Lissajou patterns

Apparently your output is exactly right. The whole point of Lissajous figures (cue "The Outer Limits" music -- "Do not adjust your screen. We control the horizontal. We control the vertical") is comparing frequencies and phases. If they're both identical, you aren't going to get any more than what you have.

You might want to try getting a second function generator, or cobbling up a PLL circuit or something else to get two different frequencies to compare.

Actually, Lissajous figures are still vitally important in electronics. If I have to read a manual or data sheet or do something important on their problem that doesn't require wrench twiddling, and they want some wrench twiddling on their problem RIGHT NOW, I have been known to set up a Lissajous figure on my bench scope with one frequency drifting slightly to cause slow but constant motion on the display. I then put the scope on my bench next to the protoboard, with a large sign stating "CAUTION -- TEST IN PROGRESS!" That has a tendency to keep non-technical people out of my hair so I can think. For some reason, they stare at the display for twenty seconds or so, then walk away with either a blank or frustrated glance. I think there's something about, say, a slowly drifting 4:3 or 3:2 display that causes great inner confusion in non-technical persons. ;-)

Good luck with the homework. Try googling with a different spelling -- there are a lot of results for "Lissajous figure setup" (no quotes).

Chris

Well I used to design these things for Tek but that was LONG ago.

With only one signal generator you are getting exactly what I would expect.

Forget scope for a moment. Just think algebra for a moment, you are going to plot a point (x,y) and the value for x is exactly the same as the value for y. So you get a point somewhere on a diagonal line y=x. You change to a different x, but the new y will be the same as the new x, so you get another point, again on that diagonal line.

How about this instead. Find a little "wall wart" plug in power supply that outputs AC, maybe 6 volts or so. Hook one of your inputs to that. Probably better use your scope probe to attach to that, instead of connecting it directly, don't want to toast your input channel.

Then set up your signal generator to be say 120 hz. Hook that to your other input. See if that gives you something other than a line. Then gently rock the generator frequency up and down a bit.

The point of lissajous figures is that the frequencies of the x and y components are related by some ratio. Thus, two signal generators are required.

You can easily build a sine wave generator, using an opamp and a few other components. Google for 'wein bridge'. There are also signal generator chips that can be had for a few bucks that will generate very nice slow sine waves, which is what you want. The waveform needs to have a stable frequency, or it's hard to match.

I saw an exhibit at the SF exploratorium, in which thin vertical rods were fixed at the bottom, and thinned along their axis in particular directions so they would oscillate at different frequencies in different directions when 'plucked'. That isn't a very good description, but the result was a lissajous figure traced out by the end of the rod when plucked. The amount of thinning along the rod determined what figure would emerge, figure 8, three loops, etc. It was very cool.

Not only do you want two signal generators, but you should get two Function generators, which are able to generate other types of waveforms apart from sinusoidal. You can get some real funky lissajou displays with waveforms like triangle waves, ramps, square etc

Dave :)

It helps if the input frequency on ch1 and ch2 is not the same or near. For example, put one channel on 60hz and another on 65hz and you get a rotating circle. If the second frequency about double (but not exactly) than the first, you'd get shifting figure 8.

It would help if you have 2 different frequency generator (both on sine wave) and you vary the setting of one.

"Wien bridge" would be better.

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

yes, it would. thanks.

As others have pointed out, with just one function generator all you will get is a diagonal line. What you see with a Lissajous setup is the graphical relationship between two signals. If both signals are the same, then what you see is what you get.

If you can get your hands on another function generator, then you're all set. Or set up a circuit to turn your sine wave into a cosine wave (shifting it by 90 degrees) and you'll get a nice circle. But it'll be easier just to get another generator.

Plus, you can experiment with wave shapes -- triangle, square, etc.

If you really want to ham it up you can get a third generator and play with the insensity of the beam -- the Z axis. You can turn the beam on and off and get some really interesting patterns. This is what laser shows did before they got computers to control everything.

wein bridge = 634 hits wien bridge = 5500 hits

surprisingly many people confused about how its spelt.

Colin =^.^=