One goal in designing this module was to be able to generate what are known as "Poincare sections" and "first return maps" in the jargon of chaos theory. In a driven system such as the EZ Chaos circuit, this involves producing sequences of output voltages obtained by sampling the flow signals every time the driving signal crosses a particular phase value. For autonomous systems, such as The Jerkster, it involves measuring the value of one variable every time a second one reaches a particular value.

Below is a circuit module for performing these functions and more. It is straightforward circuitry whose parts should be quite familiar. The upper part of the circuit takes an input that defines the timing of the events being created (Timing Signal). It compares this signal with a threshold level. When the signal crosses the threshold, standard Gate and Trigger voltages are generated and output. Although the input can actually be any signal at all, if it is the external driving signal of the chaos system, then the threshold level defines the phase of a Poincare section. If it is one of the outputs of the chaos generator, then it defines the "return" position of the first return map.

The trigger signal is also fed to the lower part of the circuit, which is a high-performance sample-and-hold circuit. This derives discrete output voltages from the Main Signal input corresponding to the timing information. An OTA is used as a high impedance current switch, which charges the 4.7 nF holding capacitor. The cap is buffered by a CA3140 MOSFET-input opamp which provides a very low droop rate of about 1.5 mV/sec. The charging time of the cap is only 30 usec, meaning that sampling rates may be in the audio range.

The LM2901 comparator and the TL074 opamp are quad devices, which allow a quad module to be made with a minimal parts count. The corresponding dual devices may also be used, if a dual module is constructed.

Please note that this module may be used as a regular sample-and-hold circuit, if the sampling pulse is fed to the Timing Signal input and the signal to be sampled is fed into the Main Signal input.

To demonstrate this module's operation on a chaotic system, I have made a short sound clip of it operating on the output of a slightly modified version of the EZ Chaos system. (The modification is the addition of an extra cross-coupling within the circuit.) The clip has four sections. The first section is the chaos circuit directly driving two VCO frequencies. For the following three sections the TGTSH was set up to sample the "x" output every time the "y" output crossed a threshold, and vice versa. Varying the thresholds changes the rate the pitches change and the range of pitches produced. Below is a shot of the attractor generating the chaotic signals.

Here is a photo of a circuit board developed for this circuit: