While shopping for a nice analog scope (found a Philips PM3211) I came across screenshots of the famous double scroll display of Chua's Circuit. The premise is that using a special non-linear device and three energy storage components (two capacitors and an inductor) a chaotic oscillator can be built. A good explanation can be found here. I balked at the usage of two trimmer potmeters and decided to modify this circuit (from the previous site):
to a fixed resistor (1k) for RPOT1. To my dismay I could not get it to work. It took me several frustrating days to figure out that the gyrator properties were incorrect and prevented Chua's diode from doing its job. When I finally replaced the 0805 SMD resistor with a nice Bourns 3296 I could nicely dial in a beautiful double scroll display (click for a short movie):
In the meantime I had simulated the circuit to death. Because at first it would not start I should have taken that warning and used the pot instead. Now it behaves like it should (click for the whole screen):
A nice trick in LTSpice is its ability to show the X-Y view. Right click on the bottom scale and select V(x) as the displayed parameter. The subcircuit for the TL074 is here.
The actual build was inspired by Valentin's excellent site. The final version of my circuit looks like this:
All in all quite a learning experience!
Latest Update: 6 December 2020