AW: Osc reset time

[Haible Juergen]

	>I knocked up a quick prototype oscillator last night on stripboard
using the
	>cap 'flipping' idea.
	>
	>I used a 4066 switch, half a 4013 flip-flop and half a LM319
comparator.
	>I used a 5 volt reference for the 'top' of the cap, and set the
comparator
	>to trigger the flip-flop to swap the ends of the cap between the
current
	>source and the 5v ref when the voltage at the current source end of
the cap
	>reached 2.5v.
	>
	>End result was as expected - a falling sawtooth between 7.5 and 2.5
volts. I
	>didn't add a diff amp around the cap for tri output, but I put my
scope
	>probes across the cap and there it was...

Good to hear that it works !

I was so fascinated by the idea that I intended to breadboard
it myself. But first I couldn't get away from my Wurlie (it's
finally working again!), and then "the monkey sat watching the
war on TV" (to paraphrase Roger Waters).

	> Also, I can add another 'sync' input that triggers the cap swap
flip-flop
	> directly. This will invert the position of the sawtooth wave
around it's
	> midpoint, and also reverse the direction of the tri wave (I
think...).

In a normal triangle VCO this would mean thru zero FM, when
you combine it with sign / magnitude extraction of the CV.

	> I still haven't figured out how I can add precise linear detune...

You still can build a V in / V out expo converter and a linear
current source. This was tricky when 741 was the standard
opamp, but nowadays we have LF411's for low offset voltage
drift ...

	>I'll add a proper expo converter with 1v/oct cv input at the
weekend and see
	>how it performs.

I'm curious if the finite resistance of the switches has an effect
on the waveform. 

JH.