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dimmer link: https://amzn.to/2qbe0O3 toroid link: https://amzn.to/3253rcZ this indelible writing method is based on powerful and short electric discharges that melt, crater and oxidize the surface of the metal, the writing tip is made of graphite, if metal it welds to the surface and does not allow writing, the circuit is very simple and safe, 2 components can be recovered from an old UPS: a large toroidal core (which can eventually be replaced by a transformer with iron sheets deprived of the original windings), a polyester capacitor that can have a maximum capacity of 2.2 microfarad or even less such as 0.47 microfarad, its plate voltage must not be less than 275 alternating volts