HOW-TO GUIDE
How to Use an Oscilloscope
By the OhmSavvy Research Team ·
Safety before your first connection
- On a mains-powered bench scope, the probe's ground clip is normally connected to mains earth through the power cord. Clip it only to a point that is at earth potential or to the ground of a low-voltage circuit. Clipping it to a point that isn't at earth potential, such as anywhere on a mains-connected, non-isolated circuit, creates a short through the ground lead that can cause damage, fire or injury.
- Never remove or defeat the scope's earth connection ("floating" the scope) to get around this. For mains-referenced circuits, use an isolation transformer on the device under test, a differential probe, or an isolated-channel or handheld scope rated for the job.
- Check the maximum input voltage and CAT rating printed on your probe and scope. Standard 1x/10x probes are not for mains work unless their rating explicitly covers it. For a first session, stick to the scope's own test output and low-voltage battery or USB circuits.
The controls you'll use in every session
Front panels differ between brands, but the same groups of controls appear on nearly every digital storage oscilloscope. Find each one on your scope before you start; the labels may be slightly different (Autoset vs Auto, Scale vs Volts/Div).
Vertical (V/div)
Sets how many volts each vertical grid division represents, per channel.
Vertical position
Moves the trace up or down without changing its size.
Horizontal (time/div)
Sets how much time each horizontal division represents.
Trigger
Decides when the scope starts drawing, so repeating signals stand still.
Autoset / Auto
Makes the scope pick starting scale and trigger settings for you.
Run/Stop and Single
Freeze the display, or capture one triggered event and hold it.
On most bench scopes these controls sit to the right of the screen, grouped roughly as in the diagram below: a knob for vertical, one for horizontal, one for the trigger, with the channel inputs and probe compensation terminals along the bottom edge.
The first session at a glance
The nine steps below follow one simple sequence. Once you have done it a couple of times, it becomes the routine you run at the start of every measurement: get to a known state, let Autoset find the signal, then take control of the scales and trigger before you trust a number.
01
Reset & connect
Default Setup, probe on CH1 at 10x
02
Test signal
Clip onto the probe comp output
03
Autoset
Let the scope pick starting settings
04
Scales & trigger
Tune V/div, time/div and edge trigger
05
Measure
Count divisions, check with Measure
1Power on and reset to a known state
Plug the scope into an earthed outlet and switch it on. Many scopes have a Default Setup (or Default/Factory) button that clears whatever settings the last user left behind. Pressing it first means every step below starts from the same place: one channel on, DC coupling, a moderate vertical and horizontal scale, and an edge trigger. If you can't find the button, check your model's manual, as the location varies.
2Connect the probe and match the 1x/10x setting
Push the probe's BNC connector onto the Channel 1 input and twist it to lock. Most probes supplied with a scope have a 1x/10x switch on the body. Set it to 10x: it divides the signal by ten, puts much less load on the circuit, and is the position most general measurements use.
For more on the ground clip, the ground spring and matching 1x/10x, see how to connect an oscilloscope probe correctly.
Then open the Channel 1 menu and set the probe ratio (sometimes called attenuation) to 10x as well. This is the step beginners most often miss. If the probe is on 10x but the channel is set to 1x, every voltage on screen reads ten times too small. Some scopes detect the probe automatically; many don't, so check.
3Hook up to the built-in test signal
Almost every scope has a small probe compensation output on the front panel, usually two terminals: one signal tab and one ground. It produces a square wave, commonly around 1 kHz; the exact frequency and amplitude vary by model, so check your manual or the label next to the terminals.
Clip the probe's ground lead to the ground terminal and hook the probe tip onto the signal tab. This is a safe signal to learn on, and it doubles as a check that your probe is working and correctly compensated.
4Press Autoset
Press Autoset (or Auto). The scope looks at the incoming signal and picks a vertical scale, a horizontal scale and a trigger level that should give you a few stable cycles on screen. For the test signal you should see a square wave with flat tops and sharp corners. If the corners show spikes or rounded edges, the probe needs compensating before you trust any square-wave measurement.
Autoset is a starting point, not the answer. It picks settings that show the signal; it doesn't know what you actually want to look at. The next three steps are how you take control.
5Adjust the vertical scale (V/div) and position
Turn the Channel 1 vertical scale knob one click at a time and watch the waveform grow or shrink. Smaller V/div values make the signal taller. Aim to have the waveform fill most of the screen height without its top or bottom running off the edge, because a clipped waveform gives wrong measurements. Use the vertical position knob to slide the trace up or down. The small marker at the left edge of the screen shows where 0 V sits for that channel; keep track of it, because readings are taken relative to that line.
6Adjust the horizontal scale (time/div)
Now turn the horizontal scale knob. A faster setting (fewer microseconds per division) stretches the waveform out so you can see edge detail; a slower setting squeezes more cycles onto the screen. For most measurements, two to four complete cycles is a good view: enough to see that the signal repeats, with each cycle wide enough to count divisions accurately. The horizontal position knob shifts the view earlier or later in time relative to the trigger point.
7Set the trigger so the waveform stands still
The trigger tells the scope where in the signal to start each sweep. Without a sensible trigger, a repeating waveform drifts or rolls across the screen. For a first session, set the trigger to:
- Type: Edge, the default on most scopes.
- Source: CH1, the channel your probe is on.
- Slope: Rising, so the sweep starts as the signal goes up.
- Level: somewhere between the signal's lowest and highest point, roughly the middle.
Move the trigger level above the top of the waveform and the display will either freeze on the last capture or start drifting unstably, depending on whether the scope is in Normal or Auto mode. Bring it back inside the signal and the picture locks again. Seeing that happen once teaches more than any explanation. The trigger guide covers modes, holdoff and single-shot capture in depth.
8Take your first measurements
There are three ways to measure, and it's worth trying all of them on the test signal:
- Count divisions. Height in divisions × V/div gives voltage; width of one cycle × time/div gives the period, and frequency is 1 ÷ period. See how to read an oscilloscope screen.
- Automatic measurements. Open the Measure menu and add peak-to-peak voltage and frequency. The scope calculates them from the captured data and shows the values on screen.
- Cursors. Two movable lines you place by hand. The scope shows the voltage or time difference between them, which is useful for measuring one specific feature.
If the automatic frequency reading roughly agrees with what you worked out by counting divisions, your probe ratio, scales and trigger are all set correctly. For more detail, see how to measure voltage and measure frequency with an oscilloscope.
9Move to a real (low-voltage) circuit
Once the test signal behaves, try a safe real signal, such as a PWM pin on a USB-powered microcontroller board. Connect the ground clip to the circuit's ground first, then touch the probe tip to the point you want to see, and press Autoset again. Keep the ground lead short and the circuit low-voltage. If you're not sure whether a scope is even the right tool for a job, our oscilloscope vs multimeter guide explains when a multimeter is quicker.
Quick reference: starting settings
A sensible starting point for a repeating low-voltage signal on a typical digital scope. Autoset will usually land close to this, and you fine-tune from there.
| Setting | Start with | Why |
|---|---|---|
| Probe switch | 10x | Less circuit loading; standard for general use |
| Channel probe ratio | 10x (match the probe) | Otherwise voltages read 10 times too small |
| Coupling | DC | Shows the full signal, including any DC level |
| V/div | Waveform fills most of the height | Better resolution without clipping |
| Time/div | 2 to 4 cycles on screen | Enough cycles to see repetition and count divisions |
| Trigger | Edge, rising, CH1, level mid-signal | Gives a stable picture on most repeating signals |
If the screen looks wrong, check these first
- Flat line: is the channel switched on, the probe tip and ground actually connected, and the trace on screen (vertical position)?
- Rolling or blurred waveform: trigger source on the wrong channel, or level outside the signal.
- Voltage ten times too small or too large: probe switch and channel probe ratio don't match.
- Rounded or spiky square-wave corners: probe needs compensating.
Which scope should you practice on?
Any digital scope with a probe compensation output will do. If you're still choosing, a bench model such as the Rigol DS1054Z (50MHz, 4 channels) or Siglent SDS1104X-E (100MHz, 4 channels) has the full set of controls described here. Pocket units like the FNIRSI DSO152 (200kHz, 1 channel) follow the same ideas with fewer knobs. The buying guide explains which specs matter, and what is an oscilloscope covers the different types.
Good first scopes
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Frequently asked questions
Should I use 1x or 10x on my oscilloscope probe?
Use 10x for most measurements. It loads the circuit far less and lets the scope see higher frequencies through the probe. The 1x setting is mainly for very small signals, where the extra sensitivity helps. Whichever you choose, set the channel's probe ratio in the scope menu to match, or every voltage reading will be off by a factor of ten.
Why is my waveform moving across the oscilloscope screen?
A rolling or drifting waveform almost always means the trigger is not locking onto the signal. Check that the trigger source is the channel you are probing, the type is Edge, and the level sits between the lowest and highest point of the waveform. If the signal is very small or noisy, enlarging it with a smaller V/div setting first makes a stable trigger easier.
Why does my oscilloscope only show a flat line?
Work through the simple causes first: the channel may be switched off, the probe tip or ground clip may not be making contact, or the trace may be off screen because of the vertical position. A V/div setting far too large for the signal can also flatten it. Pressing Autoset with the probe on the test output is a quick way to confirm the probe and channel work.
Can I measure mains voltage with an oscilloscope?
Not with a standard setup. On a mains-powered bench scope the probe's ground clip is tied to earth, so clipping it onto a non-isolated mains circuit creates a short. Mains work needs an isolation transformer on the device under test, a differential probe, or an isolated-channel or handheld scope rated for the job, plus probes whose rating covers the voltage.
What is the difference between AC and DC coupling on an oscilloscope?
DC coupling shows the full signal, including any steady DC level, which is why it is the usual starting setting. AC coupling blocks the DC part and shows only what changes, centred on the zero line. That lets you use a small V/div setting to magnify, for example, a few tens of millivolts of ripple sitting on top of a 5 V supply rail.
