[sdiy] Jen progress

[Neil Johnson]

Chris,

> WOuld one application for what you ar edoing be a MIDI controlled
> modular oscillator plus a gate/trigger?...

Well, I guess so.  Its a digital oscillator, outputting four square waves
(2', 4', 8' and 16') as well as gate and trigger signals for the Jen's
EGs (standard CMOS NOR flip-flop design, check the Jen schematics), and
link-selectable +5/+12V active-high gate output (or remove the link for
an open-collector gate output).

There is a MIDI input, which (will :-) controls the oscillator, and also
operates a 14-bit CV DAC and two 12-bit DACs for Velocity and
ModulationCC.  Pitchbend included as standard.  I've yet to hack together
the MIDI code, but I'll start off simple and add more features (a) when I
have the time, and (b) if they'll fit in the remaining code space (so far
I have used just under half the code space).

In normal use it requires two external clocks: Master Oscillator
(2.00024MHz, tune according to taste) and the glide filter clock.  If you
don't fancy a digital glide you could always remove the filter from the
software :-)

That, and it will scan a 37-note diode-matrix single-contact (i.e. no
velocity) keyboard.  It can go up to 48 notes (4 contact bars at 12 notes
each).

Oh, and there's an exponential (roughly :-) current output for driving a
sawtooth current mirror, which should be reset by the squarewave output.

The PCB layout is targetted at plugging into the M110 socket on the Jen
keyboard PCB, with only minor mods to the Jen itself (removing a few
resistors and adding a link).  It takes in +/-12V and +5V from the Jen's
PSU.

If I were going to turn this into a general purpose modular oscillator I'd
re-lay the PCB and put all connections onto a single connector, and get
rid of the keyboard scanning stuff.  Of course, the schematic and source
code (I'm putting it all on a BSD licence) will be up on the web sometime
soonish so anyone who wants to turn it into a modular oscillator is more
than welcome to hack it together.

Cheers,
Neil

--
Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
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