Dan Beaven has written up documentation on his Chinese K40 Laser upgrade:
I’ve wanted to start playing with Laser Cutter/Engravers for quite a while. I finally happened across a great deal on a Chinese made 40 watt Laser Engraver with the Moshidraw software and control hardware. Wanting something I can modify and that is of better quality I decided to use my spare RAMPS 1.4 and Arduino Mega I had sitting around. I’ve successfully upgraded the system and here are the details so that others won’t have such a hard time getting theirs up and running. One benefit with this setup is the system is completely standalone. All you need is an SD card with your gcode files on it (remember to have the .g extension)
More details at Dan Beaven’s blog.