has been discussed on the list a few
>times in the past. This would be a cool project... maybe it could be an
>add on board to an ASM1?

It's ceraintly a reaosnable project, though there are a few caveats:
The faders might not be available in all of the different configurations
you'd want for a project like that.
The more faders you want to control, the more infrastructure you'll need to
tie them together.
You'll probably need to use SCRs to drive the fader motors.

I found the datasheet for the faders:
http://www.panasonic.com/industrial/components/pdf/evab_nm.pdf
It's a little terse, and leaves me wondering how to connect the faders.

The usual motor controlled devices often have 2 tracks: one for the signal
(which can have whatever taper you need), and one for sensing where the
thing is (with linear resistance).  The sensing signal can then be A-to-D
converted, and the controlling micro can tell where it is, and move it if
need be.  This means you'll want some A-to-D on the micro.

I'd always thought the motor would be a stepper, accepting gray code control
from the host, but these Panasonics appear to only have 2 control inputs,
whereas a stepper would have 4.  It probably has something to do with the
tabs labeled A and B in the pitcure.

You'd also want a "record" mode, where you can move the faders by hand, and
let the micro observe where they are.  You could store snapshots in the
micro, though you'd probably want to transmit the fader moves to some
external box (MIDI is a likely candidate) if you wanted true "moving-fader"
automation.  Fancy moving faders use metal caps and a capacitive touch
sensing system to know when your finger is on the fader, though you could do
it the hard way by reading the A to D.

The number of faders you want to control will probably influence the
selection of a micro for the job.  A faster micro (and faster A to D) means
you can keep better track of things.  A multiplexed A to D would also help,
in fact, you'll probably want to do some degree of multiplexing: many faders
sharing a single A to D.  The speed of the motors you're controlling might
be several orders of magnitude slower than the A to D, as well...

>Ouch, I've just realized what would be difficult. Midi implementation.
>I'll leave this to someone else to ponder..

MIDI's not that tough, certainly not if you've got a micro in there!  To me,
it's also a good motivator to be able to record, edit & playback fader moves
from my favorite software sequencer.

Byron Jacquot