Build a cheap and simple full software controlled step-up (boost) converter to drive a LED string of 10 LEDs. LEDs are used as string to light up a acrylic engraved plate placed in a holder (also made out 5 layers of lasered black acrylic glas). Step up is from 5V to about 30V, current regulated to about 20mA.
Poti is for software features only. Current is measured by voltage at 10 Ohm resitor feedback to uC ADC3. Standard components like 1N4148 and BC817-40 are good enough for delivering 20mA output current (software limit here, more might be possible). Coil is a standard 100uH coil, but should be able to withstand 250mA as coil current is at least LED-current times boost-factor. Boost-factor is about 6 (30V LED vs 5V input).
Passendes Fritzing-Projekt von Cheasy: Media:LEDStepUp.fzz.zip
The software is just a small Arduino file, it needs the ATtin85 hardware lib from here to run on an ATtiny85. PWM is operated at 100kHz and duty cycle is adjusted adaptive in function 'regulate' according the desired brightness and the current measured. Main loop does set the brightness according first half of trimmer setting or does brightness up and down for second half of trimmer setting for a little effect.
All source files, schematic, Arduino code, LTSpice simulation files etc. included here: Datei:LEDStepUp.zip