Lissajous figures. JavaScript

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In another topic we saw how we can obtain a Lissajous figure with the Charts component.

In that topic we saw a link to a web page with JavaScript to get Lissajous figures online.

http://kio4.com/appinventor/lissajous.htm

Now let's adapt that JavaScript code to App Inventor.

But first we are going to repeat what Lissajous figures are about.

  • Lissajous figures are used in electronics, in the study of the oscilloscope.
    A sinusoidal signal is introduced through channel X and another sinusoidal signal of different frequency through channel Y, the union of these two signals produces the Lissajous figures.
  • Depending on the frequency ratio a figure will be obtained.

lissajous2
lissajous21180×794 58.8 KB

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1.- Lissajous figures with JavaScript.

p170D_Lissajous.aia (5.0 KB)

- Designer.
The file with JavaScript code is lissajous3.htm

lissajous6
lissajous6500×573 101 KB

- Blocks.

lissajous5
lissajous5560×548 38.5 KB

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2.- Use of Lissajous figures.

  • Through the Lissajous figures we can obtain the frequency of a sinusoidal signal knowing another pattern.

  • We have a sinusoidal signal of 25,000 Hz (blue signal)(pattern signal).

  • We introduce this signal in the oscilloscope together with another of unknown frequency (yellow)

  • We obtain the following Lissajous figure. Calculate the frequency of the unknown signal.

    lissajous7
    lissajous7347×647 70.8 KB

- Resolution.

lissajous8
lissajous8345×651 76.4 KB

  • We draw a horizontal line that cuts the figure, we observe that it cuts it in 6 points.

  • We draw a vertical line that cuts the figure, we observe that it cuts it in 4 points.

  • That is, the ratio is 6 / 4

  • For which the yellow signal will have a frequency of:

25,000 * (6 / 4) = 37,500Hz

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