NetNews Usenet Archive 1992 #23/NN_1992_23.iso/spool/sci/fractals/114

Text File | 1992-10-07 | 1.7 KB | 31 lines

Newsgroups: sci.fractals
Path: sparky!uunet!elroy.jpl.nasa.gov!sdd.hp.com!caen!uwm.edu!zazen!psl.wisc.edu!SPROTT@128.104.39.173
From: sprott@128.104.39.173
Subject: Re: Fractal Oscillator Circuitry
Message-ID: <00961BE3.44B16140@128.104.39.173>
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Organization: Univ. of Wisconsin, Plasma Physics
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Date: Wed, 07 Oct 1992 16:09:03 EDT
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If anyone is interested in building a chaotic RLC circuit that works at
audio frequencies, I can offer some advice.  Testa, et. al. used a
varactor diode (1N953) whose reverse capacitance is small and depends on
voltage.  They operated at 100 kHz, and it is difficult to lower the
frequency into the audio range with such a device.  However, an ordinary
power diode also has a voltage variable capacitance which can be very large
(microfarads) when forward biased and which also depends on voltage.  With
a good quality inductor of around 100 mH, it's easy to get the resonance
down to around 10 kHz.  Just apply a sine wave of at least 10 V peak to the
inductor and diode in series.  Connect an audio amplifier with a high
input impedance across the diode, and you will at least four period doublings
(5, 2.5, 1.25 kHz) and then chaos as you raise the oscillator voltage.
I have such a circuit that I take around the country to illustrate chaos
presentations.  Be sure the inductor has high-Q, the oscillator can put out
in excess of ten volts, and the amplifier doesn't load the circuit.  You
can also display the attractor on an oscilloscope with the oscillator voltage
on one axis and the diode voltage on the other.  Very effective and highly
recommended!