How to Get Started with Your Oscilloscope
An oscilloscope is an instrument that displays the evolution of one or more voltages over time. But how do you use it?
When you have been tinkering with electronics for a while and your projects are getting more serious, chances are that you will need an oscilloscope. An oscilloscope is an instrument that displays the evolution of one or more voltages over time.
Of course, you already invested in a multimeter, which is great, but an oscilloscope can do things you cannot do with a multimeter. However, oscilloscopes are also much more complex instruments than multimeters and so it takes some time and practice to get the most out of them.
As said at the beginning, an oscilloscope displays the evolution of a voltage over time, a ‘signal’, and it does this in the shape of a two-dimensional graph with the center in the middle of the screen. Note that I said ‘voltage’, and not ‘current’. An oscilloscope is a fancy voltmeter.
Then there is a third section called ‘Trigger’. This is probably the most important section as it determines how and when a signal is shown.
Often it is easy enough to get the signal you are measuring to fit on the screen by adjusting the horizontal and vertical axes, but making the oscilloscope display the part of the signal you are interested in can be much more difficult. The trigger section gives you control over this and it is therefore important to understand what it does and how.
This section lets you amplify or attenuate the input voltage or signal, meaning that you can adjust its amplitude, and you can adjust its vertical position. This can be set independently for every input channel.
BTW, in oscilloscope language, a signal is also called trace; single-trace means one signal or channel, dual-trace means two, etc.
We will not use this XY mode in this article, for us the horizontal axis always represents time.
Note that probes often have a switch to choose between 1:1 or 10:1. This is an extra attenuation option that allow large signals to fit or to improve the precision of measurements of sensitive signals. Some people always use 10:1 attenuation mode and there exist probes that are always in 10:1 mode. It is often possible to inform the oscilloscope about the type of probe you are using, so it can adapt the scales accordingly.
Before connecting the tip of the probe to the signal of interest, first connect the crocodile clip attached to the probe to the ground reference of the circuit under test.
As a general rule, connect it as close as possible to the signal. However, in many cases this is not so important as long as it is connected to ground somewhere. It can even be convenient to use the crocodile clip of a second probe just for connecting to ground so you can remove the crocodile clip from the measuring probe and keep it out of your way.
With the knob in the section ‘Horizontal’ you can zoom in and out on the time scale and you can move the signal to the left or to the right. Usually, the center of the screen is zero.
Triggering is what makes an oscilloscope really useful as it allows you to focus on the interesting part of a signal. A trigger is needed to start a trace. If there is no trigger, the trace will not start, and you will not see anything. This is why an oscilloscope features several options for triggering. One might even argue that the more trigger options an oscilloscope has, the better it is.
In my world, every oscilloscope features at least automatic and normal triggering, adjustable trigger level, up and down or positive and negative trigger slopes and an external trigger input.
The first thing to do is select the source for the trigger signal. Usually it is one of the signals you want to look at, but it can be a signal generated by another device altogether. In this example we will choose channel one, the same channel as our test signal.
If you set the trigger level too low or too high, the trace freezes or may not appear as it is never triggered. This mode is good for infrequent events or to filter out special events.
The Single button can be used when an event happens only occasionally, for instance only at power-on or after pressing a button, or when it is not periodic. After the trigger happens, the trace will run only once and then the oscilloscope enters Stop mode. You must press Run to restart the capture of a single event. Press Single again to go back to normal mode.
Depending on the oscilloscope there can be more trigger options. Typical other options go from triggering on both slopes, or on a time delay between slopes, a pulse so to speak, to triggering on a sequence, inside or outside a window, with delays and what not. As I said before, the more trigger options, the better.
We will stop here. Your oscilloscope probably has several other buttons not covered in this video. But now that you know how to get a stable signal on its display you can explore these functions more in depth. Whatever you do, always keep in mind that before measuring anything, you should have an idea of what to expect so that you can compare the result to what it is supposed to be.
If you don’t know what to expect, then you can’t tell if it is wrong or if it’s right.
Of course, you already invested in a multimeter, which is great, but an oscilloscope can do things you cannot do with a multimeter. However, oscilloscopes are also much more complex instruments than multimeters and so it takes some time and practice to get the most out of them.
What do you need?
Oscilloscopes used to be expensive, but today prices have dropped so much that almost anyone can afford one. For most hobbyist / tinker / maker applications, a basic oscilloscope is more than good enough. If your thing is Arduino- or Raspberry-Pi-based projects or building and repairing audio amplifiers or musical instruments or guitar effects, there really is no need to invest in a four or more channel oscilloscope with hundreds of MHz of bandwidth and many gigasamples. A 2-channel, 20 to 50 MHz oscilloscope is just fine.Not too small, please
However, even though it may seem tempting, I don’t recommend spending money on those cheap small DIY oscilloscope kits you can find online. They just do not offer the comfort and features of a low-cost but real bench oscilloscope. They may be practical when traveling or when you are really tight on space, but that’s probably all they are good for. I like my oscilloscope to stay where it is when I pull a test lead and it must have knobs and buttons that I can find quickly. An oscilloscope without knobs for the horizontal and vertical axes is not a real oscilloscope.Headless Oscilloscopes
Of course, there are headless oscilloscopes with excellent specifications, but they require a computer and a mouse. Such devices are good for doing remote measurements or for documentation or constant monitoring, for datalogging and postprocessing or for doing very precise things that require a lot of fiddling. In my lab setup, the computer is needed to show the schematic, modify firmware, read datasheets and search the internet. I don’t want it to be an oscilloscope as well. And I don’t want a second computer because it takes up too much bench space. And, of course, because I want real knobs.DSO, MSO, analog?
Today oscilloscopes are digital, and they are called DSOs. Oscilloscopes used to be analogue in the past. Analogue oscilloscopes are bulky and limited and you don’t want one unless you have very special needs. There have been hybrid oscilloscopes that could do both, but you don’t want one of those either. BTW, do not confuse these with so-called mixed-signal oscilloscopes or MSOs as these are DSOs with special features for digital signals and communication busses and things.Lets try to use it
So, now that we know a bit more about oscilloscopes, we can move on to learning how to use them. If you were smart and bought a cheap one, it will not have too many functions, and so it is easy to get going.As said at the beginning, an oscilloscope displays the evolution of a voltage over time, a ‘signal’, and it does this in the shape of a two-dimensional graph with the center in the middle of the screen. Note that I said ‘voltage’, and not ‘current’. An oscilloscope is a fancy voltmeter.
Main control sections
Because it displays signals as graphs, an oscilloscope has controls to adjust the horizontal and vertical axes of the graph. On every modern oscilloscope that I know of these controls are grouped together in a section labelled ‘Horizontal’ and a section labelled ‘Vertical’. The horizontal section is also known as the ‘Time Base’ as the horizontal axis usually represents time.Then there is a third section called ‘Trigger’. This is probably the most important section as it determines how and when a signal is shown.
Often it is easy enough to get the signal you are measuring to fit on the screen by adjusting the horizontal and vertical axes, but making the oscilloscope display the part of the signal you are interested in can be much more difficult. The trigger section gives you control over this and it is therefore important to understand what it does and how.
Vertical
But first let us look at the section ‘Vertical’.This section lets you amplify or attenuate the input voltage or signal, meaning that you can adjust its amplitude, and you can adjust its vertical position. This can be set independently for every input channel.
BTW, in oscilloscope language, a signal is also called trace; single-trace means one signal or channel, dual-trace means two, etc.
XY mode
Another point of confusion can be that input connectors besides being labelled channel one and two are sometimes also labelled ‘X’ and ‘Y’. This refers to a special operation mode of the oscilloscope in which the X input controls the horizontal axis instead of the vertical. This is the mode to create the famous Lissajous figures with that they like to show in old sci-fi movies.We will not use this XY mode in this article, for us the horizontal axis always represents time.
Connecting the probe
Connect a probe to one of the channel connectors, not to the 'Ext', 'Trigger', 'Aux' or 'Z' connector.Note that probes often have a switch to choose between 1:1 or 10:1. This is an extra attenuation option that allow large signals to fit or to improve the precision of measurements of sensitive signals. Some people always use 10:1 attenuation mode and there exist probes that are always in 10:1 mode. It is often possible to inform the oscilloscope about the type of probe you are using, so it can adapt the scales accordingly.
Before connecting the tip of the probe to the signal of interest, first connect the crocodile clip attached to the probe to the ground reference of the circuit under test.
As a general rule, connect it as close as possible to the signal. However, in many cases this is not so important as long as it is connected to ground somewhere. It can even be convenient to use the crocodile clip of a second probe just for connecting to ground so you can remove the crocodile clip from the measuring probe and keep it out of your way.
A word about ground
Note that ground doesn’t have to be ground, it can be any voltage or signal in the circuit, but it must be the same for every vertical channel. Also note that probe ground is usually connected to oscilloscope ground which can be connected to mains ground, so if you connect the probe ground to something other than ground, short circuits may be created and dangerous situations may arise. Therefore, we only connect the crocodile clip to ground.With the knob in the section ‘Horizontal’ you can zoom in and out on the time scale and you can move the signal to the left or to the right. Usually, the center of the screen is zero.
Triggering
Up to now I was supposing that you did see something on the display of the oscilloscope, but maybe you didn’t? One reason can be that the trace is not on the screen. Use the vertical level control to find it. Another reason may be that the brightness is too low. If it is, crank it up. A third reason can be a trigger problem. If your oscilloscope has an Auto Setup button or something similar, now is a good time to press it. After doing so you may not see what you expected, but you should at least see something. Use the vertical and horizontal knobs to bring the signal into range.Triggering is what makes an oscilloscope really useful as it allows you to focus on the interesting part of a signal. A trigger is needed to start a trace. If there is no trigger, the trace will not start, and you will not see anything. This is why an oscilloscope features several options for triggering. One might even argue that the more trigger options an oscilloscope has, the better it is.
In my world, every oscilloscope features at least automatic and normal triggering, adjustable trigger level, up and down or positive and negative trigger slopes and an external trigger input.
The first thing to do is select the source for the trigger signal. Usually it is one of the signals you want to look at, but it can be a signal generated by another device altogether. In this example we will choose channel one, the same channel as our test signal.
Automatic triggering
Automatic triggering is easiest to use. In this mode the oscilloscope decides when to trigger, and the user can set the trigger level and choose the slope to trigger on. This mode is useful for quickly seeing if something is “going on” on an input or to simply measure a DC voltage.Normal mode
In Normal mode the oscilloscope only triggers when the trigger level and slope conditions are met or any other trigger condition that you may have specified. After a trigger, the trace will run until it falls off at the right side of the screen. A new trigger is required to start it again.If you set the trigger level too low or too high, the trace freezes or may not appear as it is never triggered. This mode is good for infrequent events or to filter out special events.
Run/Stop & Single
It is quite probable that your oscilloscope has a Run/Stop button and a Single button. The Run/Stop button lets you freeze the display, which is handy if you want to study a signal in detail without allowing a new trigger to change it or make it disappear. Press the button again to leave this mode.The Single button can be used when an event happens only occasionally, for instance only at power-on or after pressing a button, or when it is not periodic. After the trigger happens, the trace will run only once and then the oscilloscope enters Stop mode. You must press Run to restart the capture of a single event. Press Single again to go back to normal mode.
Depending on the oscilloscope there can be more trigger options. Typical other options go from triggering on both slopes, or on a time delay between slopes, a pulse so to speak, to triggering on a sequence, inside or outside a window, with delays and what not. As I said before, the more trigger options, the better.
We will stop here. Your oscilloscope probably has several other buttons not covered in this video. But now that you know how to get a stable signal on its display you can explore these functions more in depth. Whatever you do, always keep in mind that before measuring anything, you should have an idea of what to expect so that you can compare the result to what it is supposed to be.
If you don’t know what to expect, then you can’t tell if it is wrong or if it’s right.
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