Used a Prusa I3 as base for this laser engraver. With a RAMPS 1.4 controller.
Moved in pins.h the fan from D9 to D8
Made a separate power for the laser with a step-down 12 -> 5 Volt
If you check the schematics of the RAMPS 1.4 you will see the heatbed is seperate powered. Heatbed mosfet is now laser controller.
Replaced M106 and M107 in the Marlin firmware by M03 and M05.
M03 is PWM based. It turns now the laser on. M05 turns laser off.
Details about these modification follows.