[sdiy] Using an AT90S1200 as a triple DCO

[Jaroslaw Ziembicki]

Hi,

> I'm fascinated why you chose to have the micro generate square waves
> rather than using a comparator on the sawtooth. was it to save on the part
> count?

The micro DOES NOT generate square waves!
Look at the schematic - the op-amps U4A, U4B, U4C act as comparators
and compare the sawtooth waves from U3B, U3C, U3D to the CONTROL
VOLTAGES held at their non-inverting inputs. These three op-amps are in fact
"sample & hold & compare" units.
Generating additionally three pulse waveforms, each one with independent
pulse width setting, would be definitely too much for that poor AT90S1200!

Regards,
Jarek