[sdiy] MIDI DCOs

[Neil Johnson]

HI,

> Sounds like what I did originally, before adding the programmable
> current source and integrator cap to make a sawtooth.

Same approach for the Jen: the pitch clock is actually generated
externally by a HFVCO, so I use the 16-bit counter as a programmable
divider, outputting a pulse when the counter reaches terminal count.

The control code programs the counter reload value, and also programs a
DAC for current output used to generate the sawtooth.

Another external oscillator generates interrupts for a very simple
software filter that provides portamento for all pitch data.  Getting that
to run fast enough was a little challenge :-)

Me thinks with a little jiggery-pokery this could be squashed into an
8-pin chip (MIDI In, pitch clock in, pitch out, gate/trig out).  Doing it
polyphonically would be more of a challenge.  Or perhaps use a MIDI router
to share notes across a number of these little chaps.

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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