Chua's circuit producing unexpected waves?

Question

I have built the Chua's circuit in the following diagram:

I then hook it to a soundcard oscilloscope. It produces the following wave:

Such waves doesn't change no matter how many times I repeated the experiment. It is in such form no matter how I adjust R. For large R, the frequency of the wave is larger. The wave suddenly disappears when R is decreased below something like 1.3k Ohms. What's wrong? Why is the wave like this?

I have repeated this several times, so I am sure it is not accidentally produced by poor connection. However, I use an ancient TL082 opamp...that's not ideal.

See here for simulations.

Answer 1

Chua's circuit produces a chaotic waveform only at certain operating conditions.

Depening on the the characteristics of your implementation of Chua's diode and the values of \$L\$, \$C_1\$, \$C_2\$ and \$R\$ it might produce an "ordinary" (non-chaotic) oscillation like you got; for other values you can get the expected chaotic oscillation (or no oscillation at all).

As you can see and hear e.g. in this video when varying just \$R\$ sometimes you get

• an "ordinary" oscillation (when you hear a "clean" sound),
• a chaotic oscillation (when you hear the noisy scratching sound) or
• no oscillation at all.

Answer 2

I can't make this a comment, the URL contains too many characters.

Try playing with Chua's circuit on CircuitJS. I notice that it is using op-amps in the left leg rather than the inductor, but other than that it's the same topology. You can right click on nodes and "view in scope" and see if those waveforms match what you're getting. You can also tweak the adjustable resistors with the sliders on the right-hand side of the screen.

When I've explored this circuit before I found it to be pretty twitchy, going in and out of oscillations depending on how the components are tweaked. I guess that's to be expected when working with a chaotic oscillator.