![]() ![]() ![]() You will, however, need to makesure that your arbitrary function generator has a fast rise time and theoscilloscope has a sufficiently high bandwidth. The signal can stay at -1Vfor a short period of time, and then quickly jump to +1V and stay therefor a short period of time, and repeat. What can you do then? You can tackle this by quickly cyclingthrough the different voltages you require. This is similar tohow some video formats work.Īt times, the arbitrary signal needs to be both -1V and +1V at thesame time. Inthis manner, we can create our arbitrary waveform. When it is at0V, the CH1 or “X” signal should be drawing the center row of the image.Because we know that the vertical sweep is synchronized to thearbitrary function generator, at any given sample in the arbitrarywaveform, we can predict exactly where the vertical sweep will be. When it's at -1V, the CH1or “X” signal should be drawing the bottom of the image. For example, assume thatour vertical sweep ranges from -1 V to +1 V. At any given time, the vertical sweep specifieswhere in the image we are currently drawing. Thetricky part is now how to generate the appropriate arbitrary signal todraw the desired image. To produce an image on theoscilloscope screen, for a pseudo triangle signal on the “Y” input, the”X” input can be computed based on the image's digital information. In fact, this isexactly how old cathode ray tube TVs worked. Lissajous curves are great, but what if you could draw a face, orsome other arbitrary image, on an oscilloscope? By providing theappropriate “X” and “Y” signals, you can create any pattern. ![]() Here's a more interesting Lissajous pattern. For example, generating a 2 cycle sine wave in a memory span of 64 kbytes with a sampling rate of 1.3 MHz produces the pattern shown in Figure 3. By setting an oscilloscope's channels as X and Y inputs, you can create a Lissajous pattern.īy switching the generator to its arbitrary mode of operation, you can create more creative patterns. Figure 2 shows the “X” signal in Yellow, the “Y” signal in blue, and the resultant Lissajous pattern in pink.įigure 2. 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. The capacitors at the generator's SYNC output distort the square-wave signal. Connecting two channels of a waveform waveform generator lets you create a Lissajous pattern. This creates a rough synchronized triangle wave to use as a vertical sweep.įigure 1. Then, the signal is AC-Coupled by another 470 ♟ capacitor and then through a coax cable to the oscilloscope's CH2 (or the “Y”) input. The generator's SYNC output is first bypassed to GND with a 470 ♟ capacitor to reduce its rise and fall times. Figure 1 shows how output of the waveform generator connects to the oscilloscope's CH1 (or the “X”) input. 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. To produce these patterns, you need two signal sources and a two-channel oscilloscope with the XY capability. 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. Technical journals including EDN publish creative techniques to produce interesting Lissajous patterns from time to time. Practically every engineer who has worked with an oscilloscope has, at some point, seen these patterns. Many online pages explain them in detail and show several popular patterns. It's become almost a passion which during stressful times, reminds me of the magic of waves.ĭespite jaw-dropping computer graphic technologies, creating Lissajous patterns and other images on a oscilloscope is still exciting. I enjoy creating and viewing signals in different forms, signals of all shapes and sizes. When I need a break I sometimes sit at my desk and play with waves. As a professional engineer, I'm often overworked and stressed. ![]()
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