How to Measure Pulse Width with FNIRSI DSO-152 Plus Malaysia

How do you measure the pulse width of an electronic signal using the FNIRSI DSO-152 Plus Mini Digital Oscilloscope?

Pulse-width measurement is useful when troubleshooting:

Microcontroller outputs

Arduino projects

555 timer circuits

PWM signals

Sensor outputs

Trigger pulses

Control signals

LED controllers

Motor and fan control signals

A multimeter may tell you that voltage is present, but it usually cannot show clearly how long an individual pulse remains HIGH or LOW.

An oscilloscope allows you to see the pulse against time.

What Is Pulse Width?

Pulse width is the amount of time a pulse remains in a particular state.

For example, a digital signal may switch:

LOW → HIGH → LOW

The time between the rising edge and falling edge is the:

HIGH pulse width

If the signal remains HIGH for:

2 milliseconds

then the HIGH pulse width is:

2 ms

Pulse Width Is a Time Measurement

Pulse width may be expressed in units such as:

Seconds – s

Milliseconds – ms

Microseconds – µs

The correct unit depends on how fast the signal is.

Pulse Width vs Frequency

These are different measurements.

Pulse width tells you how long one pulse lasts.

Frequency tells you how many complete cycles occur every second.

A signal can have the same frequency but different pulse widths.

Example

Suppose one complete cycle takes:

10 ms

This means the frequency is:

100 Hz

Now suppose the HIGH pulse lasts:

2 ms

The signal has:

100 Hz frequency

and

2 ms HIGH pulse width

These two values describe different characteristics of the same waveform.

Pulse Width vs Duty Cycle

Pulse width and duty cycle are closely related.

Duty cycle describes pulse width as a percentage of the complete period.

The formula is:

Duty Cycle = HIGH Time / Total Period × 100%

For example:

Period = 10 ms

HIGH pulse width = 2 ms

Then:

Duty Cycle = 2 / 10 × 100%

= 20%

Why Measure Pulse Width?

Many electronic systems use pulse duration to control or communicate information.

A circuit may use pulse width to represent:

Command

Position

Speed

Brightness

Timing

Sensor information

Therefore, measuring only voltage may not be enough.

Example: Same Voltage, Different Pulse Width

Suppose two signals both switch between:

0 V

and

5 V

Signal A stays HIGH for:

1 ms

Signal B stays HIGH for:

8 ms

A multimeter may not clearly explain this difference.

An oscilloscope makes it immediately visible.

Step 1: Identify the Signal

Before measuring, determine what signal you are probing.

Ask:

Is it PWM?

A sensor pulse?

A trigger pulse?

A clock?

A one-time event?

Understanding the signal helps you choose appropriate oscilloscope settings.

Step 2: Determine the Expected Voltage

Find out the approximate expected signal level.

For example, a low-voltage digital circuit may use:

3.3 V

or

5 V

But other systems can use different voltage levels.

Never assume every pulse signal is low voltage.

Step 3: Connect the Probe Correctly

Connect the probe to the appropriate signal point.

Connect the reference to the correct circuit reference.

Incorrect reference connections can produce:

Wrong waveform

Noise

Unstable measurement

and potentially unsafe conditions.

Understand the circuit before connecting the probe.

Step 4: Adjust the Vertical Scale

Set the voltage scale so that both the HIGH and LOW portions of the pulse are visible.

The pulse should fit clearly within the display.

If the waveform is too small or too large, adjust the vertical scale.

Step 5: Adjust the Time Base

This is especially important for pulse-width measurement.

You need enough horizontal resolution to see:

Beginning of pulse

and

End of pulse

If the pulse is compressed into a very small part of the screen, measuring its width becomes difficult.

Adjust the time base until the pulse occupies a useful portion of the display.

Step 6: Stabilise the Waveform

For repetitive pulses, use a suitable trigger.

A rising-edge trigger can help align the waveform at the beginning of the HIGH pulse.

A falling-edge trigger may be useful for other applications.

Choose the trigger based on the event you want to observe.

Step 7: Identify the Rising Edge

For a positive pulse, identify where the waveform changes from:

LOW

to

HIGH

This is the:

Rising edge

Step 8: Identify the Falling Edge

Next, identify where the signal changes from:

HIGH

back to

LOW

This is the:

Falling edge

Step 9: Measure the Time Between the Edges

The time between the rising edge and falling edge is the approximate:

HIGH pulse width

For example:

Rising edge = 2 ms position

Falling edge = 7 ms position

Pulse width:

7 ms − 2 ms = 5 ms

Example: 1 ms Pulse

Suppose the waveform rises HIGH and returns LOW after:

1 ms

The HIGH pulse width is:

1 ms

If this pulse repeats every:

10 ms

then the duty cycle is:

10%

Example: 5 ms Pulse

Suppose:

Period = 10 ms

HIGH pulse width = 5 ms

Then:

Duty cycle = 50%

This produces a waveform that spends equal time HIGH and LOW.

Example: 8 ms Pulse

Suppose:

Period = 10 ms

HIGH pulse width = 8 ms

Then:

Duty cycle = 80%

The HIGH portion now occupies most of the cycle.

Measuring Arduino Pulse Width

Arduino projects frequently generate digital pulses.

An oscilloscope can help verify whether the actual electrical output matches what the software is intended to generate.

You can check:

Is the pulse present?

Is the voltage level reasonable?

Is the pulse width changing?

Is the pulse stable?

This is useful when debugging hardware and software together.

Arduino Code Says One Value but Oscilloscope Shows Another

Do not immediately assume either the Arduino or oscilloscope is faulty.

Check:

Code timing

Interrupts

Timer configuration

Signal frequency

Measurement settings

Probe connection

Oscilloscope capability

The real waveform may differ from the theoretical value for several reasons.

Measuring PWM Pulse Width

PWM is one of the most common applications.

Suppose a PWM controller operates at a fixed frequency.

As the command changes, the HIGH pulse may become:

Narrower

or

Wider

Measuring pulse width helps confirm whether the controller is actually changing its output.

Example: LED Dimmer

Suppose an LED dimmer uses PWM.

At low brightness:

Short HIGH pulse

At high brightness:

Longer HIGH pulse

The voltage amplitude may remain approximately similar.

What changes is the amount of time the signal remains active.

Example: Motor Controller

A motor controller may also vary PWM pulse width.

If the motor does not change speed, compare the waveform at different speed settings.

Ask:

Does the pulse width change?

If yes, the command stage may be operating.

If no, investigate the controller or command input.

Control PWM vs Power Output

Be careful.

The low-voltage PWM signal from a microcontroller is not necessarily the same as the high-current waveform applied to the motor.

The power stage may include:

MOSFETs

Gate drivers

H-bridge

Inductive load

Voltage transients

The DSO-152 Plus should not be casually connected to arbitrary power-stage nodes.

Measuring a 555 Timer Pulse

A 555 timer is a useful circuit for learning pulse-width measurement.

Depending on the configuration, you may measure:

HIGH time

LOW time

Period

Frequency

Duty cycle

This allows you to compare calculated timing with the actual circuit.

Why Does the 555 Timer Pulse Width Differ from Calculation?

Possible reasons include:

Resistor tolerance

Capacitor tolerance

Supply conditions

Component characteristics

Measurement uncertainty

Real components are not perfectly identical to their nominal values.

Measuring Sensor Pulses

Some sensors produce pulses where information may be related to:

Frequency

Pulse width

or

Pulse count

An oscilloscope can help determine whether the sensor is generating the expected electrical activity.

Sensor Has Power but No Pulse

Check:

Sensor supply

Ground/reference

Output wiring

Required pull-up or interface

Physical input condition

Correct test point

Do not replace the sensor until the basic operating conditions have been verified.

Sensor Pulse Reaches Connector but Not Controller

Trace the signal.

For example:

Sensor output

→ Connector

→ Resistor

→ Signal-conditioning stage

→ Controller

If the pulse disappears between two points, investigate that section.

Measuring Trigger Pulses

Some circuits use a short pulse to trigger an event.

Examples include:

Timer activation

Counter input

Control command

Measurement trigger

If the pulse is repetitive, normal triggering may be sufficient.

If it occurs only once, Single Trigger can be useful.

Using Single Trigger for a One-Time Pulse

Suppose a pulse appears only when you press a button.

Set an appropriate trigger condition.

Use Single Trigger.

Activate the event.

If the pulse crosses the trigger condition, the oscilloscope may capture and hold it on the display.

This makes one-time events easier to inspect.

Why Can't I See a Very Short Pulse?

Possible reasons include:

Time base too slow

Trigger not configured correctly

Pulse amplitude too small

Poor probe connection

Signal too fast for the oscilloscope

The last point is especially important.

DSO-152 Plus Has Practical Limits

The DSO-152 Plus is an entry-level mini oscilloscope in approximately the:

200 kHz bandwidth class

with around:

2.5 MS/s sampling

This makes it useful for suitable lower-frequency pulse measurements.

It is not intended for accurate measurement of every short or high-speed pulse.

Short Pulse Does Not Automatically Mean Low Frequency

This is an important concept.

A repetitive signal may have a relatively low repetition frequency but contain very fast edges or narrow pulses.

Accurately reproducing those details can require substantially more bandwidth.

Therefore:

Low repetition frequency does not guarantee easy pulse measurement.

Why Does My Pulse Look Rounded?

Possible reasons include:

Oscilloscope bandwidth

Sampling limitation

Probe characteristics

Circuit loading

Signal source

Measurement connection

If the actual edge is much faster than the oscilloscope can reproduce, the displayed edge may appear rounded.

Why Does My Pulse Look Wider Than Expected?

Possible causes include:

Time-base interpretation

Trigger position

Measurement resolution

Bandwidth limitation

Probe loading

Actual circuit timing

First confirm the measurement setup using a known signal.

Why Is the Pulse Unstable?

Possible causes include:

Actual timing variation

Poor trigger

Noise

Unstable supply

Intermittent connection

Controller behaviour

Measurement setup

Observe whether the instability correlates with another event in the circuit.

Why Do I See Multiple Pulses?

The circuit may genuinely produce multiple pulses.

Possible examples include:

Pulse train

Switch bounce

Repeated trigger

Digital communication

Noise

Do not assume every group of pulses represents one simple PWM signal.

Understand the circuit function.

What Is Switch Bounce?

Mechanical switches may not transition cleanly from one state to another.

When a switch is pressed, the contact may briefly make and break several times.

An oscilloscope can help reveal this behaviour if the timing is within its capability.

This is useful when learning about:

Debouncing

and

Digital input behaviour

Can DSO-152 Plus Measure Servo Pulses?

Some hobby servo systems use pulse-based control.

Whether the DSO-152 Plus is suitable depends on the actual signal characteristics and voltage.

For suitable low-voltage servo control pulses, an oscilloscope can help inspect:

Pulse presence

Pulse repetition

Pulse-width changes

Always confirm the servo/control specification first.

Can It Measure Tachometer Pulses?

For suitable low-voltage tachometer signals, the oscilloscope may help check:

Pulse presence

Frequency

Stability

But remember:

Tachometer feedback

and

PWM speed command

are different signals.

Identify the correct wire before measuring.

Pulse Width vs Pulse Count

These are also different.

Pulse width = How long one pulse lasts.

Pulse count = How many pulses occur.

A sensor may encode information using either method.

Understand the sensor specification before interpreting the waveform.

Pulse Width vs Period

Do not confuse:

HIGH pulse width

with

Complete period

For example:

HIGH = 2 ms

LOW = 8 ms

Then:

Pulse width = 2 ms

Period = 10 ms

Frequency = 100 Hz

Duty cycle = 20%

These four values describe different aspects of the same signal.

Pulse Width vs Duty Cycle Quick Example

If:

Period = 20 ms

and

HIGH pulse = 5 ms

then:

Duty cycle = 25%

If the HIGH pulse increases to:

10 ms

while the period remains:

20 ms

then:

Duty cycle = 50%

The frequency remains:

50 Hz

This demonstrates why frequency alone cannot describe a PWM waveform.

DSO-152 Plus vs Multimeter for Pulse Testing

A multimeter may confirm:

Supply voltage

Average voltage

Continuity

But it cannot normally provide the same visual information about individual pulse timing.

The oscilloscope is more useful when the question is:

How long is the pulse?

DSO-152 Plus vs Logic Analyzer

A logic analyzer can be useful when you need:

Multiple digital channels

Digital timing

Protocol decoding

An oscilloscope is useful when you need to see:

Actual voltage waveform

Pulse amplitude

Noise

Waveform shape

Rise/fall behaviour within instrument limits

The tools complement each other.

A Simple Pulse Troubleshooting Workflow

When a pulse signal is not behaving correctly:

1. Check power

Confirm the circuit is operating.

2. Identify the signal

Know what pulse should exist.

3. Confirm expected voltage

Avoid probing an unknown signal.

4. Set the vertical scale

Display HIGH and LOW clearly.

5. Adjust time base

Make the pulse wide enough on screen to inspect.

6. Set trigger

Stabilise or capture the pulse.

7. Measure HIGH time

Determine pulse width.

8. Measure total period if repetitive

Calculate frequency and duty cycle if required.

9. Change the command

See whether pulse width changes as expected.

10. Trace the signal

Find where the pulse disappears or becomes incorrect.

Safety When Measuring Pulse Signals

A signal being called a pulse does not mean it is safe.

Pulse signals can exist in:

3.3 V microcontroller circuits

but also in:

Automotive ignition

Inverters

Motor drives

SMPS circuits

High-voltage equipment

Before connecting the DSO-152 Plus, determine:

Expected voltage

Circuit reference

Possible transient level

Signal source

Do not casually probe hazardous or floating power circuits with an entry-level oscilloscope.

FNIRSI DSO-152 Plus Pulse Width Measurement Malaysia

The FNIRSI DSO-152 Plus can be useful for measuring suitable lower-frequency pulse signals in basic electronics applications.

It can help you understand:

Pulse width

Period

Frequency

Duty cycle

Signal presence

Timing changes

For beginners, Arduino users, students and basic electronics repair, learning to measure pulse width is an important step toward understanding how digital control signals actually work.

MTM Precision supplies FNIRSI oscilloscopes and electronic test instruments in Malaysia.

If you are unsure whether your pulse signal can be measured with the DSO-152 Plus, send us:

A photo of the PCB or equipment

Signal type

Expected voltage

Expected frequency

Expected pulse width if known

Application – Arduino, sensor, motor, fan, 555 timer or other

through WhatsApp.

We can help determine whether the FNIRSI DSO-152 Plus is suitable or whether a higher-performance oscilloscope is required.

MTM Precision Sdn Bhd

Showroom & Service Centre:
No. 29-1 & 2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.

Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my

Supplying FNIRSI and electronic test instruments throughout Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.