#48: Basics of Lissajous Patterns on an Oscilloscope

is another back to basics video this one's going to talk about Lissa do patterns but several of my youtube viewers have asked me about Lucy's your patterns so there's a little back to basics video about that normally when you're using an oscilloscope the exposition of the sweet okay is controlled by your horizontal time base okay that's just kind of moving the dot across the screen the trigger is going to kick it off and it goes across the screen at speed to turn by your time base okay and then the y position or the vertical position of the dot is controlled by the voltage that appears at one of the channels or both of the channels okay Alyssa's your patterns are generated by using what's called the XY mode XY mode is where you know we still have the vertical position controlled by one of the input channels but now the x position is also controlled by one of the input channels the way to go into XY mode on most of the older analog scopes is usually by turning the horizontal time-base knob all the way down to this position where it says X Y now some other scopes will have a specific button on them say XY mode there's other other depending on the scope they'll be a different means of doing it the digital scopes we usually have a display mode where you can change that okay but here on this analog scope we would turn the horizontal time-base all the way down so in this case what I've got I've got a signal being applied to both of these inputs coming from a this little function generator right here okay so if I turn on channel 2 okay kind of tough to see that but let's change the vertical position on one of them so I can see I've got these two signals that are identical they're aligned up in phase okay so now they're both are kind of lined up and on top of each other here if I go to XY mode what's going to happen if you think about it both the x position okay horizontally and the vertical position in the Y position are going to be driven with the same voltage so in a sense if you picture the dot starting in the middle if what if the X input drives it to go in this direction the Y inputs driving to go in that direction we're going to create essentially a diagonal movement of that dot so since these two signals are in phase same frequencies are going to line up with a heart rate diagonal line so we got to rotate those all the way down there I can go see that in fact if I momentarily take and change the frequency of these of these two signals both down to something like 1 Hertz okay let's go to channel to change its frequency here to 1 Hertz as well okay and now if I take a look at the scope you can actually see that happening okay you can see that the dot is just being driven in this diagonal way because if we look at this on the screen you know what we're essentially getting is the x position being driven by this channel here back and forth this way the Y position is being driven up or down and they're the same frequency so we can actually see them just driving that to being back and forth let's change these signals back up to about a kilohertz or so so now I change one of them to a kilohertz so in this case I changed channel 1 which is going into here the x position is now at kilohertz okay so that's moving this beam back and forth a thousand times a second but the Y position is being driven by just that same one Hertz signals that's why it's just going in that direction if I change that that signal now also to one kilohertz okay and align the phase now I'm back to where we started okay so now we take these signals out let's consider what happens if we adjust the phase between them okay so if I do I set the phase of this guy to say 180 degrees 180 degrees out of phase is the inverse of the signal so now I've got one signal that's going up and down like this the other one is going down and up like that so in a sense you think about the XY mode all that's going to do is change the angle of that diagonal line okay going in the opposite direction because as the X is being driven in this direction the Y is being driven down instead of up okay so that where things get interesting is we can actually use this as a hey I know these two signals are identical but they're 180 degrees out of phase when they were in phase okay my dial is zero back in it looks like that so now what's halfway between those that would be 90 degrees so if we dial 90 degree phase shift in here I get a circle okay and again if we knock the frequency down here to something like 1 Hertz again let's go to channel 1 then let's go to the frequency at channel 2 and we've got 1 Hertz also okay you can actually see and let me align the phase of those actually see we're just traversing around in a circle okay this is kind of a slow motion version of what we were looking at to go back to a kilohertz of that guy and let's go back to 1 kilohertz of this guy as well okay and align the phase again okay so now we're back to where we are so actually we're just tracing around that circle really really fast okay and again if we go and play with the phase of this I'll move in 10 degrees steps here so that's a 90 degree phase shift there's 80 okay 70 60 50 40 30 etc down to 0 degrees and now we're lined back up again work our way back up through 90 degrees okay keep going we go to 180 degrees there we are there I keep going it draws a circle again and say well see I get up to 270 degrees that looks just like by 90 degree picture because it really is they're still the signals are still 90 degrees apart but they're 90 degrees apart the other way okay in fact the only way to really can tell the difference between whether we're to 70 or 90 degrees is if we go back to the time domain and take a look at those signals okay and see which one is leading which one is lagging okay another way to do that and actually see it visually is let's go back and change the frequency again back to one Hertz okay so if I change the frequency in this case at channel 2 to 1 Hertz let's change the frequency of channel 1 back to 1 Hertz and align the phase now I can actually see that the dot is being driven around counterclockwise okay if I got a 270 degree phase shift okay if I change that phase ship to ninety degrees okay now we see the circle going around the other direction but the problem is when you're operating at these larger or faster frequencies you really can't see the dot which direction that's going in so there really isn't a good way with Alyssa to pattern to make a distinction between a 90 degree phase shift and a 270 degree phase shift or a minus 90 okay but that's kind of what happens with phase with these lists is you patterns let's drop that back down to zero degrees and I'm going to change the frequency again of both of these signals let's make the back up to a kilohertz again channel two let's make that one kilohertz so now we're both about the same thing align the phase we're back to where we started so now what happens if the signals are different frequency okay I'm going to do this in such a way they're going to be different in frequency but still lock together okay so let's change this one here to say two kilohertz so if I go to two kilohertz so now you can see if I kind of separate these out like the easier to see there's a one signal here at our original one kilohertz frequency and here's the other signal at two kilohertz so it's moving twice as fast and that's the X input so what you might imagine is now at the x position in XY mode it's going to be driven twice as fast as the Y position okay so when we look at the list view this is your pattern okay we kind of get this kind of figure 8 pattern because this is this signal the x position being driven twice as fast then we are here okay and I've kind of got this stable because I've got kind of a locked phase condition here if I go back and adjust the phase again here I can actually rotate this this kind of pattern around okay as I kind of rotate it around kind of almost visualize this pattern kind of rotating around no in front of you here let's bring that back to zero degrees okay kind of get the figure-eight pattern again now really when signals different frequency they're really different differing in how many degrees per second they're moving okay we kind of see that here because we've got this fixed frequency difference but if I kind of unlock these things and the way I can kind of do that is just by changing this frequency so it kind of rotates it around a little bit let's kind of move it like this here so now you can actually see it rotating because what I did is I got one kilohertz on one input here the other one is two point zero zero one kilohertz you can kind of see that so there's a one kilohertz and two point zero zero one kilohertz and now looking at that looks like this signal is rotating over this the pattern is rotating and it's doing that because I don't have a fixed frequency or a integer frequency difference between the two okay but again we still kind of have the the two points versus one point of contact you know as we go we go through here so you can kind of recognize some of these patterns saying there that's a two to one frequency difference okay if I go up here and make it to say let's go back make this safe it's back space through this and let's go over here make this say three kilohertz so now you can kind of see this guy's now at 3 kilohertz okay this guy is still a 1 kilohertz so now I kind of have the three points of contact for one for every one point in contact we have the other way so you can kind of get that that kind of rotating pattern so you can actually make you know by recognizing these kinds of patterns there's 4 4 kilohertz and 5 kilohertz you can kind of get an idea of what what our frequency difference is now in this case I've got a one point zero zero one kilohertz frequency here okay so I've got a one Hertz difference between the two signals we look at them on the normal scope and kind of see this one-to-one signals walking past the other one and about every second they line up again boom boom boom right so we go to the list of your pattern we can actually see that every second we're going to hit that same horizontal position bang bang bang so you can get an idea of what's going on with these two signals by actually looking at them of listed you patterns of course there's a lot of fun things you can do listen to patterns too you can take the output of your stereo or your iPod and put it into channel 1 and channel 2 and if you're listening to something that is monochromatic it's not stereo then both signals will be traversing the at the same time you get a horizontal line but once you go into stereo the left and right channels are seeing different signals so you're going to see kind of that spread you'll see how much of your signal is monochromatic okay versus how much of it might be stereo and it's just kind of a fun thing to watch but that's just your basics of what Eliseo patterns are how they're generated what the scope is doing and how you can kind of interpret a little bit about what these patterns are telling you so anyway what turned out started out to be a short video is a 11 minutes long here but I hope you enjoyed it and got a little something out of it and of course questions and suggestions for future videos are always welcome thank you

Channel: w2aew

Views: 325,446

Rating: 4.9454589 out of 5

Keywords: W2AEW, Tek, Tektronix, oscilloscope, scope, 465, 465B, AFG, AFG3000, Lissajous, figure, figures, pattern, patterns, trace, XY, mode, horizontal, vertical, position, sweep, frequency, phase, difference, tutorial, basics, rotate, rotating, shift, degrees, degree

Id: t6nGiBzGLD8

Length: 11min 21sec (681 seconds)

Published: Mon Jun 04 2012