Generating Lissajous Figures Using a PC/Laptop Sound Card

Generating various Lissajous Figures on an oscilloscope make a very interesting experiment. Apart from that, these curves are of particular value in electronics, serving to identify the characteristics of any unknown electric signal when compared to a known one.

Traditionally, generating Lissajous Figures where the frequencies of the input signals are unequal require the use of two synchronized signal generators or a multi-channel function generator. But, nowadays most PCs and Laptops come equipped with a stereo audio output jack. This output can be used as a synchronized 2-channel signal generator and can be used to generate various Lissajous Figures on an oscilloscope.

You will need:

1. A PC/Laptop with a stereo audio output

2. A 3.5mm stereo aux cable

3. Audacity v.2.0 or above (Download here)

Open a new project in Audacity.

Goto Track -> New -> Audio Track

(alternatively use the keyboard shortcut Ctrl+Shift+N)

Create a tone of the required amplitude and frequency.

Goto Generate -> Tone

From the dialog box, select the following:

• Waveform: Sine
• Frequency: (as required)
• Amplitude: (as required)
• Duration: (as required)

Repeat the previous step to generate the second tone.

If a phase difference is required between the first and second waveform, select the appropriate starting point for the second tone using the cursor.

Now, set the Pan slider of the first tone to 100% Left and that of the second tone to 100% Right.

Connect a stereo aux cable to the audio output of your PC/Laptop.

Connect the other end of the stereo cable to the input channels of the oscilloscope as indicated in the figure.

You are all set to begin !

Now, set the oscilloscope in the XY-mode and hit the Play button on Audacity !

Play around with the frequencies of the tones to generate various Lissajous Figures.