Leon Ong Chua designed his nonlinear circuit to ease the study of chaos.
Furthermore, his circuit showed that chaos is not only a mathematical abstraction, but is indeed somehow embedded into the law of physics. Full details of the equations and their implementation in Chua's paper. Original Chua paper - Universal circuit for generating and studying chaos (1993) - PDF |

The following schema implements the equations - altough with some adjustments.

(next we will replace the 10 mH inductance

It uses two diodes and one AOP build as a negative resistor.

Exploration of its many behaviours is simply made by varying the resistance

Time series of

Parametric plot of

This FFT of the