UV counterfeit detector made of 27 UV LEDs.
You only need a 27x 5mm UV LED, a 27x resistor (depending on which LEDs you choose), an old USB cable, a soldering iron, a bit of solder and about 300g of filament.
Thanks to the use of USB, you can connect the detector to a computer, a standard USB charger or a power bank.
An example of wiring is in the last photo (I connected each row of LEDs separately).
For example, use this website for the calculation:
https://www.jan-lostak.eu/kalkulacky/elektrotechnika/vypocet-odporu-pro-led-diodu/
The total price is less than 15 USD.
The author marked this model as their own original creation.