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RFID keys are commonly used in homes, offices, hotels, and security systems, where they can be easily programmed, deactivated, or replaced. Their flexibility and reliability make RFID technology a popular choice for enhancing security and simplifying access management. An RFID system has three main parts: the key (or tag), the reader, and the control system.

RFID keys work by using radio waves to communicate with a reader, allowing quick and contactless identification. When you bring the RFID key close to a reader, the reader emits a low-power radio signal. In most access systems, the key is passive, meaning it doesn’t have its own battery, and it gets powered by the reader’s signal through electromagnetic induction. Once powered, the chip sends back its stored ID via radio waves. Inside the key—whether it’s a card or fob—there’s a tiny microchip attached to an antenna. This chip stores a unique identification code.

This image shows the “StarKey” in its assembled state.
Design: It’s designed to be rugged and waterproof. The star/flower shape in the center is the signature Verisure aesthetic.
Functionality: Each tag is uniquely registered to a specific person in the household. When you tap it against the keypad, the system logs exactly who entered or left the building.

Pro-tip: If you ever lose one of these, you should immediately log into your Verisure app and deactivate that specific tag to ensure your home remains secure!

The following images provides a rare look at the internal and external design of a Verisure StarKey (specifically the RA14 model). This is a passive RFID (Radio Frequency Identification) tag used to arm or disarm Verisure alarm systems without needing a PIN code.

Here is a breakdown of what you are looking at: Internal Components
The green circular disc is the PCB (Printed Circuit Board) that lives inside the plastic casing.
The Coil (Antenna): Notice the fine copper-colored rings around the outer edge, that is the antenna for RFID signals. Since the tag has no battery, it relies on induction. When you hold it near the Verisure VoicePad or Keypad, the reader emits an electromagnetic field that “powers up” this coil.
The “Blob” (Microchip): The black circular dome on the right is a “chip-on-board.” It contains the unique ID and encryption logic. It’s covered in epoxy to protect the delicate silicon wafer.
RA14 Marking: This is the specific model or revision number for this generation of Verisure StarKeys.
The Center Square: This area contains physical alignment guide for manufacturing and/or installinf to the casing.

Technical Details
Frequency: These typically operate on the 13.56 MHz (NFC/High Frequency) or 125 kHz (Low Frequency) band. Given the density of the coil windings visible in your photo, it looks like a high-frequency tag designed for short-range security.
Security: Unlike basic office key fobs, these use encrypted communication to prevent “cloning” (where someone could scan your pocket and copy the signal).
Convenience: The main selling point for Verisure is the “SOS” integration; if an unauthorized person forces you to disarm the system, using a specific “duress” tag (or code) can silently alert the monitoring center.

I did some testing with NanoVNA connected to magbetic field EMC measurement probe to verify the operating frequency. My measurement shows around 14 MHz resonance frequency on NanoVNA screen. This matches pretty well to 13.5 MHz frequency tag, because taking the board out from original case and the measurement arrangement can affect it’s resonance frequency somewhat.

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

Start with circuit from https://www.facebook.com/share/p/1GJ5iBFZDq/

Most of the power in this circuit is lost on that resistor, approximately 500 mW. That resistor needs to be able to handle that power. Anything less 0.5W power rating will burn out (fire danger) and 0.5W resistor will run very hot (potentially can damage the plastic case, fire danger if case is not made of heat resisrant msterial). A “0.5 W resistor” is typically rated to dissipate 0.5 W at 70 °C ambient, in free air, with an allowed body temperature often up to 155–200 °C (depending on type).
The resistor needs to be with at least 1W power rating, and it would still run pretty hot (80–125 °C).

Second circuit from https://www.facebook.com/share/p/1CK3psPmdA/

How does the circuit work with 220V?

The 220V LED bulb driver circuit works by using a capacitor (47uF 25V) to drop the voltage and limit the current to the LED. Here’s a simplified explanation:

1. The 220V AC power is applied to the circuit.
2. The capacitor (47uF 25V) acts as a reactance, reducing the voltage and limiting the current.
3. The diode (1N4007) rectifies the AC voltage, converting it to a pulsating DC voltage.
4. The resistor (56k) helps to further limit the current to the LED.
5. The LED bulb is connected across the circuit and lights up when the current flows through it.

This circuit is a simple and cost-effective way to drive an LED from a high-voltage AC source. However, it might not be suitable for long-term use due to potential voltage spikes and capacitor reliability issues.

Keep in mind that working with 220V AC can be hazardous, and proper safety precautions should be taken when building and testing such circuits. This is not a project for a beginner.

If you are used to calculating LED current of 20 mA with 3V voltage drop over the, you might wonder the component values. If you try to calculated the LED resistor for 20 mA, you would get 10850 ohms, not 56k like used in this circuit.

This circuit does not run the LED at 20 mA, but lower 4 mA current limited by resistor (only half of time). That lights up LED, but not at full brightness. With this circuit the resistor wastes 500mW power. If you change the resistor to your 10850 ohms, the power loss in resistor would be almost 5 watts (you would need a quite big power resistor that would not fit inside the case).

Why there is the series diode in the circuit? Isn’t an LED by definition a diode?
Yes. LED is diode, but they typically quite limited how much reverse voltage they can withstand (many LEDs have a 5V limit for safe reverse voltage). Another reason that there is also a capacitor to avoid the LED flickering at mains 50 Hz frequency. A diode is needed for charging the capacitor to DC that can power LED on the negative half wave the diode blocks.

And what would be the purpose of the capacitor?
With one diode rectifier, LED would flicker half time on and half time off at 50 Hz rate. That kind of LED looks flickering. Add a capacitor, and LED will stay on all the time without noticeable flickering.

I understand the current limiting of the Resistor but shouldn’t that be on the hot leg versus the neutral leg?
This kind of plug can be plugged in both ways so in circuit you can’t control if resistor get plugged to phase or neutral. There is no practical difference as long as the circuit is inside well insulated case.

Final comment: Learn from those circuits, but I don’t recommend building them. The circuits are potentially dangerous (electrocution and fire dangers). They also have very low efficiency (most power input is wasted as heat on the resistors).

This basic circuit published at https://www.facebook.com/share/p/1Gi4UZHpVh/ claims to be able to serve as an instantaneous way for you to detect whether it is in fact due to a blown fuse or not. It is a small circuit that tries to make your job as an electronic technician easier.

When the fuse is in working order the LED remains “off.” When the fuse has blown, however the LED lights up to provide you with an obvious notification of the blown fuse condition. Therefore, you do not need to guess or waste time continually re-checking the same device as this simple idea can save so much troubleshooting time and effort when working with power supplies or batteries.

#innovation #learning #electronicproject #simplecircuit

Could this build in a simpler way?
Why not simplify the circuit by wiring the LED directly across the fuse ( with a current limiting resistor )

Source: https://theorycircuit.com/electronics-projects/blown-fuse-indicator/

The downside of his idea:
1. When fuse blows, there is no reliable full isolation of load because of the current through LED
2. If load is removed, LED does not indicate blown fuse

Another way it so place a power indicator across the supply after the fuse. It works by showing if power gets through the fuse or not. The downside is that the indicator LED will consume power all the time when power is on.

Links to other ideas:
https://dmohankumar.wordpress.com/2015/10/21/blown-fuse-indicators-simple-design-10/
https://www.eevblog.com/forum/projects/blown-fuse-indicator-design-validation-automotive/
https://electronicsarea.com/blown-fuse-indicator-circuit-using-one-transistor/
https://theorycircuit.com/electronics-projects/blown-fuse-indicator/
https://www.edn.com/simple-blown-fuse-indicator-sounds-an-alarm/

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/

Copper wire vs bananas vs mud – An interconnect test
https://www.diyaudio.com/community/threads/copper-wire-vs-bananas-vs-mud-an-interconnect-test.420367/

Audiophiles Can’t Differentiate Audio Signals Sent Through Copper, Banana, and Mud in Blind Test
https://www.headphonesty.com/2026/01/audiophiles-fail-copper-banana-mud-blind-test/
https://www.reddit.com/r/audiophile/comments/1qrk2hu/audiophiles_cant_differentiate_audio_signals_sent/

Are audiophile cables a scam? Copper VS banana VS ???

View also short Video

Man Uses Baby Carrot as RCA Adapter and It Actually Works Better Than It Should
https://www.headphonesty.com/2024/12/man-uses-baby-carrot-rca-adapter/

Audiophile Carrots are a thing now.. Listen to it for yourself!

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

You are also free to post related links to comments.

The found Ukranian drone is type Antonov An-196 Liutyi.

Here is current GPS interference map from https://gpsjam.org/ with city of Kouvola added to it:

Sources:
https://www.euronews.com/2026/03/29/two-unidentified-drones-crash-in-southeastern-finland-in-suspected-territorial-violation
https://yle.fi/a/74-20217941
https://yle.fi/a/74-20217933
https://gpsjam.org/
https://yle.fi/a/74-20217966

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