[sdiy] dspic VCDO

[ryan williams]

hi all,

i built a new module a VCDO programmed in a dspic w/16bit ADC. exp
conversion is done with a lookup table. 24bit tuning word and a 32bit
phase accumulator. it does FM, sync, and triangle output. the normal
waveforms are provided with analog waveshapers. i'm especially happy
with the sine shaper which uses the OTA with feedback method. it
tracks 1v/oct very closely. i also added a linear fine frequency
offset added after the expo conversion to set constant beating but
i've only built one of these so far. aliasing is not an issue since i
sample at 500KHz and have a 2nd order (100khz fc) at the output.
really the only issue i have is that it is a power hog. it uses 120mA
off the +15v  supply. most of that is the dspic since it runs at
120MHz.

all the documents and a few sound tests are posted on my website.
http://www.homebuilthardware.com/index.php/projects/dspicvcdo/

-Ryan