What to build? Need help

Hey guys, I have to build something electronic to present at a show and tell for the library system where i live. Its a program show casing tinkering with technology and i want to build something with arduino but not really sure what.

That's were you guys come in. The show is in January so i have some time but want to get started now. What would you guys wanna build?


A wall graffiti plotter - works like a small robotic window-cleaning dolly with a spray paint nozzle. It is controlled basically like a x-y plotter, where one dimension is movement along the top rail and the other dimension the length of the cable to hang down. Extra points for a system to compensate for movements of the basket with accelerometers or gyroscopes.

To prevent problems with authorities, use chalk-water colours which will wash off with the next rain or a gardening hose.

Is that showcase enough?


I'm currently building a laser projector out of two hard drive VCMs.

As you are a beginner to arduino I would recommend something simple but interactive.
The simplest idea that engages people will go down a treat.

Perhaps look into motion sensors or distance sensors and then do sonething with LEDs or maybe a display or two. As it is for in a library, I would stay away from things that make sound. Perhaps a display which says things to people depending on how many people it detects/how close they are.

I look forward to hearing about what you do.