5 | Troubleshooting & Tips
The best advice I can give you when you are stuggling to find the double scroll, wildly tuning both pots with no luck, is to very slowly tune one at a time until you see a shape like in Figure A. Once you see this lemon shape, start tuning the other potentiometer, slowly again, until you get the double scroll. That usually works, so if you still have problems check your circuit again.
You may find that one side of the scroll is bigger than the other, as in these pictures. This is likely due to uneven voltages from the two power sources or improperly tuned parameters.
Another problem you may have is a saturated scroll, as shown in Figure B, where the scroll seems to be bounded on two sides and is flat instead of rounded. Saturation, or ‘voltage clipping’, is caused by voltage that exceeds the ideal funtional range of the component and reaches the limits of the components of the circuit.
“By definition, the Double Scroll attractor is bounded. This is important because all physical resistors are eventually passive, meaning simply that for a large enough voltage across its terminals, the power consumed by a real resistor is positive.”
[Kennedy, Robust Op Amp Realization of Chua’s Circuit, 1992]
If clipping occurs on the X variable, your C1 value is too small. Simply tuning the circuit or changing the capacitor to one compatible with the voltage you are dealing with will get rid of saturation. We have also modelled a saturated scroll in our our Matlab simulation, using a smaller value for the capacitor C1 and a larger value for the resistor R.
However, if clipping occurs on the Z variable, saturation may be caused by too small of a value for R10–in the inductor simulator.
On the circuit described here, it is possible to demonstrate saturation on a perfectly working circuit. R10 being a poteniometer makes it possible to tune the parameters to show a full double scroll or to go beyond this to demonstrate saturation.
When you finally get a double scroll attractor running, you can try using its signals (now officially chaotic) for your research, experiments or you can even try synchronizing two or more Chua’s circuits. For extra credit, you can modify the circuit and create three or more scrolls from a single circuit!
