[sdiy] Digitally controlled VCO core

[Theo]

Tried that, well almost.
What I did was using the uC set the frequency by resetting a linear ramp.
To correct for the amplitude change as pitch changes I used a 8 bit R2R DAC
as the rate setting resistor of the ramp.
So the DAC does not control the pitch it only keeps the output amplitude
constant.
IMHO the amplitude error left is neglectable.

The down side is you need a additional ADC if you want a CV input.

Theo


From: <mikko.a.helin at nokia.com>

> Hello!
>
> Has anybody tried to use a microcontroller to control the current source
and
> capacitor decharging circuit for ASM-1 style VCO core? I thought it would
> simplify the design as the CV to exp. current converter doesn't have to be
> that precise - so no expensive transistor pairs or T.C. resistors were
> needed and you could also use a 8 bit DAC - if the uC sets the time when
the
> cap is decharged and the exp converter only takes care of the amplitude of
> the waveform.
>
<snip>