Experimentally observed bifurcations: (a) experimental period-1 orbit with R1 = 3.3 kΩ; (b) experimental period-2 orbit with R1 = 2.85 kΩ; (c) experimental period-4 orbit with R1 = 2.81 kΩ; (d) experimental chaotic orbit with R1 = 2.78 kΩ.