[sdiy] MIDI to Scanned Keyboard

[rsdio at audiobanshee.com]

Interesting. I didn't realize anyone had ever made a velocity sensitive keyboard using j-wire mechanics. Seems like the j-wire is a SPDT switch, which should allow individual velocity per key.

If you're going to retrofit a MIDI keyboard to replace the analog j-wire, I would highly recommend skipping any sort of faked switching. Instead, find the CV out of the ancient keyboard and use a MIDI-to-CV converter from your MIDI keyboard to the old sound generation modules. If full velocity support is there, then there should be a CV for pitch and a CV for velocity. Any decent MIDI-to-CV converter should be able to handle that.

In any case, finding a schematic or drawing one from your existing circuit should be a good starting point.

Brian


On Jul 17, 2016, at 1:11 PM, Tom Arnold <xyzzy at sysabend.org> wrote:
> I've been pondering a project and I'm looking for ideas to on how to do it
> and perhaps not completely re-invent the wheel.
> 
> Have an old interface card for a music system.  The keyboards for the system
> are ancient and j-wire and just not a huge amount of fun to keep maintained.
> The card plugs into a standard computer bus.  I haven't drawn out the
> schematic yet of the interface card ( very simple TTL logic ) or the small
> board and diode arrays in the keyboard ( also simple TTL ) but I'm assuming
> its just key scanning and some buffering.
> 
> Here's my question.   The keyboard is velocity sensitive.  So, the time
> between contact release and second contact close is the velocity.
> 
> If I use a midi keyboard, I get a Note and a Velocity.  My first thought is
> to just simulate ( to the bus ) the contact release and contact close, but
> this will put it slightly behind when the key was actually struck.  Okay,
> simple enough but I'm curious if anyone has done something like this and if
> the delay was noticable.
> 
> I need to sit down and actually get the timings of everything, but this is
> one of many projects in a far too vast pile of them I'm juggling, so I'm
> hoping someone has some feedback I can add to my ponderings until it gets
> enough momentum that I actually do it.
> 
> Thanks.