FNIRSI DSO-152 Plus Beginner Oscilloscope Guide Malaysia – How to Start Using an Oscilloscope

You have just bought your first oscilloscope.

You turn on the FNIRSI DSO-152 Plus, connect the probe and see a line or waveform on the screen.

But what should you adjust first?

Voltage scale?

Time base?

Trigger?

AC or DC coupling?

For beginners, an oscilloscope can initially look more complicated than a digital multimeter.

The easiest way to understand it is:

A multimeter gives you a number.

An oscilloscope shows you how voltage changes over time.

This guide explains the basic concepts you should understand before using the FNIRSI DSO-152 Plus Mini Digital Oscilloscope for electronics learning and troubleshooting.

What Is an Oscilloscope?

An oscilloscope is an electronic test instrument used to display electrical signals as waveforms.

The screen normally represents:

Vertical direction = Voltage

Horizontal direction = Time

This allows you to see whether a voltage is:

Constant

Pulsing

Oscillating

Changing

Noisy

Intermittent

This is information that may not be obvious from a multimeter reading.

Example: 5 V DC

Suppose you measure a stable 5 V DC supply.

On an oscilloscope, you may see a relatively flat line representing the voltage level.

This is very different from a PWM signal, where the voltage repeatedly switches between HIGH and LOW.

Example: PWM

A PWM signal may look approximately like repeated rectangular pulses.

You can observe:

HIGH level

LOW level

Frequency

Period

Pulse width

Duty cycle

This is one reason oscilloscopes are useful for Arduino and electronics projects.

What Is the FNIRSI DSO-152 Plus?

The FNIRSI DSO-152 Plus is a compact entry-level digital oscilloscope intended for suitable basic and lower-frequency electronics applications.

It is useful for learning concepts such as:

Waveform viewing

Voltage scale

Time base

Triggering

Frequency

Duty cycle

AC/DC coupling

It is not intended to replace a high-performance professional bench oscilloscope.

What Should a Beginner Measure First?

Do not begin with:

AC mains

Inverters

SMPS primary circuits

Motor power stages

Start with known low-voltage signals.

Good beginner examples include:

Arduino PWM

555 timer output

Low-voltage pulse generator

Suitable audio-frequency signal

Known low-voltage test signal

This allows you to learn the controls without unnecessary risk.

The Four Basic Things to Learn First

Before worrying about advanced oscilloscope functions, understand these four concepts:

1. Voltage scale

2. Time base

3. Trigger

4. Probe/reference connection

Once these make sense, oscilloscope operation becomes much easier.

1. What Is Voltage Scale?

The vertical scale controls how much voltage is represented vertically on the screen.

If the waveform is too large, it may extend beyond the display.

If it is too small, it may look almost flat.

Adjust the vertical scale until the waveform fits comfortably on the screen.

Example: Waveform Looks Too Small

Suppose you expect a changing signal but see only a tiny movement.

Possible reasons include:

Voltage scale too wide

Signal actually very small

Wrong test point

Probe attenuation mismatch

Do not immediately conclude that the circuit is faulty.

Example: Waveform Goes Off the Screen

If the signal is larger than the current display scale, adjust the vertical range appropriately.

But remember:

Changing the display scale does not increase the oscilloscope's input rating.

The input signal must still be within the safe capability of the instrument and probe.

2. What Is Time Base?

The horizontal scale controls how much time is shown across the screen.

This determines whether you see:

Part of one cycle

One cycle

Several cycles

or

Many compressed cycles

For frequency and pulse measurements, the time base is extremely important.

Example: PWM Looks Like a Solid Block

If many PWM cycles are compressed into a small area, the waveform may become difficult to understand.

Use a faster horizontal scale so individual pulses become visible.

Example: You See Only One Flat Section

The opposite can also happen.

If the time base is too fast, you may see only a small portion of the waveform.

Adjust until several complete cycles are visible.

3. What Is Trigger?

Triggering helps stabilise a repetitive waveform on the display.

Without suitable triggering, a repetitive waveform may appear to move across the screen.

A trigger tells the oscilloscope when to begin displaying or capturing the waveform.

Auto Trigger

Auto is often convenient when initially searching for a signal.

The oscilloscope continues updating even if a suitable trigger condition is not found.

For beginners, Auto mode is often a useful starting point.

Normal Trigger

Normal mode generally updates when the selected trigger condition occurs.

It can be useful when you want the display to respond to a specific repetitive event.

If the trigger condition is not met, the display may appear to stop updating.

This does not automatically mean the oscilloscope is faulty.

Single Trigger

Single trigger is useful for capturing a suitable one-time event.

Examples include:

Startup pulse

Brief control event

Temporary voltage disturbance

After the event is captured, the display may remain frozen.

That is expected behaviour.

What Is Trigger Level?

Trigger level is the voltage threshold used to determine when the trigger event occurs.

Suppose a digital signal switches between:

0 V

and

5 V

A trigger level somewhere between the LOW and HIGH states may help stabilise the waveform.

If the trigger level is outside the waveform range, triggering may not occur correctly.

Rising Edge vs Falling Edge

A repetitive signal has transitions.

A rising edge occurs when the signal moves from lower voltage toward higher voltage.

A falling edge occurs when it moves from higher voltage toward lower voltage.

Triggering on one of these edges can help stabilise the display.

4. Probe and Reference Connection

This is one of the most important parts of oscilloscope measurement.

The probe measures voltage relative to a reference.

Before connecting the probe, identify:

Signal point

and

Correct circuit reference

Do not connect the reference clip randomly.

Why Is the Reference Important?

An incorrect reference connection can cause:

Wrong readings

Noise

Unstable waveform

and potentially unsafe conditions depending on the circuit.

Always understand what you are measuring.

What Is 1X and 10X Probe Attenuation?

Some oscilloscope probes provide attenuation settings such as:

1X

and

10X

In 10X mode, the signal reaching the oscilloscope is attenuated by the probe.

The oscilloscope setting and physical probe setting should correspond correctly.

What Happens If 1X/10X Is Wrong?

If the probe is physically set to 10X but the oscilloscope assumes 1X, the displayed voltage may be incorrect.

The same problem can occur in the opposite direction.

If the voltage reading appears wrong by a large factor, check attenuation settings.

Does 10X Mean Any High Voltage Is Safe?

No.

This is extremely important.

A 10X probe does not mean:

“I can safely measure anything.”

You still need to consider:

Probe rating

Oscilloscope input rating

Circuit voltage

Transient voltage

Measurement category

Reference condition

Circuit topology

Do not use probe attenuation as a substitute for electrical safety.

What Is DC Coupling?

DC coupling displays both:

DC component

and

AC variation

For example, if you are checking a 5 V PWM signal, DC coupling lets you see the waveform relative to its DC voltage levels.

This is often a good starting point for basic electronics troubleshooting.

What Is AC Coupling?

AC coupling blocks the DC component and allows you to focus on changing components of the signal.

This can be useful for examining a small variation riding on a DC level.

One example is suitable low-voltage power supply ripple measurement.

Does AC Coupling Make Mains Safe?

No.

AC coupling is a display/input coupling function.

It does not make a hazardous voltage safe to measure.

Never confuse coupling mode with electrical isolation or input protection.

How to Measure Frequency

Frequency tells you how many cycles occur every second.

The unit is:

Hertz – Hz

You can also calculate frequency from the waveform period.

The formula is:

Frequency = 1 / Period

Example: 1 ms Period

If one complete cycle takes:

1 ms

then:

Frequency = 1 / 0.001

= 1,000 Hz

or:

1 kHz

Example: 10 ms Period

If one complete cycle takes:

10 ms

then:

Frequency = 100 Hz

This relationship is fundamental to oscilloscope use.

How to Measure Duty Cycle

Duty cycle describes how much of one cycle the signal spends in its active or HIGH state.

The formula is:

Duty Cycle = HIGH Time / Total Period × 100%

Example: 50% Duty Cycle

Suppose:

Total period = 10 ms

HIGH time = 5 ms

Then:

Duty cycle = 5 / 10 × 100%

= 50%

Example: 20% Duty Cycle

Suppose:

Total period = 10 ms

HIGH time = 2 ms

Then:

Duty cycle = 20%

The HIGH pulse appears narrower.

Frequency and Duty Cycle Are Not the Same

A PWM signal can maintain approximately the same frequency while its duty cycle changes.

For example:

20%

50%

80%

may all operate at the same PWM frequency.

Only the pulse width changes.

This is important when troubleshooting motor and LED controllers.

Beginner Exercise: Arduino PWM

Arduino PWM is a useful beginner oscilloscope exercise.

Connect to a suitable PWM output and observe the waveform.

Change the PWM command.

Look for changes in:

Pulse width

and

Duty cycle

This helps you understand how software instructions become electrical signals.

Beginner Exercise: 555 Timer

A 555 timer circuit is another useful learning project.

You can observe:

Output waveform

Frequency

Period

Duty cycle

Change a resistor or capacitor value and observe how the timing changes.

This is a practical way to connect circuit theory with real measurements.

Beginner Exercise: LED Dimmer

If an LED dimmer uses PWM, observe the control signal.

Adjust brightness.

You may see the duty cycle change.

This demonstrates why an LED can appear dimmer even though the switching signal still reaches its normal HIGH level.

Why Does My Waveform Keep Moving?

Check:

Trigger mode

Trigger level

Time base

Signal stability

Probe connection

A moving waveform does not automatically indicate a faulty circuit.

Often, the oscilloscope simply needs better trigger settings.

Why Do I See a Flat Line?

A flat line can mean several things.

Possible causes include:

Stable DC voltage

No signal

Wrong test point

Poor probe contact

Incorrect reference

Wrong voltage scale

Wrong time base

Trigger issue

Inactive circuit

Do not assume:

Flat line = Oscilloscope faulty

Why Does My Square Wave Look Rounded?

Possible causes include:

Oscilloscope bandwidth

Sampling limitations

Probe characteristics

Probe compensation

Circuit loading

Actual signal shape

Fast edges require more measurement bandwidth than the basic repetition frequency might suggest.

What Is Bandwidth?

Bandwidth is one of the most important oscilloscope specifications.

The DSO-152 Plus is in approximately the 200 kHz bandwidth class.

This means it is intended for suitable lower-frequency signals.

It is not a high-frequency oscilloscope.

Can It Measure a 16 MHz Arduino Clock?

It should not be selected for accurate measurement of a 16 MHz clock waveform.

A 16 MHz signal is far above the approximately 200 kHz bandwidth class of the DSO-152 Plus.

Use a higher-bandwidth oscilloscope for that job.

But Can It Measure Arduino PWM?

Suitable Arduino PWM outputs can be much lower in frequency than the MCU clock.

Therefore, some PWM signals can be much more appropriate for the DSO-152 Plus.

Do not confuse:

Microcontroller clock

with

PWM output

They are different signals.

What Is Sampling Rate?

A digital oscilloscope measures a waveform by taking samples.

The DSO-152 Plus is around the 2.5 MS/s sampling class.

Sampling rate and bandwidth are related to measurement capability but are not the same specification.

Both matter when measuring faster signals.

What Is Aliasing?

If a signal is too fast for the measurement system, the displayed waveform may appear to have the wrong frequency or shape.

This is called aliasing.

A dangerous beginner assumption is:

“I can see something on the screen, so it must be correct.”

That is not always true.

Displayed Waveform Does Not Guarantee Accuracy

Always ask:

Is the signal within the oscilloscope's capability?

If not, the displayed:

Frequency

Amplitude

or

Waveform shape

may be misleading.

Why Does My Voltage Differ from the Multimeter?

Possible reasons include:

Probe attenuation

Peak vs average measurement

PWM waveform

AC/DC coupling

Signal variation

Different measurement methods

A multimeter and oscilloscope do not always measure or display voltage in the same way.

Example: PWM Voltage

Suppose a PWM signal switches between:

0 V

and

5 V

A multimeter may show an intermediate value depending on duty cycle and meter behaviour.

The oscilloscope shows the actual switching waveform.

Both instruments are giving different views of the same electrical signal.

Should a Beginner Buy a Multimeter or Oscilloscope First?

For general electronics work, a digital multimeter is usually essential.

It handles:

Voltage

Resistance

Continuity

and other basic checks.

The oscilloscope becomes valuable when you need to see how a signal changes over time.

Ideally, electronics troubleshooting uses both.

What Can DSO-152 Plus Help Troubleshoot?

For suitable lower-frequency circuits:

Arduino PWM

555 timer

LED controller

Fan PWM

Basic motor-control signals

Sensor pulses

Audio-frequency signals

Simple oscillator circuits

Low-voltage power supply ripple

These are practical beginner applications.

What Is It Not Designed For?

Do not expect the DSO-152 Plus to replace specialised equipment for:

RF

Multi-megahertz MCU clocks

High-speed digital buses

Professional SMPS analysis

Advanced automotive ignition

High-voltage inverter analysis

Detailed MOSFET switching

Complex multi-channel electronics

Use a more appropriate instrument for these applications.

A Simple Beginner Troubleshooting Method

When a circuit does not work, use this sequence.

Step 1 – Understand the Circuit

Ask:

What should this circuit do?

Step 2 – Check Power

Use a multimeter to confirm:

Input voltage

Power rails

Step 3 – Identify the Expected Signal

For example:

PWM

Pulse

Audio

Sensor output

Step 4 – Connect the Oscilloscope Correctly

Identify:

Signal point

Reference

Expected voltage

Step 5 – Adjust Vertical Scale

Make the waveform visible.

Step 6 – Adjust Time Base

Display several useful cycles.

Step 7 – Adjust Trigger

Stabilise the waveform.

Step 8 – Compare with What You Expect

Check:

Amplitude

Frequency

Duty cycle

Waveform stability

Step 9 – Trace the Signal

If the signal disappears, follow the circuit backward or forward to find where the behaviour changes.

This is the foundation of waveform-based troubleshooting.

Do Not Probe Randomly

An oscilloscope is most useful when you already know what you are looking for.

Before touching a test point, ask:

What should be here?

What voltage?

What frequency?

Relative to which reference?

Random probing can produce confusing results and may be unsafe.

Use a Working Board as Reference

If you have:

One working PCB

and

One faulty PCB

compare the same suitable test points.

This can be extremely useful.

Look for differences in:

Voltage

Frequency

PWM

Signal presence

Waveform stability

The working board becomes your reference.

Keep Notes or Photos

When troubleshooting, record:

Test point

Voltage

Frequency

Duty cycle

Waveform photo

This makes it easier to compare measurements later.

It is especially useful when discussing the problem with another technician or supplier.

Safety for Beginners

Do not learn oscilloscope operation by immediately probing mains-powered circuits.

Start with known low-voltage electronics.

Be particularly careful around:

AC mains

SMPS primary side

Inverters

Motor drives

High-voltage capacitors

Automotive ignition

Unknown industrial circuits

A compact battery-powered oscilloscope should not automatically be assumed to be electrically isolated or safe for every measurement.

Best First Signals to Practice On

For a beginner, consider practicing with:

Known calibration/test output if provided

Arduino PWM

555 timer output

Low-voltage pulse signal

Simple audio-frequency signal

These allow you to learn waveform controls before moving to unknown faulty circuits.

FNIRSI DSO-152 Plus Beginner Oscilloscope Malaysia

The FNIRSI DSO-152 Plus can be a practical first oscilloscope for users who want to learn how electrical signals behave over time.

The most important beginner skills are not memorising every menu.

Learn how to understand:

Voltage

Time

Trigger

Frequency

Duty cycle

Probe connection

Instrument limitations

Once these concepts become familiar, electronics troubleshooting becomes much easier to understand.

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

If you are buying your first oscilloscope and are unsure whether the DSO-152 Plus is suitable, send us:

A photo of the PCB or project

What you want to measure

Expected voltage

Expected frequency if known

Arduino, motor controller, sensor, audio, PCB repair or other application

through WhatsApp.

We can help determine whether the FNIRSI DSO-152 Plus is enough or whether you should consider a higher-performance FNIRSI oscilloscope.

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.