CHAOS GENERATOR - Electronic Circuit

Well, this time I’ll show you an electronic circuit that I thought was cool. It is called the CHAOS GENERATOR, why? Because when you see its output in the oscilloscope in the XY mode you get something like this:

So, it looks like an electromagnetic field attractor (if you remember some of you physics classes). And it is said to generate chaos because the circuit does not seem to set to into a stable mode for a reasonable period of time, that’s why the XY view looks like the signal moves without control.

The circuit that I show you here is a variation of the classic phase shift oscillator. And it is cheap and entertaining for a nothing-to-do afternoon.

Without the components inside the blue line, the circuit oscillates in a stable way, and there is a deformed sine wave at the T1 transistor collector. As show in the Bode diagrams of the classic phase shift oscillator below, the three stages of the RC ladder shift the phase 180 degrees.  So only at the frequency that produces this phase shift the circuit will oscillate, in this way the total shift around the loop will be o or 360 degrees (T1 also produces a 180° phase displacement).

For oscillations to be sustained, the gain K produced by the transistor should be inverse to the magnitude of the RC network transfer function at the frequency of oscillation.  This is to satisfy the unity-gain loop condition for oscillators.

Nevertheless, with the addition of the extra components in the blue line the output is completely different. When the amplitude increases during the booting of the oscillator, the transistor T2 will start to conduct at a certain point. This makes the resistor R5 to join the feedback loop and change the phase relation, which will force the circuit to find a new point of equilibrium.

To achieve CHAOS, the circuit should not find a stable situation, but a series of instable situations very close to each other. These situations are represented by “orbits” in the oscilloscope forming the so called “attractor.” Playing with the potentiometer P and the input voltage you can force the circuit to pass from one stable oscillation to chaos to another stable condition. Also, changing P1, R5 and C5 influence in the attractor’s shape.

The circuit contains 4 elements that store energy, for this reason the phase space has 4 dimensions. What we see in the oscilloscope is actually a 2D projection of an attractor in 4D. We can see other projections connecting the Y and Z instead of the X and Y points.

Here is a video compilation of the images I got. You can also see the video in my youtube account: http://www.youtube.com/watch?v=EvB6w3WwP_0&feature=youtu.be