Last updated: October 2026

To use an oscilloscope, connect a compensated probe to a channel, clip its ground lead to your circuit’s ground, then set the vertical scale (volts per division), the horizontal scale (time per division) and an edge trigger until the waveform sits still on screen. From there you read voltage off the vertical grid and time off the horizontal grid, or let the scope’s cursors and automatic measurements do it. This guide walks through each step on a safe, low-voltage signal: the PWM output of an Arduino.

Scope of this guide: low-voltage bench signals only (microcontrollers, function generators, battery-powered circuits). Do not probe mains wiring or anything plugged into a wall outlet with a standard passive probe. That work needs differential or isolated equipment and a qualified person; see your scope maker’s manual.

What the controls do

Every digital oscilloscope groups its controls the same way, even if the knobs look different:

  • Vertical: volts per division (V/div), vertical position, and input coupling (DC or AC) for each channel.
  • Horizontal: seconds per division (s/div), also called the time base, plus horizontal position.
  • Trigger: source channel, level, slope (rising or falling edge) and mode (Auto, Normal, Single).

Tektronix describes the seconds-per-division setting as the rate at which the waveform is drawn across the screen. The trigger decides when that drawing starts, which is what makes a repeating signal look stable instead of smeared.

Step-by-step: from power-on to a measured signal

1. Set up and ground the scope

Plug the oscilloscope into a grounded outlet using its three-prong cord, as Tektronix’s primer recommends. The scope and the circuit you probe need to share the same ground. On a standard bench scope, the probe’s ground clip is tied to the scope chassis, so that clip goes only to your circuit’s ground (GND), never to any other point.

2. Choose 1x or 10x on the probe

Most passive probes have a 1x/10x switch on the body. The tradeoffs, per Rohde and Schwarz’s guide to passive probes:

  • 10x has much wider bandwidth and loads the circuit less, because it raises the effective input impedance by a factor of 10. Use 10x as your default.
  • 1x has low bandwidth, because the scope’s input capacitance acts as a low-pass filter, but it is useful when the signal is small, for example under about 1 V peak-to-peak.

Whatever you pick on the probe, set the matching probe ratio in the channel menu. Many 10x probes are detected automatically; if yours is not, set it by hand or every reading will be off by a factor of 10.

3. Compensate the probe (10x only)

Probe compensation matches the probe’s tip capacitance to the scope channel’s input capacitance. Tektronix’s steps:

  1. Attach the probe to a channel.
  2. Connect the probe tip to the scope’s square wave reference terminal (often labeled with a square wave symbol or “Probe Comp”).
  3. Attach the ground clip to the reference ground.
  4. Display the square wave (Auto Setup is fine here).
  5. Turn the small trimmer on the probe until the corners of the square wave are square.

A poorly compensated probe shows distortion right after each edge: corners that spike above the flat top, or corners that round off before reaching it. Digi-Key’s technical forum stresses that compensation applies to the 10x setting only, not 1x, and calls mixing that up a frequent source of user error. Compensate each probe on the channel you will use it with.

4. Build a known test signal

An Arduino is an easy, low-voltage signal source. According to the Arduino analogWrite() reference, on an UNO R3 the PWM pins are 3, 5, 6, 9, 10 and 11, running at 490 Hz (980 Hz on pins 5 and 6). On an UNO R4 Minima or WiFi the same pins run at 490 Hz. The duty cycle value runs from 0 (always off) to 255 (always on).

Upload this sketch:

void setup() {
  analogWrite(9, 64);   // about 25% duty cycle on pin 9
}
void loop() {}

If you have a function generator instead, a 1 kHz square or sine wave at a few volts works just as well.

5. Connect the probe to the circuit

Clip the probe ground to the Arduino’s GND pin and hook the probe tip to pin 9 (a short jumper wire on a breadboard makes this easy). Keep the ground lead short; long ground loops pick up noise.

6. Set the vertical scale

Set the channel to DC coupling. Tektronix explains that DC coupling shows the whole signal, while AC coupling blocks the DC component and centers the waveform around zero volts. For a 0 V to 5 V PWM signal you want DC so you can see the true low and high levels.

Start at 1 V/div or 2 V/div and move the trace so the 0 V marker sits near the bottom of the screen. Then adjust so the signal covers as much of the vertical display as possible without clipping; Tektronix notes that voltage readings are more accurate that way.

7. Set the horizontal scale

One period of a 490 Hz signal is about 2 ms. A setting of 500 µs/div to 1 ms/div shows a few full cycles across a typical 10-division screen. Time measurements are also more accurate when the portion you care about fills a large part of the display.

8. Set the trigger

  1. Set the trigger source to the channel you are probing.
  2. Choose Edge triggering, the most common type.
  3. Set slope to rising (positive).
  4. Set the trigger level to about halfway up the signal, around 2.5 V for a 5 V PWM.
  5. Use Auto mode while you set up.

Tektronix explains the difference: Auto mode sweeps even without a trigger, so you always see a trace. Normal mode only sweeps when the signal crosses the trigger point; otherwise the display freezes. Switch to Normal once the level is set if you want only clean, triggered captures. Use Single to grab one event, such as a button press or a power-up glitch.

9. Read the measurement

You can count divisions by hand (volts = divisions × V/div; time = divisions × s/div), but every modern digital scope offers two faster options:

  • Cursors: place two horizontal cursors on the low and high levels for voltage, or two vertical cursors on consecutive rising edges for the period.
  • Automatic measurements: turn on frequency, period, Vpp (peak-to-peak), Vmax and positive duty cycle.

For the sketch above you should see a frequency near 490 Hz and a duty cycle near 25%. Change the analogWrite value to 128 and the duty cycle should move to about 50%. Tektronix defines pulse width at 50% of full voltage and rise time from 10% to 90%, which is how most scopes compute those readings.

Common mistakes

  • Probe ratio mismatch. The probe is on 10x but the channel is set to 1x, so 5 V reads as 0.5 V. Always check both.
  • Skipping compensation. An uncompensated 10x probe distorts square edges and amplitude.
  • Compensating in 1x mode. The trimmer only matters on 10x.
  • Ground clip on the wrong node. On a bench scope the clip is chassis ground. Only connect it to circuit ground.
  • AC coupling on a logic signal. The waveform shifts so it centers on zero, which hides the real low and high voltages.
  • Trigger level outside the signal. If the level is above the peak or below the floor, Normal mode never triggers and Auto mode shows a rolling trace.
  • Time base far too slow or fast. If you see a solid band or a flat line, change s/div by a few steps before changing anything else.

Next steps

Once a PWM signal looks right, try probing I2C or UART lines from the same board, or compare two channels at once. If you still need a scope, see our budget oscilloscope comparison. For measuring steady DC levels and continuity, a meter is the better tool; start with how to use a multimeter.

FAQ

Should I leave my probe on 1x or 10x? Leave it on 10x for most work. It has wider bandwidth and loads the circuit less. Switch to 1x only for very small signals, and remember to change the channel’s probe setting too.

Why does my waveform keep scrolling or jittering? The trigger is not locking. Make sure the trigger source matches the channel you are viewing and the level sits between the signal’s low and high values.

Can I measure a wall outlet with my oscilloscope? Not with a standard passive probe on a bench scope. Mains measurement needs isolated or differential gear and training. Leave it to a licensed electrician and follow your scope maker’s manual.

What does Auto Setup do? It picks vertical, horizontal and trigger settings automatically. It is a good starting point, but you will usually fine-tune the scale and trigger level by hand.

Sources