Harmonograph

A harmonograph is a mechanical device that converts two superimposed harmonic oscillations into a curve graph (a Lissajous figure ). Harmonographs are mainly used for demonstration and technology communication. In contrast to the oscilloscope , which is often used to show Lissajous figures as well as other things, they have hardly any technical applications .

A frequently used simple structure is drawing by means of a pen attached to a pendulum mass in a sand surface over which the mass pendulums with a pen. If you want to combine two vibrations with different frequencies, you can put the sand on a pendulum plate. It is also possible to draw the track with sand flowing out of the pendulous mass (left picture) or ink, whereby the vibrations are less braked. Other harmonographs use a pen to draw on paper.

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A harmonograph with a container swinging on a rope from which sand trickles. Several Lissajous figures produced in separate experiments.
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A harmonograph with a pendulous writing surface and a stationary pen. The vibrations are not harmonic and do not have exactly integer frequency relationships.
Two plates vibrate harmoniously in a frequency ratio of 2: 1 at right angles to each other. It is driven by crank slides . The intersection of two slits moves on a Lissajous figure , which can be registered with an inserted pen.