Sun Sep 30 09:07:30 EDT 2012

Relaxation oscillator

Current source into capacitor + threshold-based reset (cap discharge).
Should the discharge be a discrete component (PIC only controls
charging current) or should discharge be done in ISR?

ISR is more efficient with component count.

Big question: how large is the noise going to be?  Problem is that the
voltage range of interest is say 0.5 - 0.7 V, which is tiny.  A lot of
resolution is lost here.  5V -> 0.2 is a factor 25.

In theory, making the filter cap large enough, resolution is not the
problem, but in that case the control time constant might be a
problem.  I'm starting to thing this whole idea is not very realistic.

What about prefixing an opamp?

Pff... this looks a bit like a dead end.  I'm loosing interest.