Leon Chua, an American scientist, created an electronic circuit in 1983 that generates unpredictable “wild” oscillations, similar to a double pendulum. This circuit can also produce a chirping sound like an excited bird if the vibrations are placed in the audible range. This circuit is similar to the electronic canary, which was featured in an Elektor issue in the early 1970s and could have contributed to chaos theory.
Valentin Siderskiy, a student, has created a safe-to-replicate version of the Chua circuit with four operational amplifiers. He replaced the inductance on the left side with a gyrator circuit with almost ideal properties, while the right side uses a circuit composed of two more OpAmps as a limiting, negative resistance.
Siderskiy suggests using an analog oscilloscope to record Lissajous figures from the signals on both sides of the middle resistor R, as particularly interesting results can be obtained. However, he cautions that the circuit is sensitive to contact resistance and capacitors that tend to be microphonic.
Building this circuit on a breadboard and using ceramic capacitors leads to less than satisfactory results, according to Siderskiy. While it is not easy to model truly chaotic behavior with electronic means, circuits like Chua’s can serve important purposes in simulations, generating random numbers, and cryptography.
