Here's a nice how-to for moss graffiti
http://www.trueactivist.com/forums/diy/how-to-make-moss-graffiti/
http://www.trueactivist.com/forums/diy/how-to-make-moss-graffiti/
"What uses a fire extinguisher, a bike pump, and provides hours of probation, community service, and possibly jail time? If you said an automatic graffiti writer you’re correct! [Olivier van Herpt] calls this little job the Time Writer. We call it defacing property… but tomato, tomahto.
Details are a bit scarce, but you get a fine overview of the system from the video after the break. [Olivier] tagged the post as Arduino; it’s obviously running the dot matrix printer made up of seven solenoid valves on a metal rod. These are fed ink via a tube connected to a fire extinguisher which serves as the reservoir. The bike pump is used to pressurize the enclosure so that a pump isn’t necessary when out and about."
yeah much more than raspery pi.Man, Arduino really opens up a world of possibility doesn't it?