The Art of Waves: Images on an oscilloscope

August 04, 2015 //By Arash Ushani
The Art of Waves: Images on an oscilloscope
Arash Ushani considers how to create and view signals in different forms using an oscilloscope.

As a professional engineer, I'm often overworked and stressed. When I need a break I sometimes sit at my desk and play with waves. I enjoy creating and viewing signals in different forms, signals of all shapes and sizes. It's become almost a passion which during stressful times, reminds me of the magic of waves.

Despite jaw-dropping computer graphic technologies, creating Lissajous patterns and other images on a oscilloscope is still exciting. Many online pages explain them in detail and show several popular patterns. Practically every engineer who has worked with an oscilloscope has, at some point, seen these patterns. Technical journals publish creative techniques to produce interesting Lissajous patterns from time to time. A Lissajous pattern, which is essentially the display of voltage and frequency relationships between two signals has been depicted in old science fiction movies to represent "super" technology.

To produce these patterns, you need two signal sources and a two-channel oscilloscope with the XY capability. In this article I used an Analog Arts SL987 , an oscilloscope with a built-in arbitrary waveform generator; you can use an oscilloscope and waveform generator of your choosing. Figure 1 shows how output of the waveform generator connects to the oscilloscope's CH1 (or the "X") input. The generator's SYNC output is first bypassed to GND with a 470 µF capacitor to reduce its rise and fall times. Then, the signal is AC-Coupled by another 470 µF capacitor and then through a coax cable to the oscilloscope's CH2 (or the "Y") input. This creates a rough synchronized triangle wave to use as a vertical sweep.

Figure 1. Connecting two channels of a waveform waveform generator lets you create a Lissajous pattern.

The capacitors at the generator's SYNC output distort the square-wave signal. For an output frequency of about 20 Hz, the distorted SYNC signal is a pseudo triangle wave with a peak-to-peak amplitude of 1.2 V. Figure 2 shows the "X"

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