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.

This is supposed to charge LiIon battery from USB power. Identified problems:
- no current limiting
- can overcharge the battery
- red charging LED will be always on when there is USB power coming in
- green charged LED will not turn on when battery is full

This circuit, as drawn, will not work properly or safely for charging a 3.7 V Li-ion battery. In this circuit, there is nothing to limit the charging voltage/current properly. The battery may overcharge (risk of fire or explosion).

The diode blocks the backflow voltage when the USB power is off and provide 0.7 voltage drop. The design intention seems to be that this would limit the battery charging voltage to safe level.

But even with the diode you have 5V from USB, minus 0,7V over the diode, that is still 4,3V, which is too much for the LiIon battery. So battery will be overcharged.

The typical maximum safe voltage for a standard Li-ion battery cell is 4.20V, although some higher-voltage chemistries can reach 4.30V. Charging a cell above its maximum voltage can cause irreversible damage, shorten its lifespan, and compromise safety. Battery management systems (BMS) in Li-ion packs prevent overcharging and ensure the voltage remains within safe limits. This simple circuit is not proper BMS.

The USB standard specifies a nominal 5V supply but allows for a voltage range between 4.75V and 5.25V for standard USB power delivery, with some USB 2.0 and 3.x specifications permitting higher voltages up to 5.5V to account for voltage drops. If your USB power supply gives those over 5V voltage, we are very considerably over the allowed maximum voltages.

Lithium batteries need constant current (CC) and constant voltage (CV) charging, typically limited to 4.2 V max with current control.

LED “full” and “charging” indicators won’t function correctly. The green/red LEDs with just a resistor and diode cannot sense charge status. The LED will just glow depending on voltage drops, not actual battery full/charging state. Because it shares resistor with red LED, it will not be on when red LED is on.

If you want to charge a 3.7 V Li-ion battery from USB, you need:
A TP4056 charging module (very cheap, <$1). It provides correct CC/CV charging. It includes overcharge, over-discharge, and short-circuit protection (if you buy the protection version). Comes with proper red/blue LEDs for charging/full indicators. Another bad battery charger circuit. Lacking proper charging current limiting, proper control of charge stopping when battery is full, too much voltage drop on diodes to work well, green full LED can stay always on or not turn on at all depending green LED used (voltage drop can very between 1.9V and 4V on green LEDs)

This claims to be a simple Li-ion battery charging indicator circuit.
It uses LEDs, resistors, diodes (1N4007), and a USB 5 V source to:
Charge a 3.7 V Li-ion battery, and
Indicate charging (red LED) and full charge (green LED) states. The 1N4007 diodes (3 in series) will get voltage drop (~0.7 V each × 3 = 2.1 V total). The battery gets a reduced voltage because of the voltage drops across the diodes, and the pproximate voltage at the battery terminals is around 2.9 that is not enough to properly charge the battery. The voltage drop over diodes will be lower at very low current, so a little bit current could get to battery.

This is a very basic indicator circuit, not a safe Li-ion charger.
It lacks:
Constant-current control (CC mode)
Constant-voltage regulation (CV mode)
Overcharge protection
Reverse polarity protection
Temperature monitoring

So while this circuit might be able show charging/full with certain not specified green LED, it’s not recommended for actual battery charging. Use a TP4056 module or similar dedicated Li-ion charger IC instead — it’s safer and inexpensive.

- because there isn’t

https://www.facebook.com/share/p/1CvWzJAZSN/

The reason is that it looks cool so people who don’t understand anything else will pay for it.

So does he have mini pylons that he strings them across so that they don’t touch like they do now?

Definitely not sound-related for a power cord. A wider spaced transmission line with air in it, which at an estimated length of 2 m is so electrically short as to be completely irrelevant for the 6000 km free-space wavelength of the 50 Hz mains.

Obviously this help to stop RFI pickup but makes RF pickup easier. Also makes the cable more easily radiate electrical field, magnetic field and RF to nearby cables than traditional mains cables.

Making sure you get as much differential-mode coupling as you can from your home AC mains so the 60Hz hum is maximized at the equipment power input.

Who would want to twists cables.

On the technical characteristics having air between wires means lower capacitance and higher inductance than traditional wires closely each other. If you want to optimize power cable, you would want low resistance and low inductance – and even somewhat high capacitance does not hurt (may even be beneficial as filters high frequencies). The design show in the picture is pretty much opposite of that technically optimal cable.