The Truth About the OSS TEAM W01 Inductance Tester
If you’ve spent any time browsing electronics repair forums or watching diagnostic videos lately, you’ve probably seen it: A sleek, pen-sized black circuit board being waved over smartphone motherboards. The green LED lights up, and—boom—the component is declared healthy (claims many videos seen on Facebook and YouTube).

Advertisements call it a “Revolutionary Motherboard Repair Tool” that grants technicians “X-Ray Vision.” Sellers claim it can instantly stop the guesswork of component failures with a clear pass/fail signal.

But is the OSS TEAM W01 Inductance Tester truly a “secret weapon,” or is it just another over-hyped online hoax? Or something in between? Let’s strip away the marketing promises and look at what this tool actually does, how much it costs, and the hidden dangers you need to know about.

What is the OSS TEAM W01?
At its core, the OSS W01 is a compact, bare-board electromagnetic field (EMF) detector. It features:
A pointed detection tip at one end.
A central detection button you must press and hold.
A small green LED indicator light.
A Type-C power input that can run off a standard 5V power bank or phone charger.

The OSS W01 Inductance Detector is a compact, black circuit board with a pointed detection terminal at one end. It features a Type-C power input port, a detection button, and a small LED indicator light. The board is labeled with ‘W01′, ‘OSS TEAM’, and ‘INDUCTANCE DETECTOR’. Dimensions: 75mm x 27mm (approximately 2.95in x 1.06in)

I came across an advertisement for such a tester online. It claims to identify faulty components on circuit boards. I guess it’s all a hoax, though? If the green LED doesn’t light up, the component is faulty. So how can it tell? The advertisement showed testing resistors and capacitors.

OSS w01 Inductance Tester What would a product with a daily sales volume of 10,000 units look like?
https://www.youtube.com/watch?v=Mi4oGukxFTo

How It’s Supposed to Work

The marketing pitch is incredibly simple: If the green LED lights up, the inductor is functioning correctly. According to the instructions, you power up the motherboard you are troubleshooting. You plug in the W01 tester, hold down its button, and bring the pointed tip close to the inductor coil (about 1 to 3 mm away).

Green light stays on or flashes: The inductor is actively processing power; the internal coil is intact.
No light: The inductor coil is broken (open circuit) or not receiving power.

OSS TEAM W01 Type-C Inductance Tester is advertised as a Professional Repair Diagnostic Tool. The marketing promise is: If the LED lights up, the inductor is functioning correctly.

Advertisements are full of promises like:
Why This Pen-Sized Diagnostic Tool Is Revolutionizing Motherboard Repair (Hint: It Gives You ‘X-Ray Vision’)
Stop guessing component failures! Handheld tester gives clear pass/fail signal. Quality components, reinforced housing.
OSS TEAM W01 Inductance Tester, a compact and user-friendly device for rapid troubleshooting and fault detection of mobile phone inductors.
EMF Detector Type-C Inductance Tester High Precision Electronic Circuit Board Inductor Detector for Electronics Repair
Features Type-C power, rapid troubleshooting, and easy operation for mobile phone motherboard
If you’re nodding your head, you’re about to discover why thousands of repair techs are calling this pocket-sized tool their “secret weapon” against the most frustrating part of electronics repair…

I have seen an AI videos advertising these, claiming they will make your multimeter obsolete. W01 does not make your multimeter or oscilloscope obsolete. Not everyone will have a use for one of these, but if you do troubleshooting on systems with buck/boost converters for current and voltage regulation, then this could be a useful tool for doing a quick check on whether an inductor is being pulsed.

The Catch: It Doesn’t Have “Magic Vision”

The fact is that the W01 can sometimes successfully detect powered coils (if they have enough power going through them and they are not too well shielded). Sometimes the detection does not work.

While the device is a functional tool, online ads often stretch the truth. Watching how they use it…just touching around at random spots on an active circuit and they say “when the light does not come on, it is a bad component”. Some commercials show technicians using it to test resistors and capacitors and diodes. Spoiler alert: It doesn’t work on them.

The device is purely an induction and EMF tester. It detects the pulsing magnetic fields generated by a working coil. If you place it near a resistor or capacitor, the light won’t turn on—not because the component is broken, but because those components don’t generate the magnetic fields this pen is looking for.

Furthermore, metal heat sinks or shielding shells can trigger false positives by spreading interference, meaning the light might turn on even if you aren’t directly over a healthy inductor.

It can be a helpful troubleshooting tool for quick reference, but it cannot mystically diagnose your entire board. They only work for inductors that are powered with high frequency pulses. For inductors you don’t need them to be out of circuit to detect the em field generated by inductors when functioning properly. If you have a working board for comparison, you can test where you see light coming on in the working board, and then see if LED lights on the not working board.

Videos:
https://youtube.com/shorts/Mi4oGukxFTo?si=gSX3gqphKXq5ZW6L
https://youtube.com/shorts/8g822XrTB9s?si=nTPWQJiYnKNCSWkW
https://www.youtube.com/shorts/faQ0mO1lOrI

Instruction pictures
https://www.aliexpress.com/item/1005010320063815.html

Manual
https://manuals.plus/m/e92f476fbf03e51ea91d75fb8bb1c70f2db89e166420bedeb4f59ea78b0eb7e8

WARNING: The Hidden Danger of An Unenclosed Board

One of the most alarming aspects of the OSS W01 is its design. It is completely unenclosed—just a bare, exposed circuit board.Instruction manuals explicitly warn: “Place the front end close to the inductor, do not touch it, as some inductors are not insulated.”

Worse yet, some promotional videos on social media show users probing live, mains-powered electronic devices with this bare board. If an inexperienced hobbyist handles this unenclosed block, their fingers can easily slip and touch high-voltage components on the live board. This is incredibly dangerous and carries a genuine risk of electrical shock.

Video where probing live main powered device (potentially very dangerous) can be seen at
https://www.facebook.com/61577839981774/videos/-oss-inductance-detector-high-precision-electromagnetic-induction-measurement-al/868769249585152/

If you use this tool, it should strictly be confined to low-voltage motherboards (like smartphones), and you should handle it with extreme care. To avoid causing any short circuits, I recommend to add insulation around the tip of the W01 sensor (for example insulating tape or heat shrinking insulation).

Circuit analysis

Circuit diagram for the sensor part. Traced from circuit board and component values measured in-circuit

Clever inductive test probe

The circuitry is strange. Like a prototype or one that has been badly copied. It has some oddities, and the button on this unit looks like a legacy feature from the original lithium cell powered version.

This is Big Clive’s video about it. Screenshot is of his traced schematic.
https://youtu.be/VsEJgODLN6Q?si=Qfxyk_JYzV4CZZpf

Price Watch: From €1 to $17?

Perhaps the strangest thing about the OSS W01 (and its sibling, like the MECHANIC DT-001) is the wild pricing discrepancy online:
The Ultra-Cheap Tier: On websites like AliExpress, you can find this exact board selling for anywhere between €0.87 and €2.85.
The Premium Repair Tier: On specialized electronics repair sites or localized storefronts, the exact same tool is repackaged or marked up to anywhere between €16.00 and $16.99.
At less than a Euro, it’s a fun, low-risk novelty gadget to throw into your repair toolkit. At $17, the price tag starts to outpace the actual utility of a bare EMF-detecting PCB.

The Verdict: Hoax or Handy?

The OSS TEAM W01 Inductance Tester is not a hoax, but the marketing definitely pushes it into “too good to be true” territory. It won’t give you “X-Ray vision,” and it won’t replace a proper multimeter or oscilloscope. However, for a mobile phone technician who needs a 2-second check to see if an inductor coil is actively passing a signal without desoldering it, it’s a functional, handy little device. Just keep your fingers away from the live components, don’t try to use it on capacitors, and definitely don’t overpay for it!

Hacker and security researcher Samy Kamkar takes a look at a variety of hacking scenes from popular media and examines their authenticity.

Video: https://www.youtube.com/watch?v=SZQz9tkEHIg

Miten hyödyntää Moderni C++ -ohjelmointikieltä tehokkaasti ja joustavasti?
https://www.tieturi.fi/webinaari-miten-hyodyntaa-moderni-c-ohjelmointikielta-tehokkaasti-ja-joustavasti/

Modern C++ Design Patterns Full Course

C++ Design Patterns – The Most Common Misconceptions (2 of N) – Klaus Iglberger – CppCon 2024

Hands-On Design Patterns with C++ by Fedor Pikus

Design Patterns in C++

Modern C++ Design Patterns Tutorial

Design Pattern Catalogue

Singleton Pattern | C++ Design Patterns

Observer
Also known as: Event-Subscriber, Listener
Observer is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
https://refactoring.guru/design-patterns/observer

Strategy
Strategy is a behavioral design pattern that lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
https://refactoring.guru/design-patterns/strategy

How to Create Custom Memory Allocator in C++?

Template Metaprogramming in C++

From C++ Templates to C++ Concepts – Metaprogramming: an Amazing Journey – Alex Dathskovsky

Embedded C++ : to use STL or not?

Standard Template Library (STL) in C++
https://www.geeksforgeeks.org/cpp/the-c-standard-template-library-stl/
https://en.wikipedia.org/wiki/Standard_Template_Library

In embedded systems, how much memory C++ STL uses depends heavily on:
The container type
The number of elements
The implementation (libstdc++, libc++, etc.)
Whether dynamic allocation is used
Compiler optimization settings
There is no fixed memory cost, but I’ll break it down clearly.
Heap Usage (Critical for Embedded)
Most STL containers use dynamic memory (new).

Problems in embedded:
Heap fragmentation
Unpredictable allocation time
Memory exhaustion
No control over allocator unless customized

STL within embedded system with very limited memory
https://stackoverflow.com/questions/9612588/stl-within-embedded-system-with-very-limited-memory

Understanding Memory Management, Part 2: C++ and RAII
https://educatedguesswork.org/posts/memory-management-2/

This is a bad and dangerous design

This is a dangerous design. There is potentially lethal voltage on those probe pins. ⚡️☠️
I strongly discourage to build this.

Design problems
- no isolation from mains – test probes and circuit being tested dangerous to touch
- pointless filter coil in output
- open circuit voltage can be over 300V
- output capacitor in circuit directly on probes – high current surge when you connect probe can potentially damage LED being tested

According to the latest edition of the World Happiness Report, the three happiest countries in the world are Finland, Iceland and Denmark.

Finland was named the happiest country in the world for a record 9th time in a row,

There is seen a sharp drop in youth happiness in very many countries: A key factor in the sharp drop in youth happiness, researchers said, is the number of hours young people spend consuming social media or gaming. While experts say it’s important to limit time spent with the Internet overall, some ways of spending time online are healthier than others. A key question is “if they are really social media or anti-social media.”
“The digital age is reshaping the social and emotional foundations of wellbeing in Europe”

Source:
https://www.cnn.com/2026/03/18/travel/worlds-happiest-countries-2026-wellness

Friday the 13th has a reputation as a day of bad luck mainly because two separate superstitions merged over time: fear of the number 13 and fear of Friday. When they combined, the date became especially ominous in Western culture.

The number 13 has long been considered unlucky in parts of Europe and North America (bible The Last Supper and Norse mythology).
According to Christian tradition, Jesus Christ was crucified on Good Friday. Sailors and travelers in folklore believed starting a journey on Friday brought bad luck.
Modern media amplified the superstition, especially horror films like Friday the 13th.

Read more:
Why is Friday the 13th considered unlucky? The history of the superstitious date
https://www.independent.co.uk/life-style/friday-13th-unlucky-why-meaning-history-b2919712.html

This is a classic “minimalist” single-ended Class A MOSFET amplifier. While it is praised for simplicity, it is inherently inefficient and prone to significant distortion.
​In this design, the MOSFET (IRF530) is always “on,” acting as a variable resistor that pulls current through the 15 ohms load resistor.

​Circuit Analysis

​Operating Class: Class A. The transistor conducts through the full 360° of the input cycle.
​Bias Point: The schematic shows a 12V quiescent point at the Drain (half of the 24V supply). This is achieved by adjusting the 100k potentiometer to set the Gate voltage.
​Heat Generation: This circuit is a space heater. With 12V across a 15 ohms resistor, it dissipates P = (12*12)/15 = 9.6 Watts constantly, even with no music playing.
​Output Voltage: The maximum theoretical peak-to-peak output voltage is roughly 24V, but in practice, it will be less due to the MOSFET’s saturation voltage and the voltage drop across the source (if a source resistor were present).

Original source

This is a single-ended Class-A common-source MOSFET stage using a 2SK1058 with a 15 Ω drain resistor and capacitor-coupled output.

I would not expect quality with this design be specifically good but maybe useable for experimenting. Class A avoids crossover distortion is true. But this simple class A design introduces other significant distortion sources.
1. Important: This design has NO global feedback
Notice:
No feedback loop from output to input
Pure resistor load at drain
Single-ended topology
That means:
Output impedance is mostly set by hardware physics
No correction via feedback
Strong interaction with speaker impedance curve

2. Realistic Output Impedance ≈ 3–7 Ω
Most likely around: ~4–6 Ω
Damping Factor Example (8Ω speaker) is 1.6
That is very low damping factor.
For comparison:
Typical Class AB: DF 50–500
Typical Class D: DF 200–1000+

What That Means Sonically
With ~5 Ω output impedance:
Bass will be loose
Frequency response will follow speaker impedance curve
Midrange may sound “rich”
Damping is minimal
This is electrically closer to a small tube amp than to a modern solid-state amp.

3. Bias & Quiescent Current
Drain resistor = 15 Ω
Supply = 24 V
Drain biased at 12 V
Current 0.8A

Maximum Output Voltage Swing
Because this is single-ended Class A with resistor load:
Max upward swing ≈ +12 V (until drain hits 24 V)
Max downward swing ≈ −12 V (until near 0 V)
Realistically subtract MOSFET saturation (~2 V), so usable peak swing ≈ ±10 V

RMS voltage: around 7V
Realistically: 5–6 W clean max for 8 ohms speaker

Efficiency:
That 32% is theoretical.
For resistor-loaded Class A:
Maximum theoretical efficiency = 25%
With real voltage drops and MOSFET limits:
Real-world efficiency ≈ 20–25%
The MOSFET will dissipate roughly:
~10 W at idle
~8–15 W under signal
That’s why it needs a serious heatsink.

Real Maximum Clean Power into 4 Ω ≈ 1.3 watts
Efficiency 6.8%

4. Distortion Estimate
This design:
Has no global feedback
Is single-ended
Has asymmetric transfer curve
Uses resistive load
Expected distortion at:
1W output:
~1–2% THD
Near full power (5–6W):
3–8% THD

Dominant harmonic:
Strong 2nd harmonic
Some 3rd
Very little crossover distortion (it’s pure Class A)
This is why these amps are often described as:
“Warm”
“Tube-like”
“Euphonic”
But technically:
Distortion is far higher than AB or D designs (<0.01%) Distortion with 4 Ω Because the load is heavier: Clipping starts early Distortion rises quickly At 1W expect ~3–5% THD Near max (1.3W) distortion >5–10%
It will sound:
Softer
Compressed
Less controlled bass
Very low damping factor (~4Ω / ~5Ω ≈ 0.8)

This amplifier is designed for 8 Ω or higher speakers.
Driving 4 Ω:
Wastes power
Increases distortion
Severely limits output

In this amplifier the 4700 µF output capacitor is not neutral. The 4700 µF capacitor blocks DC, passes AC to the speaker and forms a high-pass filter with the speaker. It directly affects distortion, especially at low frequencies.

How It Causes Distortion
A) Capacitor Voltage Swing Effect (Major)
Electrolytic capacitors are voltage-dependent devices.
In this amp:
The cap has ~12 V DC bias across it
Audio signal adds AC swing
So instantaneous voltage varies between ~2 V and ~22 V at high output
Electrolytic capacitance changes slightly with voltage.
That causes:
Capacitance modulation
Nonlinear impedance
Added low-frequency harmonic distortion

This increases as:
Frequency decreases
Signal amplitude increases
Load impedance decreases (4 Ω worse than 8 Ω)

B) ESR (Equivalent Series Resistance)
The capacitor has small series resistance.
At high current peaks:
Voltage drop across ESR occurs
That drop is nonlinear with temperature and ripple current
Adds small distortion
Usually minor compared to mechanism A.
C) Dielectric Absorption
Electrolytics “store memory” of previous charge.
This causes:
Slight waveform asymmetry
Mostly low-frequency distortion
Small, but measurable.

How Big Is the Effect?
For 4700 µF good-quality low-ESR electrolytic:
At 1 kHz:
Distortion from cap ≈ negligible
At 50 Hz near full power:
Can add 0.2–1% THD
At 20 Hz:
Can exceed 1–2% THD
With 4 Ω load:
Roughly doubles
And remember:
Your amp already has 1–3% intrinsic distortion.
So the cap can be a significant contributor at bass frequencies.

Why Designers Add the 10µF Poly Cap in some designa.
When you have a 10µF film cap in paraller, this:
Reduces high-frequency impedance
Bypasses electrolytic ESR at mid/high frequencies
Improves HF linearity
But it does nothing for low-frequency distortion, because 10µF is too small to affect bass.

Audible Effects
Capacitor coupling often produces:
Slight bass softening
Reduced damping
Warm character
Slight compression at high bass levels
Some people like it. Technically, it is added distortion.

Final Answer
In this amplifier the output capacitor:
Has minimal effect above ~200 Hz
Adds measurable low-frequency distortion
Increases distortion more with 4 Ω load
Slightly reduces damping factor
Contributes to the “warm” character
About 75% (est) of the power just becomes heat.

Comparison to Direct-Coupled AB Amplifier with +- power supply: A DC-coupled Class AB amp:
Has no output capacitor
Lower output impedance
Much lower LF distortion
Better bass control
That’s why modern designs avoid large output electrolytics.

Improvements ideas:

Ways to Reduce Distortion
​The primary cause of distortion here is the non-linearity of the MOSFET’s transconductance and the lack of negative feedback. Here is how to clean it up:
​1. Add a Source Resistor (Local Feedback)
​Currently, the Source (S) is tied directly to ground. Adding a small resistor (e.g., 0.47 \Omega to 1 \Omega) between the Source and Ground introduces Degeneration.
​Effect: It sacrifices some gain but makes the circuit much more linear and thermally stable.
​2. Replace the Load Resistor with a Constant Current Source (CCS)
​The 15 \Omega resistor is a “passive” load. As the output voltage swings, the current through the resistor changes, which causes harmonic distortion.
​Effect: Replacing the 15 \Omega resistor with an active CCS (using another MOSFET or an LM317) ensures the IRF530 sees a constant current, significantly flattening the distortion curve and improving bass response.

​3. Implement Global Negative Feedback
​The current design has no loop to “correct” the output against the input.
​Effect: You can take a portion of the output signal (before the output capacitor) and feed it back to an earlier gain stage or the gate biasing network. This “zeros out” the difference between what the input wants and what the output is actually doing.
​4. Use a Better MOSFET
​The IRF530 is a switching MOSFET designed for ON/OFF operations, not linear audio. Its input capacitance (C_{iss}) is non-linear.
​Effect: Switching to a lateral MOSFET specifically designed for audio (like those from Exicon) or a more linear power MOSFET will reduce high-frequency harshness.

5. Improve Power Supply Filtering
​Class A amplifiers have a Power Supply Rejection Ratio (PSRR) of nearly zero. Any ripple from your 24V power supply will hum directly through your speakers.
​Effect: Use a regulated power supply or a “Capacitance Multiplier” circuit to ensure the DC rail is perfectly smooth.

Safety Note
​The 15R 40W resistor and the IRF530 will get extremely hot. Ensure both are mounted to substantial heatsinks with thermal paste, or they will fail within minutes.

Let’s break this down calmly, because this circuit looks cooler than it actually is
It works, but in the “Facebook shorts” sense, not in an engineering sense.

It’s a very simple sound-reactive LED circuit.

Big problem:
There are NO current-limiting resistors for the LEDs. It might work for some time, but at longer use danger of LEDs and/or transistor will fail.

Smaller problems:
Different color LEDs with different voltage drop in parallel – only ones with lowest voltage drop will produce light well, other very dim or not turned on at all
No mic coupling capacitor and no proper biasing network – very poor sensitivity when works, depending on mic you happen to have might not work at all

Cables come in many forms, and one of the most visually noticeable — and functionally important — design elements is braiding. But not all cable braiding serves the same purpose. Depending on the type, braiding can offer mechanical protection, electromagnetic shielding, or even define the structure of the conductor itself.

In this article, we’ll explore three common types of braiding found in cables:

1. Textile Braiding for Protection
2. Metal Mesh Braiding for Shielding
3. Braided Conductors (Unshielded but Structured)

1. Textile Braid – Protective Outer Layer

What it is:

A textile braid is an outer layer made from woven synthetic fibers (such as nylon, PET, or polyester). This braid wraps around the cable jacket, mainly for physical protection and aesthetics.

Where it’s used:

USB cables, audio cables, power cords, custom PC builds

Advantages:

• Abrasion resistance: protects the underlying cable from wear and tear.
• Tangle resistance: helps reduce cable tangling.
• Aesthetics: available in various colors and weaves.
• Flexibility: does not restrict movement like metal shielding.

Disadvantages:

• No electrical shielding against EMI.
• Can absorb moisture or fray over time.

2. Metal Mesh Braid – Electromagnetic Shielding

What it is:

A braided metal mesh (usually copper, tinned copper, or aluminum) that surrounds signal-carrying conductors inside a cable. This braid provides electromagnetic interference (EMI) shielding.

Braided wire typically consists of a mesh-like shielding woven around a cable to protect the wiring from electromagnetic interference and enhance its mechanical strength. The shielding is typically composed of numerous thin wires woven tightly in a standard mesh formation around the conductor.

Where it’s used:

Audio cables, coaxial cables, instrument cables, industrial control cables

Advantages:

• Excellent EMI protection.
• Can serve as a grounding path.
• Durable and adds mechanical strength.
• Flexible (more so than foil shielding).

Disadvantages:

• Adds cost and weight.
• Less effective at high frequencies compared to foil; often used in combination.

3. Braided Conductors – Structural and Functional

What it is:

Some unshielded cables use braided signal or power conductors. This structure improves flexibility and mechanical stability and can reduce noise through symmetry.

Where it’s used:

Speaker cables, high-end audio cables, DIY or artisan cables

Advantages:

• Excellent flexibility and routing ease.
• Reduced crosstalk and inductance in some configurations.
• Visually appealing for premium or handmade cables.

Disadvantages:

• No EMI shielding.
• More complex and labor-intensive to manufacture.
• May tangle if not sleeved or jacketed.

Summary Table

Final Thoughts

Cable braiding isn’t always just about aesthetics — it can play a crucial role in performance, protection, and signal integrity. Whether it’s shielding against interference, reinforcing the cable’s durability, or simply improving flexibility and appearance, each type of braiding serves a distinct function.

When selecting or designing cables, understanding the differences between textile, shielding, and structural braiding helps you choose the right solution for your application — whether for audio, industrial, or custom-use scenarios.

Sometimes expensive HiFi cables combine several different braiding to be able to sell their products at high price:

I post links to security vulnerability news to comments of this article.

You are also free to post related links to comments.