[sdiy] vdPol oscillator

[M.A. Koot]

Well it might be a bit out of the context but this seems an interesting
article anyway so thanks in any case ;)
I have managed to get it working though by rectifying the signal and to use
the VCA, some offset some sign-flipping and it's ok.
I gotta rewrite the schematic first, because it's a mess right now ;)
But actually the complete vdPol osscilator works now, with a variable
setting to regulate the feedback (so it's resonance is variable, great for
bandpassing). It's sounds nice, though the frequency range is somewhat
limited yet, I think due to some opamp's GBP, but that's a different thing
to look at.
The thing osscilates now, and that's great.

Thanks also all others for the feedback, I find people are always very
helpful and friendly here. Thanks again.

P.S. Ian, I don't quite understand the zener-thing you are doing in your
circuit yet, but it certainly looks interesting, is it some way to flip the
sign during the osscilation?

Michiel

> --- Ursprüngliche Nachricht ---
> Von: Harry Bissell Jr <harrybissell at prodigy.net>
> An: Ian Fritz <ijfritz at earthlink.net>, "M.A. Koot" <makoot at gmx.net>,
> synth-diy at dropmix.xs4all.nl
> Betreff: Re: [sdiy] Squaring volts
> Datum: Tue, 22 Nov 2005 07:23:49 -0800 (PST)
> 
> Sorry for the strange post... I lost the original
>   
>   Here is the Design Idea I remembered with the "negative resistor"
>   I don't know if it makes any sense in this context... I'm just skimming
> the
>   surface of this thread.
>   
>   http://www.edn.com/archives/1994/072194/15di1.htm#fig1
>   
>   H^) harry
> 
> Ian Fritz <ijfritz at earthlink.net> wrote:  At 04:24 PM 11/21/05, M.A. Koot
> wrote:
> 
> >Hi everybody,
> >
> >I'm working on a project trying to make the van der Pol osscilator in
> analog
> >electronics. To realize the circuit of the "negative resistor", I have
> >developed a system wich involves squaring of the analog signal.
> >It really seems this is needed. Now, the only way I know how to square an
> >analog signal is using a ring modulator circuit with equal inputs. Though
> >this really seems a clumsy way to achieve the squaring, and I'm also not
> >sure if it would work.
> 
> According to the analysis in Strogatz, the vdP osc can be written in terms
> of a nonlinear function F(x) = (x^3)/3 - x.  If you can work in this 
> transformed variable system, then you can use a simple nonlinear circuit 
> that approximates F(x) using zener diodes, resistors and an opamp.  I 
> happen to have such a circuit up on a temporary web page now.  It is the 
> nonlinear limiting circuit for a quadrature limit-cycle oscillator, shown 
> on the right-hand side of the schematic:
> 
> http://home.earthlink.net/~ijfritz/xfer.htm
> 
> As I have mentioned before, this is a very useful circuit for nonlinear 
> applications including chaos generation and wave folding.
> 
>    Ian 
> 
> 
> 
> 

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