Way back I mentioned making this thing speak gcode, which would greatly improve its usefulness for the masses. I tried to do it. I got stuck learning about gcode and trying to figure out the best way to make it happen. Sadly I've had to accept the fact that I just don't have time for that right now. So for now it will just speak my own custom language for transmitting instructions to the plotter. That's not such a bad thing. It has worked fine for me so far.
Another thing I've had to accept is the limitations of this technique. I learned this lesson with my "Automate the art" project as well. The image is just not going to look as good as I want it too. With lots of tuning and way too much time spent I might end up with something OK, but then I have to ask myself "Was it worth it?" In some cases, yes. But usually not.
I want to include something positive in this log too. I learned many things and increased my proficiency with coding and machine making. I produced a nice little plotter that works very well and can now draw crosshatched pictures that look pretty good. I also built an egg-bot type machine for drawing on balls that can make use of the same code.
I hope that someone else is finding this project useful or educational. If so, then at least I can say it has accomplished the goal of the hackaday prize: making something that matters.
Oh, I almost forgot. Here's the arduino code that I promised before. (See the files for this project.)