How to Check PWM Motor and Fan Controller Signals with FNIRSI DSO-152 Plus Malaysia
How to Check PWM Motor and Fan Controller Signals with FNIRSI DSO-152 Plus Malaysia
Can the FNIRSI DSO-152 Plus Mini Digital Oscilloscope be used to check PWM signals from motor controllers, fan controllers and other electronic control circuits?
For suitable low-voltage PWM signals within the oscilloscope's measurement capability, the answer can be yes.
PWM signals are common in electronics because they allow a controller to change the effective power delivered to a load by rapidly switching the signal ON and OFF.
A digital multimeter may show a changing voltage value.
But an oscilloscope allows you to see:
What the PWM waveform is actually doing.
What Is PWM?
PWM means Pulse Width Modulation.
Instead of continuously changing the voltage, a PWM controller switches between two states.
A simplified waveform may look like:
ON → OFF → ON → OFF → ON → OFF
The percentage of time that the signal remains ON during each cycle is called the duty cycle.
For example:
25% duty cycle
means the signal is ON for approximately one quarter of each cycle.
50% duty cycle
means the signal is ON for approximately half of each cycle.
75% duty cycle
means the signal is ON for approximately three quarters of each cycle.
Changing the duty cycle can change the effective control applied to a motor, fan, LED or other suitable load.
Why Is an Oscilloscope Useful for PWM?
A multimeter can be useful for checking whether voltage is present.
But PWM is not simply a fixed DC voltage.
The signal repeatedly changes between HIGH and LOW states.
An oscilloscope can help you investigate:
Pulse amplitude
Frequency
Duty cycle
Signal stability
Missing pulses
Changes in control behaviour
This provides a much clearer picture of what the controller is doing.
Example: Fan Speed Controller
Imagine an electronic fan controller has three speed settings:
Low
Medium
High
You measure the control output with a multimeter.
The voltage reading changes between the settings.
But you do not know why.
With an oscilloscope, you may discover that the controller is changing the PWM duty cycle.
For example:
Low speed → lower duty cycle
Medium speed → medium duty cycle
High speed → higher duty cycle
The exact behaviour depends on the controller design, but the oscilloscope helps reveal the control method.
What Should a PWM Waveform Look Like?
A basic PWM waveform often resembles a repeating rectangular pulse.
You may see:
HIGH level
followed by
LOW level
repeated continuously.
The important characteristics include:
Voltage amplitude
Pulse width
Period
Frequency
Duty cycle
If the controller changes operating level, one or more of these characteristics may change.
What Is Duty Cycle?
Duty cycle describes the percentage of each PWM cycle that remains in the ON state.
For example:
10% duty cycle = short ON time
50% duty cycle = equal ON and OFF time
90% duty cycle = long ON time
This is one reason an oscilloscope is useful for controller troubleshooting.
You can see whether the control signal changes when the user changes the speed or output command.
Example: Controller Command Changes but Motor Speed Does Not
Suppose a motor speed controller has:
Low
Medium
High
settings.
But the motor runs at approximately the same speed regardless of the selected setting.
You can investigate the control signal.
If the PWM waveform changes correctly between settings, the problem may be further downstream.
If the PWM waveform does not change, the issue may be related to the control stage or command.
This does not automatically identify the failed component, but it helps narrow the troubleshooting area.
Example: Motor Does Not Run
Suppose the motor does not operate at all.
A basic troubleshooting sequence might include checking:
Power supply
Control command
PWM signal
Driver stage
Motor connection
If power is present but the expected PWM control signal is missing, that is useful diagnostic information.
You can then investigate why the controller is not generating or delivering the signal.
Can DSO-152 Plus Check Arduino PWM?
For suitable Arduino PWM experiments, the DSO-152 Plus can be useful for learning and basic troubleshooting.
You can change the PWM command in your program and observe how the waveform responds.
For example, you may compare different duty-cycle settings and see how the pulse width changes.
This is a useful way to understand the relationship between:
Software command
and
Electrical waveform
For students and beginners, this can make PWM much easier to understand.
Can It Check a 4-Wire PC Fan PWM Signal?
Some computer and electronic cooling fans use separate control and feedback signals.
A typical multi-wire fan system may include connections for:
Power
Ground
Control
Speed feedback
However, the exact electrical interface depends on the fan design.
Before probing, identify the pinout and expected signal.
Do not assume that every fan uses the same voltage, frequency or control method.
PWM Control vs Tachometer Signal
These are not necessarily the same signal.
A fan or motor system may have:
PWM control input
and
Tachometer or speed feedback output
The PWM signal tells the system how it should operate.
The tachometer signal provides information about actual rotation or speed.
An oscilloscope can potentially help investigate both types of suitable pulse signals.
This can be useful when asking:
Is the controller sending the command?
and:
Is the motor/fan returning speed information?
Example: PWM Present but No Speed Feedback
Suppose you confirm that a suitable PWM control signal reaches the fan.
But the speed-feedback signal is missing.
This may suggest that the problem is not simply the controller command.
Further investigation may be needed around:
Fan operation
Feedback wiring
Connector
Sensor
Power supply
Fan electronics
The oscilloscope helps separate the command side from the feedback side.
Check Frequency as Well as Duty Cycle
Duty cycle is important, but do not ignore frequency.
Two PWM signals can have the same duty cycle but different frequencies.
For example:
50% duty cycle at one frequency
is not necessarily electrically identical to:
50% duty cycle at a much higher frequency
When troubleshooting, compare both:
Duty cycle
and
Frequency
with the expected circuit behaviour.
Why Does the PWM Waveform Look Unstable?
If the waveform moves across the screen or appears difficult to read, check the trigger settings.
Try adjusting:
Trigger mode
Trigger level
Time base
Voltage scale
A repetitive PWM signal should normally be easier to observe once the trigger and display settings are appropriate.
Also check the probe and reference connections.
Why Does the PWM Waveform Look Rounded?
A PWM waveform may not always appear as a perfect rectangle.
Possible reasons include:
Circuit characteristics
Probe loading
Measurement connection
Signal rise/fall time
Oscilloscope bandwidth
Instrument sampling capability
Electrical noise
Actual controller design
If the signal transitions are faster than the oscilloscope can reproduce accurately, the displayed waveform may look different from the actual signal.
Can DSO-152 Plus Check Motor Driver Outputs?
This depends heavily on the driver.
There is a major difference between measuring a low-voltage logic PWM control signal and measuring the actual power output driving a motor.
Motor-driver power stages can involve:
Higher voltage
Higher current
Fast switching
Inductive transients
Bridge circuits
Non-ground-referenced signals
These conditions require much more careful measurement techniques.
The DSO-152 Plus should not automatically be connected directly across a motor-driver output.
Be Careful with H-Bridge Motor Controllers
H-bridge circuits are commonly used to control DC motors.
But the motor terminals may both be actively switched.
This means neither motor terminal should automatically be assumed to be a safe ground reference.
Connecting a ground-referenced oscilloscope incorrectly can create measurement problems or potentially damage equipment.
Before probing an H-bridge, understand:
Circuit topology
Reference point
Expected voltage
Switching behaviour
Required measurement method
If you are uncertain, do not connect the oscilloscope directly.
What About Industrial Motor Drives?
Do not treat an industrial motor drive like a small Arduino PWM experiment.
Industrial equipment such as:
Variable Frequency Drives
Inverters
Servo drives
High-power motor controllers
can involve hazardous voltages, fast switching and complex measurement requirements.
A basic mini oscilloscope is not automatically suitable for measuring these power circuits.
Professional measurement may require specialised high-voltage or differential probes and an appropriately rated oscilloscope.
Where Is DSO-152 Plus Most Suitable?
The DSO-152 Plus is better positioned for:
Basic low-voltage PWM learning
Arduino projects
Electronic fan control
Suitable low-voltage controller signals
DIY electronics
Educational demonstrations
Basic electronics troubleshooting
Its role is primarily to help you see and understand suitable waveforms.
DSO-152 Plus vs Multimeter for PWM
For PWM troubleshooting, the two instruments answer different questions.
A multimeter can help answer:
Is voltage present?
An oscilloscope can help answer:
Is it actually PWM?
What does the pulse look like?
Does the duty cycle change?
Is the frequency reasonable?
Are pulses missing or unstable?
For electronics troubleshooting, using both instruments together can provide much more information.
Simple PWM Troubleshooting Workflow
For a suitable low-voltage PWM system:
Step 1: Check the power supply.
Step 2: Identify the correct PWM test point.
Step 3: Confirm the circuit reference.
Step 4: Connect the oscilloscope correctly.
Step 5: Adjust voltage scale and time base.
Step 6: Stabilise the waveform using the trigger.
Step 7: Observe frequency and duty-cycle behaviour.
Step 8: Change the controller command.
Step 9: Check whether the PWM waveform changes accordingly.
This can help determine whether the control signal is behaving as expected.
FNIRSI DSO-152 Plus for PWM Testing Malaysia
The FNIRSI DSO-152 Plus Mini Digital Oscilloscope can be a useful entry-level instrument for viewing suitable PWM signals from Arduino projects, electronic controllers, fan-control circuits and other low-voltage electronics.
It allows users to move beyond a simple voltage number and actually see how the control signal changes with time.
However, distinguish between:
Low-voltage PWM control signals
and
High-power motor switching circuits.
The second category can require much more capable and specialised measurement equipment.
MTM Precision supplies FNIRSI electronic test and measurement instruments in Malaysia.
If you are unsure whether the DSO-152 Plus is suitable for your PWM application, send us:
A photo of the controller
Motor or fan model
Expected voltage
Expected PWM frequency if known
The signal or terminal you want to measure
through WhatsApp.
We can help determine whether the DSO-152 Plus is suitable or whether a higher-performance FNIRSI oscilloscope would be more appropriate.
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 test and measurement instruments throughout Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.
06 Oct 2026
